When the grid goes down

Martha's Vineyard got off really easy in Irene, compared to what mightabeen. We lost power here for a few hours - no tragedy, to be sure, but it got me thinking again about what if we were out for days, and how frustrating it would be to have almost 5 kW of PV doing nada when the grid goes down. Grid-tied inverters look for the 60 Hertz signal from the grid to operate.

Asking around, I learned that the company that makes the inverter we used, SMA, makes an off-grid inverter called Sunny Island that can be configured to communicate with the grid-tied inverter, and working off of a small battery bank could provide power during the day and a modest amount (from the batteries) at night. I'm looking into what this will cost - it ain't cheap!

I continue to be amazed at the power generated on poor weather days. Tuesday last week it rained all day and Wednesday it was overcast with some drizzle. We received 2.5 kWh and 4 kWh on those two days. That's 6.5 kWh on two days where we used 10.5 kWh in total!

Comments

[Kim Quirk]

Hi Marc,
Just found your blogs -- really good information! I am designing a system for a client to convert his SMA grid-tie sunny boys into a grid-tie, battery back up system -- he is considering removal of the Sunny Boys and re-wiring to a Xantrex based system; and he is considering the Sunny Island.

The cost difference leans heavily toward the Xantrex system, but the efficiencies and easier installation lean pretty heavily toward the Sunny Island system.

Thanks for your detailed blogs on insulation as well. Great basement project.

Kim Quirk, Energy Emporium (with ZEB goal, in Enfield, NH)

[Marc Rosenbaum]

Kim, one question I have on this is, instead of swapping from the SMA (likely the best product on the market) to the Xantrex (I had bad experience with the predecessor company, Trace), could you add the new Xantrex high voltage charge controller, that will accept up to 600 VDC input, with a manual switch that routes the array output to the Xantrex and a battery bank when the grid goes down, and then use a less costly off-grid inverter to the emergency panel?

[Clint Rowley]

Really great blog post. Kim- I like Marc's thinking in seeing if you could just add the Xantrex charge controller, and use a manual switch that routes output for emergency times. It may be the best of both worlds.

[trane furnace]

HI Mark...!!!!

I like your blog so much i reached here for the first time but the information shared in your blog is impressive and insightful. I will follow your blog in the future for gathering more knowledge about energy and its deeds....

Regards and Thanks,
Mike