Hi
I have a 4.7K PV system that is selling back power to the grid. I am in New York, when Sandy hit I was with out power for days. It just seemed dumb that I had 4.7k on the roof and no way to use it. I would either like to change the inverter to do both or add a disconnect to disconnect the grid and switch to batteries with a generator. Is this possible? If so what would I need, for a 3k of battery bank?
Yours is a very common question. My advice is to forget about it and buy a honda inverter generator for critical loads. You were without power for a few days? You could have run a $1000 generator on just a few gallons of gasoline.
You would have to have frequent and long lasting grid outages to make an expensive battery based system cost effective.
--vtMaps
There are inverters capable of that sort of thing, but they are generally pricey. SMA Sunny island, Schneider XW, Selectronic are three that come to mind. As vt said you are going to spend in the order of 8K to achieve it, then replace the batterys every 10 years.
As mentioned SMA Sunny Island, with grid tied inverter can AC couple, if got a Sunny Boy its plug & play.
Other setups may need a diversion load when batteries are fully charged.
I have a AC coupled setup using Outback VFX3024 and 1.5kW grid tie inverter AC coupled, with 2kW diversion load.
Outback GVFX inverters or Xantrex XW inverters will do what you want for much less money than an SMA Sunny Island. It's called grid interactive or grid tied with battery backup, AC coupled systems are more complex and expensive and make less sense in your situation IMHO.
Still once you factor in batteries and charge controller, it is not cheap.
For short power outages vtmaps advice of a generator is good. Just be sure you have enough fresh gasoline stockpiled. As I recall getting gas in the time post Sandy was not easy.