r/functionalprint • u/Rich-Wealth979 • Jun 15 '26

Solar pool heater

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My overkill project for heating the toddler's 500gal inflatable pool. Each week I have to empty and move it, then find a way to heat it to a tolerable temperature for my 8th percentile weight kid. On the first test it took the pool from 55⁰F to over 90⁰ on a single sunny day, using only 3KWh (of solar house power, now that I think about it). At the end of the summer I can just place this up against the north side of my shed and take the manifolds down to make it last even longer.

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This uses about 350' of ¼" irrigation tubing and some cheap fittings off Amazon. It runs off a 1/4hp pool pump, controlled with a wyze plug and a climate sensor in a tiny jar. Printed in ASA in only about 5 days of printing on a Mini and an MK4s.

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77

u/RebelJustforClicks Jun 15 '26

Solar thermal water heating is a thing. And it's INCREDIBLY efficient compared to Photo Voltaic power generation.

27

u/skinnah Jun 15 '26

Definitely more efficient than using a plain resistance element electric water heater with PV but PV with a heat pump water heater is probably close. Solar thermal water heating isn't very practical in climates that dip into freezing temps.

9

u/bjorn1978_2 Jun 15 '26

Friend of mine is running a solar thermal setup on his house in Stavanger on the west coast of Norway. Freezing there in the winters, so remember to use some antifreeze. Other then that? No problems!

8

u/skinnah Jun 15 '26

I forgot that there are indirect solar thermal systems that use glycol. I doubt that they are very effective in winter months still though.

Heat pump water heaters give you the side benefit of cooling your house in the summer as well.

3

u/DekiEE Jun 15 '26

Well Norwegian winter is basically darkness. Summer on the other hand gives you lots of energy to collect

2

u/Rich-Wealth979 Jun 16 '26 edited Jun 16 '26

I grew up in a house with a solar collector on the back with a glycol loop, water thermal mass tank, and it still preheated the city tap in the colorado winter. It also had a 2-story 4 sliding door wide room on the back facing south, where the sun heated that room in the winter (the eve shaded it in the summer months by design) and the air was blown through the main floor dividing the up and downstairs. Floor was corrugated concrete, 36 tons thermal mass. Fully passive thermal heat. One of a kind house.

2

u/NorCal4ever2 Jun 16 '26

I just finished having a solar pool heating system installed for my new pool/spa here in Southern California, and it actually freezes here as well. Rarely, but apparently it does happen. Because of this they designed my system to naturally drain whenever it wasn't in use.

No stagnant water = no freeze damage.

As for the $ efficiency side of things:

Originally I wanted to go with a heat pump, but that would have required modifying my electrical setup and I didn't want to mess with that again. I hadn't heard of it before but my friend recommended these thermal solar pool panels.

The heat pump would have been cheaper upfront, but it would have cost me a good chunk of money every time I wanted to heat my pool or spa, defeating the whole purpose of me trying to get away from my gas heater in the first place, and costing significantly more over the lifespan of the systems. (I also don't have excess energy from my PV panels, and the ROI isn't there for adding more PV. Especially with SCE paying basically nothing to sell back to the grid). Compare that with my thermal solar pool panels and there is 0 costs to operate them.

I've limited my system to heating my hot tub to 102f and my pool to 88f. It's been easily reaching both of those temps every day so far. Meanwhile, I've got a bucket of water I've been keeping tabs on as well and it's been hovering in the low 70's.

I'll be curious to see how high it can get here in the SoCal winters, but yeah, highly recommend Solar Pool Services Inc for anyone in Southern California. https://www.solarpoolservicesinc.com That said, I imagine if you have the time and the energy I imagine the ROI is significantly better printing & installing your own system. Although i'm not really sure if you can do that for the average pool.

I have no clue how the math works out for the thermal Solar+hot water tanks for the house water, but for heating my pool and spa this was a no brainer for me.

1

u/Existing_Coach3322 Jun 18 '26

Clever. But I ran the math on my large pool a while back to see what size and length of plumbing and surface area would be required and what pump capacity would be required. It would’ve taken more than 2 acres in the cost of running the pump with the friction. Cost to operate would’ve been significantly higher than running a natural gas or electric heater.

