LOW←TECH MAGAZINE English

Communal Luxury: The Public Bathhouse

Tue, 17 Sep 2024 00:00:00 +0000

Image: Bathhouse built on top of a hot pool, Taiwan. Photo from early 20th century, public domain.

No Running Water at Home

For people in industrial societies, few activities demand more privacy than washing and grooming the body. We usually do it alone, in our private bathrooms, with locked doors. Seen in a historical context, that is unusual. Bathing in the presence of others has been the rule rather than the exception. As late as the first half of the twentieth century, many households, even in the most advanced industrial societies, did not have running water at home, let alone a private bathroom. ¹

A bathroom requires a domestic water supply, but also a sewer drain, and an energy source to heat the water. Of course, it’s possible to have a hot bath at home without these infrastructures. Ever since Antiquity, the rich have built private baths in their houses. Most often, they could do that because less well-off people - either servants or slaves - filled and emptied their bathtubs with bucketloads of water and collected firewood to heat them.

However, for most people, it was more practical to take their bodies to the water rather than the other way around. For some, that meant bathing in rivers, lakes, and springs. For others, especially in urban environments, it meant visiting the public bathhouse.

Image: Bathhouse in Aachen Germany, by Jan Luyken, 1682.

Is Bathing Unsustainable?

Modern bathing practices are a textbook example of an unsustainable lifestyle based on fossil fuels. Hot water production is the second largest energy use in many homes (after space heating and/or cooling), and much of it is used for bathing or showering. ² The modern bathroom also uses a lot of water and adds extra energy use through space heating and waste-water treatment. Building and renovating bathrooms requires resources, too.

Sustainability advocates follow two strategies to address these problems. The first strategy concentrates on technological solutions, such as low-flow showerheads, water boilers heated by solar collectors, waste-water heat recovery systems, and greywater recycling. The second strategy counts on behavioral or social changes by questioning modern standards of cleanliness and comfort: bathing or showering shorter and less frequently, taking cold showers, or doing a cat wash at the sink. ²³

These strategies are unlikely to bring much results. Many technological fixes are difficult or impossible to install in existing buildings, especially in cities. For example, as the number of floors increases, an apartment building quickly runs out of roof space to install solar collectors for all residents. On the other hand, promoting discomfort as a sacrifice for sustainability is unlikely to engage broader environmental practices. ³⁴

Communal bathing makes it easier to disconnect bathing practices from fossil fuels.

Communal bathing could be a third approach, but it’s rarely mentioned. That’s remarkable because, in terms of resource efficiency, it’s hard to beat. Building and operating a bathhouse for 1,000 people requires much less energy than building and operating 1,000 individual bathrooms. A public bathhouse is also more efficient concerning materials, money, and space. ⁵

Just as importantly, public bathing makes applying the sustainable technologies mentioned above more feasible. That further reduces energy consumption and makes it possible to disconnect bathing practices from fossil fuels. Finally, a public bathhouse can achieve significantly improved sustainability without promoting discomfort. On the contrary, pooling resources to build something for a community rather than for every household separately allows for a high level of sustainable extravagance. That may be an easier sell than cold showers.

Image: Public bathhouse in Dunkirk, France, opened in 1897.

Bathing in Rivers, Lakes, and Hot Springs

Nature has provided humans with bathing facilities through streams, rivers, pools, lakes, waterfalls, and rain showers. Humanity spent much time in tropical Africa, where bathing did not require artificially heated water for comfort. When we moved into colder climates, Nature presented us with another solution: hot springs. Many tens of thousands of thermal springs exist around the planet — only a few present-day countries lack them entirely. ⁶⁷

Bathing in hot springs was common in ancient civilizations all over the world. However, it’s a practice that goes back even further in time. Archeological evidence abundantly shows that many prehistoric settlements established themselves near hot springs. ⁶⁸ It’s impossible to prove rock solid that people used those waters for bathing, but why wouldn’t they, especially in cold regions? ⁹

Enjoying a hot bath is a practice that predates recorded history.

Today’s bathing culture relies on fossil fuels, but if we consider the historical context, enjoying a hot bath is not unsustainable. In the case of hot springs, the entire infrastructure and operation — water supply, drainage, and heat source — are already in place.

Our ancestors also invented the steam or sweat bath to take advantage of cold water in all seasons and climates. Rather than heating water, it heats people so they can bathe comfortably in cold water. The earliest steam huts, from prehistoric times, were little more than small log cabins or tent-like structures covered with woolen blankets or hides. ¹⁰¹¹¹²¹³

Painting: Bathing Place, oil on canvas, Paul Gauguin, 1886.

The Birth of the Bathhouse

Artificial bathing facilities made from brick or stone appeared around 4,000 years ago. ¹⁴ They could be an open-air pool, a bathhouse, or a private bathroom. Many bathhouses and bathing pools were built on top of natural hot springs, modifying the natural environment to make it more convenient, safe, and attractive.⁶⁸ People also began to divert water into urban bathing facilities using canals, pipes, and aqueducts. They started building baths that used artificially heated water as well.

The Ancient Romans are most famously associated with the public bathhouse, although they took much inspiration from the Ancient Greeks. Greek bathhouses comprised rooms with individual hip baths against the walls. Sitting up straight, the bathers threw hot water over themselves or had this done by a servant. In contrast, Roman bathers shared the water in large bathtubs or pools. Both used steam baths as well. ¹⁵¹⁶¹⁷¹⁸

At the height of the Empire, there were around 1,000 public baths in the city of Rome alone for a population of about 1 million people - one bathhouse per 1,000 people. ⁸¹⁹ The most prominent bathhouses were the “thermae,” which could hold up to a few thousand people bathing at the same time. These facilities, which only appeared in the largest cities, were richly decorated with mosaics, marble floors and pools, granite columns, and statues. However, most Ancient Roman bathhouses were smaller neighborhood baths called “balnea.” ¹⁵

Image: Cross-section of the Baths of Diocletian by French architect Edmond Paulin, 1880. This bath complex was the largest of Ancient Rome, with a capacity of over 3,000 people.

The Preindustrial Bathhouse

The public bathhouse’s history continues after the Roman Empire’s demise. In the East, the Roman bathhouse evolved into the hammam, which ditched the pools and concentrated more on sweating as a cleaning method.²⁰²¹ After a sweat bath, people threw water over themselves. Reminiscent of the small Roman baths known as balnea, hammams spread in large numbers in all cities of the Islamic world as they facilitated bodily cleanliness and the accomplishment of body ablutions before praying. ²²

In Western Europe, many Roman baths fell into disrepair. However, the public bathhouse returned in full swing during the late Middle Ages, when a new period of urbanization set in. ²³²⁴²⁵ In the 13th, 14th, and 15th centuries, a lot of European cities had a public bathhouse per 2,000 to 5,000 citizens.²⁶ Many were steam baths inspired by the hammam. A second type of bathhouse offered wooden bathtubs to seat a small group of people. The medieval bathhouse was known as a “stew,” which refers to the oven that either heated water for the bathtubs or filled the room with steam. ²³²⁵

Image: A former medieval bathhouse, built in 1562, in Münden, Germany. Photo by Axel Hindemith (CC BY-SA 4.0).

Image: The women's bathhouse, by Albrecht Dürer, 1496.

Painting: Rudas Baths, Ludwig Rohbock, 1850. The Rudas Baths in Budapest were built in 1550 and are still in operation.

Northern Europe and Russia - never conquered by Roman or Islamic Empires - stuck to sweat and hot air baths. For example, public “banyas” existed in towns throughout Muscovy during the Middle Ages. ¹² Asia also developed independent bathing cultures. For instance, in late medieval Japan, people shared private hot baths among families, neighbors, and friends for economic reasons. For these “cooperative baths” of mostly four to ten individuals, every bather brought a portion of firewood to heat the water. That practice evolved into larger public baths - “sento” - which experienced rapid growth from the fifteenth century onwards.²⁷²⁸

Image: Women taking a vapour bath. Wood engraving by Olaf Sörling.

Image: Men in a Japanese bathhouse, early twentieth century. Image in the public domain.

Bathing for Pleasure

Nowadays, sustainability advocates who promote shorter or less frequent showers implicitly regard bathing as a strictly utilitarian practice. However, for most of history, bathing was never just about hygiene. Apart from getting clean, people also visited public baths to relax, have fun, and socialize. Rather than a quick affair, the bathing process — no matter its form — often went on for hours. ¹⁵²⁸

The Ancient Greeks sat together in individual bathtubs, having conversations, for which the space’s acoustics were optimally suited. ²⁹ In Ancient Rome, public baths were places where people went almost daily to be seen, mingle, relax, gossip, dine, or play sports and study. Bathers accessed beauty treatments such as massages, shaving, hairdressing, and depilating. They celebrated parties and anniversaries and honored foreign guests. ¹⁵¹⁷¹⁹²⁵³⁰

Rather than a quick affair, the bathing process — no matter its form — often went on for hours.

The medieval European bathhouse continued these traditions with less splendor but not necessarily with less revelry. In particular, medieval stews with wooden bathtubs were often a place of amusement that also furnished food, drink, music, and various types of bodily care. ²³ In Japan, during the 16th century, public baths became places to gather and socialize, with large groups of people eating, drinking, and singing. ²⁷²⁸ River bathing, which continued around cities and in rural areas until the 20th century, was a kind of play in which swimming was a potential element. ³¹

At the same time, bathing was considered essential to prevent and cure diseases, following the Hippocratic ideas that people could maintain or restore the balance of bodily fluids by exposing the body to cold, hot, moist, or dry circumstances. The layout of preindustrial baths reflected these ideas, featuring pools and spaces of different temperatures. ¹⁵²¹

Image: Miniature drawing in "De Sphaera Mundi", written by Johannes de Sacrobosco, circa 1230.

Playing chess at the Széchenyi Baths in Budapest, Hungary, 1970s. Photo by Kereki Sándor. Found at [Fortepan](https://fortepan.hu/hu/).

Communal Luxury

While these elements of pleasure, social interaction, and health continue today in mineral spas, there is a crucial difference with earlier bathing practices. The present-day spa is far too expensive to substitute for a private bathroom. In contrast, the historical public bathhouse was an egalitarian institution.

Roman public baths had no or low entrance fees and were open to everyone. There were no areas reserved for higher-ranking patrons. Combined with the splendid architecture and opulent decoration of the baths, this ensured that even the most humble servant would have a taste of luxury. ¹⁵¹⁷¹⁹ These customs continued into the European Middle Ages and were shared by bathing cultures across the world. ²³ For example, in Japan, the bathhouse aided in “slowly deconstructing the existing social hierarchy and created a new cultural flow between the elite and the commoners.” ²⁸³²

The only separation happened between men and women, and it was far from universal across space and time. They would either go to different bathhouses, occupy different sections, or share the same spaces at different times of the day or the week. ¹²¹⁵¹⁷¹⁹²³

Image: A sento in Japan. Photo by [Stuart Gibson](https://stuartgibson.aminus3.com/portfolio/).

