Home made pool solar heating

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peterv

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#223576 6-Oct-2017 16:35

Hi everyone, newbie here.

I have about 400m of polythene pipe on my shed roof to help heat our inground pool. I'm now looking for a solar pump to circulate the water. I've tries a circulation pump but have had untold issues with air coming in the system and the pump not priming. Now looking at a submersible pump. Found a 12VDC 2000 GPH Bilge pump on Trademe – 8amp and will pump to 6m, ample for what I need. What I'm wondering is, would anyone have any experience on what size solar PV panel I'd need to power the pump. (From what I can gather volt x amp=watts so in this case, 12v x 8amp=96watt?), so thinking a 100w panel might work?. And what else I'd need to hook the pump and panel up.

I like the idea of PV as you don't need a solar controller to turn the pump on and off.

I've asked some questions on Trademe, but most traders aren't knowledgeable about what they sell. Hoping someone here might be able to give me some useful advise?

That would be much appreciated!

Thanks heaps everyone.

Peter

Aredwood

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#1878568 6-Oct-2017 16:43

Solar panels only output their rated power for a small part of the day - when the sun is directly facing the panel. For such a low power application just use mains power to run your pump. Temp controllers are cheap Something like this from aliexpress - set it to cooling mode. As you will need far larger than a 96W panel to run your pump reliably from solar.

If your other pump is a purpose designed circulating pump - far better just to fix the air lock issues.

raytaylor

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#1878737 7-Oct-2017 00:28

If you are pumping the water up to the roof, then the pipe drops back down into the pool then i dont think you need to worry about the height specification of the pump.

The water dropping back down the second part of the pipe back to the pool will create a sucking force that helps the pump.

I would suggest looking at a cheap pump and a 80 watt solar panel. Depending upon the pump, you may not need to run it at full speed, so you may be able to get away with slightly underpowering it.

Also something to be aware of is a 12v solar panel puts out about 17v so you dont want to blow the pump - im sure it would be fine but is something to be aware of.

If the 12v 8amp pump was running on mains power for 8 hours a day, it would use approx $5.30 worth of power a month.

This is definitley a good idea and perfectly ideal for solar as the full load will be captured and put to use rather than wasted.

I like the look of this one as it supports slow inrush current - directly hook it to the solar panel and when the sun comes up it will slowly speed up, then when the sun goes down it will slow down stopping the solar collector being used to cool the pool in the evening.

Ray Taylor

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Aredwood

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#1878743 7-Oct-2017 02:02

I do partly agree about the weight of the water on the downhill helping due to the siphon effect. Except - if you get air in the system, it the right (or wrong places). You then need alot more pressure from your pump to push it out.

Imagine your pipe starts from your pool, goes through your pump (pool height = 0). Goes up 6m (height = +6m), drops down 9m (height =-9m) then goes back to your pool. When the pipe is 100% full with water, the only head loss is friction losses.

But under certain air lock situations, the pump needs to be able to provide a min of 9m static head output to get the water flowing. Lots of plumbers don't understand this effect, that lots of little air locks can add together, and in extreme cases can make a pipe appear to be "blocked". I know of a plumber who got caught out by this on a large commercial job. Really long pipe run, supplied direct from the council main. No water coming out the other end of the pipe. End cause was air locks caused by the base of the trench not being flat. Lots of air locks adding together.

Either make sure that your pump has enough outlet pressure to push out any air locks. (and make sure that air won't get stuck in the pump itself). Or you need lots of auto or manual air vent valves on the system.

Even Watercare have lots of auto air vent valves on most of their watermains.

peterv

3 posts

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#1880219 10-Oct-2017 09:29

Thanks Aredwood and Ray ... your suggestions are much appreciated.

What Ray says makes a huge amount of sense, and I like the symbiosis between solar PV with solar heating. Thanks for pointing out the cost benefits Ray, a pool is expensive enough to run as it is!

The solar pump I currently have isn't waterproof, and like I said, if there is any air at all in the system, it won't work. So having a submersed pump that's a bit more powerful might make the system a lot more failproof? If the pump primes, and is powerful enough to push out any air that might have gotten in somehow.

