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How to Escape From the Iron Age?

Mon, 18 Mar 2024 00:00:00 +0000

Image: Steel rebar construction for the concrete foundation of a wind turbine in Gilliam County, US. Image by Goose Chap, Wikimedia Commons (CC BY-SA 4.0)

Trapped in the Iron Age

In 1836, Danish antiquarian and curator Christian Jürgensen Thomsen distinguished three prehistorical eras based on the dominant materials used for weapons and cutting implements: the Stone Age, the Bronze Age, and the Iron Age.¹ Thomsen’s classification refers to the past, but according to his criteria, we have never evolved beyond the Iron Age. Even in the 21st century, iron remains the dominant material, not just for weapons and cutting implements but for about every modern technology.

We now use most iron in the form of steel. However, according to Thomsen’s criteria, we cannot speak of a “Steel Age.” First, steel is merely an alloy of iron (>98%) and carbon (<2%). Second, humans have been producing steel since the beginning of the Iron Age. That is a little-known fact in the Western world, where steel production only took off in the nineteenth century with fossil fuels. However, Asian and African metallurgists developed high-quality steels much earlier, and this knowledge eventually allowed Europeans to do the same – on a much larger scale.²

By 2021, the global iron and steel output reached 1,950 million tonnes (Mt). That is 22 times larger than the combined aluminum and copper output (88 Mt). The global iron and steel output corresponds to five times the global plastics output (391 Mt) and dwarfs the worldwide production of silicon (8.5 Mt) and lithium (0.1 Mt).³⁴ Steel is the fundamental material of industrial societies. Without plastics, lithium, or silicon, we would still be in an industrial society. Without iron and steel, we would be thrown back 3,000 years into the Bronze Age.

Where is all that steel?

The massive presence of steel in industrial society is not so obvious.⁵ At home, we find several steel appliances such as the refrigerator, washing machine, water boiler, bathtub, and cooking, heating, and cooling appliances. However, only 2-3% of total steel production ends up in domestic appliances.⁶⁷⁸ Outdoors, there’s a lot of steel in the form of vehicles. These are especially passenger cars that use around 10% of all steel globally (20% in rich countries). Busses, trucks, trains, and ships add another 4-5%. Altogether that is still less than 20% of the global steel output.

Most steel is embedded in other materials, located underground, or far away from residential areas.

Most steel is embedded in other materials, located underground, or far away from residential areas. More than half of global steel production goes into construction, which includes buildings (residential, commercial, industrial) and infrastructures (bridges, tunnels, harbors, canals, runways, oil rigs, refineries, pipelines, power plants, transmission lines, railways, subways, and so on). Much of that steel is embedded in concrete. Reinforced concrete is the world’s primary building material, and concrete is the only material that can match the output of steel (1,819 Mt in 2021).

Roughly 15% of global steel production serves to make machinery, including machine tools, industrial equipment, electrical hardware, and construction, mining, and farming machines. Even products made of other materials – such as other metals, plastics, and wood – are shaped by steel tools.⁵ The final 15% of steel production ends up in a variety of objects, from screws over food packaging to furniture and shipping containers.⁶⁷⁸

Image: Reinforced concrete is the world’s primary building material. Hole on Interstate 84, US. Image by Tony George, Oregon Department of Transportation, Wikimedia Commons (CC BY 2.0).

The environmental footprint of the steel industry

Steel is often presented as one of the most sustainable materials. Unlike plastics, steel can be recycled without any loss in quality. The steel industry has made great advances in energy efficiency, more so than many other industries. Making one ton of crude steel now requires roughly 20 gigajoules (GJ) of primary energy on average – three times less than in 1950.⁹ This compares very favorably to other materials such as aluminum (175 GJ/t), plastics (80-120 GJ/t), or copper (45 GJ/t).⁷ Unlike plastics, steel is a biodegradable material.¹⁰ Finally, iron ore is not in short supply. It makes up 5 percent of the Earth’s crust and is fourth in abundance among the elements.¹¹ For comparison, copper only makes up 0.01%.⁵

However, despite all these advantages, the global iron and steel industry consumes more energy and produces more carbon emissions than any other industry. The total primary energy use of crude steel production was 39 exajoules (EJ) in 2021, which corresponds to 7% of all energy used worldwide in that year (595 EJ). The greenhouse gas emissions are even higher because around 75% of energy use comes from coal – the fuel with the highest carbon emissions. In 2021, the iron and steel industry produced 3.3 Gt of carbon emissions, roughly 9% of global emissions (36.3 Gt).¹² The concrete industry follows closely with 8%.

