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Recommendation for an (ideally used) small-ish solar panel for a water feature? (slrpnk.net)

submitted 7 months ago by [email protected] to c/[email protected]

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Apologies if this doesn't fit the community

I've been helping my neighbor replace his lawn with a garden - last summer our project was building a terraced raised bed thing with secondhand soil and secondhand cinder blocks, and some new pavers in the front. I'd very much like to set up a water feature on that raised bed. He spends most days sitting on his porch, reading scifi novels and talking to folks walking by, so he could hear it while he's out there. I know it's kind of a silly luxury so I'm trying to use used components and I'd really like to set it up using a solar panel to power the pump.

I can handle the wiring and electronics with some guidance, but I know very little about pumps and solar panels for finding something that'll fit our use case. I think ideally it'd be a secondhand panel a few feet in size and a pump that can handle a varying amount of power based on the time of day. I'd like to move more than a trickle of water, and I'll make sure there's some shade plants so we don't lose much water to evaporation, though we don't get many droughts where we are.

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[–] [email protected] 8 points 7 months ago* (last edited 7 months ago) (1 children)

I perhaps can help you with this. I'm working in a company that is helping smallholder farmers over the world to increase their crop yield. We used to start with a small hydropowered waterwheel but moved to solar due to the reach of the sun. I am the technical person that is sourcing pumps, solar panels, inverters etc for irrigation.

So far as I can read your question you don't need a lot of water and also not a lot of pressure. It is quite easy to calculate.

Hydraulic power need (W) / efficiencies = electric power requirement (W)-> *1.3 = solar panel (Wp)
Hydraulic power = 9,81 * height differencence of water (m) * liter per second you want to pump
Efficiencies = centrifugal pumps are approx 35% eff so (hydraulicp/0,35) *1,33= panelsize
halve a liter per second is sufficient for halve an acre (2020m2) of crops.

Please if you have more questions I would glad to be of help

[–] [email protected] 6 points 7 months ago* (last edited 7 months ago) (1 children)

As an example case, if you need to pump from the pond nearby, 2m height difference and pump 0,25liter per second. ((0,25 *2 *9,81)/0,35)*1,33 = 18,6W ->20wp panel. I did not take into account the hose size butn0,25liter per second is not a lot. And every meter height difference added will add an extra 10W to the panel

[–] [email protected] 4 points 7 months ago (1 children)

Thank you for your help! My closest analogy is fish tank pumps (measured in gallons per hour), and I'm kind of guessing based on converting units, but I think ,25 liters per second is more than enough. I only need to lift the water around 40cm.

[–] [email protected] 6 points 7 months ago (1 children)

Glad to be of help. I think you can get away with a 12v pump as most panels of this power range are made for 12/24v. I suggest very simple centrifugal submergable pump with a bit of filtering around it and direct connection to panel. No inverter or battery, that would be way overkill in my opinion.

[–] [email protected] 2 points 7 months ago (1 children)

This is really good info, thank you so much! I know I know very little about both the panels and the and pump so I should double check - is a centrifugal pump tolerant of low power/is there a type of motor I should be looking for that will handle the panel varying the power output with sun exposure?

Thank you again - this is great because it's very much the level of simplicity I was looking for.

[–] [email protected] 2 points 7 months ago (1 children)

Good question on the low power of motors. Most of the low cost pumps have often DC brushed motors which do not need a controller to steer but uses a brush. Once there is not enough power (in the morning and evening) I think there will be a point where the power will be too low to overcome the torque and the motor stops. The centrifugal pump can still rotate easily compared to other types so I would expect the startup current will be low as well. Panels will deliver a constant voltage while the current will drop when light conditions are dropping. I think the simplest is to search for these aQuarium pumps (24/7 performance) on 12v but I doubt many cars/trucks have built in fishtanks ^^)

[–] [email protected] 1 points 7 months ago (1 children)

... but I doubt many cars/trucks have built in fishtanks ...

True, but they do have windshield washer pumps. I don't know about duty cycles, but I bet they'd be fine.

[–] [email protected] 1 points 7 months ago (1 children)

I actually didn't understand the reference to cars/trucks, something to do with the 12v power input?

[–] [email protected] 2 points 7 months ago (1 children)

Yes.

Most passenger vehicles have 12v electrical systems to run everything of note. Even fully electric vehicles typically have a 12v system separate from the transport battery to run things like wipers and lights.

There may be some components that run at 3 or 5 volts because they contain computer chips. Most of the fun stuff, like pumps and motors, run directly off 12v.

You don't have to buy new, either, as there are surely wrecking/salvage yards nearby.

[–] [email protected] 2 points 7 months ago* (last edited 7 months ago)

Thanks! Yeah, I'd much prefer to use secondhand parts all around. I'll see what I can find