Placing renewable power plants (e.g. wind/solar) where there is high, and quite constant natural energy is key: from deserts to maritime areas. Equally important is making the connection between energy and material production as direct as possible (co-localization in a single plant): „waste“ energy from one process benefits the other => higher efficiency.

More than enough natural energy, but how to store it?…

The oft-quoted conclusion that we could supply the world’s energy needs (yes, even via e-fuels) via solar panels on a very small percentage of the world’s deserts is probably true. There are even deserts (usually at altitude) where wind speeds are high, hence making them desirable for combined solar/wind power generation. The big question is how to store this energy, because if it can be stored – thus flattening out fluctuations in supply and demand – the scale of the power generation installations can be minimized: that would be good for the environment. One option would be batteries on-site, connected with the grid. Such megabatteries would have enormous environmental impacts of their own due to the mining of the necessary minerals…

Coupling of energy and material economies is beneficial…

An alternative to batteries would be hydrogen or a synthetic hydrogen-carrier. The chemical industry is under as much pressure to abandon fossil fuels as any other sector: after all, much of the material it produces is ultimately burned, thus releasing CO2. In carbon/hydrogen synthetic fuels we have, in one, energy carriers and vital ingredients for the chemical industry: methanol and methane are the two most important. In general, regardless of exactly where a facility is, the coupling of activities produces not only efficiency gains, but also flexibility. Heat no longer escapes and is lost, and electricity can be turned into other energy carriers/materials, and back again.

Methane and methanol: convenient energy-carriers and raw materials…

Imagine a renewable power plant electrolyzing water to make H2, and with the heat generated by this process running parts of a CO2-capture facility on-site. In different chemical syntheses, H2 and CO2 are turned into, respectively, methanol and methane. Under the right conditions, fuels including gasoline, diesel and kerosene are produced. These syntheses provide heat necessary for high-temperature electrolysis, which produces hydrogen most efficiently. Storage of the synthetic fuels is very easy, because they are not very volatile compared with hydrogen. During periods of high demand but low natural energy availability these stores can – by reversing the direction of the synthesis unit – be re-converted into electricity. The stores would, of course, be the source of feedstocks for the chemical industry and energy for various transport sectors.

Click here for more on suitable energy generation locations…

Making storable energy in the most efficient places

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Ideal location: a desert with high sunlight hours and strong winds…

The Gobi Desert, spanning southern Mongolia and northwestern China, has these characteristics, and the potential for choosing different heights for power generation plants. It is already being studied with the aim of developing natural-energy power plants. Sun here is abundant during the day; winds reach peak at around 4 pm, but they are still quite strong at night, hence bridging the period when photovoltaic panels are inactive.

How could a renewable fuel plant work?

> Photovoltaic (solar) panels produce peak power during the day; the night is bridged via wind power.
> Electricity is used immediately for generating hydrogen and concentrating CO2 from the air.
> Hydrogen and CO2 are (using the plant’s own clean energy) synthesized into a range of chemicals, e.g.
– Methanol and methane for fuel and synthesis of chemicals and materials
– E-fuels, e.g. synthetic… kerosene for jet airplanes, methanol/gasoline for cars, and methanol/DME for trucks
> Heat released in synthesis reactions is used to drive capture of CO2 from air.

The materials produced can be easily transported/piped with existing technology to where they are needed….

We must make sensible compromises: no animal, including humans, can exist on Earth without an impact. We must reduce ours to the minimum. We can do this in the energy sector by using deserts where nobody lives, there is no agriculture, and biodiversity is relatively very low.

The products of the chemical syntheses range from methanol, through methane, to liquid fuels similar to diesel, kerosene or gasoline. It avoids a completely new storage and distribution infrastructure for pure hydrogen (greyed out in the figure below), and employs very inexpensive pipes and storage vessels. It is very easily up-scalable, and can store very large amounts of energy for very long periods without appreciable losses:

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If we use pure hydrogen as a form of storable and distributable energy, we need a very large, costly and maintenance-intensive system of high compression, cooling and high-pressure distribution, which also has a relatively short life cycle (needs replacing/repairing more frequently than conventional infrastructures. To make synthetic CO2-neutral carbon-based fuels we also need hydrogen, but at much lower pressure: it can go directly into the production pathway without needing to be stored at minus 253 oC or distributed in very long and highly-specialized pipelines; instead it is used immediately, together with CO2 (captured from air or flue gases), to make fuel that is easy to store and distribute. The analogy with green plants is very strong: plants do not store hydrogen, rather they convert it immediately into carbon-based energy carriers.

