Smart off-grid power source switch?

[pkcinna01]

I would like to power my fridge and a few other items with my off grid system only when batteries are charged and sun is providing lots of power. Then when sun goes down I would like to automatically switch back to grid power. Is there a smart switch that can change power sources based on battery voltage? I know there are switches to do something similar for generators.

I'm thinking it would have two 120V AC lines in (one from off-grid/inverter and one from my utility company provided AC) and one line out to power my fridge. Also, it would have something to adjust the voltage level for making the switch.

Is this a real thing?

[Mike90250]

Not that I know of.

Why were you unable to install a simple GT system and save the expense of batteries and switching gear ?

[pkcinna01]

This is a hurricane backup system (generators are loud and there is not always fuel). I also plan to go completely off-grid since it is looking like a comfortable retirement in the suburbs is not practical. I like micro inverters but seems like that technology is only for grid-tie. Right now my impression is solar is still kind of like the wild west and nothing is elegant as far as how the pieces fit together. Maybe in 20 years it will be different and off-grid and grid-tie will be antiquated concepts and both approaches will be covered by the same components.

[SunEagle]

This is a hurricane backup system (generators are loud and there is not always fuel). I also plan to go completely off-grid since it is looking like a comfortable retirement in the suburbs is not practical. I like micro inverters but seems like that technology is only for grid-tie. Right now my impression is solar is still kind of like the wild west and nothing is elegant as far as how the pieces fit together. Maybe in 20 years it will be different and off-grid and grid-tie will be antiquated concepts and both approaches will be covered by the same components.

Generators can be boxed in to make them quite and some can run on different fuel sources giving you more options and a longer running time.

I understand your desire to use solar and batteries but I need to tell you that a typical solar/battery system that can safely deliver 1kWh a day can cost you about $1500. Most loads like a refrigerator and fans tend to use 4 times that amount per day. So we are talking at least $6000 which may or may not provide you what you want.

So you have to decide how to spend your money for emergency power. Generators and spare fuel will be less expensive and provide more power than a solar/battery system. The choice is yours to make.

[Mike90250]

This is a hurricane backup system (generators are loud and there is not always fuel). I also plan to go completely off-grid since it is looking like a comfortable retirement in the suburbs is not practical. I like micro inverters but seems like that technology is only for grid-tie. Right now my impression is solar is still kind of like the wild west and nothing is elegant as far as how the pieces fit together. Maybe in 20 years it will be different and off-grid and grid-tie will be antiquated concepts and both approaches will be covered by the same components.

Simple - for hurricane backup, you store your solar panels in a bunker, and after the storm has passed and blown all the lawn chairs everywhere, then you bring the panels back out to the light.
Properly mounted PV panels withstand 100 mph wind pretty well. Wind blown debris, not so much.

[Sunking]

Don't be a fool. Anything you take off grid, the power will cost you 5 to 10 times more than buying it from the POCO. It also makes you a heavy heavy polluter.

You can have what you want and no solar required.

[Sunking]

Simple - for hurricane backup, you store your solar panels in a bunker, and after the storm has passed and blown all the lawn chairs everywhere, then you bring the panels back out to the light.
Properly mounted PV panels withstand 100 mph wind pretty well. Wind blown debris, not so much.

Sure hope that bunker and batteries are elevated above flood water line. Basements and underground bunkers get turned into swimming pools.

[pkcinna01]

Yup. The system is already working and cost me about 2000 USD for 900 a watt panel system. I really like it and the plan is exactly that... when storms approach put the panels in the garage and reassemble when it is safe. In the meantime it works so well I'm trying to find ways to use the excess power and minimize battery usage. The switch that I hoped for would be useful for other scenarios like when a generator runs out of gas the system would switch over to batteries (in that case the switch would trigger on 0 volts). Off-grid is a great choice for me. The only way I would consider grid-tie is if they have a way to easily plug in a battery layer at a similar price (2K).

[SunEagle]

Yup. The system is already working and cost me about 2000 USD for 900 a watt panel system. I really like it and the plan is exactly that... when storms approach put the panels in the garage and reassemble when it is safe. In the meantime it works so well I'm trying to find ways to use the excess power and minimize battery usage. The switch that I hoped for would be useful for other scenarios like when a generator runs out of gas the system would switch over to batteries (in that case the switch would trigger on 0 volts). Off-grid is a great choice for me. The only way I would consider grid-tie is if they have a way to easily plug in a battery layer at a similar price (2K).

You only paid $2k for a solar pv system with 900 watts of panel, an 80Amp MPPT CC, a 750Ah battery system and 1500 watt inverter. Great job.