Carbon Commentary newsletter

1, Long distance transmission. XLinks was a project to take power 4,000 km in an undersea cable from Morocco to western England. That idea was abandoned recently because of lack of support from the UK government (and concerns about cost). As long expected, the scheme has resurfaced but this time the destination is Germany, via a cable 20% longer. When I looked at the UK plan for an investor several years ago, transmission would have cost at least as much as the electricity and the longer distance to Germany now suggests an even higher figure. Nevertheless, at possibly around €80-90 per MWh, the price may still be worthwhile. Power companies such as E.ON and Uniper are reported to be backing the scheme, which would deliver about 5% of Germany’s electricity needs. Might it eventually make sense to ship power from Morocco to the US (or in reverse), a distance of about 7,000 km? If XLinks works, then ocean-crossing links are on the horizon.

2, Synthetic fuels. We need to watch Prometheus, a US-based early stage renewable fuels producer. Prometheus has unique technologies that convert air captured carbon dioxide and water into synthetic fuels such as methanol. It has consistently claimed very low CO2 capture costs compared to other innovators. By siting its trial plants in areas of very low electricity prices it claims it can undercut fossil fuels. In a striking recent publicity stunt it showed how its liquid fuels could run a AI programme at times of no sun powering a solar farm.

3, Tandem PV materials. We’ve heard a lot about perovskite in recent years. A thin layer of this material can be cheaply added to silicon photovoltaics. Because it collects the energy from a different part of the sun’s spectrum to silicon, perovskite can add to the overall collection efficiency of PV at relatively low cost. A similar material called kesterite – also composed of earth abundant elements - could eventually compete with perovskites after Chinese scientists managed to push the yield up to around 17% recently. Many uncertainties remain but kesterite has advantages over perovskite that may push it into faster development. These include greater chemical stability and the absence of toxicity. (Some perovskites contain lead). After a decade in which researchers gravitated to investigating perovskites, kesterite is gaining momentum.

4, Geothermal power. Rodatherm has a different approach to geothermal. Instead of passing water through hot rocks, the business uses refrigerants that travel around an enclosed underground loop. It claims radically lower costs for collecting heat from hot sedimentary basins, such as those in the west of the US. After operating in stealth since 2022, it raised $38m, which it claims is the largest first round raise by a geothermal company. Investors will have reached a favourable view on Rodatherm’s assertion that it can reduce geothermal generation costs to fossil fuel levels.

5, Climate impact of vertical farming. A study showed that vertical farming does not necessarily lead to lower emissions. Even if the farm uses renewable electricity for lighting and heating, the impact can be worse than conventional agriculture. The key ingredient in the high emissions from the vertical farming of lettuce is the carbon impact of growing the jute needed for the small plugs in which the crop grows. Vertical farming of salad vegetables used far less water than one of the comparator conventional farms in Spain but otherwise the environmental impacts were no better. However the study did not try to assess the long term impact of reduced need for agricultural area. A small vertical farm might cut the land needed for agriculture by several hectares, meaning that the freed land could capture carbon by growing trees. This would probably swing the balance back to indoor agriculture. (Thanks to Ursula Brewer)

6, The impact of aviation contrails. It’s often reported that half the global warming impact of aviation comes from the contrails that sometimes spread into clouds covering the sky which then block the flow of heat into space. Hannah Ritchie’s podcast this week discussed this point, making the simple recommendation that airlines fly their planes at levels at which contrails don’t form. (That level will vary by a few thousand feet on different days but weather forecasting can already tell pilots which level to fly at). And it is true that this will reduce the global warming effect of flying. But there’s a real confusion here; curbing contrails will NOT halve the overall effect of aviation. Contrail clouds disappear after less than a day but the CO2 from burning fossil fuels remains for hundreds of years. So, yes, if all contrails ceased tomorrow, there would be a once-and-for-all reduction in global temperatures (of a small fraction of a tenth of a degree) but the stock of CO2 would continue to rise. We can’t claim that avoiding contrails would cut the climate impact of aviation in half.

7, Datacentres and emissions. It’s not just the electricity that they’ll use, it’s also the building of these huge structures in the first place. In fact getting low carbon electricity for the operation of the datacentre may be easier than obtaining fossil free cement or steel. But Microsoft made attempts to reduce the impact this week by backing green cement manufacturer Fortera alongside buying its products and also committing to purchasing early steel from Stegra (formally H2GreenSteel) in Sweden. In both cases Microsoft will also buy up certificates guaranteeing green characteristics. We can all be cynical about the environmental claims of ‘hyperscalers’ but it does seem to me that Microsoft is at least trying to be a better global citizen.

8, Energy storage using gravity. Many have been sceptical about lifting heavy weights as a means of storing energy. GreenGravity Australia wants to prove the doubters wrong. It signed an agreement to use a disused 400m deep mine shaft in New South Wales to install a weight that can be lifted or let fall. The company claims that this will be the first commercial use of gravity for power storage. Maximum output on this trial will be 150 kW but the company claims full-scale sites will offer 10 MW for up to 20 hours of storage.

9, Synfuels versus carbon capture. Some commentators, including me, have argued for fast development of synthetic fuels to replace fossil equivalents such as methane and aviation kerosene. (See note 2). But a recent paper suggests that except when natural gas prices are very high it would be cheaper to burn fossil fuels and separately capture equivalent amounts of CO2 emissions than to make synthetic hydrocarbons. The central point is that making net zero fuels from hydrogen and carbon requires the same amount of carbon capture (once biomass sources are exhausted) as we need to neutralise the emissions from burning hydrocarbons. So it is the relative price of hydrogen compared to fossil fuels that will determine whether synthetic fuels make financial sense.

10, Wine and climate. Including the CO2 from long-distance transport, the bottle is responsible for up to 50% of the carbon emissions of wine. Jane Masters reports this in Rooted in Change, her new book on the increasingly pressing issue of the impact of climate on wine-making. One way forward is to reduce the heaviness of the bottles, which sometimes still weigh in at more than 1 kg even though much less than 400 grams is easily possible. Another is to introduce a circular system that takes back bottles and reuses them. Industry pioneer Familia Torres has just set up a scheme with a Netherlands distributor to process bottles in this way. Wine will be shipped in bulk to a bottler close to the Netherlands and used bottles will then be refilled up to ten times. Torres says this will reduce CO2 emissions from bottles by 50% and overall water use by much more. Packaging waste will be minimised. Importantly, such a scheme will enable bulk wine to be shipped by rail rather than on heavy trucks. Alongside this, Torres will be shipping more wines in kegs for supply to restaurants and bars. I can see some customer resistance here but the benefits are clear, both in carbon terms and in cost.