The iron and steel industry consumes more energy and produces more carbon emissions than any other industry.

The estimates above come from the World Steel Association and the International Energy Agency. These data are available for all metals and have been documented over a long period, allowing for historical comparisons. However, they only refer to the smelting of the metal. They do not include the energy use and carbon emissions for mining and transporting iron ore, coal, limestone, scrap, and steel products. Nor do they include the energy and emissions for coke production and ore preparation – all essential to the steel production process.⁷

Scientific studies that have set wider boundaries for the iron and steel industry conclude that the energy cost of steel production increases by 50% to 100%.¹³ One report concludes that the methane emissions from metallurgical coal mining alone could increase emissions by 27%. Another study estimates that seaborne transport of iron ore and steel adds 10-15% extra emissions.¹⁴¹⁵ Iron and steel production also create other environmental problems, such as high water use, solid waste production, and significant air and water pollution.

The carbon footprint of the iron and steel industry is incompatible with current ambitions to eliminate net carbon emissions by 2050, even less so because steel production is very likely to expand further. Steel production grew tenfold since 1950 and doubled between 2000 and 2020, growing faster than many researchers had predicted.¹⁶ Furthermore, efficiency gains have decreased, and there is a scientific consensus that current technologies have reached their thermodynamic limits.⁷⁹¹⁷ During the last two decades, the average energy use for the production of 1 ton of steel has remained around 20 GJ/t.⁹¹⁸

How to make steel without fossil fuels?

There are two ways to make steel, and one is much more sustainable than the other.¹⁹ On the one hand, there is the blast furnace or basic oxygen furnace, in which steel is made from iron ore and coal. This technology is – in its essential form – 2000 years old. On the other hand, there is the electric arc furnace, in which steel is made from steel scrap and electricity. The electric arc furnace, which is a relatively new technology, consumes much less energy than the blast furnace, makes use of a recycled resource (no need to mine iron ore), and works without the direct use of coal or other fossil fuels (the electricity can be supplied by solar, wind, or atomic power).

The most energy-efficient electric arc furnaces now consume less than 300 kilowatt-hours of electricity per ton of steel produced.⁹²⁰ Hypothetically, if we had produced all steel in 2021 (1,950 Mt) in such furnaces, the total power consumption of the global iron and steel industry would have been only 585 terawatt-hours (Twh). That corresponds to just one-third of all electricity generated by wind turbines worldwide in the same year (1,848 Twh). Unfortunately, more than 70% of global steel output was made in blast furnaces fed by coal and iron ore.⁹²⁰ A blast furnace consumes twenty times more energy and cannot be operated by electricity because coal is both the fuel source and the chemical reductant. The combustion of coal produces carbon monoxide that reduces the iron from its ore.⁷

Not enough scrap available

The solution seems obvious: let’s produce all that steel in electric arc furnaces. However, this is impossible. There’s not enough scrap available: the continuous growth of the global steel output makes a circular flow of resources impossible.²¹ It takes decades before most steel becomes available for recycling. For example, there is 543 Mt of steel stocked in ships.²² The scrap available for recycling in 2021 corresponds to the production level of 1965 when global steel production was less than one-quarter of what it is today (450 Mt).⁹¹⁰¹⁵²³ Consequently, the other three quarters need to be produced in blast furnaces using coal and freshly mined iron ore.

Image: Cars for scrapping at the Port of Cardiff. Gareth James via Wikimedia Commons (CC BY-SA 2.0).

