Energy storage allows us to move energy through time, capturing it when we have too much and saving it for when we don’t have enough.

When we have excess electricity, perhaps on a really windy day, we don’t want the extra energy to go to waste. If we can store the electricity to use later, when supply might be lower and we need some extra electricity to meet demand, it will help us keep costs down and decarbonise at the same time. 

There are lots of ways we can store energy and we are already using some storage on our electricity system. In fact, for some of the very fast acting flexibility we need, storage is the main technology providing the service. Let’s explore some types of storage. 

Storage is not new, and it has been on the system for decades. Pumped storage uses huge volumes of water to generate massive amounts of electricity. During periods where there is excess electricity on the system, water is pumped up mountains into large holding reservoirs. Then, when the electricity is required, water is released and gravity sends it back down the mountain, where it runs through turbines. This causes the turbines to spin, generating electricity which we can then use on the system.  

Pumped storage can generate electricity in quantities of gigawatts and deliver it very quickly – to give you an idea of how much electricity that is, 1GW is about 120 offshore wind turbines operating at full power. A really big offshore wind farm, like East Anglia One, is almost half a GW. So when we see demand spikes, such as the one at half time during the Euros 2020 final, we can use this stored energy to quickly provide power. 

Another way we can store energy is by using batteries. Batteries are typically created to power things like phones and cars. They can deliver lots of power very quickly, but they also run out quite quickly. Batteries can deliver electricity faster than more traditional storage such as pumped storage, but the electricity they can deliver is much more limited - you’d need hundreds of batteries to create the same power as pumped storage. 

Storage is particularly important as we decarbonise our electricity system. Fossil fuel energy sources like coal and gas plants can be switched on or off at pretty much any time to respond to changes in demand. However, we can’t get energy from wind farms when there is no wind. 

As we stop using coal and gas and rely more on renewable energy sources like wind and solar, we need to be able to store excess energy on windy or sunny days to be used when there isn’t wind or sunshine.  

Last summer we saw a period of 16 weeks with very little wind. Today, we often have to power up gas and coal power stations to fill these gaps in supply, but in the future, more and more storage is going to be needed on the system to provide flexibility. We're likely to see larger and more extended periods of both high renewable output (where storage might capture energy that would be otherwise wasted) and low renewable output (where storage could fill gaps in supply). Currently lots of options are being explored, for example, using hydrogen to store energy which can then be used in power stations to make electricity to use on the system. We can create huge caverns underground and fill them with hydrogen, storing very large amounts of energy, for very long time periods. This is probably the most credible option for taking excess electricity in summer and storing it to use in the winter. 

By 2030, the UK Government has announced there will be a ban on producing any internal combustion engine cars. This means that more of us will be using electric vehicles to get from A to B.  

As electric vehicle sales increase, we predict that we could have up to 37.4 million of them on the road by 2050. Each electric vehicle runs on a battery which is great news for storage.  Most of us will use our EVs during the day and then plug in when we get home, allowing cars to charge overnight ready to head out again the next morning.  

But a lot of us don’t mind when the car charges up in that time period, as long as it’s ready to go in the morning and being able to move their recharging periods away from peak times will be increasingly important. We're currently running trials to see how car batteries can be charged using smart charging, meaning that they will charge at lower demand times on the grid – for example when most of us are asleep in the middle of the night. This will greatly reduce demand on the network at times of peak demand like dinner time, when most of us are using electricity for other things too like cooking and lighting.  

In addition to this flexibility, once a vehicle battery is fully charged, it may be able give some electricity back to the grid, such as early in the morning when we are all boiling our kettles for a morning cuppa. This vehicle-to-grid technology is currently under development and lots of trials are already underway.  

Today, we mostly use storage over short time periods to quickly respond to a spike in demand or a fault if a piece of equipment suddenly failed.  

However, storing energy for longer periods provides a new challenge. For example, in the winter, we can expect that there will be periods of high demand if we get a particularly cold spell of weather - people will require more electricity to heat their homes. But in the winter, we won’t have lots of solar energy to help fulfil this demand and when it is really cold it is often also not windy. In this scenario, we need to have supplies of energy ready which were stored from weeks or even months ago.  

Our Bridging the Gap team is currently looking at how we can overcome this challenge, and how we can use storage to stabilise our electricity supply, not just hours and days into the future, but potentially weeks and months into the future too. With the right technology and infrastructure, storage will become a vital part of our generation mix, helping us to balance the grid on our way to net zero.