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SolarLurker
SolarLurker Solar Expert Posts: 122 ✭✭
in Advanced Solar Electric Technical Forum #1
I am planning a grid tie battery back up system I want to use sunpower panels and and sunpower inverter. I know the SMA makes the sunpower inverter, will the sunny island work with the Sunpower branded inverter?

Also, does the sunny island have generator start/stop?
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
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    SMA makes "Sunny Boy" inverters.

    Yes the SMA Sunny Island does have generator stop start and it's a nice bit of kit, but using it in conjunction with a Sunny Boy inverter is inefficient for most uses. Better to use a DC charging system with a standard charge controller.

    You might be able to trick a sunpower inverter into working on an off-grid, mini-grid controlled by the sunny island IF:
    1. It doesn't detect grid impedance (because this will be much lower in a mini-grid than on the real grid)
    2. It will disconnect from the grid at a set over-frequency value. You'll have to check the sunny island manual to see what the upper limit of the frequency control is, I _think_ it's at 2hz above normal. So if the sunpower will disconnect from the grid at 61Hz (assuming normal = 60hz), then it should work with the sunny island which will prevent your batteries from being overcharged.

    Doing the above is a dirty hack - and SMA will probably not accept any responsibility if something goes wrong. If on the other hand you instead used the sunny boy inverters it would all work much smoother and you'd have backup from SMA.

    Is there any reason you specifically want to use AC coupling for battery charging?
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  • SolarLurker
    SolarLurker Solar Expert Posts: 122 ✭✭
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    SMA makes the inverters for Sunpower, what I have not been able to determine if the Sunpower inverters are just Sunny boys with a different color or if Sunpower made any proprietary changes.

    AC coupling seems like the way to go, although I am by no means and expert, so I appreciate everyone's input.

    My plan is to have a Grid tie system solar with battery backup. I would like to also add a generator and small wind turbine. The wind turbine will be down the road quite a bit. Its not uncommon for us to loose power, and I still remember the Ice Storm in 98 that took out the power for 3 weeks. I hope that with solar and batteries the generator would only have to run at best a few hours a day.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
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    Re: Questions
    SolarLurker wrote: »
    SMA makes the inverters for Sunpower, what I have not been able to determine if the Sunpower inverters are just Sunny boys with a different color or if Sunpower made any proprietary changes.

    Ah, didn't know that.

    If your system is primarily going to be for grid feeding then I'd agree, AC coupling is the way to. The biggest complication is going to be whether it's permitted in your country. It's not permitted in europe, so SMA brought out a specific product for this called the Sunny Backup (at least it didn't have "boy" in the name) - which is really just a modified sunny island + automatic transfer box. The transfer box is the critical component that isolates the SI and SB from the electrical grid when it goes down and makes the system legal in europe. The sunny backup is not UL listed for sale in the states.

    I believe things are different in the states, so you might be able to use a manual transfer switch to disconnect the SB from the grid and connect it to the output of the SI.
    There's a schematic describing how SMA have done this with the sunny backup on page 11 of this doc: http://www.sma.de/en/products/backup-systems/sunny-backup-set-mlxl/dl/U0JVMjIwMC1URU4wODMzMjA%3D/download.html

    Have you tried the SMA america forums: forums.sma-america.com? Might be someone there who's already done this.
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