The Fuel Use of Roman Bathhouses

How sustainable was that communal luxury? Most research about the energy use of bathhouses concerns Ancient Roman baths. Historians have sometimes faulted the large bathhouses from the Empire for their wastefulness, arguing that their widespread use caused deforestation. ³³³⁴³⁵ However, in recent years, archeological research, thermal analysis, and heat transfer studies have made it increasingly clear that Ancient Roman bathhouses, in spite of their opulence, were remarkably energy-efficient buildings. ³⁶³³

The first reason was the hypocaust system. It consisted of one or more underground furnaces that distributed hot air under the floor and into the hollow walls (some baths had heated ceilings, too). Because of the large radiant surfaces, the spaces in the building could be heated at a lower temperature, saving energy. Although the water for the pools was reheated periodically in an insulated boiler close to the furnace, the heat in the floors and the walls helped to keep it warm for an extended period. ³⁶³³

A study of the Stabian Baths, one of the oldest surviving thermae, shows a fuel consumption of between 5 and 8 kg of firewood per hour, depending on the season. ³⁶³⁷ That corresponds to a wood supply of slightly more than 60 ash trees per year, which was unlikely to cause deforestation. ³⁶ Firewood consumption was probably even lower because Roman baths routinely supplemented wood with other locally available fuels, often waste products: reeds, harvest by-products (olive pits, orchard trimmings, chaff), and animal wastes (dung and bones). ³³

Many Roman baths were heated almost exclusively by solar energy on sunny days.

Following the same methodology, a study of a later bathing complex - the Forum Baths in Ostia - shows that the Romans continued improving their bathhouses’ energy efficiency. ³⁸³⁹ The Forum Baths were three times larger than the Stabian Baths - 923m2 versus 310m2 of heated spaces - but their calculated annual wood consumption is not even twice as high: roughly 100 trees per year. ³⁸³⁶ The newer bathhouse had thicker walls (two meters instead of one meter), as well as much larger glazed windows, which increased the share of solar radiation. ⁴⁰ Earlier research has shown that the Forum baths were heated almost exclusively by solar energy on sunny days. ⁴¹

The studies above assume that the Romans heated their baths for 24 hours daily and only shut them down for maintenance. Roman bathhouses likely continued to be heated through the night, as it was more practical and energy-efficient. Many baths were open daily, and it could take a whole day to heat them from a cold state. In later centuries, medieval stews and hammams often used the heat or the ashes of the furnace to bake bread and other foods at night. ⁴² Hammams and medieval stews were less energy-efficient than Roman baths. Hammams had heated floors but no heated walls and few windows, while medieval stews often had none of these.

Image: The large windows of the Forum Baths. Image: [Jan Theo Bakker](https://www.ostia-antica.org/regio1/12/12-6.htm).

Image: The hypocaust of the Great Baths complex, Ancient Dion. Imgae by Carole Raddato (CC BY-SA 2.0).

Image: Historical Reconstruction of the Roman Baths in Weißenburg, Germany, using data from laser scan technology. Credit: [CyArk](https://en.m.wikipedia.org/wiki/File:Cyark_Weissenburg_Reconstruction.jpg#filelinks). CC BY-SA 3.0

Roman Bathhouse Versus Private Shower

How does the energy use of the Roman bathhouse compare to that of the modern shower? Academic research does not provide an answer, but a quick calculation shows that the Roman bathing experience, which lasted for hours, was more energy-efficient than the present-day private shower, which lasts, on average, 9 minutes. The daily energy use of the Forum baths corresponds to the daily energy use of 557 showers. ⁴³ While we don’t know how many people visited the Forum Baths daily, they likely surpassed that number: the baths could host up to 500 bathers simultaneously. ⁴⁴

The Roman bathing experience, which lasted for hours, was more energy-efficient than the present-day private shower, which lasts, on average, 9 minutes.

Furthermore, in the calculation above, the energy use for the shower only concerns water heating, while the fuel use for the public baths also - and mainly - includes space heating. ³⁶ For example, assuming that the water in the pools of the Stabian baths was changed only once per day, heating the water accounted for less than 10% of the total energy use, corresponding to the energy use of only 52 showers. The low energy use for water heating is partly explained by the excellent thermal insulation of the heated floors and walls, meaning that space and water heating cannot be separated. However, it is also because the Romans shared the water in pools, while every shower requires freshly heated water.

The Roman bathhouse also compares favorably to the typical backyard sauna, for which the fuel consumption hovers between 5 and 15kg of firewood per session. ⁴⁵ Only sixteen such sauna sessions require as much fuel as the Stabian baths used daily. The sauna has no heated floor and walls. Furthermore, historically, it was often built partly underground to save fuel, but nowadays, it’s usually a badly insulated building standing in a cold climate.

Image: Bathing sandals for women, Saudi Arabia. Heated floors of hammams were too hot to walk on barefoot. Source: [Wereldmuseum](https://collectie.wereldmuseum.nl/) (CC BY-SA 4.0).

The Public Baths of the Industrial Revolution

Bathing practices have changed quite a lot since Roman and late medieval times, particularly in most of the Western world. Few of us will have the time or even the need to linger in a bathhouse for several hours daily, and some of us may feel uncomfortable bathing in public. ³⁰ However, a bathhouse can also take a form more in line with modern bathing habits. The public bathhouse of the Industrial Revolution demonstrates this.

In the nineteenth and early twentieth centuries, cities received large numbers of immigrants who came to work in factories. Most of these people were housed in overcrowded tenement buildings without running water, leading to unsanitary conditions. ⁴⁶ Recurring epidemics and new medical insights led to a “gospel of cleanliness” that resulted in a new wave of public bathhouses across the Western world. Many of these baths only disappeared between the 1950s and 1980s.

The public hygiene movement began in England and peaked there in the 1840s. By 1896, more than 200 municipalities in Britain were maintaining public baths. The English bathhouse emulated the splendor of Roman baths in its architecture and decoration: it was “large, handsome, and costly.” ⁴⁶ However, it did not copy the Ancient bathing customs. It now reserved different sections of the bathhouse for different social classes. Furthermore, while the pools still provided social interaction, the bathtubs were now placed in individual compartments. Finally, the modern bathhouse instituted maximum time limits for using the pool and the bathtubs. ⁴⁶⁴⁷⁴⁸

Image: Nechelles public baths in Birmingham, England, 1910. Image by Oosoom (CC BY-SA 3.0).

Image: The restored interior of the Amalienbad in Vienna, Austria, built in 1926. It was one of the largest bathhouses in Europe at the time, holding up to 1,300 bathers simultaneously. The original roof could slide open in good weather. Image by Schwimmschule Steiner (CC BY-SA 4.0).

The Shower Bathhouse

Germany, the first to follow the British on the continent, also built monumental bathhouses. ⁴⁹ However, in the 1880s, Berlin physician Oscar Lasser argued that the large baths were too costly to build in the necessary numbers. He proposed the introduction of smaller bathhouses with nothing but showers in individual compartments. Until then, the shower was only attached to a bathtub or used in barracks and prisons, where soldiers and inmates were showered with cold water. ⁴⁸⁴⁶²⁵

The shower bathhouse became the dominant public bath type in most of Western Europe and also in North America, where the sanitary reform movement took off in the 1890s. ⁵⁰⁵¹ It cleared away the last vestiges of the Ancient bathing culture by ditching the pools and switching to a more practical architecture. For better or worse, the public bathhouse from the Industrial Revolution was the “antithesis of the preindustrial bathhouse.” ⁴⁷ Although bathers still made use of communal infrastructure, there was no more space for pleasure, social interaction, public nakedness, and social mixing.

For better or worse, the public bathhouse from the Industrial Revolution was the antithesis of the preindustrial bathhouse.

As the higher social classes gradually gained access to their private water supply and bathrooms, the public bath became increasingly associated with poverty. Although shower bathhouses did not have separate sections for different social classes, they were mainly built in low-income neighborhoods, aimed at the poor only. Bathers were led to their shower cubicle by an attendant, who opened the tap, decided on the water temperature, and started a timer. People had at most 20 minutes to undress, shower, and dress again.⁴⁶⁴⁷ “The poor had to be clean but not enjoy it too much.” ⁴⁶

Image: The last bath attendant of a bathhouse in Haarlem, the Netherlands, in 1984. Image in the public domain.

Bath and shower rooms equipped with timers in Amsterdam bathhouses, 1985. Source: [Stadsarchief Amsterdam](https://archief.amsterdam/beeldbank/detail/ca27031b-8e92-023a-eb42-461dc0cf6fd2/media/728f468c-3dca-91e3-0eb9-6dca39ea8130?mode=detail&view=horizontal&q=badhuis&rows=1&page=24).

Image: Shower cubicles in a municipal bathhouse in Amsterdam, the Netherlands. Stadsarchief Amsterdam.

Image: Boiler room of a municipal bathhouse in Amsterdam, the Netherlands, 1985. Stadsarchief Amsterdam.

Bring Back the Public Bathhouse?

In Europe and North America, the public bathhouse disappeared once everyone got their private bathroom - although we still bathe together in sports centers and continue using communal bathrooms in hostels or campings. The public bathhouse survives elsewhere but is in decline almost everywhere. For example, Cairo had only eight hammams in 2000, compared to more than seventy at the beginning of the 19th century.⁵²⁵³ In 1968, greater Tokyo boasted 2,687 public bathhouses. In 2022, only 462 were left. ⁵⁴⁵⁵

Historically, the bathhouse was born out of the need for efficiency: bathing was too resource-intensive to organize individually. That is no longer the case thanks to the advance of central infrastructures - fossil fuels, electricity, water supply, sewers. However, in the context of the present environmental crisis, the resource efficiency of the public bathhouse has become relevant once again. It’s a solution that could reduce energy use relatively quickly without the need for new technologies or sacrificing comfort. Resilience is another argument for the bathhouse. ⁵⁶

Image: Municipal bathhouse at Javaplein in Amsterdam, the Netherlands. Image: Stadsarchief Amsterdam.

Image: A former bathhouse in Flensburg, Germany. Image: VollwertBIT (CC BY-SA 2.5).

What Type of Public Bathhouse Do We Want?

The metamorphosis of the public bath in the 19th and 20th centuries, which also affected public baths outside the Western world, presents a challenge to anyone wanting to revive public bathing for sustainability. What type of bathhouse do we want? Of course, the Roman bath and the shower bathhouse are both extremes, and many intermediate forms are imaginable. Nevertheless, any designer of a future bathhouse will have to make decisions that are likely to be controversial.

