The thing about a home solar power system is that it doesn’t always produce maximum power exactly when the homeowner — or the utility trying to meet peak load demand — needs it. Like, say, around 6:30 p.m. on a blistering hot August day in California’s Sacramento Valley.
But now a pilot program is going to take a whack at solving that dilemma by hooking PV-powered homes to big batteries.
The Sacramento Municipal Utility District has installed lithium-ion batteries about the size of mini-fridges in 15 homes while another 27 homes are sharing three batteries – cubes about 4-foot by 4-foot – plunked down in neighborhood common areas in Rancho Cordova.
According to a presentation prepared by SMUD for the U.S. Department of Energy [PDF], which is largely financing the project, the single-home batteries can put out 10 kilowatts of power and store 8.8 kilowatt-hours. The shared batteries can produce 30 kW while storing 30 kWh.
As part of SMUD’s “SolarSmart” program, the homes in the energy-storage demo already come with building-integrated PV modules. They’re not big systems, averaging around 2 kilowatts of generating power.
The idea behind the SMUD battery program is to keep the homes off the grid during the highest-demand times of the day – late afternoon during hot spells – when power also happens to be most expensive. The batteries will charge earlier in the day when solar accumulation is highest (PV production even during the summer tends to begin to slide around 2 p.m.), as well as from the grid during overnight hours, when power is cheaper.
This could benefit the utility by decreasing demand when it peaks, while also saving residents money by allowing them to take advantage of their homemade solar power and less expensive grid power.
“The aim of the program is to learn whether or not batteries can ease load demand and provide more electricity when renewable energy sources such as solar and wind power aren’t sufficient,” Paul Lau, SMUD assistant general manager for power supply and grid operations, said in a statement.
Lau said the project will also help give the utility better insight into “how battery storage and solar mesh with time-of-use rates, where customers pay more for electricity during peak hours and less during low-demand times. The batteries provide power during peak demand, so customers could save money by not drawing all their power from the grid during those hours.”
The SMUD battery program is costing $5.9 million. The DOE kicked in $4.3 million (the good ol’ Recovery Act again), with other assistance coming from SMUD, the California Energy Commission and SunPower.