LOW←TECH MAGAZINE English

How to Make Wind Power Sustainable Again

Sun, 02 Jun 2019 00:00:00 +0000

Illustration: Eva Miquel for Low-tech Magazine.

For more than two thousand years, windmills were built from recyclable or reusable materials: wood, stone, brick, canvas, metal. When – electricity producing – wind turbines appeared in the 1880s, the materials didn’t change. It’s only since the arrival of plastic composite blades in the 1980s that wind power has become the source of a toxic waste product that ends up in landfills.

New wood production technology and design makes it possible to build larger wind turbines almost entirely out of wood again – not just the blades, but also the rest of the structure. This would solve the waste issue and make the manufacturing of wind turbines largely independent of fossil fuels and mined materials. A forest planted in between the wind turbines could provide the wood for the next generation of wind turbines.

How Sustainable is a Windmill Blade?

Wind turbines are considered to be a clean and sustainable source of power. However, while they can indeed generate electricity with lower CO2-emissions than fossil fuel power plants, they also produce a lot of waste. This is easily overlooked, because roughly 90% of the mass of a large wind turbine is steel, mainly concentrated in the tower. Steel is commonly recycled and this explains why wind turbines have very short energy payback times – the recycled steel can be used to produce new wind turbine parts, which greatly lowers the energy required during the manufacturing process.

However, wind turbine blades are made from light-weight plastic composite materials, which are voluminous and impossible to recycle. Although the mass of the blades is limited compared to the total mass of a wind turbine, it’s not negligible. For example, one 60 m long fiberglass blade weighs 17 tonnes, meaning that a 5 MW wind turbine produces more than 50 tonnes of plastic composite waste from the blades alone.

Image: A fiberglass reinforced plastic blade. Source: [Gurit](https://www.gurit.com/Our-Business/Industries--Markets/Wind).

A windmill blade typically consists of a combination of epoxy – a petroleum product – with fiberglass reinforcements. The blades also contain sandwiched core materials, such as polyvinyl chloride foam, polyethylene terephtalate foam, balsa wood (intertwined in fibers and epoxy) and polyurethane coatings. ¹²³⁴

Unlike the steel in the tower, the plastic in blades cannot be recycled to make new plastic blades. The material can only be “downcycled”, for instance by shredding it, which damages the fibers and makes them useless for anything but a filler reinforcement in cement or asphalt production. Other methods are being investigated, but they all run into the same problem: nobody wants the “recycled” material. Some architects have re-used windmill blades, for example to build benches or playgrounds. But we cannot build everything out of wind turbine blades.

A 5 MW wind turbine contains more than 50 tonnes of unrecyclable plastic in the blades alone.

Because of the limited options for recycling and re-use, windmill blades are usually landfilled (in the US) or incinerated (in the EU). The latter approach is not less unsustainable, because incinerating the blades only partially reduces the amount of material to be landfilled (60% of the scrap remains as ash) and converts the rest into air pollution. Furthermore, given that fiberglass is incombustible, the caloric value of the blades is so limited that little or no power can be produced. ¹²³⁴

Dealing With Waste – 25 Years Later

Most of the roughly 250,000 wind turbines now in operation worldwide were installed less than 25 years ago, which is their estimated life expectancy. However, the rapid growth of wind power over the last two decades will soon be reflected in a delayed but ever increasing and never-ending supply of waste materials.

For example in Europe, the share of installed wind turbines older than 15 years increases from 12% in 2016 to 28% in 2020. In Germany, Spain and Denmark, their share increases to 41-57%. In 2020 alone, these countries will each have to dispose of 6,000 to 12,000 wind turbine blades. ⁵

Image: Old-fashioned windmills had sails made entirely from recyclable materials. Image: Rasbak (CC BY-SA 3.0)

Discarded blades will not only become more numerous but also larger, reflecting a continuous trend towards ever larger rotor diameters. Wind turbines built 25 years ago had blade lengths of around 15-20 m, while today’s blades reach lengths of 75-80 m or more. ³ Estimates based on current growth figures for wind power have suggested that composite materials from blades worldwide will amount to 330,000 tonnes of waste per year by 2028, and to 418,000 tonnes per year by 2040. ¹

The rapid growth in wind power over the last two decades will soon be reflected in a delayed but ever increasing and never-ending supply of waste materials.

These are conservative estimates, because numerous blade failures have been reported, and because constant development of more efficient blades with higher power generating capacity is resulting in blade replacement well before their estimated lifespan. ¹⁶ Furthermore, this amount of waste results from wind turbines installed between 2005 and 2015, when wind power only supplied a maximum of 4% of global power demand. If wind would supply a more desirable 40% of (current) power demand, there would be three to four million tonnes of waste per year.

Windmill Blades Through History

Yet a look at the history of wind power shows that plastic is not an essential material. The use of wind for mechanical power production dates back to Antiquity, and the first electricity generating windmills – now called wind turbines – were built in the 1880s. However, fiberglass blades only took off in the 1980s. For some two thousand years, windmills of whatever type were entirely recyclable.

The first wind turbines in Europe, built by Paul La Cour in Denmark, had traditional slatted wooden sails. Image: Paul La Cour Museum.

Old-fashioned windmills had towers built out of wood, stone, or brick. Their “blades” or “sails” were usually made of a wood framework covered with canvas or wood boards. In later centuries, parts were increasingly made from iron, also a recyclable material.

When new types of sails were invented in the eighteenth and nineteenth centuries (such as spring, patent, and rolling-reefer sails), as well as in the twentieth century (Dekkerized and Bilau sails), the design changed but the materials remained the same (eventually including aluminum). ⁷ Furthermore, contrary to modern wind turbines, which need to be replaced regularly and in their entirety, old-fashioned windmills could last for many decades or even centuries through regular repair and maintenance.

A look at the history of wind power shows that plastic is not an essential material.

The first wind turbine in the US, built by Charles F. Brush, had a 17 m diameter annular sail with 144 thin blades made of cedar wood. The first wind turbine in Europe, built by Paul La Cour in Denmark, had four traditional slatted wooden sails with a rotor diameter of 22.8 m.

La Cour’s design was copied by local enterprises in Denmark, resulting in thousands of wind turbines operating on Danish farms between 1900 and 1920. Dozens of experimental wind turbines were built during the first half of the twentieth century, including some with steel blades, such as the 1939 Smith-Putnam wind turbine in the US. ⁸

The three-bladed Gedser wind turbine relied on an air frame superstructure for blade stiffening.

In 1957, Johannes Juul – a student of Paul La Cour – built the three-bladed Gedser wind turbine. It had a rotor diameter of 24 m and relied on an air frame superstructure of steel wires for rotor and blade stiffening. The blades were built from steel spars, with aluminium shells supported by wooden ribs.

The Gedser turbine remained the most successful wind turbine until the mid-1980s. It ran for 11 years without maintenance, generating up to 360,000 kWh per year, but was not repaired when a bearing failed. When the turbine was refurbished and tested in the late 1970s, it performed better than the first wind turbines with fiberglass blades. ⁸⁹

Size Matters

The first wind turbine with fiberglass blades was installed in 1978 in Denmark, where it powered a school. With its 54 m diameter rotor, the Tvind turbine was at the time the largest wind turbine ever built. After 1980, fiberglass blades became standard in Denmark and the “Danish design” was later copied all over the world. The plastic blade, so it seems, is what defines the modern wind turbine. This presents us with a dilemma.

The switch to fiberglass blades was mainly driven by the desire to build larger wind turbines. Larger wind turbines lower the cost per kilowatt-hour of generated electricity, for two reasons: the wind increases with height, and the doubling of the rotor radius increases power output four times.

