Hydrogen will play a critical role in a net-zero electricity system, as other energy storage methods will not be able to provide the scale of back-up power required, according to a new study from the London-based Royal Society.

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The world’s oldest independent scientific academy used 37 years of weather data to determine how much energy storage would be required to back up a future British national electricity system based on wind and solar power, while also analysing the different types of storage and demand-reduction methods available and their costs.

The report, simply entitled Large-scale electricity storage, determined that up to 100TWh of storage would be needed by 2050 if the UK were to meet its legally binding net-zero target — enough to power a quarter of the country’s current electricity demand and the equivalent of 5,000 copies of the UK’s largest pumped hydro plant at Dinorwig in Wales.

Even though green hydrogen has a poor round-trip efficiency of about 41% — ie, for every 100MWh of renewable energy used to produce green hydrogen, only 41MWh would be produced by a fuel cell consuming that H2 — and that this will lead to relatively high costs, other technologies will not be able to offer the scale of energy storage required.

“Storage on this scale, which would require up to 90 clusters of ten caverns, is not possible with batteries or pumped hydro,” the society concludes.

“Storage requirements on this scale are not currently foreseen by the government. Work on constructing these caverns should begin immediately if the government is to have any chance of meeting its net-zero targets.”

Lead author Sir Chris Llewellyn Smith, an award-winning Oxford University physics professor, says that the need for long-term energy storage “has been seriously underestimated”.

“Demand for electricity is expected to double by 2050 with the electrification of heat, transport, and industrial processing, as well as increases in the use of air conditioning, economic growth, and changes in population,” he explains.

“It will mainly be met by wind and solar. They are the cheapest forms of low-carbon electricity generation, but are volatile — wind varies on a decadal timescale, so will have to be complemented by large scale supply from energy storage or other sources.”

The report also looks at other options for meeting power demand during prolonged periods of low wind and sunshine, including nuclear, fossil gas with carbon capture and storage (CCS), and bioenergy with or without CCS, which it says are all “capable of meeting a significant fraction of demand”.

However, it adds: “All are expensive or very expensive if operated flexibly to complement fluctuations in supply and variations in demand.”

The report recommends that construction of large-scale green hydrogen storage should begin now.

“Other countries have ambitious plans to develop hydrogen storage starting now. If the UK does not emulate them, the electricity storage necessary to ensure low carbon, reliable and affordable energy supply will not be available when it is needed,” it explains.

“Construction of a large green hydrogen production and storage facility would appear to be a no-regrets option. It would provide a much better idea of what hydrogen will cost and set GB [Great Britain*] on the road of cost reduction through learning. The construction of others should follow quickly.”

But the society also points out that this would requirement financial support from the government, as “the construction of large caverns is currently not justifiable commercially”.

The report calculates that 60-100TWh of hydrogen storage — the equivalent of 1.8-3.0 million tonnes of H2 — will be needed to keep Britain’s lights on during periods of low wind and solar, such as in the so-called “dark doldrums” in winter — especially if heating is primarily delivered via heat pumps. The range is due to uncertainties over costs and the exact make-up of wind and solar power.

Supplying three million tonnes of green hydrogen a year would require roughly 30GW of electrolysers and 60GW of dedicated renewable energy.

The Royal Society adds that baseload nuclear power would increase overall energy costs in a net-zero system “unless the cost of nuclear is near or below the bottom of the range of projections made by the [now-defunct] Department for Business, Energy and Industrial Strategy and/or the costs of storage are near the top of the range of estimates in this report”.

Bioenergy with carbon capture and storage (BECCS) — a potential negative-emission technology — would only lower costs in such a system with carbon credits of more than £100 per tonne saved, “but it could not provide GB with more than 50TWh/year without imports of biomass”.

Using fossil gas with CCS to provide flexibility “would lead to unacceptable emissions of CO2 and methane, and also to higher costs”.

The report also examined the potential of a wide range of energy storage options, including various batteries, liquid and (advanced) compressed air energy storage (LAES and ACAES), thermal energy storage, as well as H2, ammonia and synthetic fuels.

Vehicle-to-grid storage was also considered, but the authors concluded that even if all 33 million cars currently on UK roads were electric and had fully charged 70kWh batteries that were connected to the grid, they would only be able to provide a combined 2TWh of energy storage.

However, it does point out that “if a significant fraction of GB’s future fleet of electric vehicles were from time to time under the control of the operator of the electricity grid, the flexible power reserve that they would provide would make an extremely valuable contribution to managing the system”.

The report adds that 15GW of lithium-ion batteries would also be needed to provide rapid-response grid services, such as frequency regulation and voltage stability.

It concludes: “With wind and solar supply supported by hydrogen storage (and some batteries), it was found that, with the range of input assumptions made in this report, the average cost of electricity fed into the grid in 2050 would be between £52/MWh and £92/MWh [$65-115/MWh] in 2021 prices.

“For comparison: in 2010-20, the wholesale price of electricity hovered around £46/MWh, but it was more than £200/MWh during most of 2022.”

This could be lowered by up to 5% “or possibly more” by combining hydrogen storage with ACAES — where air is compressed and pumped into a cavern (with the resulting heat captured and stored for later use), and later slowly expanded through a power-generating turbine — “depending on what is assumed about its cost and efficiency”.

And using a combination of energy storage plus fossil gas with CCS “could lower costs significantly”, although this would demand on the future cost of natural gas, CCS and the carbon price.

“It would not remove the need for large-scale long-term storage, although it would reduce the required scales of storage and wind plus solar supply.”

The study also points out that “building the number of caverns... needed by 2050 will be challenging, but not impossible”.

A total of 50 experts — mainly university professors and academics from around the UK — contributed to the Royal Society report.

How to produce electricity from hydrogen

The Royal Society study points out that electricity can be generated from hydrogen using fuel cells, internal combustion engines, or turbines.

But it concludes that “although hydrogen burning turbines will be available by the end of this decade, they will not be discussed here as it appears that using fuel cells or 4-stroke engines would be cheaper”.

“Some savings could possibly be made by converting part of the existing fleet of ~ 30 GW of Combined Cycle Gas Turbines [CCGTs] to burn hydrogen,” it adds. “However, hydrogen firing presents technical issues, and retrofitting of GTs [gas turbines] to burn 100% hydrogen has not yet been demonstrated at scale.”

Nevertheless, most countries planning to use hydrogen for power production are focusing on gigawatt-scale power plants, with most of those to be converted fossil-gas facilities. Many experts believe that fuel cells would not be able to provide the scale required.

*Great Britain consists of England, Wales and Scotland, but not Northern Ireland (which is part of the United Kingdom).