Nowadays, China produces roughly half of the steel in the world and does that almost exclusively (+90%) in blast furnaces using coal and iron ore. Many other steelmaking nations have a higher share of electric arc furnaces. However, it makes little sense to point the finger at China. First, the US and Europe have outsourced many of their industries to China since the 2000s, a trend that corresponds neatly with the growing steel output in that country. Furthermore, twenty to forty years ago, China hardly used any steel. Consequently, there is almost no scrap available. China has no other choice than to use blast furnaces.²⁴

Ever higher grades of steel

A second obstacle is the continuous development of higher grades of steel. There are now over 2,500 different types of steel with a variety of properties, such as increased strength, tolerance to high temperatures, or corrosion resistance.⁷⁹²³²⁵ Although these higher quality steels can be produced in electric arc furnaces, they are not made from scrap, and they have much higher energy use.

Steel available for recycling forms a mix of steel grades. That mix is suitable for making plain carbon steel but not highly alloyed steels, which require scrap with similar qualities. However, that scrap is not available. For example, stainless steel, the most produced special steel grade, has a recycling rate of only 15%. Almost 60 Mt of stainless steel was produced in 2021, compared to only 4 Mt in 1980.²⁶ The traditional use of stainless steel was in cutlery, surgical tools, and medical and food processing equipment. However, it is now also used in the construction of tunnels and outdoor furniture, wastewater treatment, seawater desalination, nuclear engineering, and the production of biofuels.⁷

The low recycling rate and the need for the extraction of additional elements such as chrome and nickel make higher grades of steel more energy-intensive to produce. For example, stainless steel production requires almost 80 GJ per ton, four times more than the production of plain carbon steel.⁷²³ The continuous development of higher-grade steels is stimulated by environmental legislation (such as the use of lighter steel in cars) and by competition from other materials, mainly aluminum and plastic composites.⁷⁹²³²⁵ Ironically, the competition with these materials, which consume even more energy, makes steel less and less sustainable.

Steel and renewable energy

The steel industry is heavily dependent on the energy supply, but the energy supply is also heavily dependent on the steel industry. Almost 10% of the global steel output goes into building and maintaining energy supply infrastructure. That amount corresponds to the entire steel output in 1950. A great share of that steel goes to gas and oil infrastructure.²⁷. Oil and gas mining, production, and transportation require steel for offshore drilling platforms, pipelines, refineries, tankers, and storage tanks. Coal mining depends on steel for cutters, loaders, conveyors, excavators, and trucks.⁷

Unfortunately, the planned switch to low-carbon energy sources and the electrification of heating and transport technologies will not decrease our dependency on the steel industry – on the contrary. A low-carbon power grid requires much more steel (and other materials) than an infrastructure based on fossil fuels. Wind and solar power are very diffuse power sources compared to fossil fuels. Therefore, it takes much more materials (and land) to produce the same energy. In jargon, wind and solar have low “power density” or high “material intensity.”²⁸²⁹³⁰³¹³²

A low-carbon power grid requires much more steel than an infrastructure based on fossil fuels.

The “steel intensity” of thermal gas and coal power plants is between 50 and 60 tonnes of steel per megawatt of installed power.³³ Hydroelectric power plants have a lower steel intensity, with 20-30 tonnes of steel per MW.⁷³³ Atomic power’s steel intensity is also lower at between 20 and 40 tonnes of steel per installed MW.³³³⁴ On the other hand, solar PV requires between 40 and 170 tonnes of steel per installed MW.³³³⁵ Although there is little or no steel in the solar panels themselves, it’s the material of choice for the structures that support them.

Steel and wind power

The most steel-intensive power source – by far – is the modern wind turbine. The steel intensity of a wind turbine depends on its size. A single, large wind turbine requires significantly more steel per megawatt of installed power than two smaller wind turbines.³⁶ For example, a 3.6 MW wind turbine with a 100-meter tall tower requires 335 tons of steel (83 tons/MW), while a 5 MW wind turbine with a 150-meter tall tower needs 875 tons of steel (175 tons/MW).³⁷ The trend is towards taller wind turbines and a higher steel intensity.