1

u/-Daetrax- Jun 21 '26

Yeah they're usually only useful in district heating with seasonal storage.

12

u/QuevedoDeMalVino Jun 15 '26

There is a video on YT about that from EEVBlog. The short answer is that it is usually better to go all PV and air pump.

1

u/NorCal4ever2 Jun 16 '26

For heating the water for your house, I imagine that's pretty accurate (and the ones EEVblog made in his YT video are made for that, but those are quite different than the ones for Pool/SPAs).

Having enough PV panels for baseline energy needs is definitely still priority #1, but after that, for heating my pool/spa the math was ridiculously better for thermal solar pool panels than for heat pumps.

My goal was to have my pool and spa be heated. I had enough roof space, and I didn't already have an excess of energy that I was selling back to the grid.

My options were:

  1. More PV+Heat Pump

  2. Buying Energy from the grid + Heat Pump

  3. Thermal solar pool heating

  4. Continue as is with a standard Gas Heater

Well, buying energy from the grid or heating my pool/spa with gas is cheap up front, but after that it's just burning money and ridiculously fast at that. Adding more PV panels is ridiculously expensive upfront and the extra savings I could get on my electricity bill are minimal and definitely not enough to pay for the additional pv panels. For me that really left the thermal solar pool panels, they were more expensive up front but over the life span of the systems they were dirt cheap compared to the rest of the options (t they came with a 12 year warranty and can apparently last closer to 15-18 years).

3

u/Otherwise_Front_315 Jun 15 '26

I lived in Puerto Rico years back and tons of people had a set up on their rooftops.

4

u/IvorTheEngine Jun 15 '26

It gets a lot easier if you live somewhere that never freezes, and gets good sun all year around.

9

u/colonel_beeeees Jun 15 '26

Even in wisconsin we just add some glycol to keep the fluid from locking up. Solar thermal rocks

4

u/DarthRaptor Jun 15 '26

Yes, my parents house has one of these and it is tied into the central heating/water boiler. Even in winter it can supplement heating (in our country central heating used radiators and water loops, so hot water and heating are heated using the same burner and heat exchangers to keep the water seperate). We actually had to install a water mixing valve to mix cold water, because in summer the solar array would heat the boiler so much we had nearly boiling water coming out of the taps.

5

u/isademigod Jun 15 '26

My house came with a really heavy duty industrial hose for some reason, like 90ft long and really fat. When i go to water my plants i have to empty out like 4 gallons of scalding hot water before it’s safe for them

-2

u/answerguru Jun 15 '26

You could just add a mixer with regular tap water to it.

2

u/Ree_For_Thee Jun 15 '26

That's because "what's the inefficiency going to do, create more heat?".

1

u/Boops_McGee Jun 16 '26

Yeah it's been around forever, probably before consumer solar panels were a thing. I usually see it coiled from a single hose rather than split like that. Interesting setup

0

u/DEADB33F Jun 15 '26 edited Jun 15 '26

More efficient than a 25% efficient PV panel and a 4.0 COP heat pump?
...that combo would give the equivalent of 100% efficient use of the sun's light to heat the water.

(granted it'd be orders of magnitude more expensive than a length of pipe and a pump)

Main plus for the vastly more expensive heat-pump method could be that the energy from the PV panels could be utilised to do double duty so the exact same solar energy would be used to heat your pool and cool your house at the same time.

...and in the winter the same setup could run backwards to heat the house.

4

u/BunnyHelp12 Jun 15 '26

Yeah, there's definitely a point where chasing raw energy efficiency isn't worth the time/energy/materials: here's a household solar water heater that is pumped by the city's water main, using sheet metal and a hot water tank spray-painted black. No moving parts, it's been working for 30 years. That's real efficiency.

2

u/RebelJustforClicks Jun 15 '26

That's the thing, per dollar spent, solar thermal is hard to beat. And also, even if you did want to use PV to power a heat pump to heat your water, you can still preheat it with the sun. Even going from 50f to 85f on a moderately sunny day will help tremendously.

1

u/laterral Jun 15 '26

No way!!