What happens when grid power fail lasts longer than my batter backup

[RonFreddy]

I am designing a solar system with 20 x 400 watt panels and 2 x powerwall 3 batteries for my residence using 1000 kWh/month. What happens during an extended power failure when the batteries are exhausted? Can I still use my solar panels on a sunny day to run selected circuits in my house?

 

[chrisski]

If you design it correctly yes.

If you have a dc coupled hybrid inverter, it is a given that you can use the solar panels to charge the batteries.

If you have an AC coupled inverter, you may not be able to start charging the batteries, that's where the devil is in the details. Something needs to trigger the AC current to charge. AFAIK, the newer equipment is more likely to do do this like the newer Enphase product line compared to the older stuff. I guess the newest Tesla powerwall has an option for off grid.

If you are using 1 mWh/ month, you still need to plan the outage to be on the peak month. My summer months use 6 times the electricity of the winter months.

 

[jpwhit]

I am designing a solar system with 20 x 400 watt panels and 2 x powerwall 3 batteries for my residence using 1000 kWh/month. What happens during an extended power failure when the batteries are exhausted? Can I still use my solar panels on a sunny day to run selected circuits in my house?

Yes, with the Tesla Powerwall's you can use your solar panels to power the house and/or charge the batteries during an outage assuming the Tesla grid disconnect is installed. That has always been true with the Powerwall, it's not something new with the latest Powerwall 3.

 

[wattmatters]

What happens during an extended power failure when the batteries are exhausted? Can I still use my solar panels on a sunny day to run selected circuits in my house?

Yes, however if the batteries are exhausted because there is more household load than the PV can cover then you are SOL. The batteries will need some charge and the PV needs to be supplying more than the loads demand. IOW you will likely need to reduce load.

Generally wiring is arranged such that some power hungry circuits are excluded from receiving backup power.

 

[Roadrunner0]

A gasoline/diesel/propane generator is the cheapest option for a force multiplier.. If your system allows for battery charging while operating on the generator you will find that this is the most thrifty way to utilize your system.. Most times there is a small load that is hardly worth having the generator spinning for like a couple lights or a TV.. During these low usage times if the batteries can take that charge then the generator is more fully utilized and you can give it breaks when your solar is producing well or you want to draw power from full batteries..

 

[Ampster]

I have a 11kW solar system which generates about 50-60 kWhs a day during the summer. I also have a battery pack and use about 15kWh overnight. That means about 15kWhs of my morning production recharges the batteries and carries the house load which is 500-1000 Watts per hour. In the afternoon when the batteries are charged, I put some of that energy into one of my EVs and send the balance to the grid.

If I have a power outage the same cycle continues except that I can't send any extra to the grid. If it is hot I would be able to turn on my heat pump Air Conditioner and I might even turn down the thermostat to cool the home so as the sun sets, I don't have to use battery power to run the A/C.