Carbon Commentary newsletter

Fortnight ending 23rd November 2025

1, Medium duration energy storage. An academic paper offered data on the cost of compressed air storage, showing the relatively steep learning curve the technology has demonstrated, with costs declining about 13% for each doubling of installed capacity. For large sites, costs are now as low as about $120 per kilowatt hour of storage capacity, rivalling the level for batteries. However there’s far more complexity to deal with than with lithium ion. Surplus electricity is used to compress the air, producing heat, which should be stored. When needed, that heat is applied to expand the air, forcing it through turbines to regenerate electric power. Round-trip efficiency is unlikely to exceed 70%, industry reports suggest. Liquified air is another route to medium duration storage and leader Highview Power raised another £130m/$170m to complete its complex 3.2 GWh site in Scotland, which includes several different approaches, as well as technologies for maintaining grid frequency and voltage in what it calls a ‘stability island’. Perhaps I am being too pessimistic but I can’t see liquid air storage ever being truly competitive with the compressed air equivalent.

2, Hydrogen. As Europe increasingly worries about the cost of making hydrogen and the low levels of industrial demand, other regions continue to push for more capacity. A recent report suggested that investment plans in Africa might provide 50 million tonnes of hydrogen a year by 2035, equivalent to just under 1% of current global energy use. Much of this will be to support local fertiliser production and also for export to Europe. In China, a major petrochemicals producer inaugurated a large green hydrogen project, probably to produce methanol. Press reports are unclear but the total output seems likely to be about half a million tonnes of H2. The European Commission responded to falling interest in green hydrogen by beginning negotiations to introduce regulations that will oblige its use in the manufacturing of products such as fertiliser.

3, CO2 storage in basalt. Carbon dioxide has been successfully stored in basalt rocks in Iceland for some years. CO2 is added to water which is then injected into the porous rock and reacts to form carbonates. Both the Carbfix and Climeworks projects use this technique to permanently remove the gas from the atmosphere but total volumes are small. However scientific studies are increasingly showing that the theoretical storage opportunity is huge, particularly in countries with large volcanic deposits of basalt. A paper by Scottish scientists estimated a capacity of over 40 years of total UK emissions in three large basalt formations in Ireland and Great Britain. Other studies elsewhere have also shown major storage capacity although tonnage estimates are often shaved as practical issues arise. But the crucial conclusion is that it may well be cheaper and easier to store CO2 onshore in basalt than offshore in depleted oil or gas fields.

4, Floating offshore wind. The growth of this industry is not trouble-free. Shell withdraw from two projects totalling 3 GW in the Scottish North Sea. On the other hand two other UK schemes took steps forward. The Pentland floating offshore wind farm off the north coast of Scotland raised up to £150m/$195m to build its 100 MW ten turbine array. The money comes from UK and Scottish government sources which see floating wind as a major potential export opportunity for Scotland, although few countries other than China and France are yet to commit to developing this form of renewable energy. Ocean Winds, the development company owned by EdP and Engie took a lease for a possible 1.5 GW floating wind farm between Ireland and Britain. The company has pioneered two earlier deep-water sites off Portugal and France.

5, Low carbon steel. Australia-based Calix uses high temperature heat generated by electricity to decarbonise hard-to-abate industrial processes such as cement-making. Rio Tinto said it would invest in Calix’s first trial plant to make low carbon iron from lower grade ore in Western Australia. Heat is generated by electricity around a sealed chamber into which hydrogen will be pumped to reduce the ore to pure iron and water. Rio Tinto also said it would back away from its previous candidate for emissions reduction in iron manufacture - pellets consisting of ore wrapped up with biomass - saying this technology is not mature.

6, Green hydrogen in power plants. Los Angeles decided to convert an ageing power plant to turbines that can burn either hydrogen or natural gas. Environmentalists contested the move, saying that the power station had no guaranteed supply of hydrogen and would actually consume 100% natural gas. In addition, activists pointed to the dangers of NOx pollution in the local area should hydrogen ever be used to power the plant. The local utility was keen to stress that the power station would only be turned on when renewables and batteries were not available although the total budget of $800m seems high for such a limited task. In Germany, the government reduced its proposal for new natural gas power plants from 20 GW to 10 GW but did commit to ensuring that all those built will be able to operate on renewable hydrogen. Germany’s plans to access reliable sources of H2 are more advanced than those in California.

7, Agrivoltaics. Maintaining farming on agricultural land on which solar PV is placed seems to be a successful way of both improving community acceptability and also increasing the total productivity of the land. Energy company RWE has been experimenting with agrivoltaics in Germany for two years and has just won the rights to develop three PV farms combined with agriculture in Italy. It is already developing two similar sites in the country. A French study showed major benefits, both to animals and crops, including an 18% improvement in yields compared to a control plot on a farm in the east of the country. The IEEFA made a strong case this month that agrivoltaics could provide benefits from reducing water evaporation in hot countries as well as increasing yields and reducing local resistance to land-use change.

8, Industrial heat pumps. Clothing manufacturer Epic Group said it has commissioned a heat pump that provides water at 125 degrees for its laundry operations at a new manufacturing hub in India. The also generates its own solar power for driving the pump. The machine was made by an Indian manufacturer that makes specialised equipment for heating and cooling in industry. Epic Group stresses that the value of this heat pump will include being able to send the cool air that forms the exhaust from the heat pump into its garment factories, reducing the temperature in hot weather. (As an aside, industrial heat pumps are proving useful in many sectors that were thought to be hard to decarbonise but, despite the claims in this link, the temperature generated by this heat pump is not exceptional).

9, Synthetic fuels. German defence contractor Rheinmetall intends to build a network of several hundred small modular synthetic fuels factories across Europe. The logic is that this will help protect fuel supplies for military uses in the event of attacks on centralised refineries. Rheinmetal is working in combination with 3 German businesses covering direct air capture (Greenlyte), hydrogen production (Sunfire) and e-fuel synthesis (Ineratec). This partnership contains all the technologies necessary to make small production units for kerosene and diesel. Defence needs may be the stimulant that finally brings scale to synthetic fuels production.

10, A solar-powered electric motorcycle. No, I don’t think the panels stay open when the motorcycle is being driven.