For example, one could argue that the shower bathhouse not only fits modern bathing practices but also maximizes resource efficiency. That is especially true when the government, rather than the bather, controls shower duration and water temperature. In that way, the public bathhouse could become a technology to enforce frugality upon the whole population. However, to put it mildly, such an approach is unlikely to generate enthusiasm for reviving public bathhouses. Neither does it do much to improve social interaction. ⁵⁷

Any designer of a future bathhouse will have to make decisions that are likely to be controversial.

Advocating for the return of the preindustrial public bathhouse, which centers around social interaction and communal luxury, may be more successful in luring people away from their private bathrooms, but it also runs into obstacles. The public bathhouse has faced resistance for 2,000 years, mostly because of conflicting views about health and morals. ⁵⁸ For example, concerns about debauchery and prostitution - real and imagined - run throughout the history of the bathhouse in all cultures. ⁵⁹ Separating males and females does not fully address those worries.

Image: Scene of a bathhouse, c. 1470, painted by the Master of Anthony of Burgundy (Berlin Staatsbibliothek, Ms. Dep. Breslau 2, vol. 2, fol. 244).

Any plea for reviving public baths will also have to deal with the fear of contagious disease. For example, a “lockdown” of society, as many governments applied during the coronavirus pandemic in 2020 and 2021, is incompatible with public bathhouses. Such a measure only works when everybody has a private bathroom. ⁶⁰ The link between communal bathing and health is complex. Science has confirmed many of the health benefits of cold, hot, and steam baths and has also shown the importance of social interaction. However, bringing people together will always raise health risks, too.

How to Build a Low-tech Bathhouse?

There’s another distinction between bathhouses built before and after the Industrial Revolution: preindustrial baths worked with renewable fuels, while industrial baths ran on fossil fuels. Many modern bathhouses had an on-site coal power plant, which heated the space and the water and provided electricity for lighting. Fossil fuel-powered bathhouses are more energy efficient than fossil fuel-powered private bathrooms, but we can do better than that.

A large bathhouse heated by a hypocaust system and large windows is still hard to beat as a carbon neutral technology, at least based on sustainable wood production. ⁶¹⁶² However, biomass combustion creates air pollution, while we could also power a bathhouse with renewable energy sources that don’t have that problem. The most apparent solution for space and water heating is flat plate solar collectors in which the sun heats water. Heat-generating windmills are a low-tech alternative to solar thermal collectors in less sunny climates. ⁶³ Other potential heat sources are geothermal energy and factory waste heat.

Fossil fuel-powered bathhouses are more energy efficient than fossil fuel-powered private bathrooms, but we can do better than that.

A solar or wind-powered bathhouse’s biggest drawback is its dependency on favorable weather conditions. To compensate for that, solar or wind power can be combined with thermal energy storage, such as insulated water tanks. Storing heat in a thermal mass for longer periods is much cheaper and more sustainable than storing electricity in chemical batteries. However, it requires space that only communal bathing can offer. Steam baths and saunas are more difficult to disconnect from biomass combustion, but some innovative examples exist. ⁶⁴

Clustering bathing facilities in a shared infrastructure also creates sufficient space for a bathhouse to have extensive heat insulation (a decisive factor in energy consumption) and provide for its water supply (for example, by catching and storing rainwater) as well as wastewater treatment (for example through phytoremediation using plants).

Architects have applied some of these ideas in countries where public baths are still used. For example, in a mountain village in China, a community bathhouse for 5,000 people is largely off-the-grid, pumping up its water from a well, heating it with solar collectors, and filtering the run-off wastewater from the showers and the toilets in basins filled with bamboo plants. ⁶⁵

Image: This bathhouse in China has 24 showers and serves a community of 5,000 residents. It recycles the waste-water with bamboo plants. Source: BAO Architects.

However, a public bathhouse also fits the more high-tech vision of a centralized energy infrastructure based on solar PV panels and wind turbines that provide electricity. In such a configuration, public bathhouses could absorb excess electricity during abundantly sunny or windy days. Rather than curtailing the electricity from surplus solar and wind power, we could use it to power electric heat pumps and store the heat in the thermal mass of public baths. ⁶⁶ While this approach is less resource-efficient than off-grid bathhouses operating without electricity, it still beats a scenario in which a centralized renewable power grid supplies energy to many private bathrooms.

Kris De Decker

Many thanks to Jonas Görgen and Elizabeth Shove for their feedback on an earlier version of this article.

Marie Verdeil and Roel Roscam Abbing contributed to the selection of images.

