Solar powered pump - how powerful?

Generally solar powered pumps are disappointing. For a good one you need to be planning to pay considerably more than a mains-powered equivalent-powered pump would cost. But you won't have the cost of getting an armoured cable electricity supply to the pump, nor the cost of the electricity to run it. OTOH it will only run when the sun is shining ...

 

Hi,

As kristen said, solar pumps are very disappointing. Please allow me to explain.

Although you said you only want a dribble, a dribble will be too tiny, trust me.

The "oomph" as you put it is measured in litres / hour (or gallons / hour in old money)

Let us take a waterfall that is 2 feet high and 4 inches wide as an example.

Even though you want a small water fall, a waterfall of 4 inches wide will want twice as much water as one that is 2 inches wide, so already you can see its not easy as it first seemed.

That aside let us say this 4 inch wide waterfall needs 30 litres / hour.
Now we want to look for a pump that can deliver 30 litres / hour, you find one plumb it and it doesn't work why?

This waterfall is 2 feet high (remember) the pump we have can pump 30 litres / hour at 6 inches, at 12 inches it can pump 10 litres / hour, at 18 inches it can pump nothing, so at 2 feet it will also pump nothing. (The higher the output height is the less water you will get)

This is why pumps have a diagram on the box showing how much it will pump to what height; this is called the pump curve.

So we want a pump that can pump 30 litres/ hour at 2 feet in height. Now we have to look for a solar pump that can do this.

The next problem is solar pumps usually come as kits, mostly to run a small fountain and so they do not have a flow graph for all to see, there is also a reason they donâ??t have a flow graph, its because the flow is so small the graph would be even smaller. This then leads us to dedicated separate solar pumps and solar panels, These are quite often very expensive and in some if not all cases it is cheaper to install a mains pump, and donâ??t forget a mains pump can run any time you like, not just when the sun shines.

Please bear in mind the figures used I made up, but the principals are true.

You may also want to read This article

 

Please do keep us informed, it will be interesting.

 

Excellent! Where did you get it from please?

 

A very small and simple modification would make it work regardless of sunshine (for a while). Such a modification would involve two additional components, a rechargeable battery and a diode (and optionally a switch). Then the solar panel could charge up said battery during good sunshine, and the battery would run the pump when the solar panel output is too low. The diode would stop the charge from the battery from flowing back into the solar panel. The optional switch could be used immediately before the pump, so if you are away for a few days you can just switch it off and let all the solar panel output go to giving the battery a good charging.

 

Nice in theory clueless, pity it doesn’t work that well in practice.

As already stated by Loofah. his solar panel is 1 watt max.
If his pump uses 1 watt, what is left to charge the battery? Answer: nothing

If his pump uses just under 1 watt then assuming the voltage is around 13.7 volts it may just charge the battery for a few seconds, if the sun shines. (Under 13.7 v a 12v battery will not charge, similar for lower voltage batteries, it needs to be higher in order to charge)

In order for it to really charge a battery you need a bigger solar panel than the pump uses, in this case a 2 watt panel at least.

But also as Loofah said, it depends on the angle of the solar panel, and as the sun moves, no matter what angle the panel is the sun will move away anyway.

Loofah, how about a picture?

 

@water-garden, all true. I'd missed the bit where the solar panel was 1 watt peak. You'd need a couple of watts minimum as you say.

 

Which is also why 99% of solar pond pumps have no back up battery. They would require a bigger solar panel than the one they are supplied with. Which would, in turn put the cost up even more.

Also the water jet on most solar water fountains may be "high" (2 -3 feet, if you call that high) but it is usually very thin, which means that there really is no volume, so they are not suitable for anything else other than the fountain they were designed to be.

The opposite is also true. Some solar water features do have "wide" outlets (water falling from one bowl to another) But these are not strong enough to send a water jet "high"

Also as said, being solar they wont work none too well on a cloudy day, unlike a mains supplied pump that will work no matter how cloudy (or dark)

 

Is it not time for a picture?

 

25 days later, still no picture?