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Has anyone any success stories or otherwise regarding irrigating raised beds in polytunnels using solar-powered pumps, say using water from rain barrels or other storage?

I'm thinking about trickle irrigation through perforated piping and so a low-solar-power solution to this sounds attractive.

Apologies if this has been discussed previously; if it has, can you provide a link?

bump

Interesting question... It's something I've thought about on a smaller (greenhouse) scale, but I haven't done anything about it yet (solar power systems are on hold pending a shed rebuild). There's no reason in principle why it shouldn't work, the question is "simply" (ha! ) one of sizing the solar power system correctly.

The other question is whether you want to just buy an off-the-shelf system or build one yourself... For the OTS option, you might want to have a look here. For a homebrew system, this might be worth a look. That's just a couple of examples from a quick Google, I'm sure there are others.

Thanks g

That Waterwand, I hadn't come across that despite a search of the web. Thanks, it looks really good and not too dear though dear enough.

I have a habit, when doing custom solutions to stuff, of over-spending/belt&braces kind of thing and often find ots solutions cheaper, despite the profit margin involved.

I'll talk to swmbo and maybe get the go-ahead.

I don't have a polytunnel, but I use a solar-powered irrigation system for my regular garden.

The power source is a 15-watt solar panel, feeding a 12 volt marine (deep cycle) battery. The pump has a built-in pressure switch, and produces anywhere from 5 psi (open line) to 50 psi (shutoff pressure).

The water source is three large rainwater storage tanks totaling 4500 gallons. Two of the tanks and most of the third (until the level gets low) would feed by gravity, but only at a dribble. The pump provides enough pressure to run soaker hoses and even a spray nozzle. I have a clockwork timer on the pump output so I can set it for up to two hours and it will shut itself off.

The system is into its third (or is it fourth) season, and the battery is holding up well. At 15 watts, I don't need a charge controller, which keeps it simple.

Good system, KeithBC. Small panel, good battery.

What pump do you use?

I'd be really interested in how you do with this. Can you make sure to report progress in this thread or PM me?

The trouble with perforated piping is that it delivers more water at the source end. Over short runs that's okay, but if you're planning on running longer lengths back and forward you may find it's a problem.

Smaller perforations reduces the problem, but means that you need more pressure - until you're looking at a 'Leaky Pipe' type product which has pores rather than perforations, and can handle runs of up to 50m BUT needs 1 to 1.5 bar (some specs here). If you're using this make sure you bury it or cover it with mulch to slow down the rate of mineral deposition in the pores. I've actually been filming a short vid on dealing with this problem this very morning!

By a friend's recommendation, I contacted a supplier of polytunnels etc, - Deker - about some 'lay-flat' irrigation piping. My friend reckoned it was far superior to anything he'd tried previously, with no clogging of the holes, which are fairly tiny and are in bunches of (four?) every 20 cms.

Trouble is, it comes in 1 kilometre rolls! I might have to find a few to share it with...

Here's the response:

We have Layflat Drip Irrigation in stock.
Code: 143.Layflat20
Hole Spacing: Every 20cm
Roll Length: 1000m
Litres Per m/h: 5 Litres
Price Per Roll: €104.06 + VAT
Delivery Charge: €12.60 + VAT

Good grief! They're a trade supplier... you could cut the rest of it into lengths and sell it on Ebay. Might even make a profit!

greenorelse wrote:Good system, KeithBC. Small panel, good battery.

What pump do you use?

It's a Shur-Flo diaphragm pump. I don't recall which model - they have hundreds of them.

This has been a really useful discussion for me. Keith, is the clockwork timer on your system basically a switch that stops water flow? When it shuts off does it mean that your shurflo pump shuts off through its own built in pressure swith, i.e. the psi rises in the tube and causes the pump to go off until the timer opens the tube again? Just trying to understand this as have no experience of building irrigation systems. David

dboyce64 wrote:This has been a really useful discussion for me. Keith, is the clockwork timer on your system basically a switch that stops water flow? When it shuts off does it mean that your shurflo pump shuts off through its own built in pressure swith, i.e. the psi rises in the tube and causes the pump to go off until the timer opens the tube again? Just trying to understand this as have no experience of building irrigation systems. David

Yes, the clockwork timer is a water valve. When the clockwork runs down, the valve closes, shutting off the water.

The pump at that point is still running. The pressure between the pump and the clockwork valve rises (rapidly!!), causing the pump's built-in pressure switch to shut it off.

Initially, I ran into trouble with the rapid pressure rise when the valve closed. WIth rigid pipe, there was nothing flexible to absorb the change in pressure. As a result, the pressure would rise from 20 psi to about 200 psi in one stroke of the pump. The pump probably stalled from the back pressure before the switch had time to shut off the electricity. The rigid plastic pipe and fittings took a beating and cracked after one season.

I solved the problem by installing a simple pressure tank. It consisted of a short section of 3-inch-diameter pipe closed at both ends and connected to the water pipe by some T-fittings. The important thing was that is was located above the water pipe, so it trapped air. Now when the timer valve closes, the air in the pressure tank gets compressed as the pressure rises. The pressure increase is much more gradual, giving the pressure switch time to shut the pump down properly. The maximum pressure at shutoff doesn't rise much above the setting of the pressure switch.

Keith

I have an irrigation system watering my polytunnel but no solar power - I simply have a battery operated timer on a gravity drip system which runs off an IBC (which in turn harvests water from the tunnel roof). Not as green as solar but a single battery lasts the full season so it's very cheap and cheerful. I guess if you wanted a higher pressure water supply then you'd need to pump but I'm happy with a slow release via the soaker hose which I've buried under the soil in the beds.

Thanks Keith very helpful. Broad bean what do you mean by IBC? David

dboyce64 wrote:Thanks Keith very helpful. Broad bean what do you mean by IBC? David

Industrial Bulk Container.
One of those large cube tanks surrounded by a protective metal grid.