Higher V Pump for Direct DC to Pump Solar Thermal

So, I heat my stock tank with two parallel thermal panels. Manually plug in an ac pump to an extension cord each day. I bought a kit to control it automatically with a few T probes. It has a horrible manual, but should have the ability to heat an aux tank, so I can overheat it and then heat exchange off of it for maintaining tub heat after dark. Before I spend time making all that work, in the interim, I have a big pile of hand me down full size pv panels. I'd like to use one to drive a pump when the sun is out. I see plenty of 12/24 pumps designed to work off old school 12/24V pv, but my panels are 64V oc, 56V PowerPoint, 6A. Any suggestions for a pump? Hoping to not pay more than $150.... thanks!

hogback said:

I see plenty of 12/24 pumps designed to work off old school 12/24V pv, but my panels are 64V oc, 56V PowerPoint, 6A. Any suggestions for a pump? Hoping to not pay more than $150.... thanks!

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Interesting application.

Most of the below type pumps that I've played around have a pretty wide operating window. No personal experience with this exact model however.


I bet this one would work but then again it's not my money I'm risking. I doubt it's rated for water much over 110F but if all you're doing is to tying to deice a stock tank you're likely never getting anywhere near there.

I'd also mention that if you have big ole pile of panels you could wire them in series up to around 250v to a standard water heating element in the tank.

Edit to change pumps to panels

Thanks OZ, the most worrisome thing about that pump is that it seems too cheap for the specs. Otherwise, I've read that motors can get fried in my application by spinning too fast with too high V, or the attempted current distribution when the light is low and the pump just barely able to run. I don't need much flow at all, and there is basically no head. I have got the thing up to 124degF a few times in the middle of summer here, which obviously requires a lot of stirring to get it down to 107degF, which I consider optimal.... it's not even insulated.

And I just don't understand why pv direct pump controllers are so expensive. I have a sunpumps one on my spring, but that drives a Dankoff pump to quite high head, and has lots of settings and float switch options.

hogback said:

I have got the thing up to 124degF a few times in the middle of summer here, which obviously requires a lot of stirring to get it down to 107degF, which I consider optimal.... it's not even insulated.

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Wow... looks like a nice spot. Ohhh.... Stock tank hot tub. That's a different creature all together. Ha... I once made a hot tub out the same rubbermaid stock tank! I've made several over the decades.

hogback said:

And I just don't understand why pv direct pump controllers are so expensive. I have a sunpumps one on my spring, but that drives a Dankoff pump to quite high head, and has lots of settings and float switch options.

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I don't know either. My guess is that it's a supply and demand thing, very low demand means a very high price. Hopefully someone with experience will pop in with an answer because I sure don't have any and, at risk of being called out, I don't there's more than a few that's messed around with this stuff as much as me. What I'm saying is that is you've got a tall task.

Yeah I'm guessing the demand is a big part of it. The end game is the buffer tank, probably a 100-300gal poly tank with insulation all around it. I'd heat it with these two panels, a chofu wood burner, and dump load from main pv system. I have the sr548 controller that should be able to control the thermal panels to buffer tank pump, as well as a hx between the tub and buffer tank to keep it at the proper temps. Part of the reason that I haven't wired it all up is the manual is HORRENDOUS, and I'm not looking forward to deciphering it.

So I took everything apart to add a PT ply base with a layer of Grace shield and one layer of 2" polyiso. I also have some 1.5" neoprene for the sides, but haven't messed with that yet. Eventually would like to cover the outside with scraps from an old redwood water tank, for aesthetics and to keep UV off the neoprene.

I did manage to program the differential controller. What a pain. Probably the WORST manual I've ever had to decipher. I think I'm lucky it's working right.

Also added a chofu for winter or cloudy days. Still learning on firebox load vs. cooking myself out at 109degF!

No ideas for a lid yet - I've just been using a sheet of greenhouse film to minimize evaporative cooling. It's kind of hassle taking it on and off and not getting it muddy. Maybe more polyiso wrapped in greenhouse film. Going to use it like this for a bit, then add the neoprene sides so I can get a feel for how much they help.

Even right now with mid 60s to mid 70s degF days, the panels only brink it up to 105, but that drops to 92 or so by the time I want to use it at night. Those trees you see block the sun after about 330pm, but that will get better shortly as the sun begins to set more north of west.

Should I paint it like Thomas the tank engine?