Southern California Edison and General Electric have taken a grid edge concept -- integrating natural gas-fired turbines and batteries -- and turned it into two working models.
Last month, SCE started operations at the second of two of its new hybrid electric gas turbine (EGT) units -- GE’s term for its combination of turbines, batteries and power controls installed at the two sites. Each peaker plant is in the 50-megawatt range, and is outfitted with a set of batteries capable of providing 10 megawatts and 4 megawatt-hours of power.
The projects were rushed into operations to help SCE manage the closure of the Aliso Canyon natural gas storage facility, something it’s also done with several large-scale energy storage projects across the region.
But with its new hybrid units, SCE is testing a different set of capabilities and value propositions, tied specifically to how batteries can stretch the capabilities and lifespans of existing natural gas infrastructure. “This really does unlock value in our peaking plants,” Phil Herrington, SCE’s vice president of generation, said in a Monday phone call from the opening of the Norwalk, Calif. facility.
The secret to this lies in batteries’ use as a ramping resource, he said. Normally, peaker plants such as these are bid into the grid markets run by the California Independent System Operator as energy services -- they’re either on, or they’re off. That’s because turbines are designed to run most efficiently at full capacity, rather than in standby status. What’s more, California’s stringent air quality rules limit how many hours they can run, he said.
“Now that we have the batteries, we can provide something that for these batteries makes a lot more sense -- spinning reserve,” he said. Spinning reserve is, as its name implies, provided by generators that are up and running, ready to move up or down to meet 15-minute to 5-minute signals.
Batteries can serve as a shock absorber, ramping up to meet these signals while allowing the turbines to run less frequently, to meet sustained peaks in market demand. In that sense, “these turbines are available, 24-7, even when they’re offline," said Herrington.
Flexibility helps to manage the increasing amount of solar PV flooding its grid, SCE President Ron Nichols added. “One of the beauties of pairing batteries is that we can use the battery more flexible,” he said. “Any peaker is obviously critical as we manage more and more solar energy we have around here.” CAISO has already seen negative pricing on some mild yet sunny afternoons this spring, when the supply of utility-scale solar exceeds customer demand, and is projecting that these "duck curve" patterns could lead to multi-megawatt curtailments.
This isn't the first time storage companies have grasped on the value to be found in augmenting gas turbines. AES Energy Storage often describes how 1 megawatt of battery capacity can effectively contribute to 2 megawatts of power plant flexibility. Last year, the U.S. energy storage leader deployed a 20-megawatt lithium-ion battery array for sister company Indianapolis Power & Light, meant to serve this function.
But the two new SCE projects are the first that combine turbines and batteries in a site-specific way, according to Mirko Molinari, general manager of GE Digital Grid energy storage solutions. “Just siting a battery close to a turbine is easy,” he said. “But the trick here is how you coordinate the control system, so from the grid operation standpoint, you see a black box that delivers power how they need it, when they need it.”
GE makes its own turbines, and integrates batteries at behind-the-meter and grid scale, giving it an understanding of the complex interplay of battery and turbine operations, he said. “Really, you need to look at it as a unique system. It’s not comparable to a peaker, or to a pure battery. A pure battery at the end has the limitation of how long it can be on -- and the gas has a limitation of how quickly it can start up. When you put them together, to some extent, you can run them forever.”
SCE has also invested in controls and equipment to reduce fuel and water consumption. They are expected to reduce greenhouse gas emissions and air pollution by 60 percent, and water consumption by about 45 percent, Nichols noted. While the partners didn’t disclose financial details, the viability of the combination is reliant on Southern California’s unique set of circumstances, he said.
Still, GE is looking at the the two plants as an initial test run of a hybrid energy technology stack that could fit into other markets with similar wind and solar power characteristics, such as Germany or Australia, said Stephanie Kai, vice president of commercial solutions with GE’s energy storage business.