Step outside on a blustery or sunny afternoon, and it’s hard to imagine we’d ever run out of natural energy to power buildings and cities. But when the wind doesn’t blow and the sun doesn’t shine, how does the energy sector ensure a reliable, uninterrupted energy supply?
Storage is crucial for stabilising the grid and ensuring the supply of clean electricity meets demand. From battery systems and pumped hydroelectric to mechanical and thermal technologies, energy storage is witnessing extraordinary levels of innovation as the sector invests in building capacity and exploring new possibilities.
“It helps to tackle the issue of variability of renewable energy generation,” says Yonna Vitanova, senior policy analyst at RenewableUK. “For example, in times of high winds, the grid cannot always transport the vast amounts of clean power being generated by wind, and although grid upgrades are under way, other solutions are [also] needed to make the best use of the UK’s abundant renewable energy resources.”
But there are many challenges, notably in building long-term energy security “Resilience is ultimately the big issue,” says Robert Friel, member of the Institution of Engineering and Technology’s Sustainability and Net Zero Policy Centre. “How can you build a reserve for the one-in-20-years cold spell, and store it somewhere secure in the way that you can with gas or fuel today. If you electrify everything you need a system that is resilient at its core.”
Battery storage
Battery power is crucial for smoothing out fluctuating supply and demand and preventing blackouts in the short term. As demand dips and soars over the course of each day, battery systems, both domestic and grid scale, can ease the strain on the network and make overload less likely.
By 2030, the government aims to grow battery storage to up to 27GW, from 6GW today. More large-scale battery plants – such as the 50MW West Gourdie plant recently installed at a site in west Dundee – will be critical for a stable supply of energy.
While today’s batteries are largely based on lithium-ion – as used in smartphones – there are a host of pioneering initiatives to develop new large-scale storage solutions. One of these is the more cumbersome, less energy dense but cheaper sodium-ion batteries, which some proponents suggest are ideal for the grid because they are particularly suited to uses where size, weight and portability are not key factors.
Developments in the more energy dense but shorter-lived solid state batteries are attracting investment and could revolutionise the electric vehicle (EV) market and beyond. And flow batteries – which store energy in an electrolyte liquid, which is pumped through cells to create a reversible chemical reaction – could provide longer-term energy storage of up to 12 hours and a longer battery life.
Another potential source of battery capacity could be car batteries. While today’s EV batteries come with a warranty of up to eight years or about 100,000 miles, retired batteries could be used by homes and businesses to store excess solar energy. Some carmakers such as Nissan and Toyota are using spent EV batteries to power sports arenas in the Netherlands and convenience stores in Japan. Ultimately car batteries could fulfil a dual function and power both homes and cars, although implementing this at scale is still a long way off.
Pumped hydro
However, batteries alone won’t solve the storage puzzle, and some older methods have stood the test of time and are inspiring renewed investment. Hydropower, for instance, offers a reliable storage solution as it uses excess energy generated during periods of surplus to pump water to higher ground – it’s then released at a later date to generate electricity at the push of a button. Today pumped hydro is the most widely used method of large-scale energy storage around the world and new facilities are coming on stream.
In northern Portugal for instance, the new Tamega hydroelectric complex developed by Iberdrola has become one of Europe’s largest energy storage facilities, complete with three dams, three power plants and two windfarms, and is expected to generate enough energy to power 440,000 homes. Worldwide, pumped hydro energy accounts for almost 200GW of installed energy storage capacity.
But the UK has just 2.8GW of pumped hydro energy storage across four schemes in Scotland and Wales, with no new facilities in the past 40 years – well below the maximum 16.6GW of long duration electricity storage that the National Energy System Operator estimates we need by 2050. Hydroelectricity suits certain geographies such as Norway with its natural steep valleys and high lakes, but new facilities are expensive and there has not been a route to market in the UK.
Other innovations
On the horizon are more efficient methods to store and use thermal energy. Heat or cold, stored in materials such as salts, gravel, oils and stones, can be used to generate electricity or provide heating or cooling. Other innovative methods investigate the use of excess energy to liquefy air, which can then be stored in cryogenic tanks and released to provide energy. These technologies are in the early stages, but offer much potential: thermal energy can be extremely efficient and versatile, providing heat as well as cooling. It can also help some industries to reduce their carbon footprint by using their heat directly.
As the range of storage options expands, smart systems could help make the most efficient use of them. Artificial intelligence can be used to analyse weather forecasts, prices, and demand to predict the most efficient times to store or release energy – when demand is high and grid supply is low for instance.
“There are a lot of games at play at present about what is the right direction [for energy storage],” says Friel. “What will the mix look like – because it certainly won’t be a single solution. You need a mix of technologies that gives you resilience.”