The desire to build larger wind turbines has driven the wind industry ever since. Rotor diameters increased from around 50 m in the 1990s to 120 m in the 2000s. Today’s largest off-shore wind turbines have rotor diameters of more than 160 m, and a 12 MW turbine with a 220 m rotor diameter is being constructed in the Netherlands. ³⁶¹⁰

Improved windmill blade from the 1940s, built and designed by P.L. Fauel. Image: Rasbak (CC BY-SA 3.0)

However, with increasing size, the mass of the rotor blade also increases, which requires lighter materials. At the same time, larger blades deflect more, so that their structural stiffness is of increasing importance to maintain optimal aerodynamic performance and to avoid the blade hitting the tower. In short, larger wind turbines with longer blades place ever higher demands on the materials used, and these exceed the capacities of recyclable materials. ¹¹¹² Wind turbines have become more efficient, but also less sustainable.

Larger wind turbines with longer blades place ever higher demands on the materials used.

Right now, this trend is illustrated by the increasing use of carbon fiber reinforced plastic, which is even stronger, stiffer and lighter than fiberglass reinforced plastic. ¹¹ The use of carbon fibers – which further complicates potential recycling – has become standard in the largest wind turbine blades, mainly in highly stressed locations such as the blade root or the spar caps. Consequently, we have again entered a new era in which blades are now so large that they cannot be made out of fiberglass reinforced composites alone anymore.

Reinventing the Windmill Blade

An industry that calls itself sustainable and renewable cannot send millions of tonnes of plastic waste to landfills each year. Consequently, could we revert to building wind turbine blades from recyclable materials alone? And how large could we build them? To which extent can efficiency and sustainability be reconciled?

Improved windmill blade from the 1930s, designed by Kurt Bilau. The tower is made of stone, the sails are made of wood and aluminum. Image: Frank Vincentz (CC BY-SA 3.0).

Most research into the design of more sustainable wind turbine blades sticks with plastic as the main material. Thermoplastics can be melted and re-used, making it possible to recycle the blades into new wind turbine blades, even on-site. However, due to the material’s lower strength and stiffness, these blades have not been built larger than 9 m for now. ¹¹³

Another area of development is the substitution of glass fibers for wood or flax fibers. These blades can be larger, but they have only small sustainability advantages over fiberglass-epoxy blades. ¹⁴¹⁵ The petroleum-based epoxy is more harmful than the glass fiber, and natural fiber based composite materials absorb more of it. ¹⁶¹⁷¹²

The length of wood blades is no longer limited by the availability of large tree trunks of consistent quality.

Some engineers and scientists follow different paths and revert to more traditional wood construction. For small wind turbines, blades can be carved out of solid wood. For larger wind turbines, the blades can be composed of a hollow aerodynamic shell and an internal framework of ribs and stringers supported by a beam called the spar – all built from laminated veneer wood boards, beams and panels.

Laminated Veneer Lumber

Laminated veneer lumber – in which the wood is peeled off the tree and then glued back together in thin layers – is a wood product that appeared in the 1980s, and which has an important advantage in relation to solid wood components. The consistency of wood can vary within a single tree. Therefore, the length of the wood spars used in pre-industrial windmills was limited by the availability of large tree trunks of consistent quality. The largest traditional windmill ever built – the 1900 Murphy mill in San Francisco – had a rotor diameter of 35 m.

Patent sails with Dekker leading edges, 1940s. Image: Reboelje.

In contrast, the process of veneering spreads out defects such as knots, giving better and more predictable stiffness properties. This allows to build larger wooden blades. ¹² Wood laminates offer substantial cost and weight reductions as compared to fiberglass. Although the strength and stiffness are lower, much of the load that the blade must support is a consequence of its own weight, so a wood blade doesn’t need to be as strong as a fiberglass blade. ¹² Nevertheless, the low stiffness of wood makes it difficult to limit the elastic deflections for very large rotor blades.

In a 2017 study of a 5 MW wind turbine with 61.5 m long blades, conducted at UMassAmherst in the US, it was calculated that in order to be stiff enough and withstand the forces that it’s exposed to, a blade made of laminated wood veneer panels would be 2.8 heavier than a plastic blade (48 versus 17 tonnes) and have a laminate of over 50 cm thick. ¹² Although this suggests that it’s technically possible to build a wooden blade more than 60 m long, it’s not very practical. With heavier blades, the wind turbine needs to be built much stronger, which increases the costs and the use of resources.

Best of Both Worlds?

There’s two ways to solve this problem. The first is to design a blade largely made from laminated veneer lumber, but reinforced with carbon composite spars and covered with an outer layer of fiberglass composite. In the above mentioned study it was found that such a wood-carbon hybrid blade is stiff enough to reach a length of 61.5 m for a 5 MW turbine, and can be built 3 tonnes lighter than a fiberglass blade. ¹² Another study for a wood-carbon blade of the same length comes to a similar conclusion, although in this case the wood-carbon blade is slightly heavier than the plastic blade. ¹⁴

A blade largely made from laminated veneer lumber, but reinforced with carbon composite spars, can be built more than 60 metres long.

Wood-carbon blades contain less plastic composite material, and the plastic is not intertwined with wood throughout the blade but clearly separated from it, making blade re-use, recycling or incineration more attractive. However, according to the studies mentioned above, a wood-carbon blade still contains 2.5 tonnes ¹⁴ to 6.2 tonnes ¹² of plastic composites, meaning that a three-bladed 5 MW wind turbine would produce 7.5 to 18.4 tonnes of unrecyclable waste – compared to 50 tonnes for a conventional blade.

Smaller Wind Turbines?

The environmental damage of the carbon-epoxy spars can be viewed as acceptable, if compared to the larger damage done by conventional wind turbine blades. However, the waste problem would not be solved, and further growth in wind power would still result in ever larger waste streams.

Image: A laminated wooden blade with carbon spar caps. Source: [^14]

Alternatively, we could define sustainability in more ambitious terms, and build wind turbine blades completely out of wood again – even if this means that we have to build them smaller. There’s an extra argument to question our focus on efficiency: the decrease in sustainability not only shows in the blades. Other parts of wind turbines are also increasingly made from plastic composites – most notably the nose cone and the nacelle cover (the housing that protects the drivetrain and the auxiliary equipment from the elements). ¹²³⁴

Other trends are the increased use of electronics, which are not suited for recycling, and of permanent magnet generators based on rare earth materials, which save costs compared to a mechanical gearbox but only at the expense of more destructive mining. Larger wind turbines also kill more birds and bats. ¹⁸

By sacrificing some efficiency, we could gain a lot in sustainability.

By sacrificing some efficiency, we could gain a lot in sustainability. Wind power advocates may not agree, because it would make wind power less competitive with fossil fuels. However, more expensive wind power can always be counteracted by higher prices for fossil fuels.

What’s really problematic is our choice of cheap fossil fuels as a benchmark to determine the viability of wind power. It’s by aiming to compete with fossil fuels – and thus by aiming to provide the energy for a lifestyle built on fossil fuels – that wind turbines have become increasingly damaging to the environment. If we would reduce energy demand, smaller and less efficient wind turbines would not be a problem.

Image: The first wind turbine in the US, built by Charles F. Brush, had a 17 m diameter annular sail with 144 thin blades made of cedar wood.

How large could we build practical wind turbine blades from laminated veneer lumber alone? Nobody seems to know. I asked Rachel Koh, the scientist who calculated the requirements for the 61.5 m wood-only blade, but she couldn’t help me: “I only ran the model for the blades of a 5 MW turbine. It would be hypothetically possible to run another study to answer your question, but it’s not a small undertaking”. She also notes that it’s possible to further improve the stiffness of wood laminates with manufacturing innovations.

A Forest of Wind Turbines

Whether we opt for large wood-carbon blades or smaller wood-only blades, in both cases we could also build the tower and the nacelle cover from laminated wood products. In 2012, the German company TimberTower built a laminated wood tower 100 m tall for a 1.5 MW wind turbine. A wooden tower seems to be besides the point, because it replaces part of a wind turbine that’s already perfectly recyclable. However, a wind turbine of which the structure is almost completely built out of wood offers extra benefits.

Illustration: Eva Miquel for Low-tech Magazine

Wood could make the production of wind turbines entirely independent of mined materials and of fossil fuels, except for the gearwork and the electric components (but further gains can be achieved, whenever possible, by using wind power for direct mechanical). ¹⁹ Furthermore, wooden wind turbines could become a carbon sink – sequestering CO2 from the atmosphere in their wood components.