The spread of water supply and sewer networks took a lot of time, especially in older European cities. Before 1900, only the most expensive Paris flats had a bathroom. ²⁶ Plumbed-in private baths appeared in the wealthiest British households in the 1860s. Still, it was not until the 1950s that working-class homes were routinely supplied with hot and cold running water. ³ In the newer cities of the USA, installing a water supply and sewer infrastructure was easier. From the 1870s, American plumbing outstripped that of every other country. More than half of all American houses had a complete bathroom in 1940. For comparison, in the whole of France, only one house or apartment in ten had a shower or bath in 1954. ²⁰ ↩︎
Mist Showers: Sustainable Decadence?, Kris De Decker, Low-tech Magazine, 2019. https://qelnixcor.cloud/2019/10/mist-showers-sustainable-decadence/ ↩︎ ↩︎ ↩︎ ↩︎
Pickerill, Jenny. “Cold comfort? Reconceiving the practices of bathing in British self-build eco-homes.” Annals of the Association of American Geographers 105.5 (2015): 1061-1077. https://www.tandfonline.com/doi/full/10.1080/00045608.2015.1060880 ↩︎ ↩︎ ↩︎
The trend is towards more and longer showers ² and more, larger and more luxurious private bathrooms. For example, more than one-third of new single-family homes in the US had three or more bathrooms in 2021, compared to “only” a quarter in 2005. Source: Number of Bathrooms in New Homes in 2021, Jesse Wade, National Association Of Home Builders, November 2022. https://eyeonhousing.org/2022/11/number-of-bathrooms-in-new-homes-in-2021/ ↩︎
How much water public bathing can save depends on how exactly people bathe together. Shared pools and bathtubs bring water savings, but individual showers and bathtubs do not, even if placed in a communal space. ↩︎
Erfurt, Patricia. “Hot springs throughout history. The Geoheritage of hot springs.” Cham: Springer International Publishing, 2021. 119-182. ↩︎ ↩︎ ↩︎
Tamburello, Giancarlo, et al. “Global thermal spring distribution and relationship to endogenous and exogenous factors.” Nature Communications 13.1 (2022): 6378. ↩︎
Cataldi, Raffaele, Susan F. Hodgson, and John W. Lund. Stories from a heated earth: our geothermal heritage. No. 19. Nicholson, 1999. ↩︎ ↩︎ ↩︎
Even some animals - like snow monkeys and capybaras - are known to enjoy bathing in hot springs. See, for example: Matsuzawa, Tetsuro. “Hot-spring bathing of wild monkeys in Shiga-Heights: origin and propagation of a cultural behavior.” Primates 59.3 (2018): 209-213. https://link.springer.com/content/pdf/10.1007/s10329-018-0661-z.pdf. ↩︎
Sonntag, C. F. “The History of Baths and Bathing in Britain before the Norman Conquest.” Proceedings of the Royal Society of Medicine 13.sect_hist_med (1920): 25-46. ↩︎ ↩︎
Aaland, Mikkel. “Sweat: The illustrated history and description of the Finnish sauna, Russian bania, Islamic hammam, Japanese mushi-buro, Mexican temescal and American Indian & Eskimo sweat lodge.” (1978). ↩︎
Pollock, Ethan. Without the banya we would perish: a history of the Russian bathhouse. Oxford University Press, USA, 2019. ↩︎ ↩︎ ↩︎
The first written reference to the steam bath dates back to the fifth century BC, when Greek historian Herodotus compared the Scythian sweat bath north of the Black sea to the Greek steam bath of his time. However, it’s very likely that its origins go back to prehistoric times. Not surprisingly, the steam bath and the hot air bath initially spread in regions with cold and long winters: northwestern Europe, Russia, Alaska, and Canada. It was also used by Native Americans, and spread to Central and South America as well. ¹⁰ ↩︎
One of the earliest archeological records of human-made bathing facilities dates back to around 2300 BC in what is now Pakistan. The inhabitants of Mohenjo-daro, the probable capital of the Indus civilization, built wells and drainage systems allowing for private bathrooms in most residential buildings, as well as a large, communal bathing pool. The private bathrooms had a 1m2 shallow platform, where people threw buckets of water over themselves. The “Great Bath” was a brick basin with steps on either side and a capacity for 160 m3 of water. As the city was located in a hot desert climate, there was no need for heating the water. Sources: Graeber, David, and David Wengrow. The dawn of everything: A new history of humanity. Penguin UK, 2021 + Jansen, Michael. “Mohenjo-Daro, Indus Valley civilization: water supply and water use in one of the largest Bronze Age cities of the third millennium BC.” Geo: A new world of knowledge (2011). https://openarchive.icomos.org/id/eprint/1541/1/110601geo_06_2011_indian_edition_email.pdf ↩︎
Maréchal, Sadi. Public baths and bathing habits in Late Antiquity: a study of the archaeological and historical evidence from Roman Italy, North Africa and Palestine between AD 285 and AD 700. Diss. Ghent University, 2016. https://biblio.ugent.be/publication/7235534/file/7235545.pdf ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
Fagan, Garrett G. “The genesis of the Roman public bath: recent approaches and future directions.” American Journal of Archaeology 105.3 (2001): 403-426. ↩︎
Kosso, Cynthia, and Anne Scott, eds. The nature and function of water, baths, bathing, and hygiene from antiquity through the Renaissance. Vol. 11. Brill, 2009. ↩︎ ↩︎ ↩︎ ↩︎
Both the Greeks and the Romans also used cold baths in combination with sports facilities. Here, the act of washing was secondary. ¹⁵¹⁹ ↩︎
Hoagland, Alison K. The bathroom: a social history of cleanliness and the body. Bloomsbury Publishing USA, 2018. ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
Ashenburg, Katherine. The dirt on clean: An unsanitized history. Vintage Canada, 2010. ↩︎ ↩︎ ↩︎
Fournier, Caroline. Les bains d’al-Andalus: VIIIe-XVe siècle. Presses universitaires de Rennes, 2018. https://books.openedition.org/pur/44617#anchor-resume ↩︎ ↩︎ ↩︎
Sibley, Magda, Camilla Pezzica, and Chris Tweed. “Eco-hammam: the complexity of accelerating the ecological transition of a key social heritage sector in Morocco.” Sustainability 13.17 (2021): 9935 ↩︎
Coomans, Janna. “Janna Coomans - The Medieval Bathhouse (MA Thesis - 2013).” The Medieval Bathhouse: Bathing Culture in the Late Medieval Low Countries (2013): n. pag. Print. ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
Wurtzel, Ellen. “Passionate Encounters, Public Healing: Medieval Urban Bathhouses in Northern France.” French Historical Studies 46.3 (2023): 331-360. https://read.dukeupress.edu/french-historical-studies/article/46/3/331/381254/Passionate-Encounters-Public-HealingMedieval-Urban ↩︎ ↩︎
Büchner, Robert. Im städtischen Bad vor 500 Jahren: Badhaus, bader und Badegäste im alten Tirol. Böhlau, 2014. ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
Thirteenth century Paris, with 200,000 inhabitants, counted around 30 public bathhouses ²³²⁴, while 14th century London, with a population of 80,000, had at least 18 public baths. ²⁰ In the late 14th century Low Countries, Bruges (30,000 inhabitants) and Ghent (40,000 inhabitants) each had around twenty public baths, while smaller cities like Maastricht and Leuven (15,000 inhabitants) had around five. Vienna (Austria) counted 29 bathhouses in the fifteenth century. ²³ Medieval bathhouses, like hammams, were smaller than Roman baths. Medieval stews found in Germany and the Low Countries had a ground surface of between 100 and 200 square meters. ²³ The typical roman city bath had a surface of about 500 m2. ¹⁵ ↩︎ ↩︎
Butler, Lee. “Washing Off the Dust”: Baths and Bathing in Late Medieval Japan." Monumenta Nipponica 60.1 (2005): 1-41. https://web.archive.org/web/20190818120651id_/http://muse.jhu.edu:80/article/182356/pdf ↩︎ ↩︎
Merry, Adam M., “More Than a Bath: An Examination of Japanese Bathing Culture” (2013). CMC Senior Theses. Paper 665. http://scholarship.claremont.edu/cmc_theses/665 ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
Gill, A. A. ““Chattering” in the Baths: The Urban Greek Bathing Establishment and Social Discourse in Classical Antiquity.” (2011). https://tobias-lib.ub.uni-tuebingen.de/xmlui/bitstream/handle/10900/61481/CD27_Gill_CAA2008.pdf?sequence=2&isAllowed=y ↩︎
Górnicka, Barbara. Nakedness, shame, and embarrassment: A long-term sociological perspective. Vol. 12. Springer, 2016. ↩︎ ↩︎
A Cultural History of Parson’s Pleasure, George Townsend, PhD, Birkbeck, University of London, 2022, unpublished. See also: Dive in! A history of river swimming in Oxford. Museum of Oxford, expo 2023. https://moxdigiexhibits.omeka.net/exhibits/show/dive-in#:~:text=Dive%20In!-,A%20history%20of%20river%20swimming%20in%20Oxford,places%20for%20bathing%20and%20swimming. ↩︎
The egalitarian nature of the public bath was reinforced by the fact that people were partly or completely naked. “One stripped not only of their clothes but also of their social rank and material wealth, which become largely invisible”, concludes a historian of the Japanese public bath. ²⁸ “The true collective is a naked collective”, observes another, referring to the Russian banya. Source: Gearsimova, A. “My Banya, Your Banya: From Reality to Myth.” (2016). ↩︎
Mietz, Michael. “The fuel economy of public bathhouses in the Roman Empire.” Master’s thesis, Ghent University, Faculty of Arts and Philosophy, Campus Boekentoren, Blandijnberg 2 (2016): 9000. https://libstore.ugent.be/fulltxt/RUG01/002/303/996/RUG01-002303996_2016_0001_AC.pdf ↩︎ ↩︎ ↩︎ ↩︎
Wilson, A (2012) Raw materials and energy, in “The cambridge companion to the roman economy, scheidel 2012. ↩︎
Ancient deforestation revisited, Journal of the history of biology, 44 (1), 43-57. https://www.researchgate.net/profile/J-Donald-Hughes/publication/45407393_Ancient_Deforestation_Revisited/links/08ce17d911d2244431641d70/Ancient-Deforestation-Revisited.pdf ↩︎
Miliaresis, Ismini. “Heating the Stabian Baths at Pompeii.” Curious (2021): 83. https://library.oapen.org/bitstream/handle/20.500.12657/58973/1/external_content.pdf#page=91 ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
The study assumes that the baths were heated for 24 hours per day and only shut down for maintenance. The fuel used for heating up the bath initially (calculated at 35 kg in the case of the Stabian Baths) is added only once to the total yearly energy use. The results are also based on the assumption that the water of the baths was changed once per day (and thus had to be heated from a cold state once per day). ↩︎
Veal, Robyn, and Victoria Leitch. Fuel and Fire in the Ancient Roman World: Towards an integrated economic understanding. McDonald Institute for Archaeological Research, 2019. https://www.repository.cam.ac.uk/bitstreams/c349fc20-11d0-4ad4-a2e9-55dccca9f2df/download ↩︎ ↩︎
Miliaresis, Ismini Alexandra. Heating and Fuel Consumption in the Terme del Foro at Ostia. Diss. University of Virginia, 2013. https://libraetd.lib.virginia.edu/public_view/5d86p0445 ↩︎
Whether or not the (small) windows in the Stabian baths had glass or shutters is not entirely clear. The study concludes that energy use is pretty similar with both glazed and unglazed windows. However, the Forum baths, with windows several meters high, would have required almost 1.5 times more wood to heat rooms with unglazed windows during the month of May, and more than twice as much in the coldest month. ↩︎
Ring, James W. “Windows, baths, and solar energy in the Roman empire.” American Journal of Archaeology 100.4 (1996): 717-724. ↩︎
This may have been true for Roman bathhouses as well, but I could not find any reference to it. For hammamns, see, for example: Sibley, Magda, and Martin Sibley. “Hybrid transitions: combining biomass and solar energy for water heating in public bathhouses.” Energy Procedia 83 (2015): 525-532. ↩︎ ↩︎
A fuel use of 7.5 to 12 kg/hr averages at 9.75 kg/hr, which corresponds to 234 kg firewood per day. One kg of wood contains roughly 5 kWh of thermal energy, which brings the daily fuel use of the Forum baths to 1,170 kWh. A shower of 8.9 minutes (the average in the netherlands) takes 2.1 kWh of thermal energy. ² Conclusion: the daily energy use of the Forum Baths equals that of 557 showers. The daily fuel use of the smaller and less energy efficient Stabian baths corresponds to the energy use of 378 showers. ↩︎
Brünenberg–Jens-Arne, Monika Trümper–Clemens, et al. “Stabian Baths in Pompeii. New Research on the Development of Ancient Bathing Culture.” (2019). https://www.academia.edu/download/67567783/Truemper_et_al._Stabian_Baths_RM_2019.pdf ↩︎
The energy use of a sauna is more variable than the energy use of a shower, and I could not find any reliable academic research. The data I use are a rough estimation based on numbers that I found on internet forums and websites. Also note that climate explains part of the difference in energy efficiency: the sauna is often located in a cold climate, while most Roman baths stood around the Mediterranean. ↩︎
Williams, Marilyn T. Washing” the great unwashed": public baths in urban America, 1840-1920. Ohio State University Press, 1991. https://kb.osu.edu/bitstream/handle/1811/6282/1/Washing_the_Great_Unwashed.pdf ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
Dillon, Jennifer Reed. Modernity, sanitation and the public bath: Berlin, 1896–1933, as archetype. Duke University, 2007. https://dukespace.lib.duke.edu/bitstreams/33e2fe84-16ec-4044-91d6-75d5c87d37e3/download ↩︎ ↩︎ ↩︎
Ladd, Brian K. “Public baths and civic improvement in nineteenth-century German cities.” Journal of urban history 14.3 (1988): 372-393. ↩︎ ↩︎
The Stuttgart Bathhouse, for example, had two large pools, 300 dressing rooms, 102 bath tubs, two Russian-Roman baths, two cold water baths, a sun bath, and a bath for dogs. By the end of the century, almost every German city had erected at least one monumental bathhouse, which often included a restaurant and barber shop as well. ²⁵⁴⁶ ↩︎
New York City built 25 monumental bathhouses, and Boston included swimming pools and gymnasiums. However, other American cities exclusively built shower bathhouses for the poor classes. For example, by 1920, Chicago had erected more than twenty shower bathhouses throughout the poor and working class districts. ⁴⁶ ↩︎
Germany and Austria built shower bathhouses in poor neighbourhoods but also continued to build elaborate and expensive facilities for the higher social classes, many of them having a water supply but still lacking bathrooms. ⁴⁶ ↩︎
Talmisānī, Mayy, and Eve Gandossi. The last hammams of Cairo: a disappearing bathhouse culture. American Univ in Cairo Press, 2009. ↩︎
Damascus went down from 40 hammams in the 1940s to 13 in 2004. Source: Sibley, Magda. “The Historic hammāms of Damascus and Fez: lessons of sustainability and future developments.” The 23rd conference on passive and low energy architecture (PLEA). 2006. https://www.academia.edu/download/52232181/The_Historic_Hammms_of_Damascus_and_Fez_20170321-32624-5s2lbk.pdf Morocco is an exception. Various sources present different numbers for operating hammams which vary between 6,000 and 10,000 hammams that still operate using the traditional heating system. ⁴² ↩︎
“Tokyo starts effort to revive public bathhouses”, Julian Ryall Tokyo, October 1, 2022. https://www.dw.com/en/japan-launches-campaign-to-revive-fading-public-bathhouses/a-63282747#:~:text=In%20an%20effort%20to%20protect,pop%20into%20their%20local%20bathhouse. ↩︎
“Public baths fade from Tokyo, with nearly half gone over 15 years”, Natsumi Nakai, October 10, 2023. https://www.asahi.com/ajw/articles/15025294#:~:text=Public%20bathhouses%20are%20swiftly%20disappearing,to%20the%20Tokyo%20metropolitan%20government. ↩︎
“Fuel Crisis Forces Syrians to Use Public Baths”, Sputnik International, 2023. https://sputnikglobe.com/20230131/fuel-crisis-forces-syrians-to-use-public-baths-1106687250.html See also: “Aleppo bathhouse boom as Syria crisis turns showers cold”, Africanews, 2021. https://www.africanews.com/2021/12/30/aleppo-bathhouse-boom-as-syria-crisis-turns-showers-cold/ ↩︎
“Why we need to bring back the art of communal bathing”. Jamie Mackay, Aeon Magazine, 2016. https://aeon.co/ideas/why-we-need-to-bring-back-the-art-of-communal-bathing ↩︎
This is especially true in Western Europe, where opposition grew so strong that the bathhouse eventually disappeared in some regions between the sixteenth and the nineteenth century. ²³ The reasons for the temporal demise of bathing in Western Europe - a unique event in world history - are controversial among historians. Some point to the pressure of the Catholic and Protestant church, who increasingly perceived the medieval stews as places of immorality and sin. ⁵⁹ Others see the cause in epidemics, or point to changing medical views - doctors no longer considered hot water and steam healthy. ²³ Opposition started even before organized religion appeared. Ancient Roman philosopher Seneca was critical of the larger Roman baths and wrote several rants against them. He complained about the noise in the thermae, and accused them of extravagance and hedonism. See, for example: Moral letters to Lucilius by Seneca. Letter 86. On Scipio’s villa. https://en.wikisource.org/wiki/Moral_letters_to_Lucilius/Letter_86 ↩︎
In Ancient Rome, some bathhouses allowed mixed bathing, while others separated male and female bathers. Prostitution was legal, but the fact that a man’s wife had bathed with other men was a legitimate reason for divorce. ¹⁵ In Muslim Spain, substantial fines were assessed to men who either slipped into the bathhouse on days assigned to women, or who were caught spying through the windows of the structure. Women risked their legal rights if they did the same. Abusing a woman in a bathhouse, even verbally, carried the death penalty. See: Powers, James F. “Frontier municipal baths and social interaction in thirteenth-century Spain.” The American Historical Review 84.3 (1979): 649.667. In the Low Countries during the middle ages, authorities distinguished “honest” from “dishonest” stews. To maintain the quality of the “honest” bathhouses, they abolished, mixed bathing, set rules for bathmaids, and made prostitution in the bathhouse illegal. ²³ ↩︎ ↩︎
There’s no doubt that public bathhouses were a vector in historical epidemics. Medical tracts even advised against visiting the bathhouse. However, almost all baths remained open, very likely because they were seen as a service too essential to withdraw. At least, that was the case in the medieval Low Countries and in the Roman Empire, see: ²³²¹ ↩︎
How to make biomass energy sustainable again? Kris De Decker, Low-tech Magazine, September 2020. https://qelnixcor.cloud/2020/09/how-to-make-biomass-energy-sustainable-again/ ↩︎
Moreover, the hypocaust was further improved in the middle ages, meaning that it could be made even more energy efficient than in Roman times. See: Heat storage hypocausts: air heating in the middle ages, Kris De Decker, Low-tech Magazine, March 2017. https://qelnixcor.cloud/2017/03/heat-storage-hypocausts-air-heating-in-the-middle-ages/ ↩︎
Heat your house with a mechanical windmill, Kris De Decker, Low-tech Magazine, February 2019. https://qelnixcor.cloud/2019/02/heat-your-house-with-a-mechanical-windmill/ ↩︎
For example, researchers at the University of Stuttgart have devised a hybrid storage system consisting of a pressurized water and steam tank that serves as a storage for solar energy. The steam can be released in a sauna anytime, while the water serves to heat the space. See: Schaefer, M., et al. “Development of a zero-energy-sauna: Simulation study of thermal energy storage.” Energy and Buildings 256 (2022): 111659. https://www.sciencedirect.com/science/article/abs/pii/S0378778821009439. A very low-tech example is “Solauna”, which works with solar heat alone, basically by building a very large and well-insulated solar box cooker. See: https://www.biopiscinas.pt/en/solar-sauna/. “Lytefire” creates heat and steam by sunlight from mirrors concentrated on a metal plate or a bag of stones. See: https://lytefiresauna.com/en. ↩︎
See: https://www.designboom.com/architecture/bao-split-bathhouse/. Another example is a bathhouse in Eastern Iran, built in 2004, which runs on two solar collector fields (195 m2 total) and two thermally insulated storage tanks (3m3 each). The facility supplies hot water for twelve showers and four baths, serving the hot water demands of 150 people per day. Source: Azad, E. “Design, installation and operation of a solar thermal public bath in eastern iran.” Energy for Sustainable Development 16.1 (2012): 68-73. Researchers are also investigating the combined use of biomass furnaces and solar thermal collectors for hammams in Morocco. See: Krarouch, M., et al. “Simulation of floor heating in a combined solar-biomass system integrated in a public bathhouse located in Marrakech.” IOP Conference Series: Materials Science and Engineering. Vol. 353. No. 1. IOP Publishing, 2018. See also: Mohamed, Krarouch, and Haller Michel. “Design optimisation of a combined pellets and solar heating systems for water heating in a public bathhouse.” Energy Reports 6 (2020): 1628-1635. See also: Sibley, Magda, Camilla Pezzica, and Chris Tweed. “Eco-hammam: the complexity of accelerating the ecological transition of a key social heritage sector in Morocco.” Sustainability 13.17 (2021): 9935. See also: Zbaidi, Mourad, et al. “Improving the Energy Efficiency of a Traditional Hammam by Using Two Types of Heat Exchanger.” International Journal on Engineering Applications 11.6 (2023). ↩︎
How (Not) to Run a Modern Society on Solar and Wind Power Alone, Kris De Decker, Low-tech Magazine, September 2017. https://qelnixcor.cloud/2017/09/how-not-to-run-a-modern-society-on-solar-and-wind-power-alone/ See also: Battery Killers: Grid-Interactive Water Heaters, Kris De Decker, No Tech Magazine, May 2015. https://www.notechmagazine.com/2015/05/battery-killers-grid-interactive-water-heaters.html ↩︎

