I'm looking to add a battery backup to an existing PV system. 4 kW solar system
I've seen it mentioned that the pv inverter should be 90% or less of
the battery inverter size. What is driving that requirement? This would mean a min 4450 W battery inverter.
To save on upfront costs, I'd actually like to have the batter inverter sized at only 2 kW. Then I'd only be able to run 2 kW of equipment when the grid is down, but my upfront investment would be lower. Is this possible technically?
Is there any equipment that small?
Submitted
11 years 6 months ago
Comments
If you want to go simple you put all your loads you want to backup on a couple of power strips. Get a little 2kW standalone battery fed inverter, when the grid goes down unplug your power strips from the wall outlet and plug them into the inverter. Turn it on and you are ready to go. You can get 100W inverter if you want. Those little ones run off 12V and are for using in your car if you want to charge up your laptop.
All that is pretty easy. What's not easy is if you want to use your PV array when the grid is down to power your backup system. That's because you grid tied PV array is probably rated for 600V and there is only one 600V to battery voltage charger I know of and that is made by Schneider for their Xantrex line.
I've never heard of a 90% rule. But then again few people are putting in two inverters to make a battery backed up grid tied system. Most people go the one inverter route, much easier.
Good luck