Solar battery backup question

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ben94122

Burning Hunk
Sep 4, 2017
140
California
I'm getting bids on a solar system, and I'm trying to figure out solar battery backups. In particular, I have 2 scenarios that I'd like to figure out how to make work:
1) A California wildfire takes out the grid power to our house, and before we evacuate I turn on my roof-mounted sprinklers. Solar panels power the well pump to sprinkle while the panels are generating power during the day (probably via sprinkler timer so the battery doesn't drain by sprinkling all night), battery backup needed to turn the system on, because without a battery if the grid power goes down the solar automatically cuts off so it doesn't backfeed into a dead grid
2) longer power outage, run the well pump and freezers during the day when the panels are generating, turn almost everything off at night.

I understand there are a few inverters out there (storedge is one available now, EnCharge coming in a few months) that can do this automatically, by DC coupling, but the batteries are huge and expensive. I'm not interested in running the big loads overnight, just in keeping the panels capable of producing power during the day. A small and cheaper battery should work fine for this. Is AC coupling something I should research? Would I then have to install a generator switch to disconnect the house from the grid during a power outage? Or am I misunderstanding something basic?
 

Dataman

Minister of Fire
Sep 10, 2018
1,120
Newport, Wa
Batteries would be expensive. Why not get automatic home backup generator run off propane? Keep area around the tank clear. Do you have Natural Gas? If so that would be way I would go. If you just want pump it's going to take some big amps if it's deep well. Batteries are not good choice for big Amps. You cannot expect the system to run pump off Solar Panels. Those are for charging the expensive batteries.
 
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begreen

Mooderator
Staff member
Nov 18, 2005
96,254
South Puget Sound, WA
Take a look at systems developed for some of the larger RVs to see if there is a fit.
 

ben94122

Burning Hunk
Sep 4, 2017
140
California
Thanks guys! No natural gas or propane on the property now. I'll look into RV systems. Also, California has an incentive for home battery backup in wildfire prone areas: California Self-Generation Incentive Program. I'll look into that further.
 

Socratic Monologue

Burning Hunk
Dec 2, 2009
196
WI
Batteries would be expensive. Why not get automatic home backup generator run off propane? Keep area around the tank clear. Do you have Natural Gas? If so that would be way I would go. If you just want pump it's going to take some big amps if it's deep well. Batteries are not good choice for big Amps. You cannot expect the system to run pump off Solar Panels. Those are for charging the expensive batteries.
This would be my suggestion as well.

If you're depending on panel production to run things in an emergency, and panel production drops (smoke haze, ash on panels, clouds, etc.) high amperage draw on small battery bank will kill the batteries, and also fail to run pumps when you need them most.

Off grid solar is great for low amperage consistent draw. Backup generators are for power backup.
 

SpaceBus

Minister of Fire
Nov 18, 2018
7,086
Downeast Maine
I too am trying to figure out how to run a modern well pum, and other high amp appliances, with a grid connected solar array with storage. The batteries aren't so much a problem, it's the battery management system.
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,254
South Puget Sound, WA
Thanks guys! No natural gas or propane on the property now. I'll look into RV systems. Also, California has an incentive for home battery backup in wildfire prone areas: California Self-Generation Incentive Program. I'll look into that further.
A battery system can remain in the house envelope. If you don't mind a bit of power management then a 6 lithium ion battery bank and a decent charger/inverter coupled with about 1kW solar should sustain the household refrigeration and lighting needs. The joker in the deck is the well pump. If this is a large or deep well pump then that could very likely need a generator, but that could be sized for the well and not for the full house which might provide a bit more design flexibility.

If you want the battery backup system to cover everything then look at getting a Tesla Powerwall.
 
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begreen

Mooderator
Staff member
Nov 18, 2005
96,254
South Puget Sound, WA
I too am trying to figure out how to run a modern well pum, and other high amp appliances, with a grid connected solar array with storage. The batteries aren't so much a problem, it's the battery management system.
Covered in detail here
 
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DBoon

Minister of Fire
Jan 14, 2009
1,295
Central NY
Outback Power Systems makes inverters that will work as you describe. They are about 4 to 5 times more expensive than a standard utility-coupled inverter. They operate with many types of off-the-shelf battery systems.

A good variable-speed pump controller for your deep submersible pump should solve the inrush current problems that would overload a generator or backup inverter. This might require changeout of the pump to something compatible with variable speed control.
 

ben94122

Burning Hunk
Sep 4, 2017
140
California
An update: August of 2020 we had a company install an 8.5kW roof-mounted solar array with an LG 9.6 kWh battery and a StorEdge inverter. The solar array runs the well pump, freezers, internet, and charges the Tesla (slowly) with no problems. We had a busy summer for wildfires, with multiple power cuts and a 3-week evacuation. The system ran the sprinklers and freezer as described above, with no issues. The well is 350' deep.
 
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peakbagger

Minister of Fire
Jul 11, 2008
7,681
Northern NH
Would you mind revealing order of magnitude cost before incentives?.

Hybrid systems are definitely on the "bleeding edge" currently, lot of announcements of products to come but few on the market. Tesla has a shortage of batteries so they use them to sell high end systems like the solar roofs. LG is an alternative except that they had a very large battery recall. My guess is in couple of years hybrid systems will be far more available. The next big upgrade is to have the system plug into electric car battery to use it for storage.

Lot to be said for a buried bulk fuel tank and an inverter generator in a fire proofed structure.
 

ben94122

Burning Hunk
Sep 4, 2017
140
California
$35k, including wiring up the sub panel with backed up loads. We are 3 hours drive from the installer, so that may have factored into pricing.
 

peakbagger

Minister of Fire
Jul 11, 2008
7,681
Northern NH
Thanks for following up (here and on solar panel talk).

No doubt plenty of Federal and California incentives to reduce out of pocket. I wonder if an insurance company would give a discount as its fart more likely a house will survive with sprinkers and back up power?.
 

ben94122

Burning Hunk
Sep 4, 2017
140
California
Thanks peakbagger for the thoughtful and experience-based solar advice through the years! If I can provide you any info, I'm more than happy to.

As for insurance, the commercial insurers have largely fled our area after large fires in 2017, 2020, and 2021. The new plans are mainly underwritten by the state (Calofornia FAIR plan).
 

tlc1976

Minister of Fire
Oct 7, 2012
1,139
Northwest Lower Michigan
Lot to be said for a buried bulk fuel tank and an inverter generator in a fire proofed structure.
Yes, especially if the grid that got taken out includes the natural gas pumping station.
 

peakbagger

Minister of Fire
Jul 11, 2008
7,681
Northern NH
Yes, especially if the grid that got taken out includes the natural gas pumping station.
I have to admit I dont have a lot of experience with natural gas transmission systems. I know that at least some of the big compressor stations are driven by natural gas engines running on pipeline gas so they should not be affected by grid outages. Electric compressors are going to somewhat less expensive (but still steep as everything has to be explosion proof. On the CHP plants equipped with gas turbines, the utilities are pretty insistent that the low pressure street gas is pretty well guaranteed to be there unless someone digs up the line.