Finally, the space between wind turbines on a wind farm, which is not suited as a residential area, could be used to grow a forest that would provide the wood for the next generation of wind turbines. The lumber could be sawed, processed and assembled on-site, which eliminates the energy use associated with the transport of wind turbine parts. The energy required for manufacturing the laminates and for constructing the turbines could come from the windmills, as well as from forest biomass. Especially if blades are made of wood only, the wind turbine could become a textbook example of the circular economy.

What about solar panels?

A forthcoming article investigates the sustainability of solar panels. Is toxic and unrecyclable waste inherent to solar PV power? Could we build solar panels using sustainable materials? And what would that mean for the affordability and efficiency of solar power?

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Ziegler, Lisa, et al. “Lifetime extension of onshore wind turbines: A review covering Germany, Spain, Denmark, and the UK.” Renewable and Sustainable Energy Reviews 82 (2018): 1261-1271. https://www.sciencedirect.com/science/article/pii/S1364032117313503 ↩︎
Lefeuvre, Anaële, et al. “Anticipating in-use stocks of carbon fiber reinforced polymers and related waste flows generated by the commercial aeronautical sector until 2050.” Resources, Conservation and Recycling 125 (2017): 264-272. https://www.sciencedirect.com/science/article/pii/S0921344917301775 ↩︎ ↩︎
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Lundsager, P., Sten Tronæs Frandsen, and Carl Jørgen Christensen. “Analysis of data from the Gedser wind turbine 1977-1979.” (1980). http://orbit.dtu.dk/files/33441311/ris_m_2242.pdf ↩︎
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Koh, Rachel. “Bio-based Wind Turbine Blades: Renewable Energy Meets Sustainable Materials for Clean, Green Power.” (2017). https://scholarworks.umass.edu/dissertations_2/1102/ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
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Heat your House with a Mechanical Windmill

Wed, 27 Feb 2019 00:00:00 +0000

Image: Illustration by [Rona Binay](https://ronabinay.com/) for Low-tech Magazine.

Renewable energy production is almost entirely aimed at the generation of electricity. However, we use more energy in the form of heat, which solar panels and wind turbines can produce only indirectly and relatively inefficiently. A solar thermal collector skips the conversion to electricity and supplies renewable thermal energy in a direct and more efficient way.

Much less known is that a mechanical windmill can do the same in a windy climate – by oversizing its brake system, a windmill can generate lots of direct heat through friction. A mechanical windmill can also be coupled to a mechanical heat pump, which can be cheaper than using a gas boiler or an electric heat pump driven by a wind turbine.

Heat versus Electricity

On a global scale, thermal energy demand corresponds to one third of the primary energy supply, while electricity demand is only one-fifth. ¹ In temperate or cold climates, the share of thermal energy is even higher. For example in the UK, heat counts for almost half of total energy use. ² If we only look at households, thermal energy for space and water heating in temperate and cold climates can be 60-80% of total domestic energy demand. ³

In spite of this, renewable energy sources play a negligible role in heat production. The main exception is the traditional use of biomass for cooking and heating – but in the “developed” world even biomass is often used to produce electricity instead of heat. The use of direct solar heat and geothermal heat provide less than 1% and 0.2% of global heat demand, respectively ⁴ ⁵. While renewable energy sources account for more than 20% of global electricity demand (mostly hydroelectric), they only account for 10% of global heat demand (mostly biomass). ⁵ ⁶

Direct versus Indirect Heat Production

Electricity produced by renewable energy sources can be – and is being – converted to heat in an indirect way. For example, a wind turbine converts its rotational energy into electricity by the use of its electrical generator, and this electricity can then be converted into heat using an electric heater, an electric boiler, or an electric heat pump. The result is heat generated by wind energy.

In particular, the electric heat pump is promoted by many governments and organisations as a sustainable solution for renewable heat generation. However, solar and wind energy can also be used in a direct way, without converting them to electricity first – and of course the same applies to biomass. Direct heat production is cheaper, can be more energy efficient, and is more sustainable than indirect heat production.

Image: prototypes of heat generating windmills, built by Esra L. Sorensen in 1974. Photo by Claus Nybroe. Source: [^13]

The direct alternative for solar photovoltaic power is solar thermal power, a technology that appeared in the nineteenth century following cheaper production technologies for glass and mirrors. Solar thermal energy can be used for water heating, space heating or industrial processes, and this is 2-3 times as energy efficient compared to following the indirect path involving electricity conversion.

Almost nobody knows that a windmill can produce heat directly

The direct alternative for wind power that everybody knows is the old-fashioned windmill, which is at least 2.000 years old. It transferred the rotational energy from its wind rotor directly to the axis of a machine, for example for sawing wood or grinding grain. This old-fashioned approach remains relevant, also in combination with new technology, because it would be more energy efficient compared to first converting the energy to electricity, and then back to rotational energy.

However, an old-fashioned windmill can not only provide mechanical energy, but also thermal energy. The problem is that almost nobody knows this. Even the International Energy Agency doesn’t mention direct conversion of wind into heat when it presents all possible options for renewable heat production. ¹

The Water Brake Windmill

The original type of heat generating windmill converts rotational energy directly into heat by generating friction in water, using a so-called “water brake” or “Joule Machine”. A heat generator based on this principle is basically a wind-powered mixer or impeller installed into an insulated tank filled with water. Due to friction among molecules of the water, mechanical energy is converted into heat energy. The heated water can be pumped into a building for heating or washing, and the same concept could be applied to industrial processes in a factory that require relatively low temperatures. ⁷ ⁸ ⁹

Image; a heating system based on a water brake windmill. Source: [^8]

The Joule Machine was originally conceived as a measuring apparatus. James Joule built it in the 1840s for his famous measurement of the mechanical equivalent of heat: one calorie equals the amount of energy required to raise the temperature of 1 cubic centimeter of water by 1 degree Celsius. ¹⁰

A heat generator based on this principle is basically a wind-powered mixer or impeller installed into an insulated tank filled with water.

The most fascinating thing about water brake windmills is that, hypothetically, they could have been built hundreds or even thousands of years ago. They require simple materials: wood and/or metal. But although we cannot exclude their use in pre-industrial times, the first reference to heat producing windmills dates from the 1970s, when the Danes started building them in the wake of the first oil crisis.

Image: the heat generator of a heat generating windmill. Source: [^8]

At the time, Denmark was almost entirely dependent on imported oil for heating, which left many households in the cold when the oil supply was disturbed. Because the Danes already had a strong DIY-culture for small wind turbines generating electricity on farms, they started building windmills to heat their houses. Some chose the indirect path, converting wind generated electricity into heat using electric heating appliances. Others, however, developed mechanical windmills that produced heat directly.

Cheaper to Build

The direct approach to heat production is considerably cheaper and more sustainable than converting wind or solar generated electricity into heat by using electric heating devices. There’s two reasons for this.

First, and most importantly, mechanical windmills are less complex, which makes them more affordable and less resource-intensive to build, and which increases their lifetime. In a water brake windmill, electric generator, power converters, transformer and gearbox can be excluded, and because of the weight savings, the windmill needs to be less sturdy built. The Joule Machine has lower weight, smaller size, and lower costs than an electrical generator. ¹¹ Also important is that the cost of thermal storage is 60-70% lower compared to batteries or the use of backup thermal power plants. ²

A windmill with water brake built at the Institute for Agricultural Techniques in 1974. Photo by Ricard Matzen. Source: [^13]

Second, converting wind or solar energy directly into heat (or mechanical energy) can be more energy efficient than when electric conversion is involved. This means that less solar and wind energy converters – and thus less space and resources – are needed to supply a certain amount of heat. In short, the heat generating windmill addresses the main disadvantages of wind power: its low power density, and its intermittency.

Mechanical windmills are less complex, which makes them more affordable and less resource-intensive to build, and which increases their lifetime

Furthermore, direct heat generation greatly improves the economics and the sustainability of smaller types of windmills. Tests have shown that small wind turbines – which produce electricity – are very inefficient and don’t always generate as much energy as was needed to produce them. ¹² However, using similar models for heat production decreases embodied energy and costs, increases lifetime, and improves efficiency.