Choice of location: Exploring the feature in more detail…

There are many largely barren areas on Earth that are suitable for EITHER photovoltaic OR wind power, and these are also attractive sites for power plants. Bridging of energy troughs between photovoltaic and wind power could be done non-locally via power lines. Many of these already exist as part of the normal grid, and enlarging its carrying capacity is a moderate challenge. A few places on Earth — largely on, or near, oceans — have such high winds throughout the 24 hours of a day that wind power alone could form a constantly-running high-output and high-efficiency fuel synthesis facility. A pilot plant already exists near Punta Arenas in southern Chile. This type of approach uses hydrogen from splitting water with electricity, and CO2 filtered from the air, or from industrial flue gases.

Why are sunny and high deserts so attractive for such facilities? The higher in altitude one goes, the less biodiversity one has to be careful of; also, in high deserts one generally has more wind, which is particularly important at night. The synthesis plant needs, for maximum efficiency, to stay active day and night. On the scale of a few hours, even small batteries may be a good solution to bridging the troughs in solar energy. In biological cells, the strucures called „mitochondria“ store electrical energy for very short-term use; for longer term use, i.e. via storage, and for transportation of energy, biology uses carbon-based substances.

Extent of fossil fuel replacement: An example…

If we envisaged all three types of location in the image at the start of this page, we could probably generate enough electricity to replace all current gasoline consumption worldwide. To do that, we would use less than 1% of the area of all deserts and largely barren, constantly windy places on Earth. Even better would be to reduce gasoline consumption drastically at the same time!

Click here for more on integration of energy and material processes…

Integration of energy/material economies is a must.

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The days of power generation at location X and material manufacture at location Y are numbered…

Energy is never „lost“: it can only change form, and if we can re-capture it before it diffuses into the surroundings, then we can minimize the loss: we can use the energy given off by one process to (partly, or completely) drive another one. A very basic example is the low-pressure, but still quite hot, steam from a power station, which can be fed via insulated pipes to residential areas for heating.

Making e-fuel production more efficient…

Another example would be a wind generator running fairly constantly in a windy part of the world. Directly on-site would be an electrolyser, making green hydrogen from water. The heat generated from this reaction would feed into the machinery for capturing CO2 from the air, which requires the absorptive filters to be heated to around 85 oC to release the CO2. Further heat could be used partly to power the fans and compressors of this plant. Energy losses would, hence, be reduced by integration.

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Integration brings flexibility between energy and crucial materials…

But there’s more than just efficiency to be gained by integration: also flexibility. Integration is key to the diversification and success of biology. The cells with the largest evolutionary diversity are so-called „eukaryotic“ ones. They contain tiny machines (mitochondria) that initially burn carbon-containing energy-carriers (fats and sugars) to make electricity. This is almost immediately converted into biologically useful chemical energy (ATP), and materials for the rest of the cell. Similarly, human economies use carbon in a massive variety of products. The biological cell can easily reverse most of this biochemistry, and make energy from carbon-based substances. Plant cells basically make all of the biological energy and materials that support the rest of life on Earth, and the chloroplasts in plant basically split water — initially releasing hydrogen — just like electrolyzers that humans build.

Chemical synthesis plants that do very similar interconversions to cells have already been built. They rely on the concept of reversibility between energy-carrying chemicals and electrical energy: basically they „catalytically burn“ chemicals — in an analogous way to cells in all living organisms — to generate electricity, and use electricity to make chemicals out of raw ingredients. In so doing, they can easily constitute a single facility that serves energy storage, electricity re-regeneration and production of feedstocks for the chemical industry.

Methanol and methane: Examples of e-fuels frequently discussed…

Two very important energy-carriers and chemical feedstocks are methanol and methane. These are immediate products from well-established chemical synthesis reactions (Fischer-Tropsch, and Sabatier, respectively). Hence, we can construct facilities where, for example, methanol and methane are…

> produced with abundant natural energy on-site, with energy capture and use in other processes (see below);
> stored in quantities sufficient to even out energy troughs, particularly large seasonal ones;
> used by chemical plants on-site to make usfeul substances, with energy capture feeding back to increase efficiency;
> transported for use as portable fuel in transport sector;
> piped or transported to other users, e.g. steel/cement industry;
> used in reverse to generate electricity at times of need to feed directly into the grid.

Further reading:

> Choice of optimal sites for desert-situated photovoltaic plants
> Potential for wind energy and photoelectric energy generation in Saudi Arabian desert
> Choice of optimal sites for wind energy generation
> How much of current energy demand could be satisfied by renewable energy plants in low-impact areas of the Earth?
> Microalgae as model system demonstrating energy/material transitions between chloroplasts and mitochondria
> Reversible Solid-Oxide Cell Stack for generating fuel from electricity, and electricity from fuel

Copyright Andrew Moore 2024