Solar On The Roof And A Big Battery Nearby

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.

SMUD solar battery test

image via Sacramento Municipal Utility District

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.


  • Reply July 7, 2012


    Hi folks,
    The battery pack cost may be better spent if they assisted in the purchase of an EV for each of the 27 houses.  If the car has a lithium battery pack in it, 27 of them could probably store enough energy to the the house through the ‘hump’ of peak use and could recharge during the 1:00 am to 5:00 am low use period.  27 houses x $ 30,000 is $ 810,000 and the owners of the 27 houses probably wouldn’t mind adding a lease payment to their utility bill for the use of the EV and fuel savings (with optional buyout at the end).  Don’t get me wrong, I’d rather have a battery in the back yard than a nuclear plant, but let’s not rush into spending money before we figure out the best options.  TY – Jay

    • Reply July 7, 2012


      That’s a good point and I don’t think there’s any doubt that eventually we will see EVs used to help smooth grid demand. But remember, it takes some brains and hardware to turn that EV into an energy storage device for home use, especially if it’s going to have smart grid capabilities (two-way communication with the utility) the way these systems in Rancho Cordova do. Nissan just introduced a product in Japan that can turn the Leaf into an energy storage device for your home, and it’s $6,000:

      • Reply September 3, 2012

        Karl Brown

        Dam this isn’t trivial to find and there is nothing more evil on the horizon to my knowledge then further subsidising cars by putting them into service keeping ice off the grid. ICE- THAT’s Ice as in frozen h20 also known as the solid state- it’s the immense amounts of energy necessary to prevent 32 degree water in motion from getting warmer if it’s let still that allows it to absord ‘nearly’ as much before becoming fully liquid again while still. Such still waters should be rolled out far and thin but six foot deep in SMUD for example- but instead we see it topping APS who was denied in trying to sell fossil fuels by burning them at nearly FOUR cents delivered by instead succeeding in pricing it at BARELY TWO!!!!!!!!

        I kid not.

        We desperately need to protect our rolling stock of useful cars from the crusher- as we learn to park them still instgead of in slow motion on our highways for much of the day. Any EV needs to NEVER PARK- it’s needed rolling in replacement to private parked vehicles 24×7.

        To call this obvious is to call you all idiots- but that is of course the definition of the word.

        I was SHOCKED to hear about this battery business in SMUD. THey eliminated there ice up front incentive and continued to seek out rooftops to waste money that could of been spent on efficiency and how- a practice they still engage in and are so far behidn the ball on it’s breakign there budget for half a decade or longer now.

        Cars are done. Those being killed by them are like hold outs on some island half a century after the war ended taking a bullet because they don’t believe the voice on the loudspeaker not having heard about vacuum tubes and such. Or the phonograph, the literally hollowed out bull’s horn, the ostrich eggs connect by dried out pigs gut phone ‘gadget’

        Fards are barely dozens of dollars each. Batteries are done. The grid is finished. Only debt service and those moronos willing to pay it remain. SMUD enjoyed howevermany decades of discounted power- adn now have no 3rd party equity holders to takethe loss of no longer being needed having not paid that forward. ALmost all the rest of us though are ‘insured.’ that god! What’s going to happen now wold be even bloodier but for that.

  • Reply July 7, 2012


    Hi again folks,
    I realize the $ 5.9 milion may have also paid for the solar systems, but this sounds like a very expensive network to cover 27 houses.  I do believe it is a step in the right direction though as we continue to learn of the energy source that has powered all of nature since all of this got started.  Do you have any information on what was purchased in this package?

    • Reply July 7, 2012


      Jay — You need to think of this as a study, not as a project to install energy storage systems for 27 houses (and, actually, it’s 42 houses). DOE and the other partners are funding this not to help out 42 houses, but to gather information about the viability of such systems. So there money spent in designing the systems, building them, and in implementing them in a way that allows for maximum information gathering. The goal is to find out whether it makes any sense to try to pursue widespread implementation of such systems. See the SMUD PDF linked to in the story for more details:

Leave a Reply