There are four ways to heat your pool with solar energy: a pool cover (the cheapest and most underrated), a solar collector with black mats or a dome, a DIY build using black garden hose, or solar panels that drive a heat pump. Expect water that is 5 to 10 degrees warmer if you combine things cleverly. The cover is the free foundation under everything, because it holds the heat that the rest puts in.
That is the short answer.
Now the honest version, because I have seen plenty of neighbours get this sort of thing wrong.
I am Fred. I build, I do the sums, and I do not like throwing money away. So let us work through this calmly.
Grab a coffee. We are going to warm up your pool.
How many degrees warmer can you really get?
Let us start honestly, because most sales pitches are not.
In a temperate climate you realistically get 5 to 10 degrees
extra from solar energy. No more.
Combine a cover with a solar collector and you sit at the top of that range. Do just one thing and you sit at the bottom.
A comfortable swimming temperature is between 26 and 28 degrees. Children love 28, sport swimmers are happy with 26.
Without heating, a pool in summer sits between 18 and 23 degrees. With a good approach you lift that to those 26 to 28 degrees and keep it there too.
And that makes a difference: it is the gap between “brr, grit your teeth” and “the kids won’t get out”.
The biggest heat leak: your water surface
Almost every article misses this, and it is exactly the most important thing.
Your pool does not lose most of its heat through the floor or the walls. It leaks away at the top, through evaporation.
Warm water that evaporates carries energy away with it. And at night that bare water surface cools down hard.
That is why the first question is never “how do I heat it up”. The first question is “how do I hold onto it”.
A cover that sits on the water at night is the cheapest heat pump you will ever buy. Only the other way round: it keeps the heat in instead of generating it.
Remember this. Everything that follows works twice as well if you cover up.
Method 1: the pool cover (cheapest and most underrated)
This is where you start. Always.
A pool cover, also called a solar cover or bubble cover, does three things at once:
- It stops evaporation, your biggest heat loss.
- The bubbles catch sunlight and warm the water by a few degrees on their own during the day.
- At night the air in the bubbles acts as insulation, so the heat stays in the pool.
A good bubble cover on its own already gets you 4 to 6 degrees. For pocket money.
Such a cover costs between 30 and 150 euros, depending on the size of your pool. A thicker cover (400 to 500 microns) lasts a good five years.
Which side up?
Lay the bubbles facing down, towards the water. Then the heat sits against the water and the cover floats nicely.
Small trick, big difference.
Tip: put the cover on in the evening as soon as you are done swimming. During the day in the sun it can stay on, so the water just keeps warming up. Only take it off briefly when the pool is in heavy use.
Do nothing else but this? Then you have already won compared to half the pool owners on the street.
Method 2: the solar collector (black mats or dome)
Now we start heating actively.
A solar collector is simple in concept. Your filter pump forces the pool water through black mats or a black dome. That black plastic gets scorching hot in the sun and passes that heat to the water running through it.
The water goes in cold and comes out warm, back into the pool. Free heat, because the sun charges nothing.
There are two types you see in gardens:
EPDM mats (solar mats)
Flat black rubber mats that you lay on the roof, the fence or a sloped frame. You link them together until you have enough surface.
Solar dome
A round dome with a coiled black hose inside. More compact, easy to connect, ideal for smaller above-ground pools.
How much surface do you need?
Here is the rule of thumb that counts: your collector surface should be 50 to 80 percent of your water surface.
Do the sums with me.
A pool of 8 by 4 metres has 32 square metres of water surface. So you want 16 to 25 square metres of mats. Yes, that is a lot. And yes, this is exactly where people buy too little and then complain that it does not work.
Take a bit too much rather than too little. More surface means more degrees.
Where do you put the collector?
Facing south, in full sun, with as little shade as possible.
Lay the mats at a slight angle of around 30 degrees towards the sun if you can. On a flat roof or a south-facing fence it works fine.
Important: the longer your filter pump runs, the more water passes the collector and the warmer your pool gets. More on that further down.
What does a solar collector cost?
| Type | Price | For which pool |
|---|---|---|
| Solar dome | 100 to 200 euros each | Small above-ground pool, up to approx. 5,000 litres per dome |
| EPDM mats | 40 to 55 euros per m2 | Medium to large |
| Set of mats (approx. 4 m2) | 150 to 250 euros | Expandable per set |
For a pool of 8 by 4 metres with enough mats you quickly reach 800 to 1,400 euros in materials. Connecting it yourself saves you the installation costs.
Pros and cons
Pro: after purchase there are no energy costs. The sun is free, your filter pump was running anyway.
