The ability to store renewable electricity is crucial to the UK freeing itself from dependency on fossil fuels. But how exactly does it work, and who’s building it?
A few years ago, when people in Bristol’s Feeder Road district learned of plans to install 48 diesel generators near a local nursery school, they weren’t best pleased. As part of a group called Residents Against Dirty Energy (RADE), they campaigned hard against it. But they were up against a compelling argument: without such backup power plants, the UK’s electricity grid could cease to function.
Balancing electricity supply and demand is an essential task for the grid. Even in the days when most of the UK’s electricity came from large coal plants, some of these always had to be kept on ‘spinning reserve’ – ready to send more power down the wires as demand surged at peak times. With a growing proportion of our electricity coming from renewable sources, notably wind and solar, the fine art of grid balancing is even more important today. Renewables are, by their nature, variable: the wind doesn’t always blow; the sun’s intensity isn’t always consistent. So backup supplies are essential.
But that doesn’t have to mean ranks of diesel plants next to nursery schools – or anywhere else. A few years on from RADE’s campaign, a spanking new power plant is indeed being built on that very site, but this time it’s one that meets with the residents’ approval: a bank of batteries.
It’s one of two such storage plants owned by Thrive Renewables, which complement the sustainable investment company’s growing portfolio of wind, solar, hydro and geothermal power projects. Essentially, it acts just like any rechargeable battery we might use for a phone or laptop – but on a larger scale, and tied to the needs of the grid. As Thrive’s investment manager Tom Barratt says, it is ideally suited to the grid in the sense that a certain level of fine-tuning is required to maintain its frequency. “The clever bit is the way the battery is run: it can inject a short burst of power – a few minutes, a few seconds, even – to stabilise the frequency of the grid when required.” Technologically, this is a lot more sophisticated than firing up an old coal plant.
Battery plants can also help reduce the overall carbon footprint of all those electrons flowing down the wires, explains Thrive’s managing director, Matthew Clayton. “Electricity wholesale prices are set for periods of half an hour: when demand is high, the requirement for fossil fuel sources of power such as gas is high, so the price is high. That’s when batteries can be used to reduce the cost and the carbon intensity of the energy. When demand is lower, or there is more supply coming from renewable sources, the price falls, so that’s the time to recharge the battery. Essentially this means that it charges up with low-carbon power, and then exports electricity to mitigate high-carbon generation – because price and carbon intensity tend to track each other.”
For Thrive and other battery developers, this makes pleasing business, as well as environmental sense. At present, Thrive’s investments in storage are relatively small-scale: the Feeder Road plant has a capacity of 20MW, and can produce electricity when fully charged for 90 minutes at a stretch (so providing 30MWh of power to the grid). Its second plant, at Wicken, near Milton Keynes, has a 5MW (7.5MWh) capacity. Set against a total installed capacity of 1,300MW across the country, this may seem like small beer – especially when, according to National Grid, the UK needs 10 times that by 2030 to be on track for its net zero targets.
With a growing proportion of our energy coming from renewable sources, notably wind and solar, the fine art of grid balancing is even more important today
But the beauty of small-scale battery plants is that they can be rolled out surprisingly quickly. The Feeder Road plant only starts construction this spring, but will be online in the autumn. (Compare that to the decade – or longer – lead times of a nuclear plant.) And multiple battery storage projects across the country can effectively operate as a single, distributed power plant, offering greater resilience compared to single-site generators.
They have another advantage, too. “Batteries are absolutely the cheapest source of flexible power” in terms of ensuring stability of grid frequency, says Clayton, “and will be the cheapest in terms of overall grid balancing”. At least until other forms of storage, such as pumped hydro, are introduced at scale. Site constraints mean there can only be so many of these.
Like most batteries, Thrive’s depend on lithium, the sourcing of which can be controversial. For its part, says Clayton, Thrive does a lot of due diligence with its suppliers, making sure as far as possible that they stand up to ethical scrutiny. Meanwhile, he points to the potential for sourcing significant supplies of lithium closer to home, from the brine water produced as part of Thrive’s planned geothermal plant in Cornwall. “Carbon-free Cornish lithium is a really exciting prospect!”
So, can batteries help power our way to net zero? Absolutely, says Clayton. Their ability to provide vital energy storage and grid balancing services gives him confidence that the prospect of something approaching a 100 per cent renewably powered future – without a material increase in energy costs – is within reach.
“It’s just a question of whether we are bold enough to move that far, that fast”, he concludes, adding: “If the will’s there, then the technology’s there to deliver it.”
Main image: Houses in Bristol, UK. Credit: Shauking