Image: Steel towers for wind turbines in the port of Rotterdam. Image: Melle Smets.

Steel consumption further increases for offshore wind turbines. Onshore wind power plants rely on reinforced concrete for their foundations, but offshore wind turbines need massive steel structures such as monopiles and jackets.³⁸ The steel intensity for offshore wind turbines is calculated to be around 450 tonnes per MW for a 5 MW turbine – eight times higher than the steel intensity of a thermal power plant.³⁶. As these wind turbines get taller and move into deeper waters, their steel use further increases.

The most popular offshore wind turbine nowadays has a capacity of 7 MW, while the largest ones have a capacity of 14 MW.³⁶ If we make a conservative estimate based on the data above (the steel intensity doubles for every doubling of the power capacity), a 14 MW offshore wind turbine would require 1,300 tons of steel per MW or 18,200 tonnes in total. Such a wind turbine thus consumes 24 times more steel than a coal or gas power plant of the same power capacity.

Shorter life expectancy

The difference between renewable power sources and fossil fuels becomes even larger if the steel intensity is calculated per unit of energy rather than power (MWh instead of MW). In contrast to coal and gas power plants, the output of wind and solar power plants depends on the weather, and they do not always produce their maximum power capacity. Therefore, replacing 1 MW of fossil electricity generation capacity requires the installation of (on average) 4 MW of solar power or 2 MW of wind power.³⁹ A 14 MW offshore wind turbine thus has a steel intensity that is almost 50 times higher than a fossil fuel power plant for every kilowatt-hour of electricity produced.⁴⁰

A 14 MW offshore wind turbine has a steel intensity that is almost 50 times higher than a fossil fuel power plant for every kilowatt-hour of electricity produced.

Solar and wind power plants also have shorter lifetimes (20-30 years) compared to thermal power plants (30-60 years).³¹ While this does not affect the steel intensity per MW of power installed, it again increases the steel intensity per unit of energy produced over time. That does not always lead to a doubling of steel use because foundations for offshore wind turbines and structures for solar panels may have longer lifetimes than the power sources they support and could thus be reused.⁴¹

Power transmission infrastructure

The data above only include the steel used in the power plants themselves. For fossil fuel power plants, they do not include the steel used in the pipelines, oil rigs, coal excavators, and the like. However, the same goes for the low-carbon power sources. Because they need much more resources than thermal power plants (steel but also other metals and materials), they depend on a global mining and transport infrastructure that is just as steel-intensive as the supply chain for fossil fuels.

Furthermore, because they are more diffuse power sources with intermittent and unpredictable power production, often located far away from energy consumption centers, renewable power plants drive the expansion of transmission infrastructure. That infrastructure is also based on steel – from switchyard equipment over towers to conduction cables.²⁸²⁹³⁰³¹³²⁴²

Finally, low-carbon power sources also have a high need for special grades of steel, which are more energy-intensive to produce. Steel for off-shore wind turbines should resist corrosion, and stainless steel is increasingly used for solar panel support structures.⁴³ Electrical lamination steel (iron-silicon) is indispensable for transformers in the power network.⁷ Nuclear power plants may have a relatively low steel intensity but are completely built up of energy-intensive specialty steels. For example, cladding the fuel elements containing fissionable uranium requires zirconium steel, while all structural elements contain austenitic stainless steel.⁷⁴⁴

Low carbon grid cannot be made from recycled steel

The high steel intensity of low carbon power sources confronts us with a so-called “catch-22”, a situation in which there seems to be no escape from a problem no matter what we do. We need much more steel if we replace thermal power plants with renewable ones. Because there is not enough steel scrap available, we can only produce that extra steel from iron ore in blast furnaces burning fossil fuels. To address climate change, we need to build low-carbon sources quickly and in great numbers. However, to achieve circular material flows and build low-carbon power sources from scrap and renewable electricity, we would have to do the opposite: slow down the development of a low-carbon power grid.

Image: Steel foundations for off-shore wind turbines. Image by Glen Wallace, Wikimedia Commons (CC BY 2.0).

