Natural gas prices have been steadily climbing since last summer, with the war in Ukraine increasing the pressure. Combined with efforts against climate change, it’s never been clearer that the world needs to move towards renewables.
However, there’s an obvious problem – most forms of renewables don’t produce energy on demand. The power needs to keep flowing even when the wind doesn’t blow and the sun doesn’t shine.
According to power generation firm Drax, that means the amount of energy storage on the UK grid will need to expand from 3GW today to more than 30GW in the coming decades.
The words ‘power storage’ might make you think of batteries. However, there are big problems using such systems for large-scale storage. The development costs and end-of-life disposal of lithium-ion batteries are high, while their lifespan generally isn’t all that long. They also require rare and expensive materials like cobalt, nickel and lithium.
Pumped hydro
Battery technologies are making steady progress, but other methods are required. Currently, the main form of energy storage around the world is pumped hydro, which sees water moving between two reservoirs at different heights. When there’s demand for electricity, water is released from the upper reservoir, spinning turbines and generating electricity. When power needs to be stored, conversely, the same turbines use electricity to pump water from the lower to the upper reservoir, ready for release once again.
But while pumped hydro is widely used around the world, it has its limitations. For one, only certain sites are suitable, and these may not be the most convenient sites for energy generation.
However, this may be about to change. For example, Dutch startup Ocean Grazer has started building a subsea version of pumped hydro that can be used to store energy from onshore and offshore wind farms by pumping seawater in and out of huge bladders on the ocean floor.
“I think we could find our solutions being deployed at almost any location where there’s a wind farm being built,” says chief executive Frits Bliek. “We have talked to the main offshore wind developers and effectively they all want to test and exploit the possibilities that it can provide.”
Other new energy storage technologies are emerging. One example is thermal storage. Like a domestic hot water tank, this involves storing energy in the form of heat until it’s required. The largest installation of this kind is currently under construction in Vantaa in Finland, storing water heated to 140°C in a cavern measuring a million cubic metres.
The Vantaa Energy Cavern Thermal Energy Storage (VECTES) project will have a storage capacity equal to the annual heat consumption of a medium-sized town. It will allow excess heat – such as waste heat from air conditioners, solar and geothermal – to be stored in the summer, then used to cut demand peaks in winter.
Harnessing gravity
Many methods of energy storage are limited by where they can be located. However, one technique that’s relatively efficient and can be used almost anywhere is gravity storage.
Spare energy is used to hoist a weight to the top of a tower or an underground shaft, with the energy released when the weight is lowered.
“Current storage solutions are insufficient. With pumped hydro – which is currently 90% of the market – and chemical batteries, both face significant issues with scalability, economics and environmental risks,” says Robert Piconi, co-founder and CEO of Energy Vault, which is constructing a demonstration unit in Arbedo-Castione, Switzerland. His company believes its model will yield 30-40% lower ‘levelised costs’ – the ratio of the total costs of a plant to the amount of electricity generated over the plant’s lifetime – than lithium-ion batteries. The technology also has a long lifespan.
With so many promising possibilities, the UK government recently allocated £68m to fund a Longer Duration Energy Storage competition. The aim, according to energy and climate change minister Greg Hands, is to “allow us to extract the full benefit from our homegrown renewable energy sources, drive down costs and end our reliance on volatile and expensive fossil fuels”. Nearly £7m has been awarded so far covering 24 projects, with more funding to come for those deemed worth commercialising.
One of the candidates is B9 Energy Storage’s Ballylumford project in Northern Ireland, which will initially receive nearly £1m for a storage system known as power-to-x. This uses spare energy to create fuel which can then be used at a later date. This is generally hydrogen, as in the case of B9 Energy Storage.
“Northern Ireland has world-leading levels of renewable penetration, but mechanisms to store surplus renewable generation at times of low demand are urgently required to minimise the curtailment of this energy,” says Mark Alexander, energy transition manager at project member Mutual Energy. He says the power-to-x storage medium can fulfil a long-term need, because it potentially exceeds the levels of energy storage needed for ‘net zero’.
However, the future of energy storage will inevitably involve a mix of different techniques, he says. “While power to hydrogen is essential to deliver robust security of energy supply within a net-zero context, providing an energy storage solution for renewable energy over days, weeks, months, or even years, it does not remove the need for other storage technologies, particularly those that operate on intra-day cycles such as batteries, compressed air, pumped hydro etc,” he says.
Future prospects
According to McKinsey, long-duration energy storage could handle up to 10% of all electricity consumed by 2040 globally. It could avoid releasing 1.5-2.3 gigatons of CO2 equivalent per year, around 10% to 15% of today’s power sector emissions.
There’s a good chance these technologies will be cost-effective, says the firm. Projections indicate significant cost reductions are achievable and in line with those experienced in other emerging energy technologies in the recent past, including solar photovoltaic systems and wind power.
Dr Jonathan Radcliffe is reader in Energy Systems and Policy at the University of Birmingham. He says the potential costs of failing to increase energy storage need to be factored in, particularly in the new global environment.
“Up until now, we have had energy stored in fossil fuel, giving us security - though actually the current energy crisis shows in part that we have taken even storage of natural gas for granted,” he says.
“As we move to a net zero electricity system and many tens of gigawatts of offshore wind are deployed over the next 10 years, markets really need to adjust to reflect the value of reliability and resilience under conditions where we could face long periods of time without generation from renewables.”
