Can I use grid-tie solar to run a well pump during the day during a power outage?

[Ben94122]

I'm getting bids on a grid-tie 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) We're home for a 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?

My power company is a small coop which doesn't participate in the SGIP battery incentive, and doesn't have time of use pricing

[solarix]

The answer is no. A well pump is a sizable load and takes a serious inverter and a sizable battery to drive. There is the SMA SunnyBoy inverter with the Secure Power Outlet that will drive small loads, but there is nothing short of a sizable investment in off-grid capability that will run well pumps.

[Ampster]

Also as far as roof mounted sprinklers are concerned, they are not the only solution. If you have vents in your eaves you may need to replace them with spark proof vents. Many of the fires in Sonoma during 2017 were caused by wind driven embers coming into the attic through vents under the eaves and starting the fires in the attic. In addition the wind is often strong at night so batteries may be essential if you want that protection.

[Ben94122]

I guess I don't understand why the 8.4 kw array they're proposing won't run the motor for the well pump, which is rated for 8 amps @ 240v (about 1.9kW)...Again, I don't want to drive it off a battery; I just want a battery so the panels don't shut down during a grid outage. Help me understand why the ample power coming from the panels won't be able to drive the well pump?

As far as your suggestion, Ampster, yes the house is fire-hardened in many ways; cement siding, asphalt roof, no large soffit or gable vents, no propane or firewood near the house, no wood deck, trees limbed and duff cleared, etc. But watering the area nearby is another recommended strategy for surviving a wildfire. Lots of good info is coming from seeing which houses survived the recent Calfornia fires, including the Camp fire. It is true that there is some fire activity at night, but generally they are much more active in terms of burning into new territory when the temperatures climb during the day.

[littleharbor]

The SMA secure power feature is going to give you up to 2000 watts at 120 volts. Not sure if you had a pair of inverters you could get the phases to sync into a 240 split phase.

[solarix]

No, you can't pair up two SMA's secure power outlets. They don't sync.

No, An 8.4kW array is DC electricity and your typical well pump needs AC. You might go with a DC type pump, but that is a whole different can of worms. To drive an AC pump, you need an off-grid type inverter which needs batteries to buffer the large current surges the inverter creates.

There is a lot more to electricity than "its an 8.4kW array" and "its a 1.9kW pump". Yes, there is enough raw power, but everything else is incompatible.

[Ben94122]

No, you can't pair up two SMA's secure power outlets. They don't sync.

No, An 8.4kW array is DC electricity and your typical well pump needs AC. You might go with a DC type pump, but that is a whole different can of worms. To drive an AC pump, you need an off-grid type inverter which needs batteries to buffer the large current surges the inverter creates.

There is a lot more to electricity than "its an 8.4kW array" and "its a 1.9kW pump". Yes, there is enough raw power, but everything else is incompatible.

I don't mean to sound argumentative, but in a grid-tie system, the 8.4kW DC coming off the panels goes through an inverter and is converted to AC power at ~95% efficiency, which is then available to backfeed into the AC grid or power the AC appliances of the house. Many neighbors use 4kW generators to run their houses, including well pumps, during a grid outage. I don't see what the difference might be. Of course the well pump needs less power once it is working and more power on startup, but it works fine for my neighbors with 1/2 the available power than I will have.

Just saying "trust me it won't work" isn't a satisfying answer.

[josepr]

Yes and no. Yes if you replace your current pump with an expensive off grid “friendly” pump. Supposedly you can connect it to a 120 volts outlet. Supposedly, it has an AC/DC permanent magnet motor with no surge start up. According to the article, see below, “[t]hey actually can operate on 30-300 VDC or 90-240 VAC at 50/60 Hz with no extra components. Their internal electronics are designed to operate AC or DC and over a wide range of voltages.”

Check this web site:

http://solarhomestead.com/best-off-grid-well-pumps/

[Ben94122]

There's no need to use a 120V pump; the inverter puts out 240V. If the startup energy requirement of the pump overwhelms the system, there are "soft-start controllers" readily available to damp out that initial surge in energy demand without replacing the pump motor.

[foo1bar]

There's no need to use a 120V pump; the inverter puts out 240V.

A grid tie inverter puts out 240V <b>when connected to the grid.</b>

The SPS on Sunnyboy does 120V to one GFCI outlet - good enough for charging your cell phone and such. It doesn't do 240V.

A hybrid grid-tie / off-grid system can do both normal grid tie (with the benefits of net metering, and the ability to go into an off-grid mode)
But that will be more expensive for the inverter/charge controller, AND the batteries that you will need (which you'll have to replace after a few years)

Probably your most economical option is a small generator.

but if you've got money to burn, you can look at a hybrid system, or look at getting a PowerWall system.

[Mike90250]

...........Just saying "trust me it won't work" isn't a satisfying answer.

Then do it. And tell us the results. GT inverters have absolutely no buffer reserve. You pump likely takes 5x it's running power to start.
The shadow from a bird flying overhead will glitch the array and shut the system down
There are dozens of reasons it wont work, and I don't know of any condition without a Charge Controller, batteries and a Hybrid inverter, that it could work

There is a lot more to electricity than "its an 8.4kW array" and "its a 1.9kW pump". Yes, there is enough raw power, but everything else is incompatible.

Truth

Well Pump Motor Specs.jpg

[sdold]

I don't see what the difference might be.

A grid tie inverter needs to be connected to a working grid to operate, but a generator does not.

[azdave]

Can I use grid-tie solar to run a well pump during the day during a power outage?

No. If it could easily be done, then thousands of other people would already be doing it long before now. Nearly every grid-tie customer in the world would like to be able to run heavy loads when the grid goes down. You aren't the first person who imagines they should be able to switch a grid-tie system into a daytime use standalone system without a substantial financial hit for components.

[MichaelK!]

It's doable with the investment in the right components. The grid-tie inverter is designed to automaticly shut down in a power outage. Your grid-tie inverter would need to be replaced with a 240VAC off-grid inverter such as Schneiders XW6848. It's running at about 2700$ right now. You'll also need a 48V DC battery bank large enough to support that inverter. The Schneider is designed such that it can not work without a 48VDC battery bank. Eight 6V Trojan L-16 batteries wired in series would work OK. That will run you about 2800$. Add a couple of charge controllers to handle that much wattage. Let's say 1200$ for good charge controllers. Toss in another 1500$ for transfer switches, wire, power panels, and breakers. Maybe another 1000+$ or so for a certified electrician to wire it together in a code-compliant system. It's critical that the electrician wire the system with a transfer switch so your power won't energize the grid. So, for about 10,000$ you'd have something that works.

[solardreamer]

It's doable with the investment in the right components. The grid-tie inverter is designed to automaticly shut down in a power outage. Your grid-tie inverter would need to be replaced with a 240VAC off-grid inverter such as Schneiders XW6848. It's running at about 2700$ right now. You'll also need a 48V DC battery bank large enough to support that inverter. The Schneider is designed such that it can not work without a 48VDC battery bank. Eight 6V Trojan L-16 batteries wired in series would work OK. That will run you about 2800$. Add a couple of charge controllers to handle that much wattage. Let's say 1200$ for good charge controllers. Toss in another 1500$ for transfer switches, wire, power panels, and breakers. Maybe another 1000+$ or so for a certified electrician to wire it together in a code-compliant system. It's critical that the electrician wire the system with a transfer switch so your power won't energize the grid. So, for about 10,000$ you'd have something that works.

Just curious, would Li-x batteries be better to provide the surge watts required to start loads like well pumps?