Direct Solar Power: Off-Grid Without Batteries

Fri, 25 Aug 2023 00:00:00 +0000

Image: a laptop running on direct solar power. Photo: Marie Verdeil.

Conventional solar installations do not question our dependence on fossil fuels and the energy-guzzling lifestyle that results. Both rooftop solar panels and large-scale solar farms provide us with all the power we want, even when the sun is not shining. That is because these systems use the central power grid, which largely runs on fossil fuels, as a kind of battery to cope with power shortages.

Although grid-connected solar panels can reduce the fossil fuel consumption of thermal power plants, these savings are at least partly offset by the additional fossil fuels required to build and maintain what is essentially a dual energy infrastructure. Combining solar and wind power can further increase the share of renewable energy in the power grid, but this requires further infrastructure development. Apart from energy, this also demands a lot of money and time.

Replacing fossil-fuel-fired power plants with energy storage, so that surplus electricity generated on sunny days can be stored for when there is no or insufficient sun, encounters the same problem. Energy storage, whether integrated into a power grid or located at individual households (off-grid systems), is very expensive and carbon-intensive to build and maintain.

Autonomous solar installation

The production of solar panels obviously costs money and energy. However, the financial and energy costs of the associated back-up infrastructure are many times higher. For grid-connected solar installations, these costs are very difficult to calculate precisely, but for autonomous solar installations (without grid connection and with their own energy storage) it is a lot easier. As an example, I will therefore take the small autonomous solar installation that powers my living room in Barcelona.

This system consists of two 50W solar panels on the balcony, a 100 Ah lead-acid battery and a 10A charge controller. The energy generated is used for lighting, the music system, and charging laptops and other electronic devices, among other things. The initial financial investment was 340 euros: 120 euros for the solar panels, 170 euros for the battery and 50 euros for the charge controller.

But while the solar panels should last 30 years and the charge controller about 10 years, I have to replace the lead battery on average every three to five years. ¹ Over a 30-year lifespan, the costs then amount to €120 for the solar panels, €150 for the charge controllers and – in the best case scenario – €1,020 for the batteries. The batteries (and associated charge controllers) therefore account for about 90% of the total lifetime costs.

Energy storage also dominates the plant’s “embedded” energy (and resulting carbon emissions). Producing my lead-acid battery took 1,200 megajoules (MJ) of energy. ² Over a 30-year lifetime (six batteries at best), that equates to 7,200 MJ. The three charge controllers add another 360 MJ over a 30-year lifetime, bringing the total energy consumption for the battery system to 7,560 MJ. ³ In contrast, the production of the solar panels costs only 2,275 MJ out of a total of 9,835 MJ. ⁴ Conclusion: more than 75% of total fossil energy consumption is due to energy storage.

Image: To the right on the balcony are the two 50W solar panels that power my flat's living room. Next to it is the 30W solar panel that makes this website work. Photo: Marie Verdeil.

Image: The structure for the solar panels, built from waste wood. Photo: Kris De Decker.

Image: The 100 Ah lead-acid battery powering the living room after sunset. Photo: Kris De Decker.

Other types of batteries would not significantly change this conclusion. For a comparable off-grid system with lithium-ion batteries, energy storage would account for about 95% of the total lifetime cost (which is almost double that of a system with lead-acid batteries). Assuming an optimistic lifetime (10 years) and including charge controllers, lithium energy storage accounts for some 70% of the energy invested in a solar grid system. ⁵ ⁶ For nickel-iron batteries, energy storage would account for 85% of the total lifetime cost (there are no energy cost data). ⁷

The scale and location of the solar installation also make no difference. A larger system needs more solar panels, but also larger batteries and more expensive and powerful charge controllers. The ratios remain the same. ⁸ The only factor that may give the solar panels a slightly larger share of the total cost is the structures on which they are mounted. I don’t take this into account because I built them myself from waste wood. However, if the solar panels are mounted on a roof, a DIY solution is less obvious. But even in that case, the cost of energy storage remains by far the biggest consideration.

Direct solar energy: much cheaper and more sustainable

Unlike fossil fuels, the sun and wind are not available on demand. The problem with our approach to renewable energy is that we insist that power should always be infinitely available, regardless of the weather, seasons or time of day. Matching energy demand to supply – as was done in the past – would lead to dramatic reductions in the cost and use of fossil fuels.

For example, if I omitted the battery storage of my solar installation, my system would become about 10 times cheaper: 120 euros instead of 1,290 euros over a 30-year lifetime. Alternatively, I could spend 1,290 euros on solar panels alone, which would give me a solar system of 1,075 watts. That’s ten times the capacity of the setup with batteries, more than what would fit on the balcony.

Without the battery and charge controller, the energy cost of the installation also drops from 9,835 MJ to 2,275 MJ. In other words, I could generate at least four times as much solar energy with the same investment in fossil fuels.

How can direct solar power be practical?

All well and good, but the sun does not shine after sunset and the amount of solar energy varies throughout the day and year. So how then can using solar panels without batteries (or other back-up infrastructure in the case of grid-connected installations) be practical?

To answer that question, we look at a pioneer of “direct solar power”: the Living Energy Farm. This environmental education community in the US state of Virginia is completely “off-the-grid” thanks to solar power, but only 10% of the solar power generated passes through a (nickel-iron) battery. However, the solar panels provide power for several homes, a communal kitchen, a metal workshop, and a farm. ⁹ ¹⁰

Image: direct solar power at the Living Energy Farm.

The solar installation has been in operation since 2011 and consists of separate systems with a total peak power of 1,400 watts. ¹¹ In comparison, the average peak power of a residential solar installation in the UK and the US – for one household – is 4,000 watts and 6,500 watts, respectively. As in my flat, the Living Energy Farm uses energy sparingly, but the fact that hardly any batteries are used has other reasons.