A well-cited study from 2013 concluded that if wind and solar power would supply 25,000 Twh of electricity – which corresponds to total global electricity demand in 2021 – we need about 3,200 Mt of steel to build the power plants alone.³³⁴⁵ Global electricity demand is projected to grow to between 52,000 and 71,000 terawatt-hours in 2050, which would increase the extra steel demand to between 6,400 and 8,960 Mt.⁴⁶ Spread out over the lifetime of solar panels and wind turbines (25 years), we would have to produce 256 to 358 Mt extra steel per year to make wind turbines and solar panel structures – comparable to the steel demand for passenger cars (195 Mt) and other transportation modes (98 Mt) combined.

That is still a very optimistic estimation. Electricity demand only makes up around 20% of total energy demand. If the total energy demand (177,000 Twh in 2021) would be supplied by wind and solar, we would need 22,400 Mt of steel. That’s an extra 896 Mt steel per year – as much as the global production in the early 2000s. You could argue that electricity can be used more efficiently than fossil fuels, for example, in cars and heating systems. However, at the same time, total energy demand is expected to rise further, countering the gains made by increased energy efficiency.

The high-tech solutions

The steel industry counts on technological solutions to make steel production carbon neutral. One option is to replace coal by gas, an approach that is already common in the Middle East and North America. Gas-based steelmaking results in somewhat lower carbon emissions, but they are still much higher than in the case of the electric arc furnace. Therefore, most attention goes to hydrogen, which can replace purified coal (coke) as a reducing agent in a direct reduction shaft furnace.⁴⁷ However, hydrogen-based steelmaking does not offer an escape from the catch-22 because it further increases the need for a steel-intensive infrastructure.

The production of hydrogen is energy-intensive. It takes 50-55 kilowatt-hour to make 1 kg of hydrogen and 60 kg of hydrogen to make 1 ton of steel.⁴⁷ The production of 1 ton of steel from hydrogen thus consumes 3,000 kWh of electricity, which is ten times higher than the electricity use of an electric arc furnace making steel from scrap. Consequently, hydrogen-based steelmaking requires roughly ten times more wind turbines and solar panels than scrap-based steel production – and thus ten times more steel. On top of this comes the steel for building the pipelines and storage tanks that are part of the hydrogen infrastructure.

Image: Worker in a blast furnace. Bundesarchiv, B 145 Bild-F079044-0020 / CC-BY-SA 3.0.

Carbon capture and storage, in which the carbon emissions of steelmaking plants are captured and then stored underground, faces the same problems. It requires a steel infrastructure and extra energy, thus indirectly raising the use of fossil fuels. Reverting to older, preindustrial steelmaking processes is not the answer either. Today’s blast furnace is essentially still the blast furnace from earlier centuries, only much more energy efficient.⁷

The low-tech solutions

The picture painted above seems to offer little hope for carbon-neutral steelmaking and power production. However, there is a low-tech solution that could achieve it. We could adjust steel production to the available scrap supply both in quantity and quality. That would allow us to produce all steel from scrap in electric arc furnaces, dramatically reducing energy consumption and eliminating almost all carbon emissions. Of course, the intent should not be to replace steel with plastic composites and aluminum because they are even more energy-intensive to produce. The only solution is to reduce material use overall.

We could adjust steel production to the available scrap supply both in quantity and quality.

Reducing the steel output and using more common steel grades would not bring us back to the Bronze Age. As noted, global end-of-life ferrous scrap availability was approximately 450 Mt in 2021, which would allow us to produce roughly one-quarter of the current steel output. Furthermore, the scrap supply will continue to rise for the next 40 years, enabling us to produce more and more low-emission steel each year. By 2050, scrap availability is expected to rise to about 900 Mt, almost half of today’s global steel production.⁴⁸ All that extra steel could be invested in expanding the low-carbon power grid without raising emissions first.