Con: no sun, no heat. When it is cloudy and in the evening the warming stops. You depend on the weather.
Method 3: DIY build with black garden hose (real DIY)
Now it gets fun. You can actually build a solar collector yourself.
The principle is exactly the same as the expensive mats: black material, water through it, sun on it. Only now you pay a fraction.
A long black garden hose on a sunny roof or fence does a surprising amount. Black absorbs heat, and if the water crawls through slowly enough it comes back nicely warmed up.
How to build your own solar collector
What you need
– 100 to 200 metres of black garden hose or black PVC hose (thinner = warmer, thicker = more volume)
– A sheet of plywood or an old door as a base
– Optionally an old glass sheet or transparent panel to lay over it (greenhouse effect)
– Hose clamps and connectors to hook up to your filter pump
– Screws and brackets to fix the hose in place
Step 1: pick a sunny spot.
A flat roof, a shed roof or a south-facing fence. Full sun, all day.
Step 2: lay down the sheet and paint it black.
Black draws heat. A matt black sheet as a base under the hose really adds degrees.
Step 3: lay the hose in a snaking pattern.
Lay the black hose back and forth across the sheet, as close together as possible. Fix it with brackets or clamps so it stays in place.
Step 4: connect to your filter circuit.
Tap off after the filter pump, send the water through your coiled hose and then let it run back into the pool. A T-piece with a small tap lets you adjust how much water passes through.
Step 5: lay a glass sheet over it (optional).
A transparent panel on top catches the heat like a little greenhouse. That lifts your output considerably.
Step 6: set the flow rate.
Let the water flow gently, not too fast. The longer it stays in the hose, the warmer it comes back. Measure with a thermometer at the outlet and adjust your tap.
For a hundred euros of hose and an afternoon’s work you lift your water by a few degrees. For a real hands-on type this is the finest project there is.
Honest downside: DIY is less neat and efficient than proper mats, and you will have to fiddle with it a bit until it runs. But it works, and it costs almost nothing.
Method 4: solar panels plus heat pump (the most efficient)
If you want to be independent of the direct sun, this is where you end up. This is the serious solution.
Watch the difference, because this is where articles often go wrong:
- A solar collector heats the water directly with solar heat.
- Solar panels (PV) make electricity. That electricity drives something else.
So solar panels do not heat your pool themselves. You need a device that turns that electricity into heat. And that is a heat pump.
Why a heat pump is so clever
A pool heat pump draws heat from the outside air and pumps it into your water. The beauty: it delivers far more heat than the electricity it uses.
We express that in the COP, the coefficient of performance. A good pool heat pump has a COP of 5 to 6. That means: 1 kilowatt of electricity in, 5 to 6 kilowatts of heat out.
Feed that electricity with your own solar panels and you heat your pool practically for free. And you do not need 25 square metres of mats in the garden.
This is the most energy-efficient combination there is.
How many panels and what does it cost?
For an average pool you reckon on 6 to 8 solar panels to feed a heat pump properly. If you already have panels on your roof for the house, you run the heat pump on your summer surplus. Even better.
| Component | Price |
|---|---|
| Pool heat pump | 800 to 2,500 euros (small to large pool) |
| Heat pump for large in-ground pool | 4,000 to 6,000 euros |
| Solar panels (6 to 8 units) | 1,500 to 3,000 euros |
Pro: works even when cloudy, extends your season significantly, heats to the exact degree.
Con: highest purchase price. And without your own solar panels it costs electricity, though that stays nicely low thanks to that COP of 5 to 6.
Which method suits you?
Everything at a glance, so you know straight away what to look for.
| Method | Warm-up | Material cost | Energy cost | For whom |
|---|---|---|---|---|
| Pool cover | +4 to 6 degrees | 30 to 150 euros | None | Everyone, always do it |
| Solar collector mats/dome | +5 to 7 degrees | 100 to 1,400 euros | None | Hands-on types with a sunny spot |
| DIY garden hose | +2 to 5 degrees | 50 to 150 euros | None | Real tinkerers |
| Solar panels + heat pump | +8 degrees and more, adjustable | 2,000 to 6,000 euros | Very low (COP 5 to 6) | Anyone who wants weather independence |
My sober advice: start with the cover. Want more, build or buy a collector. Want rock-solid warm water all season, go for the heat pump on solar power.
The filter pump: your indispensable helper
Quickly, something people forget.
With a solar collector your filter pump does the work. It pushes the water through the mats. If the pump does not run, nothing flows and nothing warms up.
