Solar City PPA: DIY Battery Backup

[eddiejay84]

Hello Everyone,

Newly registered.

I just had Solar City install a 10kW PV System. It is a Power Purchase Agreement at .15 per kW.

My question, Can I build a battery bank to store the extra power produced during the day & draw the stored battery electricity at night. I'm also getting ready to buy a 27kwh Kia Soul EV that would get charged at night.

Can someone explain how the battery bank will store from the solar city system but not from the utility grid.

Are there any caveats/restrictions to this since I have a Solar City PPA.

Thanks,

P.S. I will post photos of the PV array shortly.

[Sunking]

You can get paid 15-cents per Kwh to sell it, or you can pay 60-cents per Kwh to store it and use it later. Ready to sign up to buy $10,000 worth of batteries and equipment to pay 60-cents a Kwh? Or would you prefer to sell it for a profit?

[SoCalsolar]

if its a PPA

If it's a PPA with SC it is unlikely you are able to do anything with their solar system. It's not your equipment they own it if it's a PPA. They are starting to push battery backups legally I believe you would be in violation of the TOS you signed. It would likely be better to contact them and see what they can offer you. PPAs aren't all bad but they have very strict limitations for modifications.

[eddiejay84]

Thanks for the input. I might have to rethink this option.

[Amy@altE]

IF you are allowed to add batteries, what you are proposing is called AC Coupling. We get that a lot after crazy storms that knock out the grid for days or weeks, people rethink the whole "grid goes out, so do you" thing. You would add a battery based inverter, like a Schneider XW, OutBack Radian, or Magnum PAE, or SMA Sunny Island and batteries, and a critical load panel. The output of the grid-tied inverter points at the output of the battery based inverter, which is also connected to both the batteries, critical load panel, and the grid. If the grid is up, all is well, the battery based inverter makes sure the batteries are full, and passes the solar power through to the grid. But when the grid goes down, the battery based inverter disconnects from the grid, but because it is pointing at your existing grid-tied inverter, your inverter sees the beautiful sine wave output of the battery inverter, and stays on, thinking the grid is still up. Since the battery inverter is between the grid and the grid-tied inverter, the grid is happy, you have shut down to them, no problem there. But your battery based inverter is also connected to a critical loads panel, and it powers your fridge, well pump, lights, etc, while the formerly grid-tied inverter backfeeds power into it, charging the batteries. Depending on the inverter, you could also program it to act as a micro-grid, providing power for your car at night.

It's a fairly new concept here in the US, so it's not perfect. Different manufacturers handle turning off the battery charging differently, and none are perfect, but all are working on ways to make it better, because it is becoming very popular. However, I bet you dollars to donuts your PPA won't allow it. But it can't hurt to ask. And the big advantage is getting battery backup, not saving money.