An energy storage expert from the organisation contracted to the first battery energy storage system (BESS) project on the Shetland Islands has explained the role of batteries in building resilience on islanded grids.
Wärtsilä Energy will supply a 68MW BESS in Lerwick, Shetland, known as The Shetland Standby Project. It is scheduled to go live in 2026 and will enable the Lerwick Power Station to move into a standby role, cutting fossil fuel use and helping integrate more renewable energy from Shetland’s abundant wind.
Speaking to NCE, Wärtsilä Energy data science director Luke Witmer said: “Batteries provide a strengthening factor to island grids.
“As you bring in more renewables, you want to shut off your traditional generation but unless you have enough grid strength and resilience, which the batteries can provide, you can’t actually do that.”
In the event of an outage or planned maintenance on this transmission line, the Shetland Standby project BESS will maintain uninterrupted power to Shetland’s homes and businesses.
Witmer continued to explain why batteries are still so important for island grids even when they are connected to a mainland grid.
“Even if an island has some connection, it almost certainly won’t be able to supply all of the power that the island needs, it’s very rare that you have subsea cables that can actually power a whole island, there’s normally some generation there,” he asid.
“In all these kinds of places where you have growing offshore wind and growing renewables in general, you end up in a position where you have massive curtailments, where you have to keep some of the thermal plants running for stability, for voltage control and reactive power needs.
“They’re running on a very low load, which is very inefficient, and they’re still producing a lot of CO2.”
With the powering up of the Shetland Link came the beginning of operation for SSE Renewables’ Viking Wind Farm, predicted to become the UK’s most productive onshore wind farm.
“Even with the Shetland Link, the whole UK is going through this transition where the grid in general is weak,” Witmer explained. “If you connect over to the UK grid, it has its own issues of weak times and so having batteries on both sides of that connection is actually very important for a really robust and reliable grid where you can actually shut off the thermal plants.”
Shetland is the windiest area of the UK, according to the Met Office, with an average annual wind speed of 14.6 knots (27k/h), The Viking Wind Farm features 103 Vestas turbines and has an installed capacity of 443MW. It is forecast to produce around 1.8TWh of renewable electricity annually.
While the wind only stops on occasion in the Shetland Islands, Witmer stated how even with islands providing an abundance of renewable energy, batteries should be used when that generation is not available.
“Either way, the battery serves as a bridge where if you’re running on very high renewables and then the wind suddenly collapses, it’s an insurance policy,” he said.
“That buys you enough time to get those other thermal plants back up and running so as a consumer the lights never go off.”
The Shetland Standby Project will have use innovative technology such as grid-forming inverters and AC choppers. These offer a method of “strengthening the grid” by helping to absorb excess wind power during shutdowns. Wärtsilä Energy is supplying this technology for Zenobē, developer of the project.
Witmer explained how another side to the technology is its autonomous nature.
“When it comes to decision making, so in our islanded grids, where there isn’t some kind of central dispatch authority that is sending us the signal we’re deciding ourselves based on solar forecast and wind forecasts, when does it make the most sense to charge or discharge the battery?” he said.
“We’re also measuring grid quality and if the grid quality is suddenly deteriorating because some plant nearby tripped offline or is suddenly ramping down, the battery then just steps into contingency mode and just fixes the issue.
“If the grid needs more power, the battery just outputs more power, it behaves very autonomously.”
To help demonstrate the suitability of batteries for the Scottish islands, SSE commissioned a 6 MWHr battery energy storage system as a test plant, located on the main island generating station in Lerwick.
Witmer explained that the size of a BESS is figured out based upon the size of the island’s grid.
“At first, it’s size is based on the single biggest point of failure in the grid,” he said.
“If you look at your biggest generation asset, you look at your biggest transmission cable, you figure out with everything on what’s the worst case scenario if one thing were to fail that we need to have instantaneous backup for.
“Those are the things that are really the driving factory, it’s figured out on the power dimension. We’re not even looking if the battery can discharge for only one hour versus four hours.”
While batteries are currently a very efficient solution for islanded grids as the world moves to using more renewable energy generation for its grid mix, Witmer believes they will only become more useful in time.
A lot of batteries that are being built now could be seen as an interim measure, he indicated.
“They’ll increase the size of the batteries two, three years from now, as battery prices keep getting cheaper and as the renewable installations keep expanding.
“They are just stepping stones in the journey to increase decarbonisation.”
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