The answer is yes and no. No you can not likely afford enough batteries to power your entire home if the grid is down for a week; but yes you can power the Critical Load items of your home or business from a Photovoltaic Battery Back-up system.
If we use a 10kW photovoltaic system as our base line example, it is realistic to run that power through an inverter/battery combo system that would be very capable in keeping one’s home/business operating for a few days without the grid. It requires a process of either physically segregating certain consumption items in your main circuit breaker panel to what is called a critical loads circuit panel or electronically controlling which circuits receive the battery/PV power during grid outages.
-Items we recommend you many want to power are:
– Furnace blower motor and igniter
– One frig freezer combo
– a few lights
– a few outlets
– Garage door electric openers
– Medical health equipment
What to learn more… read on
When deciding on how powerful a battery system and how large a solar system you need, there are three factors to keep in mind that function together but are separate limits on power availability when the grid is out.
– Inverter size, measured in kW
– Batter size, measured in kWh
– Critical load panel loads, measured both in kW and kWh
So back to our example, a 10kW dc solar system with a 7.6 kW AC inverter coupled with one 9.8 kWh batter is a very common set up. During an average day of consumption with good solar radiation this system would power the critical loads panel circuits and charge the battery. At night this battery has a max discharge of 5kW, which if you used that much power it would be depleted in just
under 2 hours. Instead if you just had one 100 watt light bulk running the battery would last 98 hours (100w x 98 hours = 9800 watt/hours)
If one increased the battery size to 2 – 9.8 kWh batteries you could have 10kW of instantaneous draw capability and double the life, or 19.6 kWh. It is important to keep in mind that with a battery system we are not attempting to power the entire structure, just the critical items that maintain some normal functionality. (To power everything would be an off grid system)
So as a consumer, what should you do before you decide to start shopping for a battery and photovoltaic system? Determine what items you really want powered during power outage and for how many days you think you want these items powered. In that way we can start by sizing a battery to meet your goals and work backwards to size an inverter and Photovoltaic system that all have the capability to perform as desired.