How Much Heat Can a Windmill Produce?

The Danish water brake windmill from the 1970s was a relatively small machine, with a rotor diameter of around 6 meters and a height of around 12 meters. Larger heat generating windmills were built in the 1980s. Most used simple wooden blades. In total, at least a dozen different models have been documented, both DIY and commercial models. ⁷ Many were built with used car parts and other discarded materials. ¹³

Image: A Calorius windmill producing up to 4 kW of heat. Image provided by the [Nordic Folkecenter](http://folkecenter.eu) in Denmark.

One of the smaller early Danish heat generating windmills was officially tested. The Calorius type 37 – which had a rotor diameter of 5 meters and a height of 9 meters – produced 3.5 kilowatt of heat at a wind speed of 11 m/s (a strong breeze, Beaufort 6). This is comparable to the heat output of the smallest electric boilers for space heating. From 1993 to 2000, the Danish firm Westrup built a total of 34 water brake windmills based on this design, and by 2012 there were still 17 in operation. ⁷

A much larger water brake windmill (7.5m rotor diameter, 17m tower) was built in 1982 by the Svaneborg brothers, and heated the house of one of them (the other brother opted for a wind turbine and an electric heating system). The windmill, which had three fiberglass blades, produced up to 8 kilowatt of heat according to non-official measurements – comparable to the heat output of an electric boiler for a modest home. ⁷

Further into the 1980s, Knud Berthou built the most sophisticated heat generating windmill to date: the LO-FA. In other models, heat generation happened at the bottom of the tower – from the top of the windmill there was a shaft down to the bottom where the water brake was installed. However, in the LO-FA windmill all mechanical parts for energy conversion were moved to the top of the tower. The lower 10 meters of the 20 meter high tower were filled up with 15 tonnes of water in an insulated reservoir. Consequently, hot water could literally be tapped out of the windmill. ⁷

The tower of the LO-FA windmill was filled up with 15 tonnes of water in an insulated tank: hot water could literally be tapped out of the windmill.

The LO-FA was also the largest of the heat generating windmills, with a 12 meter diameter rotor. Its heat output was estimated to be 90 kilowatt at a wind speed of 14 m/s (Beaufort 7). This results seems to be excessive compared to the other heat generating windmills, but the energy output of a windmill increases more than proportionally with the rotor diameter and the wind speed. Furthermore, the friction liquid in the water brake was not water but hydraulic oil, which can be heated up to much higher temperatures. The oil then transferred its heat to the water storage in the tower. ⁷

Renewed Interest

Interest in heat generating windmills resurfaced a few years ago, although for now it concerns only a handful of scientific studies. In a 2011 paper, German and UK scientists write that “small and remote households in northern regions demand thermal energy rather than electricity, and therefore wind turbines in such places should be build for thermal energy generation”. ⁸

The researchers explain and illustrate the workings of the water brake windmill, and calculate the optimal performance of the technology. It was found that the torque-speed characteristics of wind rotor and impeller must be carefully matched to achieve maximum efficiency. For example, for the very small Savonius windmill that the scientists used as a model (0.5m rotor diameter, 2m tower), it was calculated that the impeller diameter should be 0.388m.

The researchers then ran simulations over a period of fifty hours to calculate the windmill’s heat output. Although the Savonius is a low speed windmill which is ill-suited for electricity generation, it turns out to be an excellent producer of heat: the small windmill produced up to 1 kW of thermal power (at wind speeds of 15 m/s). ⁸ A 2013 study using a prototype obtained similar results, and calculated the efficiency of the system to be 91%. ⁹ This is comparable to the efficiency of a wind turbine heating water through electricity.

A 2013 study using a prototype calculated the efficiency of the system to be 91%

Obviously, it’s not always stormy weather, which means that the average wind speed is at least as important. A 2015 study investigates the possibilities of heat generating windmills in Lithuania, a Baltic country with a cold climate that’s dependent on expensive fuel imports. ¹⁴ The researchers calculated that at the average wind speed in the country (4 m/s of Beaufort 3), generating one kilowatt of heat requires a windmill with a rotor diameter of 8.2 meters.

A heat generating windmill with a water brake, placed inside the bottom of the tower. The mill was built by Jorgen Andersen in 1975, and stood in Serritslev. Photo by Claus Nybroe. Source: [^13]

They compare this with the thermal energy demand of a 120 m2 energy efficient new building, heated to modern comfort standards, and conclude that a heat generating windmill could cover from 40-75% of the annual heating needs (depending on the energy efficiency class of the construction). ¹⁴

Heat Storage

The average wind speed is not guaranteed either, which means that a heat generating windmill requires heat storage – otherwise it would only provide heating when the wind blows. One cubic meter of heated water (1 ton, 1,000 liters) can hold up to 90 kWh of heat, which is roughly one to two days of supply for a household of four persons.

The same windmill as the one pictured above, seen from below. Source: [^7]

Providing enough storage to bridge a week without wind thus requires up to 7 tonnes of water, which corresponds to a volume of 7 cubic meters plus insulation. However, energy losses (self-discharge) should also be taken into account, and this explains why the Danish heat generating windmills usually had a storage tank holding ten to twenty thousand liters of water. ¹³

A heat generating windmill can also be combined with a solar boiler, so that both sun and wind can supply direct thermal energy using a smaller water tank.

A heat generating windmill can also be combined with a solar boiler, so that both sun and wind can supply direct thermal energy using the same heat storage reservoir. In this case, it becomes possible to build a pretty reliable heating system with a smaller heat storage tank, because the combination of two – often complementary – energy sources increases the chances of direct heat supply. Especially in less sunny climates, heat generating windmills are a great addition to a solar thermal system, because the latter produces relatively less heat during winter, when heat demand is at its maximum.

Retarders and Mechanical Heat Pumps

The most recent and extensive studies to date are from 2016 and 2018, and compare different types of heat generating windmills with different types of indirect heat generation. ¹ ¹⁵ In this second type of heat generating windmill, heat is produced with mechanical heat pumps or hydrodynamic retarders, not with a water brake.

A mechanical heat pump is simply a heat pump without the electric motor – instead, the wind rotor is directly connected to the compressor(s) of the heat pump. This involves one less energy conversion, which makes the combination at least 10% more energy efficient than an electric heat pump driven by a wind turbine.

The hydrodynamic retarder is well known as a brake system in heavy vehicles. Like a joule machine, it converts rotational energy into heat without the involvement of electricity. Retarders and mechanical heat pumps have the same advantages as Joule Machines, in the sense that they are much smaller, lighter, and cheaper than electrical generators. However, in this case a gearbox is required to achieve optimal efficiency.

Different types of direct and indirect heating production compared. Source: [^15]

The study compares heat generating windmills based on retarders and mechanical heat pumps with indirect heat production using electric boilers and electric heat pumps. It compares these four technologies for three system sizes: a small windmill aimed at heating an off-the-grid household, a large windmill aimed at supplying heat to a village, and a wind farm producing heat for 20,000 inhabitants. The four heating concepts are ranked based on their yearly capital and operational expenditures, assuming a lifespan of 20 years. ¹ ¹⁵

Directly coupling a mechanical windmill to a mechanical heat pump is cheaper than using a gas boiler or the combination of a wind turbine and an electric heat pump.

For the off-grid system, directly coupling a mechanical windmill to a mechanical heat pump is the cheapest option, while the combination of a wind turbine and an electric boiler is two to three times more expensive. All other technologies are in between. Taking into account both investment and operational costs, small-scale heat generating windmills with mechanical heat pumps are equally expensive or cheaper than conventional gas boilers when assuming the typical performance of a small windmill (which produces – over a period of one year – 12% to 22% of its maximum energy output).