TBH I don't know how air gets in in the first place, although it could be that I never managed to get all the air out of the poly tube to start with? There's a lot of length up on the shed roof.

Thanks guys ...

Peter

tripper1000

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#1880244 10-Oct-2017 10:05

Just a cautionary note - bilge pumps are not designed to be permanently underwater. They're designed to tolerate being immersed intermittently and when permanently underwater the motors tend to fill up with water an break down. If you can, set it up so that the impeller is just underwater, but the motor portion of the body is above the water level.

At the end of the day if a bilge pump in a boat is doing it's job properly, it does not live underwater but in air.

I have a friend who has a similar system and he raves about it. It keeps his pool up around 30 deg (it is capable of higher temps at the peak of summer) and extends the length of the pool swimming season. He has digital controller that turns on when the sun is shining, turns off when the pool is warm enough and also shuts the system down from April - October so he doesn't ever need to think about it.

hairy1

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#1880331 10-Oct-2017 13:14

I would install a decent one way valve after the pump to prevent back feeding when the pump is off. That might sort out your issue. I have one on my filter which works well. I'll see if I can find the model online somewhere. We ran out of money for solar although the pool is piped for it. One day.....

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hairy1

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#1880333 10-Oct-2017 13:17

This is very similar to mine:

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chimera

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#1882678 12-Oct-2017 22:14

I have the bonus of having a heat pump for my pool but was also considering supplementing the heating using solar via black PVC piping. Anyways, the point of my post is... I did some measurements on wattage used for the heat pump vs the return pump (bear in mind the return pump sends water via the heat pump before returning to the pool, no separate pump) I noted that on average the heat pump draws about 180W's. The return pump on the other hand draws about 800W's That's over 4 times as much power from the return pump than the heating (plus the heat pump doesn't always run throughout the day - once at temperature, it automatically turns off) It would probably be a good idea to check what draw your return pump is, as that could be a higher portion of the cost. Of course, if you're just putting solar heating in because you want a warm pool then all good, however I wouldn't skimp on a crappy pump. For me, I'm considering PV panels instead now to supplement the return pump and heat pump (as they run from 8am - 6pm) plus help run the spa pump/heating (runs for 10 mins every 1 hour) plus the usual draw from household appliances. My power bill is around $500 a month so would be nice to reduce it a bit (but I think being partially off-grid is a nice to have too, regardless of just the cost)

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#1882698 13-Oct-2017 00:42

@chimera If you are going to get a new pool or spa pump. Consider a Davey Sliensor pool pump. It is water cooled, which means it is both quieter, and the waste heat from the motor heats your pool instead of getting dumped. Im not aware of any other company that makes water cooled swimming-pool pumps.

Although I did hear of a case where someone installed a Sliensor pump on a spa, and they had issues with the water temp getting hotter than the thermostat set point. The cause was that the spa was so well insulated, that when the motor was running with the cover installed on the spa. The waste heat from the motor was more than the heat loss from the spa. Some careful programming of the timer would be the easiest way to manage that issue.

peterv

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#1882820 13-Oct-2017 09:42

Interesting discussion, especially about the watercooled pump.

And something I wondered about, if a heat pump heater can create 3 times the energy it uses, then it would be interesting to see running a heat pump heater purely from PV power, as it should be more efficient then using solar heating? Apart from the expense of course ... but would that be correct?

Thanks ... I will post an update if I have so ething worthwhile to say!!!

Peter

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#1882833 13-Oct-2017 10:14

peterv:

Thanks Aredwood and Ray ... your suggestions are much appreciated.

What Ray says makes a huge amount of sense, and I like the symbiosis between solar PV with solar heating. Thanks for pointing out the cost benefits Ray, a pool is expensive enough to run as it is!

The solar pump I currently have isn't waterproof, and like I said, if there is any air at all in the system, it won't work. So having a submersed pump that's a bit more powerful might make the system a lot more failproof? If the pump primes, and is powerful enough to push out any air that might have gotten in somehow.

