In a renewably powered future, how will the grid cope when the sun isn’t shining and the wind isn’t blowing? Rachel Brazil looks at the options
Getting to net zero isn’t just about shifting to low-carbon renewable energy sources, it will also need massive increases in our energy storage capacity. ‘There will be periods where renewable energy generation is in excess of demand and periods where demand can’t be met by generation. The goal for energy storage is to try and bridge that gap,’ says Emma Woodward, an analyst at the global energy analytics company, Aurora Energy Research. According to the UK’s National Grid, the country will need energy storage capable of supplying 50GW by 2050 to ensure a balance in supply and demand. The whole of Europe will likely need more than 400GW, but current storage is now below 10% of that capacity according to Oliver Schmidt, a visiting researcher in clean energy economics at Imperial College London, UK.
In 2021 there was estimated to be only 27GW of power from energy storage available globally. But the problem is more than just increasing capacity – we currently don’t have the established technologies necessary for the task. We are at a point where there are ‘thousands of concepts’ says Schmidt, including systems that use gravity, heat and electrochemistry, all providing alternative methods, but most still unproven at scale. So can we find the right technology for the task and can we do it quickly enough?
The energy storage technology most widely deployed now is pumped hydroelectric power – a 19th century technology, where water is pumped from a lower to higher reservoir and released through a turbine to generate electricity when needed. The UK currently has less than 3GW capacity. ‘Something like 24 [further] sites have been identified, mostly in Scotland or in north Wales,’ says Woodward, ‘but it is very expensive, with very high upfront cost.’ Plus it needs sites with the right geography, which are limited and often correlate to areas of natural beauty, far away from areas of high demand.
Storing renewable energy isn’t the only way we will reach net zero. As well as reducing our energy consumption there is also a push towards interconnecting electricity grids across Europe and ultimately even across the world, so renewable energy can be moved to where it’s needed. 2021 saw the North Sea Link begin operating, a 720km 1400MW sub-sea interconnector linking the UK and Norway electricity systems, and adding to existing links to Belgium, France and the Netherlands. ‘It is definitely part of the solution,’ says Woodward, but it can’t guarantee a supply – storage capacity will still be crucial.
Batteries and physics
Lithium-ion batteries are the one storage technology that has made progress in the last decade (see Building better batteries). ’There’s been massive investment going into this technology simply because [of] electric vehicles,‘ says Schmidt. But while the lithium-ion battery is king for short-term storage – up to four hours – the technology isn’t ideal for the medium- to long-term storage that the grid needs. The batteries suffer from power fading over multiple cycles, limiting their lifetimes, and there are also safety and reliability issues – a number of fires caused by thermal runaway have been reported, such as the major data centre fire in Pangyo, South Korea, in 2022 which caused disruption to internet service for days.
With lithium prices rising (see The lithium rush), the costs are likely to be too high for long-term storage, which Schmidt defines as ‘any technology that is economic when discharging for more than eight hours’. One alternative idea is to use gravity in ways that are less geographically limited than pumped hydrothermal systems. It can be as simple as using a crane to lift concrete blocks. Schmidt says it’s a little more sophisticated than it sounds but has the advantage of using ‘super cheap materials’. One such project comes from Edinburgh-based Graviticity, who plan to cite their storage in disused mineshafts. In 2021 the company constructed a 250kW grid