Image: Water brake windmill developed by O. Helgason (left), water brake with variable load system (right). Images from \"Test at very high wind speed of a windmill controlled by a water brake\", O. Helgason and A.S. Sigurdson, Science Institute, University of Iceland. Source: [^7]

On the other hand, the combination of a small wind turbine and an electric heat pump requires a windmill with a “capacity factor” of at least 30% to become cost-competitive with gas heating – but such high performance is very unusual. Larger systems present the same rankings – the combination of mechanical windmills and mechanical heat pumps is the cheapest option – but they have up to three times lower capital costs due to economies of scale. Larger windmills have higher capacity factors (16-40%), which result in even larger cost savings.

Due to the large energy losses for heat transportation, the heat generating windmill is at its best as a decentralised energy source, providing heat to an off-the-grid household or – in the optimal case – a small city.

However, larger systems also reveal a problem when scaling up the technology: storing heat may be cheaper and more efficient than storing electricity, but the opposite holds true for transportation: the energy losses for heat transportation are much larger than the energy losses for electricity transmission. The scientists calculate that the maximum distance that is cost-achievable under optimal wind conditions is 50 km. ¹⁵

Consequently, the heat generating windmill is at its best as a decentralised energy source, providing heat to an off-the-grid household or – in the optimal case – a relatively small town or city, or an industrial area. For even larger systems, energy needs to be transported in the form of electricity, and in that case direct generation of heat – with all its benefits – becomes unattractive.

Blinded by Electricity

Heat generating windmills are also investigated for renewable electricity production, mainly because they offer a better solution for energy storage compared to batteries or other common technologies. ¹⁶ In these systems, the generated heat is converted to electricity by the use of a steam turbine. The storage system is similar to that of a concentrated solar power plant (CSP), and the solar concentrators are replaced by heat generating windmills.

An \"eddy current heater\". Source: [^9]

Because high temperatures are needed to produce electricity efficiently with a steam turbine, these systems can’t make use of joule machines or hydrodynamic retarders, but instead rely on a type of retarder called an “eddy current heater” (or “induction heater”). These are comprised of a magnet mounted on a rotating shaft, and can reach temperatures of up to 600 degrees Celsius. Using eddy current heaters, windmills could provide direct heat at higher temperatures, making their potential use in industry even larger.

However, using the stored heat for electricity production is considerably more costly and less sustainable compared ro using heat generating windmills for direct heat production. Converting the stored heat into electricity is at most 30% efficient, meaning that two thirds of the wind energy is lost due to needless energy conversions – and the same is true when solar thermal is used for power production. ¹⁵

Direct heat production thus offers the possibility to save three times more greenhouse gas emissions and fossil fuels using the same number of windmills, which are also cheaper and more sustainable to build. Hopefully, direct heat production will be given the priority it deserves. Despite a warming climate, the demand for thermal energy is as high as ever.

Nitto, Dipl-Ing Alejandro Nicolás, Carsten Agert, and Yvonne Scholz. “WIND POWERED THERMAL ENERGY SYSTEMS (WTES)”. ↩︎ ↩︎ ↩︎ ↩︎
Integration of Thermal Energy Storage into Energy Network, Sharyar Ahmed, 2017 ↩︎ ↩︎
The bright future of solar thermal powered factories, Kris De Decker, Low-tech Magazine, 2011 ↩︎
Solar Heat Worldwide, edition 2018, International Energy Agency (IEA). ↩︎
Renewables 2018, Heat, International Energy Agency (IEA). ↩︎ ↩︎
World Bank: Renewable electricity output. ↩︎
The Rise of Modern Wind Energy: Wind Power for the World. Pan Stanford Publishing, 2013. See chapter 13 (“Water brake windmills”, Jørgen Krogsgaard) and chapter 16 (“Consigned to Oblivion”, Preben Maegaard). These seem to be the only English language documents on Danish water brake windmills. ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
Chakirov, Roustiam, and Yuriy Vagapov. “Direct conversion of wind energy into heat using joule machine.” Fourth International Conference on Environmental and Computer Science (ICECS 2011), Singapore, Sept. 2011. ↩︎ ↩︎ ↩︎
SMALL WIND ENERGY SYSTEM WITH PERMANENT MAGNET EDDY CURRENT HEATER, BY ION SOBOR, VASILE RACHIER, ANDREI CHICIUC and RODION CIUPERCĂ. BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI. Publicat de Universitatea Tehnică „Gheorghe Asachi” din Iaşi Tomul LIX (LXIII), Fasc. 4, 2013 ↩︎ ↩︎
Joule’s experiment: An historico-critical approach, Marcos Pou Gallo Advisor. ↩︎
Okazaki, Toru, Yasuyuki Shirai, and Taketsune Nakamura. “Concept study of wind power utilizing direct thermal energy conversion and thermal energy storage.” Renewable energy 83 (2015): 332-338. ↩︎
Real-world tests of small wind turbines in Netherlands and the UK, Kris De Decker, The Oil Drum, 2010. ↩︎
Selfbuilders, Winds of Change website, Erik Grove-Nielsen. ↩︎ ↩︎
Černeckienė, Jurgita, and Tadas Ždankus. “Usage of the Wind Energy for Heating of the Energy-Efficient Buildings: Analysis of Possibilities.” Journal of Sustainable Architecture and Civil Engineering 10.1 (2015): 58-65. ↩︎ ↩︎
Cao, Karl-Kiên, et al. “Expanding the horizons of power-to-heat: Cost assessment for new space heating concepts with Wind Powered Thermal Energy Systems.” Energy 164 (2018): 925-936. ↩︎ ↩︎ ↩︎ ↩︎
Okazaki, Toru, Yasuyuki Shirai, and Taketsune Nakamura. “Concept study of wind power utilizing direct thermal energy conversion and thermal energy storage.” Renewable energy 83 (2015): 332-338. ↩︎

How to Run the Economy on the Weather

Thu, 21 Sep 2017 00:00:00 +0000

Image: Stoneferry (detail), a painting by John Ward of Hull.

Before the Industrial Revolution, people adjusted their energy demand to a variable energy supply. Our global trade and transport system — which relied on sail boats — operated only when the wind blew, as did the mills that supplied our food and powered many manufacturing processes.

The same approach could be very useful today, especially when improved by modern technology. In particular, factories and cargo transportation — such as ships and even trains — could be operated only when renewable energy is available. Adjusting energy demand to supply would make switching to renewable energy much more realistic than it is today.

Renewable Energy in Pre-Industrial Times

Before the Industrial Revolution, both industry and transportation were largely dependent on intermittent renewable energy sources. Water mills, windmills and sailing boats have been in use since Antiquity, but the Europeans brought these technologies to full development from the 1400s onwards.

At their peak, right before the Industrial Revolution took off, there were an estimated 200,000 wind powered mills and 500,000 water powered mills in Europe. Initially, water mills and windmills were mainly used for grinding grain, a laborious task that had been done by hand for many centuries, first with the aid of stones and later with a rotary hand mill.

Image: \"Een zomers landschap\" (\"A summer landscape\"), a painting by Jan van Os.

However, soon water and wind powered mills were adapted to industrial processes like sawing wood, polishing glass, making paper, boring pipes, cutting marble, slitting metal, sharpening knives, crushing chalk, grinding mortar, making gunpowder, minting coins, and so on. ¹² Wind- and water mills also processed a host of agricultural products. They were pressing olives, hulling barley and rice, grinding spices and tobacco, and crushing linseed, rapeseed and hempseed for cooking and lighting.

Even though it relied on intermittent wind sources, international trade was crucial to many European economies before the Industrial Revolution.

So-called ‘industrial water mills’ had been used in Antiquity and were widely adopted in Europe by the fifteenth century, but ‘industrial windmills’ appeared only in the 1600s in the Netherlands, a country that took wind power to the extreme. The Dutch even applied wind power to reclaim land from the sea, and the whole country was kept dry by intermittently operating wind mills until 1850. ²

Image: Abraham Storck - A river landscape with fishermen in rowing boats, 1679.

