Skip to content

Solar and swimming pools

Something for background information.

A swimming pool needs both heating and also electricity for pumping. To filter the water etc.


This is not something that is particularly time dependent. Has to be for x hours a day, no more than that.

Sounds like something that a solar panel would be useful for. And, possibly, just a small one. There’s enough insolation in a day to pump the water through the filters and heat it as well. On a, you know, just think out loud basis.

My assumption is that it could also be pretty small, that panel. Thus pretty cheap. Because one is not trying to produce enough to run an oven, just a pump and heater.

Now, as you all know, I know fuck all about this sort of thing. So, looking to be corrected here.

The other thing I misunderstand about this sort of stuff is that solar produces DC. You need an inverter to get AC. Inverters, these days, are the exdpensive bit of a solar system.

Hmm. So, do DC pumps and heaters exist for swimming pools? Can one whack up a cheap solar panel, gain filtration and heating, with a dedicated, small and cheap system? That isn’t connected to anything else etc?

Or is this me – as usual when talking machines – being stupid?

42 thoughts on “Solar and swimming pools”

  1. Heating anything takes a fair amount of energy

    Heating water takes silly amounts of energy (4.2 kJ Kg-1 degC-1)

    So without knowing how big your pool is, how hot you want it, or how insulated the building is for heat losses, etc…
    I’d still say you’ll need a half decent sized solar array.

    That’s assuming you are using it to heat from scratch. If you’re just using it to maintain a temperature it could be smaller. But then you’d have to fill the pool to start with from the kettle (or other method).

    You also need to account for backup batteries for when the sun isn’t shining.

    It’s doable.
    But is it cheap? I doubt it.

    Cheaper I would think to have a propane heater for the heating part and a genset to run the pump.
    A lot cheaper, readily available and reliable.

  2. My starting point is that I’m in the Algrave. Currently 15oC which has everyone packed up in their winter woollies….

  3. Two different orders of magnitude.

    1- A small. low volume. lo pressure pump to circulate water when the sun is shining is no problem. Plenty of solutions out there with small panels.

    2- Actually heating the water to an appreciable degree requires much more heft. That’s a big project – high tech and price. Probably better not to have a solar panel -> electricity -> heater (which is very inefficient), but a solar absorber panel that is designed to heat water directly from sunlight. Quite low tech and price.

    If you want some evidence, as a numerate chap you just need to calculate the volume of the pool and the amount of energy needed to raise the temp by 1°C. The answer will surprise you.

  4. I agree with the others. Yes, you can run all this off a solar setup, but the more heating you want the more solar power you’re going to need as well as a thermal cover to keep the heat in when not in use.

    What is the capacity of the pool in litres or m3?

    What temperature do you want the pool at?

  5. My school’s Olympic standard swimming pool was solar powered in the 80s so I’m pretty sure it can be done.

  6. For example:
    Pool is 12 x 4 x 1.8m / 1200 x 400 x 180 cm
    Volume of water: 86’400’000 cc = 86’400 litres ~ 86’400 kg
    Energy required to raise the temp from 15°C to 20°C = 502.80 kWh.
    Now look at your electricity bill…
    NB I have a propane room heater with a max output of 4.2kW. That would barely make a dent in the temp of your pool.
    Swim in a cardy…

    and many others if you search for ‘solar water heater’.

  7. I agree with fos. For heating the pool don’t go solar PV -> inverter -> heater, you’re looking at significant losses. Circulate the water through a solar absorber to get all of the heat into the water. Cheap and dirty hack: old CH radiators painted black. Friends of mine do it and it’s surprisingly effective. Of course, it only works when the sun shines, your pool will definitely be unheated on cloudy days.

  8. A black tarpaulin to go over the surface when the sun is shining. An insulated cover (bubble wrap style) for when the sun isn’t.

  9. Well it is in times of least sunshine and low ambient temperatures that heating might be needed.

    I ran my filtration for 2 periods of 4 hours each (10m x 5m, average 1.5m deep).

    Pool water is heated in a heat exchanger (usually in the pump house) in-line with the main pipe work to and from the pool, which means the water has to be circulating through it to be heated.

    If the pump is off, the pool temperature will fall. That means to maintain temperature you need to run the pump more or less continuously for the period during which you want to use the pool, not just during the time needed for filtration. And if the pump has been off for a time, say at night, it will need to run for a couple of hours (depending on pool size) before you get in it.

    Use of solar for pool heating is (or was) not pv but the water heater type. These days air/water heat pumps are available for pool heating.

    PV Solar are not a good idea for pumps, because pumps have a high start-up load. For example, if it is a 2kW pump, that is 2kVA. If the voltage is 230V that means a current (amps) of about 8.5A. But on start up the current could be double, which means the solar pv supply must have a much higher rating (= more panels = more expensive) than the operating rating.