Some appliances are only used during the day

A first reason is obvious: some electrical appliances and machines are only used during the day. This is true, for example, of all machines in the metal workshop, including a band saw, compressor, grinder, circular saw, lathe, milling machine and drilling machine. It also applies to agricultural machinery such as a grain mill and a deep well pump. Linked directly to solar panels, these machines offer all the capabilities of modern grid-powered technology, with the exception that they can only be used during the day. ¹⁰

On a much smaller scale, I have used direct solar power for a soldering iron, glue gun and irrigation pump (for the balcony) at home. Other examples of appliances and machines that could be used only during the day include hoovers, sewing machines, washing machines, game consoles, laser cutters and 3D printers. It is not so difficult to imagine a modern society where activities such as vacuuming and DIY chores only take place during the day. It is certainly not a return to the Middle Ages.

Image: several workshop tools at the Living Energy Farm, most of them run on direct solar power. Image: Alexis Zeigler.

Image: Metal lathe running on direct solar power, Living Energy Farm. Image: Alexis Zeigler.

Image: Soldering with direct solar power. Photo: Marie Verdeil. [Watch the video](https://www.youtube.com/watch?v=qozZCJU4IOc).

Moreover, not all electrical appliances require constant attention. Washing machines or dishwashers that trigger automatically when the sun shines are often cited example applications of a “smart” power grid. But that approach relies on an extensive infrastructure of electricity transmission, communication networks, and electronics-packed appliances.

In contrast, in a decentralised direct solar approach, the intelligence is provided by the sun and the rotation of the planet. A direct solar-powered washing machine or dishwasher can be fully charged and switched on in the evening. The machine then starts up “automatically” in the morning. You can even use timers (electronic or mechanical) to run different appliances one after the other.

Whether clouds pose an additional limit to a direct solar installation, and to what extent, depends on the size of the solar panels. Doubling the area of solar panels guarantees sufficient solar power during moderate cloud cover, while the installation remains much cheaper and more sustainable than a system with batteries or other backup infrastructure.

An even larger area of solar panels could provide sufficient energy even during heavy cloud cover, but increasing the size of the system tenfold brings the cost back to the level of an autonomous system with batteries. Quadrupling the area makes the system equally dependent on fossil fuels again.

Many appliances already have batteries

Direct solar power does not rule out the use of electrical appliances after sunset either. As mentioned, the Living Energy Farm has a modest battery system, providing power for lights, fans, and electronic devices after sunset, among other things. ¹⁰ In addition, many modern appliances already have built-in energy storage. This is the case for all kinds of electric vehicles, for most electronic gadgets, and for older electrical appliances with AA batteries.

Consequently, these types of devices can be charged with direct solar energy during the day and then used for several hours after sunset thanks to the built-in battery. Combined with a lithium-ion power bank, a direct solar panel can also make it possible to charge USB devices after sunset. This strategy can even work for lighting, as there are many battery-powered lamps that you can use as modern torches, hung in different parts of rooms and buildings.

Image: A mobile phone on direct solar power. Photo: Marie Verdeil.

Of course, outsourcing chemical energy storage to the device is not the most sustainable option. The production of lithium-ion batteries requires fossil fuels, and (unlike lead-acid batteries) they are not recycled. The best solution, of course, is to reduce the use of electrical devices. But charging them with direct solar energy is a lot more sustainable and efficient than via other batteries or a fossil-fueled electricity grid. If we use high-tech devices, then preferably in the smartest way possible.

Non-electric energy storage

A third reason why direct solar power is more practical than it initially seems is that some electrical appliances can be used after sunset thanks to thermal energy storage. This is much cheaper and more sustainable than electrical energy storage. Thermal energy storage is already fairly well established for space and water heating systems, which store solar-heated water in an insulated boiler or (for space heating only) in the building envelope. It is no surprise that the Living Energy Farm has such systems, and solar thermal energy also provides hot water in my flat.

However, the same approach also works for two important household appliances that need to work after sunset and also consume a lot of electricity: the fridge and the cooker. Instead of storing electricity from a solar panel in a battery to then power a fridge or cooker after sunset, these appliances on the Living Energy Farm use thermal insulation. This keeps the heat inside (in the case of the cooker) or outside (in the case of the fridge) when there is no power supply. The thermal insulation also ensures very high energy efficiency, which means that each of these appliances can already operate on a solar panel of just 100-200 watts.

A direct solar-powered fridge

It is perfectly possible to connect a conventional fridge or freezer directly to a solar panel, but such an appliance would heat up very quickly at night. Even refrigerators with the most energy-efficient labels have a relatively limited insulation thickness (usually 2.5 cm). However, if that insulation thickness is increased to about 12.5 cm, the energy consumption of a refrigerator drops by a factor of four. ¹² ¹³ The passive cooling capacity of a refrigerator can be further increased by adding thermal mass in the form of a water tank inside the appliance. During the day, the solar panel cools the water or converts it to ice. At night, this cold water or ice slows down the heating of the refrigerator. ¹⁴

A direct solar-powered fridge also opens at the top, not at the front. Cold air is heavy, and so much less energy is lost that way when someone opens the door. All these design choices add up to spectacular energy efficiency. A study of direct solar refrigerators in very sunny regions (Texas and New Mexico, USA) showed that they maintained their cooling capacity for 6 or 7 days without power supply. The units operated year-round with solar panels of only 80W to 120W. ¹⁵ The Living Energy Farm powers its solar refrigerator with a 200W panel. ¹⁰

Image: The Sundanzer DDR165. A refrigerator designed specifically for direct solar power. Photo: Sundanzer.

Unlike solar heating, solar cooling is optimally tuned to seasonal variations in solar radiation. Cooling requires more energy in summer, when there is more solar energy. The aforementioned refrigerator in New Mexico recorded electricity consumption of 406 watt-hours per day in summer and only 230 watt-hours in winter. ¹⁶ Moreover, the technology can be used throughout the cold chain, of which the household refrigerator is only a small (but essential) part. Another application is air cooling, although this is less well researched and more challenging. ¹⁷

A direct solar electric cooker

In principle, a conventional cooker can also be connected directly to a solar panel, but as with a conventional fridge, it is not very practical. You can only cook during the day, and you have to install a lot of solar panels. A single hot plate needs 1,000 watts of electrical power. A solar electric cooker solves these problems by packing the cooktop with thermal insulation. The technology is basically a combination of an electric cooktop and a haybox.

Image: Test of an electric solar cooker. Photo: California Polytechnic State University (Cal Poly).

Thanks to thermal insulation, an electric solar cooker slowly accumulates heat during the day, which can then be used for cooking after sunset. In this way, a much lower power supply can be sufficient to achieve high temperatures. Think of it as “charging” your cooker, not with electricity but with heat.

Researchers at US California Polytechnic State University (Cal Poly) built the first solar electric cooker in 2015. Their 12-volt device, which has since been further developed, needs only a 100W solar panel to work. It boils a litre of water in an hour. With a full day of sunlight, it can cook almost 5 kg of beans, rice, stew or potatoes. ¹⁸

Cooking after sunset is possible by using a cooking pot with a much thicker bottom (5-10 kg). Cal Poly’s research team managed to bring the temperature of that solid heat storage to 250°C in five hours with a 100W solar panel. They were then able to boil a litre of water in three seconds after sunset. In another test, they stir-fried 1 kg of vegetables in two minutes. The ideal configuration consists of two cooking pots: one with and one without heat storage. Thus, an electric solar cooker can cook both slowly and quickly, depending on the time of day and the dish. ¹⁹

Image: The principle of a solar electric cooker with solid heat storage. Drawing: California Polytechnic State University (Cal Poly).

Thermal or electric?

Like solar water and space heating systems, cooking and cooling can work both with and without electricity – with PV panels on the one hand and solar thermal collectors on the other. But while solar space and water heating are more cost- and energy-efficient without electricity, for solar cooling and solar cooking it is just the opposite.

Space and water heating require relatively small temperature differences, which can be provided by low-cost solar thermal collectors made of glass plates and water pipes. In contrast, cooling and cooking require larger temperature differences, which require more sophisticated (vacuum tube or parabolic) solar collectors – and these are more expensive than PV panels. ²⁰ ²¹

The only exception is a simple solar cooker – an insulated box with a glass top – but it cannot achieve such high temperatures. Moreover, an electric solar cooker has some additional advantages. With a non-electric appliance, you have to cook outside, which is less practical but also less efficient, especially in winter: a thermal solar cooker will lose more heat to the environment. An electric solar cooker is also more energy-efficient because it is insulated on all sides. It also works better in cloudy weather and can be used after sunset. At the Living Energy Farm, the parabolic solar cooker is only used in optimal conditions – at full sun and high outdoor temperatures.

What are the technical challenges?

Although the Living Energy Farm is putting all these applications of direct solar energy into practice, there are some technical challenges for those who want to follow suit. Almost all our modern technology is designed to operate with a stable and uninterrupted power supply. It doesn’t have to be that way, but for now, direct solar power usually requires some tinkering. A direct solar system is much easier to build than an autonomous system with batteries, but it often requires modifications on the appliance side.

Some devices can be connected directly to a solar panel: it is enough to connect the positive and negative contacts of the solar panel and the device. For example, machines with a DC motor tolerate large fluctuations in the power supply. The metal workshop and agricultural machinery at the Living Energy Farm work this way. If clouds block the sun, the combined electrical load can become greater than the power supply from the solar panels, but this does not stop the machines. All the engines will slow down because they share the available energy, but they all continue to do useful work. ¹⁰ ²²

The same applies to all appliances that work on the basis of resistive heating elements, such as kettles, hotplates or electric heating systems. They work regardless of power or voltage, just slower or faster. A direct solar-powered fridge preferably operates on a variable DC compressor, which can adjust its speed according to the varying solar power production. ¹⁰ ²³

Many other devices need a specific and stable voltage input, which usually does not match what the solar panel produces. This can be solved by placing a DC-DC converter (a “buck” or “boost” converter) between the solar panel and the device. This is a small electronic module that converts the fluctuating voltage of a solar panel into a constant output voltage for a low-voltage device (5V, 12V or higher). ²⁴

Image: Experiments with direct solar power. Photo: Marie Verdeil.

If you use an inverter in addition to this, even mains appliances can operate directly on a solar panel. ²⁵ DC-DC converters are essential for all appliances that contain electronic components. This is the case for many appliances today, including those, such as washing machines or coffee machines, that until recently operated without electronics. That often gives you two options to run such appliances on direct solar power. You can either fit a DC-DC converter or modify the appliance by bypassing the electronics.

DIY manuals & commercial devices

Most direct solar power applications operate at low voltage, so you can safely do it yourself. Low-tech Magazine will soon publish a manual on this. However, the Living Energy Farm uses direct current with higher voltages for a number of applications. Examples are the machine tools in the metal workshop (90V) and a number of powerful electric solar cookers (48V, 180V). It is not a good idea to build these systems yourself unless you have the help of a qualified electrician, as these voltages can lead to fatal accidents.