The use of wind power for transportation – in the form of the sailboat – also boomed from the 1500s onwards, when Europeans ‘discovered’ new lands. Wind powered transportation supported a robust, diverse and ever expanding international trading system in both bulk goods (such as grain, wine, wood, metals, ceramics, and preserved fish), luxury items (such as precious metals, furs, spices, ivory, silks, and medicin) and human slaves. ³

Even though it relied on intermittent wind sources, international trade was crucial to many European economies. For example, the Dutch shipbuilding industry, which was centred around some 450 wind-powered saw mills, imported virtually all its naval stores from the Baltic: wood, tar, iron, hemp and flax. Even the food supply could depend on wind-powered transportation. Towards the end of the 1500s, the Dutch imported two thousand shiploads of grain per year from Gdansk. ³ Sailboats were also important for fishing.

Dealing with Intermittency in Pre-Industrial Times

Although variable renewable energy sources were critical to European society for some 500 years before fossil fuels took over, there were no chemical batteries, no electric transmission lines, and no balancing capacity of fossil fuel power plants to deal with the variable energy output of wind and water power. So, how did our ancestors deal with the large variability of renewable power sources?

To some extent, they were counting on technological solutions to match energy supply to energy demand, just as we do today. The water level in a river depends on the weather and the seasons. Boat mills and bridge mills were among the earliest technological fixes to this problem. They went up and down with the water level, which allowed them to maintain a more predictable operating regime. ¹⁴

To some extent, our ancestors were counting on technological solutions to match energy supply to energy demand, just as we do today.

However, water power could also be stored for later use. Starting in the middle ages, dams were built to create mill ponds, a form of energy storage that’s similar to today’s hydropower reservoirs. The storage reservoirs evened out the flow of streams and insured that water was available when it was needed. ⁴⁵

The Horse Mill, a painting by James Herring. Ca. 1850.

But rivers could still dry out or freeze over for prolonged periods, rendering dams and adjustable water wheels useless. Furthermore, when one counted on windmills, no such technological fixes were available. ²⁶⁷

A technological solution to the intermittency of both water and wind power was the ‘beast mill’ or ‘horse mill’. ⁸ In contrast to wind and water power, horses, donkeys or oxen could be counted on to supply power whenever it was required. However, beast mills were expensive and energy inefficient to operate: feeding a horse required a land area capable of feeding eight humans. ⁹ Consequently, the use of animal power in large-scale manufacturing processes was rare. Beast mills were mostly used for the milling of grain or as a power source in small workshop settings, using draft animals. ¹

Obviously, beast mills were not a viable backup power source for sailing ships either. In principle, sailing boats could revert to human power when wind was not available. However, a sufficiently large rowing crew needed extra water and food, which would have limited the range of the ship, or its cargo capacity. Therefore, rowing was mainly restricted to battleships and smaller boats.

Adjusting Demand to Supply: Factories

Because of their limited technological options for dealing with the variability of renewable energy sources, our ancestors mainly resorted to a strategy that we have largely forgotten about: they adapted their energy demand to the variable energy supply. In other words, they accepted that renewable energy was not always available and acted accordingly. For example, windmills and sailboats were simply not operated when there was no wind.

Painting: [Mills in the Westzijderveld near Zaandam](https://commons.wikimedia.org/wiki/File:Claude_Monet_Mills_in_the_Westzijderveld_near_Zaandam.jpg), a painting by Claude Monet.

In industrial windmills, work was done whenever the wind blew, even if that meant that the miller had to work night and day, taking only short naps. For example, a document reveals that at the Union Mill in Cranbrook, England, the miller once had only three hours sleep during a windy period lasting 60 hours. ² A 1957 book about windmills, partly based on interviews with the last surviving millers, reveals the urgency of using wind when it was available:

“Often enough when the wind blew in autumn, the miller would work from Sunday midnight to Tuesday evening, Wednesday morning to Thursday night, and Friday morning to Saturday midnight, taking only a few snatches of sleep; and a good windmiller always woke up in bed when the wind rose, getting up in the middle of the night to set the mill going, because the wind was his taskmaster and must be taken advantage of whenever it blew. Many a village has at times gone short of wheaten bread because the local mill was becalmed in a waterless district before the invention of the steam engine; and barley-meal bread or even potato bread had to suffice in the crisis of a windless autumn.” ¹⁰

In earlier, more conservative times, the miller was punished for working on Sunday, but he didn’t always care. When a protest against Sunday work was made to Mr. Wade of Wicklewood towermill, Norfolk, he retorted: “If the Lord is good enough to send me wind on a Sunday, I’m going to use it”. ¹¹ On the other hand, when there was no wind, millers did other work, like maintaining their machinery, or took time off. Noah Edwards, the last miller of Arkley tower mill, Hertfordshire, would “sit on the fan stage of a fine evening and play his fiddle”. ¹¹

Adjusting Demand to Supply: Sailboats

A similar approach existed for overseas travel, using sail boats. When there was no wind, sailors stayed ashore, maintained and repaired their ships, or did other things. They planned their trips according to the seasons, making use of favourable seasonal winds and currents. Winds at sea are not only much stronger than those over land, but also more predictable.

Sailors planned their trips according to the seasons, making use of favourable seasonal winds and currents.

The lower atmosphere of the planet is encircled by six major wind belts, three in each hemisphere. From Equator to poles these ‘prevailing winds’ are the trade winds, the westerlies, and the easterlies. The six wind belts move north in the northern summer and south in the northern winter. Five major sea current gyres are correlated with the dominant wind flows

The Maas at Dordrecht, a painting by Aelbert Cuyp, 1660.

Gradually, European sailors deciphered the global pattern of winds and currents and took full advantage of them to establish new sea routes all over the world. By the 1500s, Christopher Columbus had figured out that the combination of trade winds and westerlies enabled a round-trip route for sailing ships crossing the Atlantic Ocean.

The trade winds reach their northernmost latitude at or after the end of the northern summer, bringing them in reach of Spain and Portugal. These summer trade winds made it easy to sail from Southern Europe to the Caribbean and South America, because the wind was blowing in that direction along the route.

Wind map of the Atlantic, September 9, 2017. Source: [Windy](https://www.windy.com)

Taking the same route back would be nearly impossible. However, Iberian sailors first sailed north to catch the westerlies, which reach their southernmost location at or after the end of winter and carried the sailors straight back to Southern Europe. In the 1560s, Basque explorer Andrés de Urdaneta discovered a similar round-trip route in the Pacific Ocean. ¹²

The use of favourable winds made travel times of sailboats relatively reliable. The fastest Atlantic crossing was 21 days, the slowest 29 days.

The use of favourable winds made the travel times of sailboats relatively predictable. Ocean Passages for the World mentions that typical passage times from New York to the English Channel for a mid-19th to early 20th century sailing vessel was 25 to 30 days. From 1818 to 1832, the fastest crossing was 21 days, the slowest 29 days. ¹³

The journey from the English Channel to New York took 35-40 days in winter and 40-50 days in summer. To Cape Town, Melbourne, and Calcutta took 50-60 days, 80-90 days, and 100-120 days, respectively. ¹³ These travel times are double to triple those of today’s container ships, which vary their speed based on oil prices and economic demand

Old Approach, New Technology

As a strategy to deal with variable energy sources, adjusting energy demand to renewable energy supply is just as valuable a solution today as it was in pre-industrial times. However, this does not mean that we need to go back to pre-industrial means. We have better technology available, which makes it much easier to synchronise the economic demands with the vagaries of the weather.

Shipping in a calm, a painting by Charles Brooking, first half 18th century.

In the following paragraphs, I investigate in more detail how industry and transportation could be operated on variable energy sources alone, and demonstrate how new technologies open new possibilities. I then conclude by analysing the effects on consumers, workers, and economic growth.

Industrial Manufacturing

On a global scale, industrial manufacturing accounts for nearly half of all energy end use. Many mechanical processes that were run by windmills are still important today, such as sawing, cutting, boring, drilling, crushing, hammering, sharpening, polishing, milling, turning, and so on. All these production processes can be run with an intermittent power supply.