    This is why solar panels on peoples’ roofs, must have mains back up to avoid constant circuit breakers shutting off current whenever the fridge starts up.

  10. Everything everyone else said about heating vs electricity – making solar electricity to heat water (in these ranges) is just barmy. Harvest the solar heat directly. Surface area is the key, old radiators are handy but not very efficient at harvesting solar heat. Around here (in Michigan, USA) the folks that do this make large arrays of tubes with solar concentrators to concentrate the light onto the tubes – the coolest ones I’ve seen use recycled soda cans, the insides of which are close to a mirror finish. You’ll need a circulating pump, which can certainly be solar-powered, and a heat exchanger – maybe best to buy a really well-engineered commercial piece, for maximum efficiency. You’ll also need some way of disposing of excess heat on very sunny days, you don’t want your working fluid boiling.

    We water the garden (1/4 acre) using a shallow well, a tiny pump (made for ornamental fountains) and a 30W solar panel. It only pumps a trickle, filling an IBC, but it pumps all day, every day, all summer – we never run out. That’s the key with solar – the unit yield is small, the benefit is in harvesting it all the time. Charge the batteries in the cars, the RV, tractors, mowers and electric golf cart, all off a couple of 100W solar panels.



  11. If you want to use the sun to hear the water, just paint the inside of the pool black or use black tiles.

  12. There are good uses of solar and there are bad ones. Heating and cooling are the biggest draws of energy in almost all houses. As a rule of thumb, using solar to power air conditioners is a fantastic idea, to power heaters is a bad one. For hopefully obvious reasons.

    If you’re looking to power a pool pump with solar, why? If it’s somewhere off-grid and you’ve got a propane/oil tank to heat the water then it’s kinda understandable. If there’s (reliable-ish) mains ‘leccy then use it.

    One of my bits of beef with a lot of solar systems is that they invert DC to AC only to rectify it back to DC for battery storage, which is utterly pointless, so I get where you’re coming from with the question. A pump is driven by a motor, and that motor can be AC or DC. If it’s DC then you have to be careful about the voltage you feed it, and DC voltage regulation that doesn’t just involve wasting energy against a resistor is quite expensive, so you’re probably best off swallowing the cost of the inverter and a slightly larger solar panel rather than trying to re-engineer the pump.

    I saw a while ago a heater that included a sterling engine. If you’re using fuel for heating, this would probably generate more than enough electricity to power the pump for basically free if you’re running the heater anyway.

  13. Regarding painting the inside of the pool black – er, no. The pool is full of water. Incoming solar radiation will be largely reflected off the surface at any angle of incidence other than normal. There will be some heating of the surface layers of the water, but nothing-like the amount required.



  14. Say your pool is average 1.5m deep, 10 m long x 5 m wide. That’s 75 m3, = tons.
    A calorie heats 1 gram of water by one degree C.
    So to heat your pool by say 10 degrees you consume 750 million calories or somewhere north of 3 billion joules
    That sounds a lot.

  15. Reminds me of a great energy saving tip.

    If you use a lot of boiling water for cooking during the week (vegetables, pasta etc) why not boil a huge volume of water on a Sunday and then keep it in the freezer to use later in the week.

  16. Cheap solar panels for heating water. Mmm…
    Tried some experimenting with this. Take one of those polycarb multi-walled panels used for roofing conservatories. Basically they’re a load of square walled tubes open at the ends. You’ll need some 2″ plastic wastepipe. Cut 2 lengths a bit longer than the width of the panel. Now you need to make a jig that the pipe will sit in & allow you to cut a slot in the pipe with the appropriate sized router cutter, the same length the panel is wide. One fits in t’other. You can glue & seal the panel into the pipe with a gap filler you can buy at any good plumbing suppliers. But you don’t want the panel touching the opposite wall of the pipe or it’ll block the flow. Way I did it was to run a circular saw across the ends of the panel producing a 45° chamfer. A 45° router cutter would achieve the same. From there it’s all standard pipe fittings to connect to the pool plastic. You need a couple of tees in the pipe from the filter to to the pool with a shut off valve between the two to regulate the flow & a couple of shut-offs from the tees to the panel for servicing. Best to keep your pipework out to the panel in 2″ as well. Painting the non-sun facing the side of the panel matt black will raise efficiency. But you could use your panels to roof a structure, so might not want to. Unless it’s a car port.
    You’re pumping the pool water through this lot, so the pool chloro/bromo should stop algae formation. For wintering, might be worth erecting it all with falls & a drain-off (inc shut-off), so you can empty the system.
    Speaking from memory, you can pick up 1 metre wide 4 metre triple wall panel for well under 100€. Pipe & fitting costs depend on your runs. How many you want’s up to you & how quickly you want to heat your pool. I’d connect multiple panels in parallel rather than series to get a better flow rate. To adjust the diverter, you want about the same volume going into the pool with the panel as you get without. So with more panels, more water can be diverted through them.
    Worked fine the system I set up. We did it as a car port 4 x 4 metres. Whole lot including the structure was under a grand. Still working as far as i know. A bought in system does the same is thousands.