Those wishing to build their own (low-voltage) electric solar cookers will find comprehensive manuals at both Living Energy Farm and Cal Poly. ²⁶ The devices can be made with simple materials. The insulation material should be fireproof. Example materials are rock wool, fibreglass, natural wool or clay.goed

Different technologies can be used for heating elements, but embedding nichrome wires in cement is the simplest option. These wires can be taken from a variety of appliances such as toasters, ovens and hotplates. In principle, the heating wires can be attached directly to the cooking pot, but it is more practical to make a heated “nest” in which a pot can be placed.

Image: Inspired by Cal Poly's work, Living Energy Farm also developed a number of electric solar cookers, one of which they [offer for sale through their website](https://livingenergylights.com/product/roxy-solar-electric-oven/). The Roxy Oven can be used as a hotplate or an oven, for example for baking bread. The door also remains closed when used as a hot plate. This solar cooker has no energy storage.

Image: The Roxy Oven without the door and with the glass wool insulation visible. The device - made in the metal workshop with direct solar power - runs on 48V and requires a solar panel of 200 to 500 watts. Living Energy Farm also offers Sunstar's solar refrigerator [for sale online](https://livingenergylights.com/product/sunstar-direct-drive-8-cuft-chest-style-refrigerator-freezer/).

Does direct solar power waste energy?

The sustainability of a solar installation depends not only on the energy required to produce and maintain the infrastructure, but also on the energy produced by the solar panels during their lifetime. Some people will argue that direct use of solar power is inferior to conventional grid-connected or battery-powered solar installations in this respect.

After all, the hoover, washing machine and power drill are not used every day, and if no electrical appliance is connected then a solar panel will not produce power either. Consequently, the amount of electricity produced by the panel will decrease over its lifetime, while the energy needed to manufacture the panel remains the same. This makes the power from a direct solar panel more carbon-intensive.

However, because energy storage in batteries (or the grid-connected alternative) accounts for such a large proportion of the total energy invested, a standalone solar panel can waste quite a lot of energy before it becomes less sustainable than its counterpart with battery storage or grid connection.

Moreover, direct use of solar power avoids the charging and discharging losses caused by batteries, or the energy losses in the transmission infrastructure for grid-connected systems. Both have to be offset by additional solar panels. Furthermore, solar panels connected to batteries or the grid also waste power – a consequence of the large difference in energy production between summer and winter.

Maximising direct solar power with collective services

Nevertheless, it is important to maximise the energy production of a direct solar panel. In that context, it is useful to return for a moment to the original example system located on my balcony. Direct solar power could be a nice addition to this system, especially for the fridge and cooker. It was because of these appliances that I concluded in 2016 that it was impossible to completely disconnect my flat from the grid.

However, the Living Energy Farm shows that it could be done: there is room for a further 200 watts of solar panels (4 x 50W) on the balcony, enough to power both a thermally insulated fridge and hob. Additional battery capacity would not be needed.

For other appliances, however, direct solar power is of little use in my case. It would not be very efficient to install an extra solar panel for the washing machine or the power drill, as they are only used occasionally. This seems to play into the hands of a “smart” electricity grid, because that way many households can use the same solar power – there is always someone who needs to wash clothes or drill a hole.

However, such a smart grid does require a lot of infrastructure, even if direct solar power were to be used at that scale. It may not require batteries or fossil fuels as backup, but it does require transmission and communication infrastructure.

Image: A record player on direct solar power. Photo: Marie Verdeil. [Watch the video](https://www.youtube.com/watch?v=_LjSigJv0-0).

The Living Energy Farm demonstrates an alternative solution: the communal organisation of household tasks and work. Instead of a communal power grid distributing energy to many indidvidual households, we can set up collective services with decentralised energy production.

In the Living Energy Farm communal workshop, direct solar power can be used much more efficiently than in an individual workshop that is only used occasionally. A collective laundry in each street would also use direct solar power much more efficiently. Moreover, we save a lot of energy on building appliances this way, and gain a lot of space.

Direct wind power?

This strategy becomes even more important if we choose not direct solar power but direct wind power – or a combination of both. The Living Energy Farm is located in a sunny region, but the same approach could also work in windy places.

However, there is an important difference between solar power and wind power. The efficiency of a solar panel does not depend on its size, which makes solar power ideal for decentralised energy production. In contrast, the efficiency of a wind turbine increases more than proportionally as the rotor diameter increases. Much better than one wind turbine per household, therefore, is a somewhat larger wind turbine for a community of households, e.g. for powering a collective laundry or workshop.

The service life of lead-acid batteries depends on many factors. If they are discharged too deeply or are not fully charged regularly, the service life can be shorter than three years. On the other hand, a lead-acid battery that is hardly used or not discharged at all can last much longer than five years. However, the academic literature states a life expectancy of three to five years and this has also been my experience with the batteries I have used since 2016. See, for example, “Optimal Sizing and Life Cycle Assessment of Residential Photovoltaic Energy Systems With Battery Storage”, A. Celik, in “Progress in Photovoltaics: Research and Applications”, 2008. & “Energy pay-back time of photovoltaic energy systems: present status and prospects”, E.A. Alsema, in “Proceedings of the 2nd World Conference and Exhibition on photovoltaics solar energy conversion”, July 1998. ↩︎
Manufacturing a lead-acid battery (based on largely recycled materials) takes about 1 MJ of energy per watt-hour of storage capacity. My 100 amp-hour battery equates to a storage capacity of 1,200 watt-hours, and so the embedded energy equals 1,200 MJ. Over a 30-year lifespan, I need six of these batteries at best, so 7,200 MJ in total. Source: “Energy Analysis of Batteries in Photovoltaic systems. Part one (Performance and energy requirements)” and “Part two (Energy Return Factors and Overall Battery Efficiencies)” (PDF). Energy Conversion and Management 46, 2005. ↩︎
Not much research has been done on the embedded energy of charge controllers. The most relevant data I found is a value of 1 MJ per watt maximum power: Kim, Bunthern, et al. “Life cycle assessment for a solar energy system based on reuse components for developing countries.” Journal of cleaner production 208 (2019): 1459-1468. For a capacity of 120W (my charge controller has a maximum capacity of 10A x 12V = 120W), this amounts to 120 MJ. For the estimated lifetime, I found values of 7 and 12.5 years: same reference as above, as well as: Kim, Bunthern, et al. “Second life of power supply unit as charge controller in PV system and environmental benefit assessment.” IECON 2016-42nd Annual Conference of the IEEE Industrial Electronics Society. IEEE, 2016. I therefore made the calculation on an estimated lifetime of 10 years. ↩︎
Nawaz, I., and G. N. Tiwari. “Embodied energy analysis of photovoltaic (PV) system based on macro-and micro-level.” Energy Policy 34.17 (2006): 3144-3152. According to this widely quoted source, it takes 3,500 MJ to produce 1 m2 of solar panel. My two solar panels together measure 0.65 m2, representing a total energy cost of 2,275 MJ. A more recent literature review puts the energy cost for producing different types of solar panels at between 1,034 and 5,150 MJ/m2. The most recent studies of silicon solar panels in this review put the energy cost at around 1,000 MJ/m2, much lower than the figure I am using. See: Ludin, Norasikin Ahmad, et al. “Prospects of life cycle assessment of renewable energy from solar photovoltaic technologies: A review.” Renewable and Sustainable Energy Reviews 96 (2018): 11-28. ↩︎
Lithium-ion batteries are a lot more expensive than lead-acid batteries, but unlike lead-acid batteries, they can be discharged deeper (up to 15% of their total capacity) and have a longer lifespan (7 to 10 years). Consequently, fewer and smaller batteries are needed. Taking these factors into account, the lifetime cost of the battery is €750, compared with €1,020 for lead-acid batteries. On the other hand, lithium-ion batteries require a more sophisticated and more expensive charge controller: a 10A charge controller costs between 200 and 600 euros, depending on the quality. Assuming a price of 400 euros for the charge controller and a 10-year lifetime for both the battery and the charge controller, battery storage accounts for 95% of the total lifetime cost (a total of 2,070 euros, much more than the total cost for the system with lead-acid batteries). Sources: https://www.lithiumion-batteries.com/products/product/12v-50ah-lithium-ion-battery & https://www.lithiumion-batteries.com/products/12v-lithium-ion-battery-chargers/ ↩︎
Although the production of a lithium-ion battery costs more energy than the production of a lead-acid battery (1.4-1.9 MJ/Wh versus 1 MJ/Wh), this is offset by a longer lifespan and greater discharge capacity. The energy cost of lithium-ion batteries over a 30-year lifetime is then about 3,000 MJ, significantly less than a comparable lead-acid battery system. In contrast, the charge controller contains more complex electronics. Unfortunately, no data is available for the energy cost of such a charge controller. So there is no alternative but to estimate the energy cost based on the financial cost, which is four to twelve times more expensive than a charge controller for a lead-acid battery. Assuming a four times higher cost, the embedded energy of the charge controller increases to 480 MJ, or 1,440 MJ over a 30-year period. The total energy cost for the system is then 6,685 MJ, less than a comparable system with lead-acid batteries. Of this, almost 70% is attributable to battery storage. ↩︎
Nickel-iron batteries are even bigger and heavier than lead-acid batteries and they need regular maintenance. But they can be fully discharged and have a very long service life (20 years). Moreover, they can be used with the same charge controllers as lead-acid batteries. The lifetime cost over 30 years for the battery is €750, cheaper than the six lead-acid batteries of similar capacity. The total lifetime cost for a nickel-iron battery system with 100W solar panels is €1,020, of which 85% goes to energy storage. Unfortunately, nickel-iron batteries are hard to find, especially the smaller models. Sources: https://beyondoilsolar.com/product/nickel-iron-battery-industrial-series/ & https://beyondoilsolar.com/product-category/batteries/nickel-iron/ ↩︎
Actually, the price of solar panels in a somewhat larger solar installation would be proportionally even smaller. This is because solar panels with small sizes (such as 50W) are proportionally more expensive per watt of peak capacity than solar panels with more conventional sizes (from 250W onwards). More or less the same applies to the energy cost. ↩︎
https://livingenergyfarm.org ↩︎
Alexis Zeigler, founder of the Living Energy Farm, wrote a book about the project, which is available in full online: Empowering Communities. A Practical Guide to Energy Self Sufficiency and Stopping Climate Change. It can also be ordered in hard copy. ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
Since direct solar power does not require a charge controller for each separate system, splitting up a solar system does not involve any additional costs or energy consumption. ↩︎
Research shows that doubling the insulation thickness from 2.5 cm (standard insulation) to 5 cm reduces the annual electricity consumption of a refrigerator (50 litre capacity) from 250 to 125 kilowatt hours. ¹³ With an insulation thickness of 10 to 12.5 cm, electricity consumption halves again to around 60 kilowatt hours per year. Even thicker insulation brings a smaller reduction in electricity consumption and is no longer attractive because thicker insulation also increases the cost and size of the refrigerator. The study concerns a solar-powered AC fridge that operates thanks to an inverter and a battery, which is less energy-efficient than a direct solar-powered fridge. ↩︎
Gupta, B. L., Mayank Bhatnagar, and Jyotirmay Mathur. “Optimum sizing of PV panel, battery capacity and insulation thickness for a photovoltaic operated domestic refrigerator.” Sustainable Energy Technologies and Assessments 7 (2014): 55-67. ↩︎ ↩︎
This thermal mass can literally be a container of water placed inside the fridge. or some water bottles for drinking. But the water can also be stored in reservoirs along the side of the appliance, behind an inner lining that keeps them in place and hides them from view. Water has a higher heat storage density than air, keeping the temperature stable for longer. ↩︎
Ewert, M., et al. “Photovoltaic direct drive, battery-free solar refrigerator field test results.” Proceedings of the solar conference. American solar energy society; American institute of architects, 2002. ↩︎ ↩︎
This advantage only applies if the fridge is set up in an unheated room. The modern habit of placing a fridge in a heated kitchen when the outside temperature in winter is equal or lower than that in the fridge is obviously absurdly wasteful. But neither is this advantage valid in tropical countries, where temperatures are high all year round. ↩︎
The use of direct solar power for space cooling has not been analysed as thoroughly as for domestic refrigerators. See: Luerssen, Christoph, et al. “Life cycle cost analysis (LCCA) of PV-powered cooling systems with thermal energy and battery storage for off-grid applications.” Applied energy 273 (2020): 115145. Moreover, it is unlikely to achieve equally large energy savings. A refrigerator is always insulated, but in the case of an air-cooled room or building, this is not necessarily the case. Moreover, a refrigerator is set up in a room where there is a stable temperature. A building is subject to greater temperature fluctuations and can also be heated by direct solar radiation. So direct solar air cooling is a lot more complicated. See: Qi, Ronghui, Lin Lu, and Yu Huang. “Parameter analysis and optimisation of the energy and economic performance of solar-assisted liquid desiccant cooling system under different climate conditions.” Energy conversion and management 106 (2015): 1387-1395. ↩︎
Solar Electric Cooking, Pete Schwartz, Cal Poly Physics. See also this PowerPoint by the same author. ↩︎
Insulated Solar Electric Cooker with Solid Thermal Storage, Andrew McCombs et al., 2022. See also this video. ↩︎
See: Ferreira, Carlos Infante, and Dong-Seon Kim. “Techno-economic review of solar cooling technologies based on location-specific data.” International Journal of Refrigeration 39 (2014): 23-37. ///// Riffat, James, et al. “Development and testing of a PCM enhanced domestic refrigerator with use of miniature DC compressor for weak/off grid locations.” International Journal of Green Energy 19.10 (2022): 1118-1131. ///// Du, Wenping, et al. “Dynamic energy efficiency characteristics analysis of a distributed solar photovoltaic direct-drive solar cold storage.” Building and Environment 206 (2021): 108324. ///// Alsagri, Ali Sulaiman. “Photovoltaic and photovoltaic thermal technologies for refrigeration purposes: an overview.” Arabian journal for science and engineering 47.7 (2022): 7911-7944. ↩︎
For lack of research, whether the same applies to embedded energy consumption is not clear. ↩︎
In both cases, however, it is necessary to bypass the device’s switch, because DC electricity produces more heat than AC electricity. Instead, a suitable external switch can help, but in doing so you bypass the device’s safety mechanism, which is obviously a risk. ¹⁰ Again, this does not have to be the case: it is technically possible to make devices suitable for direct solar power. ↩︎
A fixed-speed compressor can only use 50% of the solar power produced in a useful way, while a variable-speed compressor uses about 75% in a useful way. ¹⁵ A capacitor is needed to provide the compressor with an energy boost during the start-up phase. ↩︎
Instead of a DC-DC converter, you can also install a small “buffer battery” and a charge controller. Like a DC-DC converter, the charge controller will ensure a stable output voltage. In addition, the small battery can provide limited energy storage that can be useful to handle short spikes in power consumption. For example, some devices have a current spike when charging. The disadvantage of a buffer battery is that the cost and embedded energy increase, and additional components can fail. A capacitor is an alternative technology to absorb power peaks. ↩︎
However, using low-voltage direct current devices is a lot more energy-efficient because solar panels also produce low-voltage direct current: https://qelnixcor.cloud/2016/04/slow-electricity-the-return-of-dc-power/ ↩︎
Insulated Solar Cooker Construction Manual, Living Energy Farm. Insulated solar electric cooker manual, Pete Schwartz, Cal Poly Physics. Roxy Oven Manual, Living Energy Farm. Video presentation manual solar electric cookers, Alexis Zeigler, Living Energy Farm. Video manual for making heating wires. Thermal heat storage: Insulated Solar Electric Cooker with Solid Thermal Storage, Andrew McCombs et al., 2022. Also see this video. ↩︎