The same goes for food production processes (mincing, grinding or hulling grains, pressing olives and seeds), mining and excavation (picking and shovelling, rock and ore crushing), or textile production (fulling cloth, preparing fibres, knitting and weaving). In all these examples, intermittent energy input does not affect the quality of the production process, only the production speed.

Many production processes are not strongly disadvantaged by an intermittent power supply.

Running these processes on variable power sources has become a lot easier than it was in earlier times. For one thing, wind power plants are now completely automated, while the traditional windmill required constant attention. ¹⁴

Image: “Travailler au moulin / Werken met molens”, Jean Bruggeman, 1996.

However, not only are wind turbines (and water turbines) more practical and powerful than in earlier times, we can now make use of solar energy to produce mechanical energy. This is usually done with solar photovoltaic (PV) panels, which convert sunlight into electricity to run an electric motor.

Consequently, a factory that requires mechanical energy can be run on a combination of wind and solar power, which increases the chances that there’s sufficient energy to run its machinery. The ability to harvest solar energy is important because it’s by far the most widely available renewable power source. Most of the potential capacity for water power is already taken. ¹⁵

Thermal Energy

Another crucial difference with pre-industrial times is that we can apply the same strategy to basic industrial processes that require thermal energy instead of mechanical energy. Heat dominates industrial energy use, for instance, in the making of chemicals or microchips, or in the smelting of metals.

In pre-industrial times, manufacturing processes that required thermal energy were powered by the burning of biomass, peat and/or coal. The use of these energy sources caused grave problems, such as large-scale deforestation, loss of land, and air pollution. Although solar energy was used in earlier times, for instance, to evaporate salt along seashores, to dry crops for preservation, or to sunbake clay bricks, its use was limited to processes that required relatively low temperatures.

We can apply the same strategy to basic industrial processes that require thermal energy instead of mechanical energy, which was not possible before the Industrial Revolution.

Today, renewable energy other than biomass can be used to produce thermal energy in two ways. First, we can use wind turbines, water turbines or solar PV panels to produce electricity, which can then be used to produce heat by electrical resistance. This was not possible in pre-industrial times, because there was no electricity.

Augustin Mouchot's solar powered printing press, 1882.

Second, we can apply solar heat directly, using water-based flat plate collectors or evacuated tube collectors, which collect solar radiation from all directions and can reach temperatures of 120 degrees celsius. We also have solar concentrator collectors, which track the sun, concentrate its radiation, and can generate temperatures high enough to melt metals or produce microchips and solar cells. These solar technologies only became available in the late 19th century, following advances in the manufacturing of glass and mirrors.

Limited Energy Storage

Running factories on variable power sources doesn’t exclude the use of energy storage or a backup of dispatchable power plants. Adjusting demand to supply should take priority, but other strategies can play a supportive role. First, energy storage or backup power generation capacity could be useful for critical production processes that can’t be halted for prolonged periods, such as food production.

Second, short-term energy storage is also useful to run production processes that are disadvantaged by an intermittent power supply. ¹⁶ Third, short-term energy storage is crucial for computer-controlled manufacturing processes, allowing these to continue operating during short interruptions in the power supply, and to shut down safely in case of longer power cuts. ¹⁷

Binnenshaven Rotterdam, a painting by Jongkind Johan Berthold (1857)

Compared to pre-industrial times, we now have more and better energy storage options available. For example, we can use biomass as a backup power source for mechanical energy production, something pre-industrial millers could not do – before the arrival of the steam engine, there was no way of converting biomass into mechanical energy.

Before the arrival of the steam engine, there was no way of converting biomass into mechanical energy.

We also have chemical batteries, and we have low-tech systems like flywheels, compressed air storage, hydraulic accumulators, and pumped storage plants. Heat energy can be stored in well-insulated water reservoirs (up to 100 degrees) or in salt, oil or ceramics (for much higher temperatures). All these storage solutions would fail for some reason or another if they were tasked with storing a large share of renewable energy production. However, they can be very useful on a smaller scale in support of demand adjustment.

The New Age of Sail

Cargo transportation is another candidate for using renewable power when it’s available. This is most obvious for shipping. Ships still carry about 90 percent of the world’s trade, and although shipping is the most energy efficient way of transportation per tonne-kilometre, total energy use is high and today’s oil powered vessels are extremely polluting.

Image by Arne List [CC BY-SA 2.0], via Wikimedia Commons

A common high-tech idea is to install wind turbines off-shore, convert the electricity they generate into hydrogen, and then use that hydrogen to power seagoing vessels. However, it’s much more practical and energy efficient to use wind to power ships directly, like we have done for thousands of years. Furthermore, oil powered cargo ships often float idle for days or even weeks before they can enter a port or leave it, which makes the relative unpredictability of sailboats less problematic.

It’s much more practical and energy efficient to use wind to power ships directly.

As with industrial manufacturing, we now have much better technology and knowledge available to base a worldwide shipping industry on wind power alone. We have new materials to build better and longer-lasting ships and sails, we have more accurate navigation and communication instruments, we have more predictable weather forecasts, we can make use of solar panels for backup engine power, and we have more detailed knowledge about winds and currents.

Thomas W. Lawson was a seven-masted, stell-hulled schooner built in 1902 for the Pacific trade. It had a crew of 18.

In fact, the global wind and current patterns were only fully understood when the age of sail was almost over. Between 1842 and 1861, American navigator Matthew Fontaine Maury collected an extensive array of ship logs which enabled him to chart prevailing winds and sea currents, as well as their seasonal variations. ¹⁸

Maury’s work enabled seafarers to shorten sailing time considerably, by simply taking better advantage of prevailing winds and sea currents. For instance, a journey from New York to Rio de Janeiro was reduced from 55 to 23 days, while the duration of a trip from Melbourne to Liverpool was halved, from 126 to 63 days. ¹⁸

More recently, yacht racing has generated many innovations that have never been applied to commercial shipping. For example, in the 2017 America’s Cup, the Emirates Team New Zealand introduced stationary bikes instead of hand cranks to power the hydraulic system that steers the boat. Because our legs are stronger than our arms, pedal powered ‘grinding’ allows for quicker tacking and gybing in a race, but it could also be useful to reduce the required manpower for commercial sailing ships. ¹⁹

Speed sailing records are also telling. The fastest sailboat in 1972 did not even reach 50 km/h, while the current record holder — the Vestas Sailrocket 2 — sailed at 121 km/h in 2012. While these types of ships are not practical to carry cargo, they could inspire other designs that are.

Wind and Solar Powered Trains

We could follow a similar approach for land-based transportation, in the form of wind and solar powered trains. Like sailing boats, trains could be running whenever there is renewable energy available. Not by putting sails on trains, of course, but by running them on electricity made by solar PV panels or wind turbines along the tracks. This would be an entirely new application of a centuries-old strategy to deal with variable energy sources, only made possible by the invention of electricity.

Wind and solar powered trains would be an entirely new application of a centuries-old strategy to deal with variable energy sources.

Running cargo trains on renewable energy is a great use of intermittent wind power because they are usually operated at night, when wind power is often at its best and energy demand is at its lowest. Furthermore, just like cargo ships, cargo trains already have unreliable schedules because they often sit stationary in train-yards for days, waiting to become fully loaded.

Cardiff Docks, a painting by Lionel Walden, 1894

Even the speed of the trains could be regulated by the amount of renewable energy that is available, just as the wind speed determines the speed of a sailing ship. A similar approach could also work with other electrical transportation systems, such as trolleytrucks, trolleyboats or aerial ropeways.

Combining solar and wind powered cargo trains with solar and wind powered factories creates extra possibilities. For example, at first sight, solar or wind powered passenger trains appear to be impossible, because people are less flexible than goods. If a solar powered train is not running or is running too slow, an appointment may have to be rescheduled at the last minute. Likewise, on cloudy days, few people would make it to the office.

Solar PV panels cover a railway in Belgium, 2016. Image: Infrabel.

However, this could be solved by using the same renewable power sources for factories and passenger trains. Solar panels along the railway lines could be sized for cloudy days, and thus guarantee a minimum level of energy for a minimum service of passenger trains (but no industrial production). During sunny days, the extra solar power could be used to run the factories along the railway line, or to run extra passenger (or cargo) trains.

