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Published on August 17th, 2012 | by Chelsea


Adding Batteries to Solar Homes to Ease Grid Pressure

August 17th, 2012 by  

Solar panels are swell and dandy, except when they aren’t enough. And they aren’t enough when homeowners with solar panels are not able to utilize excess energy accumulated earlier in the day during peak sunny hours. The Sacramento Municipal Utility District (SMUD) is trying out a program, called SolarSmart, that attaches batteries to homes to store energy that can be accessed when residents are consuming more power, like late afternoon on a hot day.

The lithium batteries are about the size of mini fridges and can be attached to one home or shared by a couple. The shared batteries can produce 30 kilowatts and store 30 kilowatt-hours. The single batteries can produce 10 kilowatts and store 8.8 kilowatt-hours. At this time, 27 homes are sharing three batteries and 15 homes have their own.

The SMUD battery program costs about $5.9 million. All the batteries are wired for monitoring so SMUD and residents can learn about the pattern of consumption and storage for their home and neighborhood.

Allowing homes and neighborhoods to support themselves with their own stored solar is expected take the pressure off the power grid and reduce the price of power for residents, making solar panels swell and dandy again.

Source: Earth Techling
Image: esbobeldijk via Shutterstock 

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About the Author

is a former newspaper reporter who has spent the past few years teaching English in Poland, Finland and Japan. When she wasn't teaching or writing, Chelsea was traveling Europe and Asia, sampling spicy street food along the way.

  • Bob_Wallace

    I’d love to hear the quite room thinking that came up with this plan.

    Storage at the grid level rather than home level makes more use of the batteries. Putting the batteries in individual homes lets consumers move electricity from more expensive to less expensive times which allows the utility duck expensive high peak demand problems. But the batteries are not available for the more frequent need of smoothing, dealing with shorter term supply/demand problems.

    Does it all come down to retail customers being more able to recover the battery cost because of the very high rates they can pay during peak hours?

    Perhaps it’s simply a test. It would save the utilities some real estate costs to spread the batteries around various homes. And perhaps they are considering renting back the batteries for grid storage. Let customers furnish space and capex money.

    • Ronald Brak

      It comes down to the difference between what consumers pay for grid electricity and what they can sell electricity for. Where I am we now have to pay about $800 a year just to be connected to the grid no matter how much grid electricity we use, in a few years we might have people dropping off the grid in Australia because it will be cheaper to use solar and battery storage (and potentially mini wind turbines) than to remain connected. Electricity distributors will need to drop their fixed charges to keep people on the grid, but this will raise costs per kilowatt-hour and further increase the attractiveness of point of use solar, so demand for grid electricity will still drop.

      We have a large ready made market for battery storage in off grid farms, communities, and mines which currently depend on diesel generation at night. As storage technology is supplied to them costs will come down and increasing numbers of grid connected people will purchase energy storage. Getting some storage along with a PV system might become pretty standard. We may even end up with electricity distributers fighting to keep solar feed in tariffs so people will stay on the grid, which would be mildly amusing.

      • Bob_Wallace

        Do you have some data on how extensive those off the grid systems might be? How much total?

        Aquion is looking at remote health clinics as its first customers. Those clinics need a way to keep medicines cold and solar plus storage is a good solution for them. They have a need which allows them to look at more expensive options.

        If there is a lot of off the grid in AU I’ll get that info to Aquion in the even they might not have considered looking there for a market that might be willing to pay ‘early adapter’ prices.

        • Ronald Brak

          Well, lead acid battery systems are available now, but I don’t know how much they cost. I do know they are not cheap. One person estimates them as storing electricity at an all up cost of 30 cents a kilowatt-hour, but I don’t know how accurate that is. But new technolgy is cheaper. Car battery packs were $658 per kilowatt-hour in the first quarter of this year, giving a cost of very roughly 16 cents per stored kilowatt-hour in Australia, which is around the break even point for home energy storage in large parts of this country.

          Now as far as I’m aware these newer battery systems are not yet readily available for homes in Australia at the moment, but people are working on this as there is quite a large market in Australia for them, starting with off grid applications. And there are plenty of businesses currently installing modern battery packs as part of an uninteruptable power supply system. Obviously, connecting them to solar PV on the roof is a logical step.

          • Bob_Wallace

            The problem with lead acid batteries is the relatively low number of cycles one can get from them. Aquion claims that their sodium-ion batteries will cost about the same as lead acid but have several times more cycles.

            They’re projecting at least 5,000 cycles and a price that would make storing cost $0.06.kWh and expect to be at 10,000 cycles soon. That drops cost to $0.03/kWh.

            Longer term they are projecting 20,000 cycles which would make storage $0.015/kWh – dirt cheap.

            We’ll see if they can pull it off….

          • Ronald Brak

            Hopefully they can pull of 6 cents a kilowatt-hour storage soon. That would be the death of fossil fueled electricity production in Australia. But even 10 cents a kilowatt-hour storage would help.

          • Bob_Wallace

            Eliminating fossil fuel use in Australia would put the country in an interesting position of being a fossil fuel exporter but not a user. Sort of like farmers who grow tobacco but don’t use it.

