Illustration Mikal Bednarski
Built to store energy from wind, solar or hydro power, battery systems are becoming an important part of achieving a flexible and modern fossil-free energy system. And, considering the recent UK-wide power outage, they are also crucial to maintaining supply when the National Grid comes under pressure.
The outage in August was caused by a large-scale frequency drop, and batteries are designed to rapidly input to or draw power from the grid – what is known as enhanced frequency response (EFR).
The market was kickstarted by the National Grid's EFR project in 2016: four-year contracts were offered to energy companies to provide frequency response. There is around 700MW of large-scale storage in the UK – up from 530MW in 2016, so the sector is growing well. Next year, the UK's largest site will be built at Whitelee in Scotland, storing power generated from 215 nearby wind turbines.
Vattenfalls, 22MW facility at Pen y Cymoedd in Wales was one of eight battery systems that helped back up the National Grid during the outage. Storing electricity produced by its neighbouring wind farm, it is made up of six shipping container-sized units, five of which house 450 lithium-ion cells – the same as those in BMW's i3 electric cars. After around 15 year's the cells will be at the end of their operational lives and will go back to BMW to be recycled.
The ancillary service provided by batteries replaces – among others – what was provided by coal-fired power stations. As coal comes offline EFR systems will step up, although it's important to recognise that renewable power production varies with the weather, and that variability sometimes does not always match demand.
Battery owners can be paid to store energy when, for example, high winds lead to a surplus of electricity being generated. But to claim renewable energy subsidies for their facilities, they must be able to demonstrate that they can separate the charging of the battery with renewable energy from fossil-based energy drawn from the grid.
Installing a high-voltage EFR system also comes with safety and security considerations: they need to be behind high-perimeter fencing, and protected as sites of critical national infrastructure.
If that sounds a lot for prospective owners to take on, consider the long-term benefits. Combine batteries and other storage infrastructure with smart meters and a smart grid, and the peaks and troughs of renewable energy generation are smoothed out. The result is more stable prices and reliable supplies of fossil-free electricity for consumers.
"When large-scale outages occur the batteries are designed to input power to the grid rapidly"