On March 23, at exactly 11:19 in the morning, the combined output of California’s copious solar panels and wind farms briefly supplied 49.2 percent of the state’s power demand for the first time. The record was a good omen for America’s most populous state, which is striving to use renewables for half of its electricity consumption by 2030.
But this laudable goal comes with a few hurdles. Customers want their electricity always on, but the wind can weaken and, even in California, the sun hides behind a cloud. “It’s not always possible to meet the full demand with renewables in the mix,” says Selma Kivran, a general manager for aeroderivatives at GE Power Services. “You need something else to fill the gap.” (An aeroderivative is a fast turbine that uses parts from a jet engine to generate power.)
In the absence of grid-scale batteries to bridge supply gaps — batteries remain expensive and limited in use — that something else has been “peakers.” These natural-gas-burning turbines can quickly ramp up and pick up the slack when renewables drop off. But even the fastest peakers take several minutes to reach full power, forcing operators to run them at minimum load to keep them ready, burn gas and put more wear on the machines. “This is inefficient combustion that needs extra fuel, costs money and generates unnecessary greenhouse emissions,” Kivran says. “It’s not the ideal, and not the only possible solution.”
That’s why Kivran and her colleagues at GE Energy Connections decided to bring peakers and batteries together and wrap them in a single, efficient package with sophisticated power management software. With this hybrid system, the turbine can be turned off, and the battery will respond instantly. Southern California Edison (SCE) is deploying the solution — the first of its kind in the world — at two sites near Los Angeles. “It’s a hybrid of both worlds,” says Mirko Molinari, general manager for digital grid at Grid Solutions from GE Energy Connections. “The battery is quick and clean, and the turbine is giving you the power you need. It’s reliable power because it’s always there, and you also get the environmental benefits.”
Economic benefits are important, too. “It’s just like cars,” Molinari says. “We would love to have electric vehicles everywhere, but the amount of energy you can pack into a battery on a cost-efficient basis can only last a limited number of hours. Battery costs continue to drop, but in the meantime hybrids are the next best thing.”
Under the hood of GE’s California grid-scale hybrid, there’s the company’s LM6000 gas turbine — a nimble peaker with jet engine technology at its core that can reach 50 megawatts (MW) in just 5 minutes — and a 10MW battery assembled from lithium-ion cells that lasts up to 30 minutes. When a wind farm output drops, the battery can kick in immediately and give the turbine the time to start up without cutting off from the grid.
GE engineers developed software that allows the utility to manage in the most optimal way how fast the battery discharges and how quickly the turbine needs to ramp up from full stop. “Anybody can put a battery next to a turbine,” Molinari says. “The magic is in integrating the controls.”
Molinari says the California Independent System Operator (CAISO) already has software that is always listening to what’s happening on the grid. When it detects that the power line frequency is dropping, it will send a signal to the battery-turbine hybrid to get ready and also the utility’s central control room. It will keep the amount of power racing through the lines the same even after the renewable source drops off. “When you speed up in a hybrid car, you don’t really know how much power comes from the gas engine and how much from the battery,” Molinari says. “This solution does the same thing for the power consumer.”
Besides fighting dips in renewables production, the solution could be also useful in fighting the dreaded California duck — the nickname for the duck-like curve that describes the sharp difference between power supply and demand after the sun sets and the state’s plentiful solar panels stop producing electricity. “This solution is scalable,” Kivran says. “We’ve optimised the energy storage to meet desired cost proforma, but given its design is modular, there is no reason why we could not go to 100MW or more.”
Says Kivran: “As California marches into its higher renewable targets, the curve is only going to get more severe. We will need more solutions like this to support the higher renewable mix.”