          • Ronald Brak

            Exporting coal is like selling cigarettes. Burning coal is like making children smoke cigarettes. Of course exported coal is going to be burned, but via moral ju-jitsu we can put the blame on the people who buy it. But with six cent storage, it wouldn’t be long before demand for thermal coal exports dropped.

          • Bob_Wallace

            If China can get affordable storage I suspect they will quickly cut back on coal use.

        • Ronald Brak

          I will mention that my state, South Australia, has been almost entirely wind and solar powered for more than the past 24 hours without using any storage, but I’m certain that electricity has been exported to a neighboring state. Wholesale electricity prices have averaged under half a cent per kilowatt-hour in this time.

  • Did they consider other storage technologies? Lithium is light, but not cheap.

    • Bob_Wallace

      Yes, a company called Aquion should be producing grid storage batteries using a sodium-ion chemistry in a few months.

      Their batteries should be much cheaper than lithium-ion batteries and independent testing of their prototype reported more than 5,000 cycles with little decrease in performance.
      These batteries aren’t as lightweight and compact as lithium-ion batteries so aren’t as usable in EVs, but should be fine for stationary storage such as homes/businesses/large battery banks.
      (SMUD may not have considered them, but when/if they come to market they’re going to get a lot of consideration.)

      There are other promising technologies that aren’t as close to being proven. One that is very interesting is MIT’s liquid metal battery. It uses very cheap materials which should last a long time. They have prototype batteries working but I’ve heard nothing about how close they might be to production.

      If this battery pans out it might be a game changer. It could make storage so cheap that we’d quickly move to a wind/solar/storage grid. It’s not a battery we would expect to see used in households because of the temperatures at which it operates, but certainly at the grid level.

  • “Swell and dandy”? Thanks for that trenchant analysis, clean technica. The battery vs. grid debate all boils down to what does battery storage cost as back-up as opposed to what does your pro rata share of the grid cost. Neither of which we’re going to get from this article, apparently.

  • Ronald Brak

    In Queensland, Australia, the feed in tariff for solar power is now 8 cents a kilowatt-hour while households need to pay about 25 cents for electricity from the grid. Because of the wide spread between buy and sell prices there is room for arbitage using a battery storage system. In other words, a household can save money by storing electricity for their own use rather than selling it to the grid. Currently it appears that home storage systems can store energy at a cost of around 15 cents per kilowatt-hour. That means a Queensland household with storage would roughly break even. If the cost of storage decreases then households will come out ahead.

    • Bob_Wallace

      Utilities buying power from their customers at 8 cents and selling back at 25 cents is criminal.

      Is there something else going on here?

      • It may be criminal but the ratio is very similar here in Hungary.

        Fortunately, here we have a one-year settlement period so that you get that low fit rate only for the surplus you fed back over your yearly consumption.

      • Ronald Brak

        At first I thought dropping the feed in tariff to 8 cents in Queensland was unfair as wholesale coal power costs around 8 cents during the daytime in Queensland. But then I realised that with all the point of use solar capacity being built, wholesale prices in the day will soon average much lower than 8 cents a kilowatt-hour. So while the new feed in tariff will be fair in that it will be higher than the market price, I think the low tariff might be short sighted given the benefits of solar power.

        But in New South Wales at the moment I think new point of use residential solar may get nothing or next to nothing for electrcity they export to the grid. That is definitely unfair. As for whether or not it is criminal, well it may violate consumer protection laws, but I have no idea if that is actually the case.

      • srsly.

  • Svenonia

    The idea of needing batteries on grid tied solar systems is silly. This is just a tactic to raise the price of renewables and delay when its use is cheaper than the utility.

    Solar panels produce energy when grid demand is the highest. Dont store it power during peak demand. Sell it back to the Utility. Why pay for the cost of a battery sytem

    • dcard88

      Its smart if one can save money. With a battery sys you can save up to a thousand in install cost and if the difference in price covers the cost of the batteries a savings is likely

    • When the rate paid by the utility for electricity provided during peak demand is less that the rate charged for electricity during the night (when you may be charging your BEV), the cost of battery storage might balance out over the life cycle costs of storage. It all depends on the cost of storage vs. the potential added costs of buying from the grid.

    • Maybe so, but I would definitely apply if some subsidized home-battery scheme was implemented here.

      I am all for making our grid more resilient.

    • RobS

      Say you live in area with time of use metering, where power overnight can be bought for 5c/kwh, and power during the day can be bought or sold back at 30c/kwh. Now say you can buy a battery system whose cost and lifespan mean that it costs 15c/kwh stored. You can now charge this battery overnight at a total cost of 20c/kwh and then sell it back to the grid at peak demand for 30c/Kwh for a 10c/kwh profit. So you can make money, save the need for new generating capacity, buffer intermittent renewables by charging when there is excess solar or wind output and by save on transmissin upgrades by supplying power at the point of use and to neighbouring properties. The savings in new generating and transmission capacities means it may be cheaper for a utility to subsidise storage systems thereby attracting private investment then to make the expensive upgrades themselves.

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