  17. What others have said – for the pump, a couple a solar panels is probably fine. For actually heating the pool, forget it it. My family had solar heating for our pool back in the 80s (eek, I’m getting old) but that was old school sheets of black rubber tubing and we had the advantage of being in the middle of 50 acres of market garden with a big machinery shed we could put something like 50m2 of circulation on. Direct thermal, if you have the space and sunlight, is the best way to go. There’s probably better stuff out there now but PV for pool heating, I doubt it.

  18. Bloke in North Dorset

    I’m not sure its a good idea to connect a pump directly to solar panels. A boat/motorhome/general use leisure battery would be a better option. Use the solar panels to charge the battery and that will also give extended running periods if necessary.

  19. A bit of perspective on solar heating of pools. Back in the ’80s a neighbour in the UK warmed a pool in an unheated indoor area with outside solar mat type tubing. This didn’t make things tropical seas warm but did keep the water quite tolerable for sustained fun on summer days. A friend in the Algarve had a large unheated outdoor pool that was still Baltic in July; fifteen minutes and even the hardy kids had had enough (this quite suited the owner).

    A little solar goes a long way, but if you want James Bond villain pool heating you’ll have to pay a lot for it.

  20. My assumption is that it could also be pretty small, that panel. Thus pretty cheap. Because one is not trying to produce enough to run an oven, just a pump and heater.

    The heater will have to be an oven in order to heat the pool in a reasonable time and keep it heated.

    Sure, the cost of running the pump for the filter is pretty neglible – heating the pool will likely be greater than your total AC/Heating bill for the highest month of the year.

  21. Tim Worstall
    December 6, 2023 at 12:07 pm
    My starting point is that I’m in the Algrave. Currently 15oC which has everyone packed up in their winter woollies….

    Short of a spa/jacuzzi sized tub, generally even out here in the desert we just cover the pool up for the winter rather than pay to heat them. And its about 15C out here right now at 9 in the morning.

  22. Regarding painting the inside of the pool black – er, no. The pool is full of water. Incoming solar radiation will be largely reflected off the surface at any angle of incidence other than normal. There will be some heating of the surface layers of the water, but nothing-like the amount required.

    Infrared won’t penetrate very far, but visible wavelengths and shorter will easily reach the walls. Infrared might also just about reach depending on what wavelength and depth of pool we’re talking about.
    Once the visible/UV reaches the walls, it’s going to be absorbed and then remitted, usually as longer wavelengths – infra red. Because black body radiation and thermal equilibrium etc . Thus it will heat the pool a bit.
    Maybe not much, I’m wrestling with an infant so don’t have time to do the numbers.
    But it would also look boss.

  23. Solar Thermal rather than PV is the way to go. Even for the pump PV may be a stretch (the storage will need to cope with initial load) but doable.

    For the heating, cheap Solar Thermal panels , a water filled mat or tubing will provide free heat.

    Depending where it is placed, you “may”not even need a pump for that. (but likely you will)

    I have a heatbank (store) in Devon and even in winter my solar thermal happely contributes.
    Very low (or no) maintenance and low initial investment. YouTube is your friend if your into making something yourself. Good luck

  24. A black tarpaulin to go over the surface when the sun is shining. An insulated cover (bubble wrap style) for when the sun isn’t.

    In the UK, you really need a floating cover for when the pool isn’t in use (to reduce crap falling in) and there are ‘solar’ options (similar to bubble wrap) that deliver a useful heat boost. In the Algarve? I recall swimming in an unheated outdoor pool in California (Los Gatos) in June that was 104°F! You really need a ‘cooler’ not a heater – many heat pumps offer this facility (they just run in reverse).

  25. Two points

    It’s more practicable to heat the smaller object, ie your body. Try various rubber suits, the kind you can pee in.

    In the Algarve, according to Saint Greta it surely can’t be long before your pool temperature year round is about the same as Old Faithful.

  26. Solar panels are 3-5cm thick. Supposedly better at taking energy in from sunlight than plant life now, and they get quite hot when the sun hits them directly for an hour or more.
    From what I can work out they float, possibly a little too buoyant for optimal, but just laying them on the surface of your pool will make the water below hotter unless I’ve missed something.

