DC boost converter for solar well pump?

[zzrider]

So I'm looking at DC submersible well pumps for an off-grid home water supply. For example, this:

https://pumpsupermarket.com/product...72v-1200watts-600-gph-model-3hr1200-180-2-3c/

I'm trying to figure out how to satisfy the controller's 72V desired input from battery when the solar isn't producing. This seems to be the situation with all these solar DC pump systems.

The two options I can think of are either a 72 battery bank or a DC boost converter on a conventional 24V or 48V battery bank. Either option requires hardware which seems to be unusual and difficult to find - high voltage MPPT charger controller for the former, or a large (>1000w) boost converter for the later.

So, is anyone here doing a DC pump system like this, and what did you use for the battery side of it?

 

[OzSolar]

So that's a solar direct pump optimized for applications like irrigation and pond filling during the daytime. It's specifically designed to be battery-less.

If you told us more about your application we could probably help you choose the correct pump.

 

[zzrider]

So that's a solar direct pump optimized for applications like irrigation and pond filling during the daytime. It's specifically designed to be battery-less.

If you told us more about your application we could probably help you choose the correct pump.

Sure. Application is an off-grid homestead, well to be used for domestic potable water supply and small-scale crop and livestock watering.

Well is scheduled to be drilled in February, I expect it will end up around 150-200' deep based on neighboring wells.

I know the easiest solution is likely to be to pump to a storage tank and use a surface pump to pressurize the domestic supply, but I don't know yet how the county feels about that with respect to code & permitting. This is why I'm thinking of the alternative, with just the well pump powered by solar & battery.

I know I need to talk to the county (I'm in south Florida), just trying to get as informed as possible first.

Appreciate your input!

 

[OzSolar]

I forgot to welcome you to the forum!

What do you think the static water level will be? How many gallons per day are you shooting for?

People don't use storage tanks in my area and I'm not sure why. Maybe because they can freeze in the winter and people don't want to give up the room inside?

Nearly all of the wells for homes I see use a ~30 gallon pressure tank with a pressure switch that turns the pump on/off. That's probably the easiest solution if you weren't trying to run it off grid. The Grundfos SQ pump is very off grid friendly though. It doesn't take up much room and is probably easier and cheaper to set up than a surface storage tank with a pressure pump. You do need to add the pressure to static water level. EG: 50 PSI will add another ~116 feet (50x 2.31).

If you want to do a storage tank that would be a great set up for a solar direct pump. At first blush that pump you picked out seems to be for wells up to 590 feet. If you choose a pump that is for ~250' or less you can likely get more water per day with less power needs. It could be as simple as 3 to 6 100 watt panels in series. You're after voltage more than you are wattage in most cases.

 

[zzrider]

I forgot to welcome you to the forum!

What do you think the static water level will be? How many gallons per day are you shooting for?

People don't use storage tanks in my area and I'm not sure why. Maybe because they can freeze in the winter and people don't want to give up the room inside?

Nearly all of the wells for homes I see use a ~30 gallon pressure tank with a pressure switch that turns the pump on/off. That's probably the easiest solution if you weren't trying to run it off grid. The Grundfos SQ pump is very off grid friendly though. It doesn't take up much room and is probably easier and cheaper to set up than a surface storage tank with a pressure pump. You do need to add the pressure to static water level. EG: 50 PSI will add another ~116 feet (50x 2.31).

If you want to do a storage tank that would be a great set up for a solar direct pump. At first blush that pump you picked out seems to be for wells up to 590 feet. If you choose a pump that is for ~250' or less you can likely get more water per day with less power needs. It could be as simple as 3 to 6 100 watt panels in series. You're after voltage more than you are wattage in most cases.

Thanks for the input!

I dont know what the static water level will be, I assume I'll know that after the well is drilled.

As far as usage, my primary requirement is to satisfy domestic consumption, so 5-6 gpm and ~50 psi. I figure around 250 gal/day would be a generous high estimate.

As you said, I think I'd prefer to just have a submersible well pump that I can run off both direct solar and battery. Essentially, I just want to do whatever is simplest and easiest to get past building code and permitting requirements.

 

[Hedges]

That pump you linked seems like a good way to go.
PV panels and an above-ground storage tank. Most of the power is consumed lifting water 200' (equivalent to 100 psi).
Instead of storing energy in a battery, store it with gravity. Float switch for reasonably infrequent cycling.
Small booster pump to provide 20 ~ 30 psi to house when water is consumed.
Maybe 1000 gallon tank, to allow 4 days without sun. Rain catchment system to extend beyond that?

Voltage If Using Battery (V)

72

Power (W)	1200
Max Head (ft)	590

So there you go.
At 200', maybe 1/3 power 400W?
Could keep six 12V AGM batteries charged, reconnect in series when needed (if you don't find a 72V SCC).

 

[OzSolar]

As you said, I think I'd prefer to just have a submersible well pump that I can run off both direct solar and battery. Essentially, I just want to do whatever is simplest and easiest to get past building code and permitting requirements.

FWIW, most DC pumps have a pretty decent voltage range and can be ran at lower than thier rated voltage without any issues. Less GPM and head of course. Ideally everyone would publish those specs but few do.

I'd suggest a pump that can do least 10GPM for convenience purposes. We have a 15 GPM pump and the pressure drops noticeably in the house when we are watering the garden and not even at full blast. If you do a 5 GPM pump that probably does push you down the road of surface storage. Of course if your well can't deliver more than a few GPM you won't have any choice.

Below are the specs for the pump I picked up on Alibaba a few months ago. It's not for our house but a spare well that I have elsewhere on the property. I wanted to add some resiliency to our water supply. It's been a really fun project, here is the thread with some pictures.

Mine is highlighted in yellow. I'm currently running it off two 370 watt panels in series. At ~80v MPPT it needs 250 watts to pump 7.5 gpm with a static water level of 50'. $180 plus another $180 for shipping included the controller. It does pump a bit over 2 gpm at ~40v (one panel).




I bumped into The Solar Store while looking for another Grundfos SQ Flex a while back. You might take a look at them as they have several pump options that might suit you well. They have what appears to be knock off of the SQFlex at a lower price point. First time I've seen that so I can't speak to it. We've installed around two dozen SQFlex's and if you can get over the price tag they are unbeatable. We have some that are 20 years old and trouble free.

Either one can run off of battery, AC or solar direct.

The Grundfos SQFlex solar pumps can be directly powered by solar or wind power or can be run on an inverter, a generator, a battery or the utility grid, or any combination of these sources. Virtually any source of power, 30-300 VDC and 90-240 VAC, can be used to run the pump. They can operate on a series string of PV modules with a total peak power voltage over 30 volts, but the pumps efficiency will be much higher at voltages over 100 VDC.