It happened at a terrible time – just before the Friday rush-hour. At 4:55pm on Friday, August 9, outages at two major UK power plants caused a sudden, major drop in the nation’s electricity supply. With more than one gigawatt of power lost from the system, National Grid had to reduce the load on the grid by forcibly cutting selected customers off.
Trains were left waiting on the tracks for hours. Tunnels on the London Underground went dark. A backup generator at Ipswich Hospital failed to start, leaving some to struggle down stairs after the lifts ground to a halt. In total, nearly a million people faced blackouts.
But it could have been even worse. Within seconds of problems hitting the grid, a fleet of batteries dotted around Great Britain were able to pump power into the system, preventing a rapid drop off in transmission frequency.
Upside Energy is one firm that lent a helping hand by supplying six megawatts (MW) from five large lithium-ion batteries located on a solar farm near Luton Airport. “Those batteries responded immediately – actually it was sub-second,” says the firm’s chief executive Devrim Celal.
Six megawatts may not sound like much. It’s about the same capacity as a single medium-sized wind turbine, but in the context of national electricity supply that can make a difference, says Tim Green, co-director at Imperial College London’s Energy Futures Laboratory. “A home on average is consuming about two kilowatts – six megawatts gets you 3,000 homes maybe.”
In recent years, more companies that manage battery storage have signed up to provide National Grid with a stand-by service. If there is a sudden fall in electricity supply, the batteries are ready and waiting to switch on.
Fail-safes have always been important to the grid. But in the past, operators had to rely on generators or power plants able to boost their generation at short notice. Such sources of electricity have one major drawback versus batteries: they don’t come online as quickly.
During a power cut like Friday’s, time really is of the essence. This is because of the need to manage the electrical frequency of the grid. Frequency means how quickly alternating current (AC) is changing from one direction to the other. In the UK, this oscillation happens 50 times per second – so 50Hz is the agreed frequency of the grid and all power sources have to stick as closely as possible to that output. When demand exceeds supply on the grid, frequency falls. It’s the symptom of a system struggling to cope.
On Friday, frequency fell to 48.9Hz, which is a huge dip. And it gets worse. The lower the frequency, the harder it is for traditional power plants to push electricity into the grid. “For big generators, their performance drops off as the frequency goes down, they produce a bit less and that’s a potential runaway system,” says Green.
The big advantage of batteries is they are not hampered by stalling frequency. They just switch on and send electricity straight out, at 50Hz.
Another company that manages battery assets is RES. It provided 80 megawatts of power at the critical moment. And Limejump had 27 megawatts’ worth of battery power at its fingertips. A spokesperson says most of those batteries were only installed in the last two years.
Battery supplies provided a much-needed safety net that held the fort while heftier power sources came online, such as the pumped-storage hydroelectric station at Dinorwig in Wales. Batteries alone couldn’t replace all of the lost generation – one gigawatt is a lot of power – but they did help to prevent the downward cascade of frequency loss tumbling out of control.
“Anything you’ve got that comes in and provides a bit more power really saves you from going down that ladder and disconnecting more demand,” says Green. Celal says Upside Energy plans to increase the total capacity of its batteries on the British grid to 100 megawatts by the end of the year, with further additions expected in 2020.
It’s not just big battery units at power plants that can could come into play, though. It might also be possible to pay electric car owners to sign up to a rapid response system. Should a power cut hit while they’re charging their vehicles, the cars could reverse flow and push energy back into the grid. It’s what the battery-managing firms do, just on a smaller scale.
Upside Energy is already exploring how to make this happen, though there are questions over using vehicle batteries in this way as it could affect their lifespan. “We are still learning how these batteries will perform in the long run,” says Celal.
Either way, batteries of one kind or another are increasingly being connected to the grid. If they work as intended, power cuts like Friday’s might be much less dramatic in the future. The plan is as follows: the batteries switch on, grid frequency stabilises quickly – and Britain isn’t stopped so rudely in its tracks.
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