  27. The sort of pumps normally used are AC induction motors, which can’t be run directly from a solar panel. And they don’t take kindly to considerable supply variations. You will have to make use of battery storage and an inverter, which needs to have a surge rating well above the normal running load (especially if it’s starting a water filled pump). Old style brush type DC motors are going out of fashion these days, having been largely replaced in industrial applications with variable speed inverter drives and 3 phase AC motors. These could (theoretically) be fed from a DC source, because they convert from AC to DC then back to a variable frequency AC output, but I don’t know if anyone makes such a device. Unless you can find a specialist manufacturer of suitable DC motors, you’re back to needing an AC supply!

  28. Is your pool really going to be cooler than the river I swam in every summer as a boy? I’ll bet it’s not as cool as my favourite North Sea beach.

    Is this a case of getting a bit sissie in late middle age?

  29. Because one is not trying to produce enough to run an oven, just a pump and heater.
    Er…yes you are. A 1½ HP pump pulls about 1200 W. About double that spinning up. An oven might pull a bit more getting up to temperature. But maintaining temperature is more like 200 W, averaged. And you still haven’t heated any water. If 1½ HP is sufficient for the pool. The pump for our villa pulled more like 3kW. There’s some complicated calculations about volumes, turnover, flow rates, filter diameters etc in choosing pool pump sizes. I used to be involved in designing & building pools.
    As for powering that with solar. You’re getting into the same realm as solar PV for a house. To get the required turnover will require the pump running for a certain period. (That’s excluding backwashing, hoovering etc) Divide that period into your day’s insolation will produce area of PV’s/battery capacity required (adjusting for losses in inverter, cabling etc.) That is going to be far from cheap. (10K+?) And it’s not as if you’re going to get the same payback as a house. You need to have water turnover to match maximum pool usage. But that’s unlikely to be for more than a limited part of the year. During the rest of the year the capacity goes unused.

  30. My last house here in Minnesota (North – cold!) had a pool. We had a 140k BTU natural gas heater for it. Used lots of gas.

    The I bought a solar cover – bubbles arranged to capture solar energy into the water. Didn’t need the heater much after that. Pool could get too hot on sunny hot days.

  31. ” with a dedicated, small and cheap system”

    The key word here is “dedicated”.

    Lots of possible solutions, most of which are covered in the earlier comments.
    Thing is, this kind of stuff tends to be specific to the pool in question, including the hardware around it, and the environment it is in.

    Even if you opt for one of the “generic” solutions to the problem, it will have to be adapted/adjusted to the pool itself.
    And its general occupants.. Some peeps are fine with 21centigrade water, others want to run a very large hot tub…
    Which…. tends to determine a lot in terms of energy requirements….

    I do miss the most obvious ( and Metal…) solution though…
    The wood-stove/BBQ/smoker/pool heater combo..
    And yes…. That is a Thing… A pretty popular one at that, that can be self-built, in places that are… not as balmy in winter as the Algarve..

  32. “Is it me being stupid”?. NO. Difference between stupid and ignorant, Even non-stupid people are ignorant about almost everything. Please everyone stop using these terms interchangeably.

  33. A good little engineering brain teaser to start my day…

    A friend of mine here in Blighty (52oN) heats a biggish pool with solar collectors made of radiators behind dutch light glass and black alkethere pipes through a large 400m2 glasshouse. Pumped system, works OK in the summer.

    Two thoughts:
    1. If you want to get decent solar energy collection in the winter it would be necessary to have the collectors set nearer to vertical. Insolation doesn’t drop that much in winter but the sun is lower and you want the panels to be perpendicular to the rays (output drops with the cosine of the angle).

    2. If you happen to be on a slopey bit of the world you could probably get the system to thermosyphon by putting the collectors downhill of the pool.

  34. Andrew C- great top tip! my fave. Submarine designers – place all your pipework on the outside of your sub, thus ensuring any leaks caused by depth charge attacks won’t flood the sub with water.

  35. Just fiddling around with a few numbers and had these thoughts (lots of rounding used here)
    Area of world ocean – 3.6 * 10^6 km2
    Sea level rise due to nature and climate change is about 3mm a year
    Extra ocean volume added per year 10^10 m3

    Volume of Timmy’s pool is around 100 m3 (thank you fos for your estimate of that).

    So if the world builds and fills 100 million pools every year the size of Timmy’s then the sea level rise aspect of climate change is dealt with.
    May not even need that many as it’s the difference between sea level rise in an interglacial and the extra sea level rise from us lot that we’d like to offset. And extra surface aware of water attenuates heating anyways as it takes a lot of energy to boil.

    COP29 – I accept my invitation and will submit my proposal to repeal any and every impediment to the digging of deep outdoor pools, ponds and reservoirs in all the planning systems in the world.

Leave a Reply

Your email address will not be published. Required fields are marked *