Question

Is it possible to have a solar PV system with batteries power my home with the grid as backup power?

Asked by Curtis
Miami, FL

I've bought books and read many instructions, articles, etc. online, but all of them give three options: off-grid, grid-tied, or part off-grid and part on-the-grid. I'd like the option to power my home from a battery bank (windmill and solar panel charged) and have the grid as backup. Either the grid takes over when the battery charge is low or the grid charges the batteries when the charge gets too low. I know that there's an issue with the types of electricity, but don't they make Inverters or other devices that can make this possible? Where I live, there's enough sun and wind to go off-grid, but I'd like the grid to be there as a backup just in case.

Answer

Florian Speier

Answered by Florian Speier

San Francisco, CA

Zeitgeist Sustainable Residential Design

August 30, 2010

The grid is really your battery. The reason you don't find the solar power configuration you are describing in books or articles is that in practical use it does not make sense.

I understand why you might want to go this route, as it makes you feel somewhat independent but you have the safety of the grid when you need it -- but please, it does not make sense and is not green either.

  • A grid-tied system basically uses the grid as a giant battery, by giving it power when you have too much and taking back when you need it.
  • In comparison to a battery, the losses are small. Batteries give you back significantly less kWh than you put into them, unlike the grid.
  • The grid-tied means you don't have to buy batteries, which are made of toxic chemicals. (Without going into much detail, I think you believe me that "lead-acid batteries" are not the greenest building material around.)

Embrace the grid as the best battery ever invented, and charge it with energy from your renewable systems.

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