Human Powered Air Compressor and Energy Storage System

Sun, 09 Jul 2023 00:00:00 +0000

Image: Human powered air compressor and energy storage system. Photo by Andy Lagzdins.

When I look around my motorcycle shop, pneumatic tools are everywhere. From handheld tools such as impact guns, sanders, shears, saws and grinders to large equipment including a sandblast cabinet and tire machine; air is a vital part of taking on a wide variety of tasks.

The air compressor I’ve used since the 1990’s uses a 220V, 7hp electric motor to turn a two stage air pump at 800 rpm, which fills the 80 gallon tank to 150 psi in about five minutes. It has been a very reliable machine, to the point where I hardly ever think about it. Only when there is a power outage do I realize how much I rely on a ready supply of compressed air.

In a rapidly changing world where inexpensive and reliable energy going forward is no longer a given, I set out to build a system to fill my air tanks without the use of electricity or fuel. My design would be free of electronics of any type, and with minimal maintenance the components should last a lifetime. I wanted to use as many second hand parts as possible, in an effort to reduce costs and inspire recycling and repurposing.

Components

The first order of business was to find an air tank. I found an 80 gallon Ingersoll Rand air compressor that was manufactured in 1952. I removed the air pump and electric motor. The original air pump was replaced with a new Speedaire unit that is rated for 115 psi and normally requires a ½hp motor to run it. The pump is mounted onto the top of the air tank with a steel plate that bolts on to the original motor plate.

In the location of the electric motor, I installed a solid steel shaft on self centering pillow block bearings. This shaft holds three 20kg compressor pulleys used as flywheels to smooth out the operation. These pulleys have a 1 ⅜” bore and are 16” in diameter. A single 4L series v-belt connects the flywheel shaft to the air pump.

Image: Compressor and compressor pulleys used as flywheels. Photo by Andy Lagzdins.

Image: Solid steel shaft with three compressor pulleys used as flywheels. Photo by Andy Lagzdins.

Next on the agenda was finding a human power source to spin the flywheels. I found a 1970’s Schwinn exercise bike that was very well constructed from almost all steel components. I stripped it down to the bare essentials, and installed a Sturmey Archer eight speed internally geared bicycle hub in place of the original spoked wheel. This hub has a ratio range from 1:1 to 3.25:1, and the gear changes are done using a selector switch on the handlebars.

To handle the force of hard pedaling, the crank assembly was replaced with tubular Cr-Mo alloy crank arms, sealed bearings, and platform pedals from a BMX racing bicycle. The handlebars and stem were replaced with Cr-Mo components to minimize flex during hard use, and the highest strength 1/8” bicycle chains are used for reliability.

At this point the bicycle and air tank were aligned to one another, and mounted on 6”x6” treated wood frames in the correct position. The bicycle output sprocket is connected by another chain to a similar sprocket on the end of the flywheel shaft, and the drive system is now complete.

Image: A 1970’s Schwinn exercise bike. The crank assembly was replaced with tubular Cr-Mo alloy crank arms, sealed bearings, and platform pedals from a BMX racing bicycle. Photo by Andy Lagzdins.

Image: Sturmey Archer eight speed internally geared bicycle hub. Photo by Andy Lagzdins.

To manage the air flow, I incorporated a two stage system. A 10 gallon tank and the 80 gallon tank are valved separately so I can fill each one independently, both together, or transfer air from one tank to the other. Gauges on each tank used to monitor pressures. When the large tank is initially filled, I take it up to 50 psi by feeding it directly from the air pump. At that point, I start filling the small tank by itself up to 100 psi and then dumping it into the large tank.

Eight speed transmission

The eight speed transmission helps considerably during the filling process. When the tank pressure is low, the bicycle can be pedaled in the higher gears. When the pressure gets in the 70-100 psi range the lower gears are used to overcome the resistance of the air pump.

The process of filling the empty tanks to 100 psi takes 5-10 pedaling sessions per day for roughly a week. When I am busy at the shop, getting on the bike for a little while is actually a nice way to clear my head and in cold weather it warms me up and gets my blood flowing. I can put the bike in low gear and pedal while using my phone or listening to music.

Having to pedal to create the compressed air really makes me concentrate on not wasting air when using tools. It is also crucial to make sure there are no leaks by sealing all the fittings properly.

Image: Compressed air power tools. Image by Andy Lagzdins.

The parts of this machine that are most susceptible to wear are the air pump seals, the drive belt and chains, the sprockets, and the single rubber hose. I keep spares of these items on hand to ensure trouble free operation for years to come. Any maintenance or repair work can be accomplished with basic hand tools, and all the parts are serviceable and rebuildable.

An additional benefit of using compressed air for energy is the low cost of air tools. The current trend is pushing toward more battery powered equipment, so people are selling off their “outdated” pneumatic tools. There are many used air compressors for sale that have faulty motors or pumps, and are therefore quite inexpensive. There is a good supply of used stationary bicycles; most likely due to people buying them with the intention of starting a workout schedule but not following through with the plans. The next modification will be to add another 80 gallon tank to increase the storage capacity.

To sum it up, the bicycle powered air compressor’s main benefits are: no external power is needed, it can be operated in remote areas at any time, it is constructed of mostly recycled components that are easily rebuildable, and it does not cost anything to run. The additional side benefits are numerous, and more and more positive effects are still unfolding as I use this machine. At the core of the results are a healthy body from pedaling and a healthy mind from thinking outside the box.

Image: Human powered air compressor and energy storage system. Illustration by Andy Lagzdins.

Specifications:

Main Air Tank: 80 gallon Horizontal, Ingersoll Rand
Fill tank: 10 gallon, 125psi, SnapOn
Air Pump: Single Stage, 1hp Max, 115psi, Speedaire 40KH94
Stationary Bike: Schwinn Exerciser
Transmission: 8spd Internal Gear Hub, Sturmey Archer S80 XRK8
Flywheels: Cast Iron, 16” diameter, 1 ⅜” bore
Bearings: P207 sealed, self centering, solid foot
Belt: 4L Series V-belt
Chains: 1/2x1/8 KMC Z1EHX Wide
Valves: ½” NPT ball valves, brass
Air Filter: K&N pod, cloth and steel mesh

Video

See how the pedal powered air compressor works in this video.