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Solar pump question (from lazy gardener)


Beachside

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My sister in law has one on her bathtub tank, as Ira said, not much chop really - I don't know if it has batteries or if they are stuffed, but as soon as your shadow falls over the solar panel it stops.

I don't think they do have batteries, not normally anyway.

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I have/had one (it appears my solar panel or the tiny fountain pump dont work currently, working on this) Anyways it worked really well and there was one that had a battery that got charged. Google rock solar fountain in google images and you should see it.

I got it on Trademe but have seent similar in mitre10 mega

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Most of those simple solar things (fairylights and the like) had an AA battery or two to store the charge. If your device starts to get pathetic or brief after some time you can pull it apart and replace the batteries.

Bunnings sells them really cheap. (ones designed for solar features, not the expensive ones for cameras etc)

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I have a little one that looks like the Jaycar one (bought on TM). Before i bought it I phoned everywhere to see what else was available - especially that might be better. A landscape supplies trader said they used to have solar pumps that were over $1000 and very hard to sell so they didn't restock after they finally sold the last one. No one else I rang had any knowledge of solar pumps.

The little one I bought is tiny, but does achieve some water movement when it is operating. It says is has electronic 'smarts' to cope with cloud, but has no battery and I think really goes off as soon as the sun goes.

The problem I wanted to solve was water stagnating in the deep hole at the bottom of my 700 lite pond. I have the solar panel up on the fence, the little pump just under the water surface, and a hose from the outlet to the bottom of the pond. It does work - just keeps a tiny bit of water movement going and seems to be preventing the build up of bad water in the bottom.

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you can buy just solar panels off jaycar...

12v panel + car battery or even a motorbike wet-cell might work + 240v inverter + any normal pump you can imagine.

then again, an extension lead dug in might make more sense and be cheaper

+ solar panel controller to control the charging of the car battery, Jaycar has then for $35. There are more than enough 12v pumps around, no need to add inefficiencies and cost of an inverter.

A car battery will be destroyed pretty quickly if you draw more than about 5 amp hours or 60 watt hours from it before recharging. They really suck for anything but high instantaneous loads, even the 5 amp hours will slightly damage it. You'd probably want to limit yourself to a pump that won't draw more than that over about 20 hours. So that leaves you about 3 watts maximum draw.

You'll need a solar panel that will top that off each day even in bad weather, so on top of the 3 watts you'll want a solar panel that will top the battery off even mid winter when you'll get some 8 hours of daylight, but it will be cloudy frequently so probably need something that can produce that 60 watt hours in full sunlight in 2 hours. If you don't you'll never even top off the battery on a dark day damaging it So, at a minimum you'll want a 30 watt solar panel. Your options from Jaycar are a 20 watt for $180 that isn't really good enough so you'll want a pair or a 40 watt for $455.

So we have, a car battery $100ish, Solar panel for $360ish, controller for $35 and then you have the pump. This is all before buy the pump.

First place I'd improve though is the battery, like I said, lead acids SUCK for this kind of thing. If you build a 10 series nimh pack though, you can get buy the batteries off Trademe for about $120 and they don't mind being discharged more than a tiny percent. So they'll probably last a LOT longer.

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  • 5 months later...
LOL how much for a transformer,

Depends on how powerful you want and how much DIY you want. There are a couple server power supplies that could probably supply the 240 watts you mention below for $20-50.

20 metres of cable

Depends how much current you want to carry. If you're wanting 240watts that's going to be some serious current at 20 amps. Probably about $100 for 12 gauge wire.

and 10 years of current draw @ 240v 1 amp?

$5256 at $.25/kwh

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