By Jason Deign
Batteries look set to face a major challenge in a pilot where energy delivery is needed when it makes more commercial sense to store it.
The business model for storage will be tested to the full in the Southern California Edison (SCE) Preferred Resources Pilot (PRP) because load peaks are expected to coincide with maximum solar output periods.
This means energy in the pilot area of central Orange County, California, will be at its cheapest precisely when it would usually be best to store power rather than discharge it.
The unusual set of circumstances is likely to occur because the area has heavy daytime peak loads with little local generation capacity following the closure of the 2.2GW San Onofre Nuclear Generating Station.
As a result, energy needs to be brought in from outside the area, straining the transmission network served by two SCE substations, Johanna and Santiago, and increasing flows with neighbouring San Diego Gas & Electric’s grid.
Growing energy demand
For now, this strain is manageable.
But energy demand in the pilot area is forecast to grow by 300MW up until 2022. And further generation shortfalls are expected from 2020, when SCE’s other Orange County ocean-cooled power plants are scheduled to close.
The standard utility response to such a situation would be to build new gas-fired stations. However, SCE wants to see if a combination of distributed renewables, energy efficiency, demand response and storage can do the trick instead.
These are the ‘preferred resources’ referred to in the pilot. SCE is planning to deploy around 66MW of them by 2017.
The utility, which supplies electricity to nearly 14 million people across most of Southern California, has given itself until the end of 2017 to prove that its PRP strategy can work. If not, it still has time to build a gas plant.
“The need is in 2025,” Caroline McAndrews, PRP director, told Energy Storage Report.
Distributed renewable assets
SCE launched the PRP in November 2013 and the pilot is now in a ‘demonstration and proof’ stage in the run-up to 2017. As part of the project, SCE is already piling on distributed renewable energy assets.
Last month it announced it had signed up 42.6MW of rooftop solar, on top of 1GW of PV generation already installed across its service area.
“As part of the procurement effort, SCE also sought projects to serve the Orange County area that could enhance the reliability of the local grid,” said the utility in a press release.
“One of the projects approved by the commission is a 1.63MW direct current rooftop project in Orange County, where renewable generation in the densely populated area is currently less than 3%.”
SCE has also commissioned a 2.4MW, 3.9MWh grid energy storage site from NEC in Orange County.
Assuming the pilot is success, the utility will work between 2018 and 2022 to bring a further 88MW of preferred resources online by 2021, to allow it to put off new gas-fired generation indefinitely.
A current portfolio design
Although it is perhaps early to say just how important energy storage will be in PRP, one current portfolio design shows assets kicking in around midday and then between 2pm and 6pm.
Demand response, meanwhile, will take the sting out of afternoon power consumption that is expected to peak at around 315MW around 3pm by 2022.
The design shows up to around 50MW of storage coming into play between 5pm and 6pm. At least half of this may need to be online from 2pm, though.
The load profile suggests lithium-ion batteries might be suited to the PRP, although McAndrews said: “We are not pushing any one technology. We are relying on the market.”
Likely a more important issue, though, will be how to pay for the storage needed.
The dreaded duck curve
The interval between noon and around 6pm is roughly when the rest of California is likely to be suffering the worst effects of the dreaded duck curve, a daytime period of over-generation from solar power.
In the period between 6pm and 9pm, meanwhile, load across California is predicted to ramp up by about 13GW in 2020.
This means Californian energy storage owners are likely to get the best returns on their assets if they store during the day and dispatch from 6pm onwards, the opposite of what is needed in the PRP area.
That is a challenge for the PRP, McAndrews admits. “Energy storage depends on price signals,” she said.
“When people are getting lots of solar across the state it may be less expensive for charging at parts of the day when we need them to discharge.”
For now, how to get around this problem is still unclear. SCE has until 2018 to work it out.