Consequences for Society: Consumption & Production

As we’ve seen, if industrial production and cargo transportation became dependent on the availability of renewable energy, we would still be able to produce a diverse range of consumer goods, and transport them all over the globe. However, not all products would be available all the time. If I want to buy new shoes, I might have to wait for the right season to get them manufactured and delivered.

Production and consumption would depend on the weather and the seasons. Solar powered factories would have higher production rates in the summer months, while wind powered factories would have higher production rates in the winter months. Sailing seasons also need to be taken into account.

If I want to buy new shoes, I might have to wait for the right season to get them manufactured and delivered.

But running an economy on the rhythms of the weather doesn’t necessarily mean that production and consumption rates would go down. If factories and cargo transportation adjust their energy use to the weather, they can use the full annual power production of wind turbines and solar panels.

A Windmill at Zaandam, a painting by Claude Monet, 1871.

Manufacturers could counter seasonal production shortages by producing items ‘in season’ and then stocking it close to consumers for sale during low energy periods. In fact, the products themselves would become ’energy storage’ in this scenario. Instead of storing energy to manufacture products in the future, we would manufacture products whenever there is energy available, and store the products for later sale instead.

However, seasonal production may well lead to lower production and consumption rates. Overproducing in high energy times requires large production facilities and warehouses, which would be underused for the rest of the year. To produce cost-efficiently, manufacturers will need to make compromises. From time to time, these compromises will lead to product shortages, which in turn could encourage people to consider other solutions, such as repair and re-use of existing products, crafted products, DIY, or exchanging and sharing goods.

Consequences for the Workforce

Adjusting energy demand to energy supply also implies that the workforce adapts to the weather. If a factory runs on solar power, then the availability of power corresponds very well with human rhythms. The only downside is that workers would be free from work especially in winter and on cloudy days.

However, if a factory or a cargo train runs on wind power, then people will also have to work during the night, which is considered unhealthy. The upside is that they would have holidays in summer and on good weather days.

Nachtelijk werk in de dokken (Night work at the docks), a painting by Henri Adolphe Schaep, 1856.

If a factory or a transportation system is operated by wind or solar energy alone, workers would also have to deal with uncertainty about their work schedules. Although we have much better weather forecasts than in pre-industrial times, it remains difficult to make accurate predictions more than a few days ahead.

However, it is not only renewable power plants that are now completely automated. The same goes for factories. The last century has seen increasing automation of production processes, based on computers and robots. So-called “dark factories” are already completely automated (they need no lights because there is nobody there).

It’s not only renewable power plants that are now completely automated. The same goes for factories.

If a factory has no workers, it doesn’t matter when it’s running. Furthermore, many factories already run for 24 hours per day, partly operated by millions of night shift workers. In these cases, night work would actually decrease because these factories will only run through the night if it’s windy.

Finally, we could also limit the main share of industrial manufacturing and railway transportation to normal working hours, and curtail the oversupply during the night. In this scenario, we would simply have less material goods and more holidays. On the other hand, there would be an increased need for other types of jobs, like craftsmanship and sailing.

What About the Internet?

In conclusion, industrial manufacturing and cargo transportation — both over land and over sea — could be run almost entirely on variable renewable power sources, with little need for energy storage, transmission networks, balancing capacity or overbuilding renewable power plants. In contrast, the modern high-tech approach of matching energy supply to energy demand at all times requires a lot of extra infrastructure which makes renewable power production a complex, slow, expensive and unsustainable undertaking

Adjusting energy demand to supply would make switching to renewable energy much more realistic than it is today. There would be no curtailment of energy, and no storage and transmission losses. All the energy produced by solar panels and wind turbines would be used on the spot and nothing would go to waste.

Marina, a painting by Carol Popp de Szathmary, 1800s.

Admittedly, adjusting energy demand to energy supply can be less straightforward in other sectors. Although the internet could be entirely operated on variable power sources — using asynchronous networks and delay-tolerant software — many newer internet applications would then disappear.

At home, we probably can’t expect people to sit in the dark or not to cook meals when there is no renewable energy. Likewise, people will not come to hospitals only on sunny days. In such instances, there is a larger need for energy storage or other measures to counter an intermittent power supply. That’s for a next post.

Part of the research for this article happened during a fellowship at the Demand Centre, Lancaster, UK.

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Hills, Richard Leslie. Power from wind: a history of windmill technology. Cambridge University Press, 1996. ↩︎ ↩︎ ↩︎ ↩︎
Paine, Lincoln. The sea and civilization: a maritime history of the world. Atlantic Books Ltd, 2014. ↩︎ ↩︎
Reynolds, Terry S. Stronger than a hundred men: a history of the vertical water wheel. Vol. 7. JHU Press, 2002. ↩︎ ↩︎
One of the earliest large hydropower dams was the Cento dam in Italy (1450), which was 71 m long and almost 6 m high. By the 18th century, the largest dams were up to 260 m long and 25 m high, with power canals leading to dozens of water wheels. [2] ↩︎
Although windmills had all kinds of internal mechanisms to adapt to sudden changes in wind speed and wind direction, wind power had no counterpart for the dam in water power. ↩︎
This explains why windmills became especially important in regions with dry climates, in flat countries, or in very cold areas, where water power was not available. In countries with good water resources, windmills only appeared when the increased demand for power created a crisis because the best waterpower sites were already occupied. ↩︎
Tide mills were technically similar to water mills, but they were more reliable because the sea is less prone to dry out, freeze over, or change its water level than a river. ↩︎
Sieferle, Rolf Peter, and Michael P. Osman. The subterranean forest: energy systems and the industrial revolution. Cambridge: White Horse Press, 2001. ↩︎
Freese, Stanley. Windmills and millwrighting. Cambridge University Press, 1957 ↩︎
Wailes, Rex. The English windmill. London, Routledge & K. Paul, 1954 ↩︎ ↩︎
The global wind pattern is complemented by regional wind patterns, such as land and sea breezes. The Northern Indian Ocean has semi-annually reversing Monsoon winds. These blow from the southwest from June to November, and from the northeast from December to May. Maritime trade in the Indian Ocean started earlier than in other seas, and the established trade routes were entirely dependent on the season. ↩︎
Jenkins, H. L. C. “Ocean passages for the world.” The Royal Navy, Somerset (1973). ↩︎ ↩︎
Windmillers had to be alert to keep the gap between the stones constant however choppy the wind, and before the days of the centrifugal governor this was done by hand. The miller had to watch the power of the wind, to judge how much sail cloth to spread, and to be prepared to stop the mill under sail and either take in or let out more cloth, for there were no patent sails. And before the fantail came into use, he had to watch the direction of the wind as well and keep the sails square into the wind’s eye. [11] ↩︎
Apart from electricity, the Industrial Revolution also brought us compressed air, water under pressure, and improved mechanical power transmission, which can all be valuable alternatives for electricity in certain applications. ↩︎
A similar distinction was made in the old days. For example, when spinning cloth, a constant speed was required to avoid gearwheels hunting and causing the machines to deliver thick and thin parts in rovings or yarns. [3] That’s why spinning was only mechanised using water power, which could be stored to guarantee a more regular power supply, and not wind power. Wind power was also unsuited for processes like papermaking, mine haulage, or operating blast furnace bellows in ironworks. ↩︎
Very short-term energy storage is required for many mechanical production processes running on variable power sources, in order to smooth out small and sudden variations in energy supply. Such mechanical systems were already used in pre-industrial windmills. ↩︎
Leighly, J. (ed) (1963) The Physical Geography of the Sea and its Meteorology by Matthew Fontaine Maury, 8th Edition, Cambridge, MA: Belknap Press. Cited by Knowles, R.D. (2006) “Transport shaping space: the differential collapse of time/space”, Journal of Transport Geography, 14(6), pp. 407-425. ↩︎ ↩︎
Rival teams rejected pedal power because they feared radical change, says Team New Zealand designer. The Telegraph, May 24, 2017. ↩︎