So in summer you run that pump longer than usual, easily 8 to 12 hours a day during the sunny hours. During the day when the sun is on your collector, not at night.
Timer on it, done. Set it so the pump runs when the sun shines.
More running hours means more warmed water, but also a little more electricity use from the pump. If you have solar panels, you simply run that pump on your own electricity. Nicely rounded off.
Combining is winning
The secret is not in one method. It is in stacking.
The ideal combo for most people:
Cover + solar collector.
The collector warms your water during the day. The cover holds that heat overnight, so you do not start from zero every morning.
Without a cover you literally pump your heat into the air at night. With a cover you build heat up, day after day.
That is how you climb from a meagre +3 degrees to a solid +8 to +10. That is the difference the combination makes.
Extending your swimming season
With solar energy you stretch the season considerably.
Without heating you swim roughly in June, July and August. Three months, and even then with reluctance at the start.
With a cover and a collector you push that to April through October. Seven months of pleasant water.
With a heat pump on solar power you can stretch it even further, into the colder edges of the season, because it keeps heating even in cloudy weather.
More than a doubling of your swimming pleasure. Mostly on free sunlight.
Maintenance and winterising
Quickly the boring but important bits, because otherwise something freezes and breaks.
During the season
– Keep the mats and hoses clean, rinse away leaves and dirt.
– Check your connections for leaks, especially on DIY builds.
– Keep your filter clean, a dirty filter chokes the flow.
Before winter (winterising)
– Drain all collectors, mats and hoses completely. Water left standing in the hose freezes, expands and splits your material open.
– Disconnect the collector from the filter circuit.
– Store mats and dome frost-free if you can, that extends their lifespan considerably.
– Do not forget your heat pump: it needs winterising too, water out.
Do this properly and your kit lasts for years. Skip it and you buy new next year. Such a waste.
Payback time: what does it return?
Let us be realistic, because this is a pool, not a savings account.
The cover pays for itself in no time. For a few euros you save a mountain of heat loss and evaporation, and you have to top up less. Recouped within one season.
A solar collector or DIY build has no energy costs after purchase. Set that against what electric heating would guzzle in power and you earn it back in a few seasons. DIY even faster, because it costs almost nothing.
The heat pump on solar power is the most expensive purchase, but thanks to that COP of 5 to 6 and your own free electricity the cost per swimming day is very low. Reckon on several seasons before you earn it back, depending on how much you swim.
The real gain, by the way, is not only in euros. It is in those extra months of swimming pleasure and water the kids won’t get out of. You do not put that in a table.
Frequently asked questions
Can you heat a pool with solar panels alone?
Not directly. Solar panels make electricity, not heat. You need a heat pump or a heating element that converts that electricity into warm water. If you want to use sunlight directly as heat, choose a solar collector with black mats or a dome.
What is the cheapest way to heat my pool?
A pool cover, without a doubt. For 30 to 150 euros you gain 4 to 6 degrees and hold the heat at night. If you want to build it yourself, a solar collector made from black garden hose for under 150 euros is the cheapest active heating.
How many degrees warmer does my pool get with solar energy?
Realistically 5 to 10 degrees in a temperate climate, provided you combine methods. A cover plus a well-sized solar collector lifts you from a chilly 20 degrees to a pleasant 26 to 28 degrees.
How big does a solar collector need to be for my pool?
Reckon on 50 to 80 percent of your water surface in collector surface. For a pool of 32 square metres you want 16 to 25 square metres of mats. Take a bit too much rather than too little, otherwise the warm-up disappoints.
Does solar pool heating also work in a temperate climate?
Yes, but be honest about the limits. In sunshine it works fine and you extend your season to April through October. When it is cloudy and at night a collector stands still. If you want to be independent of the weather, a heat pump on solar power is the better choice.
Does my filter pump need to run longer for the collector?
Yes. The filter pump pushes the water through the collector, so no pump means no warming. Run it 8 to 12 hours during the sunny hours in summer, with a timer. On your own solar power that costs you next to nothing.
To finish
Heating a pool with solar energy does not have to be an expensive affair.
Start with a cover, that is the free foundation everything rests on. Want more, build or buy a solar collector and set your filter pump to the sunny hours. And if you dream of warm water all season, put a heat pump on your own solar panels.
Simple tools, common sense, and the sun doing the work.
Want to go deeper into using solar energy cleverly and saving energy around the house and garden? In my energy-saving guide I explain exactly how to crush your consumption with your own solar power, from your pool pump to your whole house.
Good luck. And let me know how warm you get it.
Cheers,
Fred