# How to heat up a swimming pool with the sun

I'm trying to figure out how to heat my pool most efficiently using the sun.

Currently, I've got 2 black panels (made up of a bunch of black pipes) on the roof that the pool pump cycles the water through as part of the normal cycle through the pool filter. That pump uses 0.75kw of power just to pump the water to the roof which seems extremely inefficient if it's for heating water.

So I went and bought a very small pump that pumps the water up to the roof and then through a couple of black pipes before pumping it down.

A couple of questions:

1. The water is cold(by feel right now) when it comes back out with both methods. Would it help if I stop the water with the small pump, wait for it to heat up a bit and cycle? I don't know enough about thermal conductivity to know if heat is transferred more efficiently when water is moving vs standing still as well as the temp of water relative to the plastic pipe being heated by the sun. Edit: ok, I see that the higher the difference in temp, the faster heat flow happens. Still don't understand the part of it being heating up for bot a long time before going back into pool.
2. Assuming I can repurpose the energy used for the pump (from my solar panels) would it make sense to just rather use a 600w heating element and cycle the water through a geyser / container with an element (don't want element in pool for safety)?
3. Anything else that's more efficient?

To add, I've got a thick pvc tarp over it (for kids) and I assume because of the air gap between tarp and water most of the heat is not transferred effectively.

The pool is around 15000 liters and ~2.5*5m (not sure of depth).

• It takes a lot of energy to heat water. Rough dimensions of pool? If the sun is incapable of heating the pool with the pool's large surface area, do you think the sun is capable of heating it with a small surface area. Nov 18 '20 at 16:30
• Good questions, thanks. I'm not aiming to make it super hot, merely a couple degrees to make it a little more comfortable. I'll add to the original question to make it clear but, if the pipes are black my assumption is that instead of reflecting sun it will absorb as opposed to the water surface. Also, I've got a thick pvc tarp on it for safety reasons. Nov 18 '20 at 17:49
• Black tube solar water heating panels exist that one can also walk on, but you need between half to two thirds the surface area of the pool for it to work, so 6 to 8 m^2 of panels. So a flow rate of 6 to 8 l/min. Nov 18 '20 at 18:21
• Thanks @Solar Mike. Any thoughts on my questions? Nov 18 '20 at 19:05
• If the pool is not covered , is is loosing substantial heat by evaporation , also depending on humidity. Nov 18 '20 at 19:24

As a rule of thumb, your solar collector's area should be 60% to 100% of the pool area.

They should be oriented for optimal sun exposure. Many of the home supply stores like Home Depot have the parts and usually a video screen or set of posters giving DIY info. Usually, you wouldn't need a separate pump.

You need a sensor and an automatic valve to bypass the flow of pool water from the panels when the panels are not warm enough. If you plan and install them by the manufacturer's instruction they are very effective. You need a permit from the city.

If you are comfortable with electronics you can use Arduino and an IoT dongle to control the system by your cell phone.

Here is a diagram.

• Thanks for the answer. I've got the setup above apart from the conventional pool heater. Nov 18 '20 at 19:03
• To add, I'm a) extremely curious about the science, specifically the thermal conductivity part and b) cheap so I don't want to spend so much on electricity. I live in a third world country where electricity is getting significantly more expensive year on year and can't justify spending too much money to heat up the pool. Nov 18 '20 at 19:09
• the panels have charts of BTU per daily sun exposure. I think if you take advantage of the fact that warm water rises by planning the layout and using check valves at the right places you don't need any power, just for priming. Nov 18 '20 at 19:22
• Thanks @kamran. From the little I understand about thermal conductivity, you would be using the water to transfer the heat then which would decrease the rate of transfer significantly? Nov 18 '20 at 19:50
• If you are worried about electricity use, design a thermosyphon system - saw one that worked for 20 years... elegant. Nov 19 '20 at 4:49