Underground potential: hydrogen storage could redress intermittent renewables

Hydrogen stored in vast salt caverns could be used in a low-carbon energy system to generate clean, load-following power, but only if the UK starts preparing its infrastructure now, says Den Gammer.

The Energy Technologies Institute (ETI) recently completed an assessment of the potential of using salt caverns to store hydrogen for power generation when the demand for electricity peaks daily. We found that hydrogen storage could be important in a future low carbon energy system because it could deliver clean, grid-scale load-following power at a competitive price.

The UK’s energy landscape is changing rapidly. More renewable power supplies are being installed and, although clean, they are often intermittent, increasing the need for a low-cost, clean, on-demand power supply as a back-up.

ETI’s report uses the findings from a techno-economic study carried out by Amec Foster Wheeler into the technologies used in hydrogen production, the stores themselves and the power plants that convert hydrogen (H2) into electricity. The equipment needed to convert fossil fuel, biomass or waste into H2, and capturing and storing the co-produced CO2 with carbon capture and storage (CCS) is expensive, so we don’t want it to be idle when power is not needed.

The ability to store H2 means we can keep equipment running at peak efficiency all of the time and fill the store. When power is needed, most of the H2 fed to the turbines to generate electricity can come from the store. Only the turbines need to be sized for peak demand loads. The equipment producing H2 can be sized for the average load, which may be much smaller. This creates a system a bit like charging an electric vehicle – you can charge it with a few kilowatts of power when the vehicle is not needed from a cheap (domestic) source, but enjoy 40kW ‘engine’ performance for the commute to work. System level analysis shows that H2 storage schemes become cost effective in the time period 2030/40. Power generators using CCS that operate at high load factors do not require stores and are better off using more conventional configurations.

Salt caverns are man-made underground holes created by washing salt out of large geological structures. More than 30 large caverns are in use in the UK to store natural gas and the study focused on areas where they are already in use, such as Teesside, East Yorkshire and Cheshire. These are all at different depths and have different cost structures. A large cavern could supply the peak power requirements of a city the size of Hull.

So, yes, it does seem feasible and attractive to add H2 storage when rebuilding our ageing power sector with cleaner technologies. Once bulk H2 is available in such stores, it could be used to decarbonise other sectors such as industry or transport through use of H2 fuel cells.

The ability to store H2 changes inflexible gasification and reforming technology into competitive components of a highly flexible system offering load-following power services based on fossil fuel, biomass or waste-fed power stations.

Because of its ageing energy infrastructure, the UK will need new energy capacity regardless of whether we choose to tackle climate change and decisions on the most cost-effective way of implementing those changes need to be made soon to ensure proper planning, testing, development and investment.

At the ETI, we have developed a national energy system design and planning capability – ESME (Energy System Modelling Environment), which suggests the UK can afford a transition to a low carbon energy system by 2050, but it is crucial that the country spends the next decade developing and proving the capability of a basket of key supply and demand technology options. Preparing properly now means the UK can build capacity to provide a launchpad for implementation and invest resources where they will have the best economic leverage in the long term.

Although renewable energy sources will have a significant role to play, we cannot rely on them alone, so there will also be a need to develop CCS and nuclear power to ensure there is a balanced, secure and economic mix of low carbon technologies.

By 2025, choices must be made regarding infrastructure design for the long term. Closing down our options too soon could prove unnecessarily costly, but the bigger threat is failing to build up those options at all.

Den Gammer, CCS strategy manager, Energy Technologies Institute