There is a lot of room to reduce the steel intensity of modern society. All our basic needs – and more – could be supplied with much less steel involved. For example, we could make cars lighter by making them smaller. That would bring energy savings without the need for energy-intensive high-grade steel. We could replace cars with bicycles and public transportation so that more people share less steel. Such changes would also reduce the need for steel in the road network, the energy infrastructure, and the manufacturing industry. We would need fewer machine tools, shipping containers, and reinforced concrete buildings. Whenever steel intensity is reduced, the advantages cascade throughout the whole system. Preventing corrosion and producing steel more locally from local resources would also reduce energy use and emissions.¹⁰¹⁴

The continuous growth of the steel output – the increasing steel intensity of human society – makes sustainable steel production impossible. No technology can change that because it’s not a technological problem. Like forestry can only be sustainable if the wood demand does not exceed the wood supply, steel is sustainable or not depending on the balance between (scrap) supply and (steel) demand. We may not be able to escape the Iron Age, but we have an option to escape the catch-22 that inextricably links steel production with fossil fuels.⁴⁹

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Forthcoming article, Kris De Decker, Low-tech Magazine. Subscribe to Low-tech Magazine’s newsletter. ↩︎
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See, for example: Hatayama, Hiroki, et al. “Outlook of the world steel cycle based on the stock and flow dynamics.” Environmental science & technology 44.16 (2010): 6457-6463. This paper predicted steel demand to reach 1.8 billion tonnes only by around 2025. ↩︎
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About 5% of global steel is produced by a third method: gas-based direct iron reduction. These furnaces use gas instead of coal and have therefore lower carbon emissions. However, emissions are still much higher than in the case of the electric arc furnace. Gas-based steelmaking mainly happens in the Middle East and North America. ↩︎
He, Kun, and Li Wang. “A review of energy use and energy-efficient technologies for the iron and steel industry.” Renewable and Sustainable Energy Reviews 70 (2017): 1022-1039. This source gives a value of 1-1.5 GJ/ton of crude steel. ↩︎ ↩︎
This also holds true for many other materials. See: “How circular is the circular economy?”, Kris De Decker, Low-tech Magazine, November 2018. https://qelnixcor.cloud/2018/11/how-circular-is-the-circular-economy/ ↩︎
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In the West, the expansion of steel use happened over a period of 150 years, in tandem with technological evolution. In contrast, China compressed this technological evolution in just a few decades: shipping and railways, electrification, steel buildings, the car and the airplane, the internet, and renewable power technologies. There are still large parts of the world where the steel intensity of society is very low, such as India and Africa. There is thus still a lot of room for the growth of the steel output. Source: Smil, Vaclav. Still the iron age: iron and steel in the modern world. Butterworth-Heinemann, 2016. ↩︎
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Gervásio, Helena, et al. “Comparative life cycle assessment of tubular wind towers and foundations–Part 2: Life cycle analysis.” Engineering structures 74 (2014): 292-299. & Rebelo, Carlos, et al. “Comparative life cycle assessment of tubular wind towers and foundations–Part 1: Structural design.” Engineering structures 74 (2014): 283-291. ↩︎
Assessing the significance of steel to the global wind industry, S&P Global, Commodity Insights. December 2021. https://www.spglobal.com/commodityinsights/en/ci/research-analysis/assessing-the-significance-of-steel-to-the-global-wind-industry.html ↩︎
Bolson, Natanael, Pedro Prieto, and Tadeusz Patzek. “Capacity factors for electrical power generation from renewable and nonrenewable sources.” Proceedings of the National Academy of Sciences 119.52 (2022): e2205429119. https://www.pnas.org/doi/10.1073/pnas.2205429119 ↩︎
This result corresponds well with Vidal, Olivier, Bruno Goffé, and Nicholas Arndt. “Metals for a low-carbon society.” Nature Geoscience 6.11 (2013): 894-896. The data are in the supplementary info: https://www.nature.com/articles/ngeo1993#Sec5 ↩︎
For off-shore wind turbines, the lifetime of the foundations is estimated to be 100 years, so in principle they could serve for replacement wind turbines of the same size. On the other hand, it is not self-evident that these steel foundations will eventually be recycled. First, only around 10% of decommissioning costs can be recovered by recycling the metal, meaning that it is not economically and perhaps even energetically interesting to do it. Second, in some cass marine life has flourished around the foundations. The four offshore wind farms that had been decomissioned in 2019 lasted for 15, 18, 20 and 26 years. Source: Topham, Eva, et al. “Recycling offshore wind farms at decommissioning stage.” Energy policy 129 (2019): 698-709. ↩︎
See https://www.fedsteel.com/insights/steels-role-in-the-us-power-infrastructure/ ↩︎
See https://industry.arcelormittal.com/products-solutions/Products_in_the_spotlight/magnelis ↩︎
Maziasz, Philip J., and Jeremy T. Busby. Properties of austenitic stainless steels for nuclear reactor applications. Oak Ridge National Lab.(ORNL), Oak Ridge, TN (United States), 2012. ↩︎
Part of this has already been built. The researchers start from the solar and wind power production in 2013, which was 400 Twh, while both power sources produced 2,894 Twh in 2021. ↩︎
Electricity consumption worldwide from 2000 to 2022, with a forecast for 2030 and 2050, by scenario. Statista. https://www.statista.com/statistics/1426308/electricity-consumption-worldwide-forecast-by-scenario/#:~:text=According%20to%20a%20recent%20forecast,on%20the%20energy%20transition%20scenario ↩︎
Bhaskar, Abhinav, et al. “Decarbonizing primary steel production: Techno-economic assessment of a hydrogen based green steel production plant in Norway.” Journal of Cleaner Production 350 (2022): 131339. ↩︎ ↩︎
Scrap use in the steel industry, World Steel Association. May 2021. https://worldsteel.org/wp-content/uploads/Fact-sheet-on-scrap_2021.pdf ↩︎
Another motivation for reducing the steel intensity of modern society is to limit the consequences of geopolitical conflicts. The more steel we produce for peaceful purposes, the more steel becomes available for war and destruction. Remarkably, the production of military equipment is absent from modern steel statistics, and if mentioned, its share is very low. However, in times of war, steelmaking facilities switch to producing steel for military purposes. The steel industry can thus be converted into a weapons industry at any moment, and there is now a lot more steel production capacity available than there has ever been in history. ↩︎

