Converting existing well pump to solar

System · December 2011

I am helping a non-profit that has a large pond that is pretty dry. The dam used to leak but that has been fixed but unfortunately, there has not been enough rain to fill it. They want to help fill the pond up and have a very nice sounding well that they could pump into the pond. However, they could not afford the electric bill to run this thing all day. Someone suggested that running it via solar panel might be a good idea and various folks are willing to chip in for the costs and I was tasked to try to figure all of this out.

Unfortunately, I am not sure yet what are the right questions to ask to begin nailing this down and am hoping you folks could help. The well currently has a typical 3/4 HP 220 V well pump. I am not yet sure how much the lift is, but am trying to get a handle on that. Once above ground, we would run it in a pipe downhill to the pond.

What else do we need to find out? The well used to provide all water to the place, so there is plenty of good water but they put in a better system a year or two ago and don't use it any more, although I am told it is in good working order. It seem to me that since they don't need the 220VAC pump it might be a better option in the end to replace the pump with a DC pump and do away with an inverter, but again I know nothing about these things. Another question I have, generally, is would a battery be a good, cost effective addition? Wouldn't 'need' one, I don't think, but the more hours per day, the faster the pond fills up.

What do I need to find out about the system to start being able to figure out a decent system.

Cariboocoot · December 2011

Re: Converting existing well pump to solar

Welcome to the forum.

To be brief and blunt, solar is probably not the cheapest solution here.
A 3/4 HP pump is probably submersible and that usually indicates significant depth to the water. There are direct-from-solar pumps that can do this job, but they're not cheap. Poke around NAWS solar/DC water pumps section and you'll see what I mean: http://www.solar-electric.com/sodcwapu.html

Why is the utility power too expensive? Solar power tends to be far more so, especially if you have to change the pump out to use it. Will this be a long-term application or short-term? To just refill the pond may not be worth any significant investment, but if the water will continue to be needed/used it becomes more practical to spend some serious money.

Until we know what sort of depth the water is coming from and what flow rate is required it's impossible to offer any solid solutions.

mike95490 · December 2011

Re: Converting existing well pump to solar

Panels, and specialty pump, will cost a lot.

Obtainng a small generator - in the 2000 watt ballpark, may be your best bet. But running a pump, to fill a pond, that's going to take a LOT of water, time, and fuel.

And if the generator shuts off while it's powering the pump, several bad things can happen.

I'd wait for rain, and till then, bank the water in the well.

System2 · December 2011

Re: Converting existing well pump to solar

Cariboocoot wrote: »

Welcome to the forum.
Why is the utility power too expensive?

Thanks for the welcome.

I will get the details on depth, etc.and am trying to figure out what else I need to track down from them.

The problem is not that the utility power is too expensive (although they purchase from a rural coop, so it isn't cheap, but still cheaper per MWh than solar for sure) it is that they are largely publicly funded and there simply is no budget for such operating expenses. I looked at generators but it won't work for the reason above and a couple other idiosyncrasies. So, we are basically going for high capital cost, low operation cost. However, I can get any PV panels we need for free and if the cost is terrible for the rest of it, I can get donations to buy and install the equipment from folks who want that pond filled again, so hopefully it won't be too terrible if we can figure it all out.

Again, thanks for the welcome and for the suggestions.

westbranch · December 2011

Re: Converting existing well pump to solar

IFF, and a big iff, the pond is below the static level of the well ,

fill a pipe/ hose with water and gravity can take over and siphon the water out of the well. Slow but cheap, yet will take some fiddling.

tmarch · December 2011

Re: Converting existing well pump to solar

If you can get the solar panels free and make a rack you will have a large part of the investment covered.
I have no idea of the amount of head you would be looking at, but if it isn't too much, solar can be done pretty inexpensively.
Sure be cheaper than buying a windmill and less maintenance.

TheBackRoads · December 2011

Re: Converting existing well pump to solar

How big is the pond? Any pictures?

scotthi · May 2020

I too am trying to power a well pump with solar. My well pump is 74 feet down and the pump draws 8.2 amp at startup and is a 220v pump. I have a 200W set of panels with a controller managing the charging of my eight 12V batteries whick works fine. To remove the well pump from the house power, I decided to install a manual transfer switch. This is where I ran into trouble. I can't seem to find anyone who knows enough to tell me what size and type of inverter or whatever to install to provide the AC power to the pump. I tried going to AIM Power Inverter but they can"t seem to get it right because I have already spent almost $2000 on different inverters they have said should solve the problem. Can anyone shed any light on what I should be using?

mcgivor · May 2020

Welcome to the forum @scotthi

You mention 8 ×12V batteries but no information regarding capacity or configuration for a nominal voltage. The pump will on startup have a high inrush current for a few milliseconds, this is not to be confused with startup current or what is measurable with meters not capable of inrush capture. This inrush current can overwhelm the inverter, wiring, battery or all three in combination, this is especially so if the nominal voltage is 12V as the voltage conversation ratio would be 22:1, since current is inversely proportional to voltage the current on the DC side using the stated startup value of 8A @220VAC, would be 176A @12VDC. The inrush could be higher perhaps >50A so the battery along with the inverter need to cope with 1100A or more which will likely cause an inverter to fault due to overcurrent and under voltage.

To receive useful information, you need to provide details specific to your application, nominal voltage and pump specifications etcetera. It would also be best to start a new discussion to avoid confusion with previous psts responding to a 9 year old thread.

BB. · May 2020

Delayed post... As Mcgivor says, and:

Can you tell us a bit more about your battery bank (the batteries--Like 12 volt @ 110 AH * 8--In series or parallel, or series parallel--I.e., 12/24/48 volt battery bank, flooded cell/AGM/etc.)?

And can you tell us what inverters you have tried (AIMS 4 kWatt TSW or MSW, etc.)? And how did they "not work" (inverter cut out, pump did not start, battery bus voltage fell below 10.5/21/42 volts, etc.)?

Also, what is the pump? Franklin 2 wire or 3 wire, etc.? 1 HP, 1.5 HP, 2 HP, etc.?

Have you operated it on Utility power? A generator (what size), did it work or not? Has it every worked?

I am no well expert, but you are probably looking at a 4 kWatt AC inverter (ideally) PSW/TSW. And an 800 AH @ 24 volt or 400 AH @ 48 volts...

Just guessing here--There are others here with more experienced than I that can probably help.

-Bill

mike95490 · May 2020

here's the generic pump numbers

Converting existing well pump to solar

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