Saturday, November 29, 2014

When batteries beat traditional power

Battery storage is usually seen as being a handy adjunct to help renewable energy square up to traditional power plants. But on frequency regulation, at least, it seems batteries may actually be better than the generation sources they are helping to supplant.

That, at least, is the consensus emerging from early operating experience at Europe’s largest commercial battery power plant, the 5MWh lithium-ion facility that WEMAG has commissioned from Younicos in Schwerin, Germany.

“Whereas coal-fired and other thermal plants typically take up to 30 seconds to adjust production up or down, and then just hit the neighbourhood of where they are supposed to be, batteries react within milliseconds,” explains Philip Hiersemenzel of Younicos.

The fact that batteries might beat traditional power plants for frequency regulation has long been touted as a big selling point for battery storage and has already helped sell projects in the US.

Now the performance of WEMAG’s installation is strengthening that business case.

As well as being able to respond to frequency shifts more quickly and accurately, says Hiersemenzel: “The second reason batteries are better suited is that they don’t require CO2 emissions to adjust the frequency.”

No must-run capacity

Furthermore, he says, batteries do not create any ‘must-run’ capacity. In other words, they don’t need to remain operational when not being used for frequency regulation, reducing overall power generation.

This can have a significant impact on carbon emissions. Younicos says most thermal power plants need to run at around 70% of total capacity just in order to provide decent frequency regulation, and in German coal-fired plants the level is about 90%.

“This creates an overall must-run capacity of 25GW in Germany alone,” Hiersemenzel states; “25GW of coal and nuclear power must be fed into the grid at all times.”

Natural gas plants are more flexible and can provide frequency response while running at as little as 40% of capacity. “But they’re also more expensive than coal,” says Hiersemenzel.

“Since we’re already competitive against the marginal cost of a completely written-down coal plant, imagine how competitive we are against a new gas plant.”

At the WEMAG plant’s grid-connecting ceremony a fortnight ago, Younicos’s chief technology officer Clemens Triebel pointed out that the facility was essentially providing the same level of frequency control as a 50MW conventional turbine.

Avoiding economic impact

“Coal-fired power plants can only use a fraction of their output for control power,” he said. “This blocks space in the grid, increasingly forcing wind and solar generation to be taken offline. Our battery park avoids this economic impact.”

The WEMAG battery plant features Samsung SDI lithium-ion cells and serves a grid area where 80% of power already comes from wind and solar generation.

It was backed by EUR€1.3m from the German Environment Ministry’s innovation programme and will compete on the primary frequency regulation market, Younicos says.

Younicos expects this capability alone will provide a positive return on investment for the plant. But the facility is also due to earn its keep in other ways. One is by replacing WEMAG’s current ‘black-start’ generators.

“Like all regional grid operators, WEMAG keeps diesel gensets solely for the purpose of black-starting the grid after a power cut,” says Hiersemenzel.

“Such cuts typically happen not so much because of electrical problems in the grid, or even renewable generation, but for much more profane reasons: a car hitting a power line, say.”

Using batteries instead of gensets

When this happens, the grid operator has to coax its power stations back online using smaller genset units. Only WEMAG should now be able to rely on its battery plant instead, and save the expense of maintaining gensets.

The facility, which has been praised by the German Vice-Chancellor and Energy Minister Sigmar Gabriel, and Mecklenburg-Western Pomerania’s Minister-President Erwin Sellering, could also be used for other auxiliary services, such as voltage control.

In fact, for another Younicos project, the 6MW, 10MWh Smarter Network Storage plant being built for UK Power Networks in Leighton Buzzard, UK, batteries will be used for at least six different functions, including peak shaving, and possibly all at once.

Trying to squeeze that much functionality out of a single battery plant will probably cut the lifetime of the batteries, Hiersemenzel points out.

But it is the operator’s choice whether to try to stretch the lifespan of their investment or get the most value possible out of it over a shorter period.

For now, what the WEMAG plant and other early grid-connected battery facilities are showing is that energy storage is no longer about making renewable-laden grids as good as traditional ones; it is about making them better.

Written by Jason Deign

Source: Energy Storage Report

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