Workshop in Rotterdam: How to Build a Bike Generator

Fri, 06 Oct 2023 00:00:00 +0000

Afbeelding: Low-tech Magazine workshop in Rotterdam, the Netherlands. Poster: Marie Verdeil. Image: Sara Vercauteren

The workshop takes place on behalf of the “House of the Future”, a spinoff of the Human Power Plant project. The House of the Future will bring the Human Power Plant’s “Human Powered Neighbourhood” scenario to life in Bospolder-Tussendijken, Rotterdam, in the coming years. You can already get a taste of it at the Museum Boijmans van Beuningen’s online exhibition (in Dutch).

Since this community will run largely on human power, we need human power plants. Therefore, Kris De Decker and Marie Verdeil organise an open and collaborative workshop where we will build a fully working bicycle generator based on a second-hand spinning bike. You are welcome to learn, experiment, teach, and help.

During the workshop, we will mount a generator on the bike, build a control panel, and modify devices to run on low voltage. This bicycle generator will be specifically designed to serve as a power source in the communal workshop, so that we can use it to build more stuff we need (including more bike generators).

Programme:

Tuesday 10 October (14h-18h): open day House of the Future
Wednesday 11 October (15h-17h): introduction workshop
Thursday 12 October (10h-17h): workshop
Friday, October 13 (14h-19h): workshop
Saturday, October 14 (14h-17h): workshop

We speak Dutch, English, French, and Spanish. The introduction (11 oct) will be in Dutch only.

Admission is free. To participate: just walk in (Jan Kobellstraat 56A, Rotterdam) or send an email to contact [] huisvandetoekomst [] org.

All future events will be published on our events page.

Illustration: Future vision of the human powered housing block in Rotterdam. Drawing: Melle Smets.

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. ↩︎