TBH I don't know how air gets in in the first place, although it could be that I never managed to get all the air out of the poly tube to start with? There's a lot of length up on the shed roof.

Thanks guys ...

Peter

How about just connect a valve and hose adapter near the pool intake so you can prime the whole thing by connecting a garden hose and using mains pressure water to push thought the pipe?

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chimera

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#1882853 13-Oct-2017 10:34

peterv: And something I wondered about, if a heat pump heater can create 3 times the energy it uses, then it would be interesting to see running a heat pump heater purely from PV power, as it should be more efficient then using solar heating? Apart from the expense of course ... but would that be correct?

That was kind of what I was eluding too, however there are losses with PV panels, so most definitely cost becomes an issue.

Take a hot water cylinder for example, the general consensus is that it is far more efficient to heat it using solar PVC tubing than solar PV panels - I would assume this "general consensus" (Google knows all...) also takes the capital cost into consideration, not just operating costs.

If cost was not an issue, then PV makes more sense because if it were sized large enough then it can of course power more than just your heating needs. Personally, I would suspect peoples mileage would vary based on many factors, and each individuals home would need its own calculations done to work out what the best option would be.

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#1883142 13-Oct-2017 20:54

With regards to household water heating, the trend is moving towards installing grid tied PV panels, and using a heat pump hot water cylinder.

Its much more efficient at heating water from sunlight than standard solar tubes due to the heat pump efficiency, and allows you to more effectively have a useful dump load for excess power before selling back to the grid.

Of course directly driving a heating element from PV is less efficient than solar tubes but driving a heat pump swaps that around.

Ray Taylor

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#1883182 13-Oct-2017 22:00

Bilge pumps (assuming it's a centrifugal pump) are designed to sit submerged in water and push it up. They have no suction head.

They are designed to work with an open ended discharge head of a few feet, via a couple of metres of the widest pipe that fits the pumps discharge nozzle. For example on my boats bilge pumps I have 40mm ID hose.

I'm not sure that a little bilge pump will enjoy pushing water through a long, skinny hose. It will probably cavitate a little and create bubbles. It's possible these will accumulate somewhere in the system and create and airlocks.

I'm also not sure a bilge pump will survive chlorine very well (if it's a chlorinated pool).

Mike

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#1883223 14-Oct-2017 01:06

peterv: Interesting discussion, especially about the watercooled pump.

And something I wondered about, if a heat pump heater can create 3 times the energy it uses, then it would be interesting to see running a heat pump heater purely from PV power, as it should be more efficient then using solar heating? Apart from the expense of course ... but would that be correct?

Thanks ... I will post an update if I have so ething worthwhile to say!!!

Peter

You can't run a heatpump directly from PV panels. You need to buffer it with grid power or batteries. Imagine your heatpump draws 1.5KW when running for say 4KW of delivered heat output. (A pool or hot water heatpump wont be an inverter heatpump) Lets say you have a 3KW PV array. In full sun you are only using 1/2 of the PV output, with the rest getting exported and you getting paid ~7c per unit. When it is an overcast day, you would only get 500W or so from the PV. Nowhere near enough to run the heatpump. So you need to import grid power at 25c per unit to make up the shortfall.

Connect the PV array to a decent diversion controller, and you can dump the full PV output if needed. With the controller accurately matching the baseload in your house. You can then get over 90% self consumption with a good system, without the expense of buying batteries. And a 3KW heating element is way cheaper to buy than a heatpump. And has far lower maintenance costs. Far better real world returns despite a lower on paper efficiency. Anyone who claims to be running heatpumps etc directly from solar PV is probably either in a country that has net metered PV import/export. Or they don't care in the slightest about actually matching the PV and heatpump.

And is an inverter heatpump with an external power output control even available? In otherwords, send a command to the heatpump - use 700W of input energy [sun gets brighter] Increase power input to 750W [sun goes behind a cloud] reduce input power to 150W [5min later there is full sun] increase input power to 2150W. As to have any hope of matching a heatpump to solar PV, you will need a heatpump with this ability. I have never seen one for sale. (please tell me if you know of one that is available)