Previous in Forum: Caption This.   Next in Forum: LV Cable
Close
Close
Close
32 comments
Guru
Engineering Fields - Manufacturing Engineering - New Member Hobbies - Target Shooting - New Member United States - Member - New Member Hobbies - Hunting - New Member

Join Date: Dec 2006
Location: Charlotte, NC USA
Posts: 785
Good Answers: 17

Solar In Ground Pool Heater

01/29/2025 4:52 PM

My wife has been bugging me for years about finding a cheap way to heat our in ground pool. I acquired a 340W solar panel, and was thinking that might work. I was thinking about buying a hot water heater element, building a housing, and putting it into my return line from the pool pump. What I’m finding is 2000W elements and similar elements. What would happen if I attached the solar panel to the element, would it produce enough energy to heat the water at all? Also, the box that houses the element would be made out of PVC material, would there be any danger of the PVC melting?

thanks

Laby

__________________
Be careful of what you wish for .....
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#1

Re: Solar In Ground Pool Heater

01/29/2025 5:29 PM

If you want it to actually work you first have to know your pool capacity in gallons...a typical solution would be a designed for purpose heat pump...Depending on how much roof surface you have facing the solar path during the heating months, you could just go with ABS coils on the roof, that would work sometimes... sketchy at best....but probably your cheapest option....

... I would go with a heat pump, if it's too expensive you can always shut it off...also would get a pool cover for when not in use to save heat....

Energy-Saving ComforTemp Pool Heat Pump 80,000 BTU to Heat 15,000 Gallons

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply Score 1 for Good Answer
Guru
Engineering Fields - Manufacturing Engineering - New Member Hobbies - Target Shooting - New Member United States - Member - New Member Hobbies - Hunting - New Member

Join Date: Dec 2006
Location: Charlotte, NC USA
Posts: 785
Good Answers: 17
#2
In reply to #1

Re: Solar In Ground Pool Heater

01/29/2025 5:37 PM

The pool is 12,000 gallons, the filter is 2hp, feeding it through 2” PVC pipe. The flow rate is considerable at 18psi. So I don’t see coils on the roof as an option, but I could be wrong.

__________________
Be careful of what you wish for .....
Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#3
In reply to #2

Re: Solar In Ground Pool Heater

01/29/2025 6:19 PM

Typically the line in feeds a header set up...

A parallel rather than series arrangement... then you engineer the number of coils to match the circulation flow for maximum heat gain...

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply Score 1 for Good Answer
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#4
In reply to #3

Re: Solar In Ground Pool Heater

01/29/2025 6:37 PM
__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#5
In reply to #4

Re: Solar In Ground Pool Heater

01/29/2025 7:24 PM
__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply
Power-User

Join Date: Apr 2007
Posts: 236
Good Answers: 13
#16
In reply to #3

Re: Solar In Ground Pool Heater

01/30/2025 11:51 PM

OK, how did that end up with an odd number of hoses?

Register to Reply
Guru

Join Date: Oct 2006
Location: 44.56024"N 15.307971E
Posts: 7806
Good Answers: 264
#17
In reply to #16

Re: Solar In Ground Pool Heater

01/31/2025 4:00 AM

Entry end of manifold not seen (got'ta have a supply hose)

__________________
"A man never stands so tall as when he stoops to help a child." "Never argue with a stupid person.They will drag you down to their level and beat you with experience" "Homo homini lupus"
Register to Reply
Power-User

Join Date: Apr 2007
Posts: 236
Good Answers: 13
#26
In reply to #17

Re: Solar In Ground Pool Heater

02/03/2025 10:48 PM

Gotta have an exit, too!

Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#19
In reply to #16

Re: Solar In Ground Pool Heater

01/31/2025 5:55 PM

Obviously one hose is yet to be installed....

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply Score 1 for Good Answer
3
Guru

Join Date: Jul 2016
Posts: 1246
Good Answers: 90
#6

Re: Solar In Ground Pool Heater

01/30/2025 1:45 AM

Your solar panel will on a good day produce 340 Watts for about 6 hours. That's about 7,000 BTUH per day. So that's about 840 gallons of water heated 1 Degree F.

You will want a heater element that matches your voltage, so that your panel delivers the power, at about 38 volts you will get 9 amperes. So your heater will be about 4.2 ohms. A 4500 watt heater at 240V is about 13 ohms. So if you put 3 in parallel, you should be able to load down your panel, directly connected.

Normally you would interlock the heat with the flow, but in this case convection will probably keep everything from getting too hot.

Loss due to evaporation is shown here https://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html

Register to Reply Good Answer (Score 3)
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32049
Good Answers: 838
#31
In reply to #6

Re: Solar In Ground Pool Heater

02/05/2025 10:04 AM

<...840 gallons of water heated 1 Degree F...>

...or 12,000 <...gallons heated by...> 0.07 <...Degree F...>, of course.

No wonder someone <...has been bugging...for years about finding a cheap way to heat...ground pool...>!

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: May 2018
Location: Under the spreading Bunya Trees, South Burnett, Queensland, Australia
Posts: 759
Good Answers: 64
#7

Re: Solar In Ground Pool Heater

01/30/2025 5:20 AM

Why not scout around for more replaced panels. Here superseded panels of 250 to 300W can be bought for $20 to $30. All you need is enough panels connected in series to give you the current and voltage you need for the immersion heater.

I have a many panels which I was given to save the contractor paying the dumping fee when a 5KW system was replaced. You may be as fortunate as I was in your neck of the woods. Happy hunting.

Just work on the full load current not the open circuit voltage when designing your system. A simple frame of galvanised angle will make an excellent mounting platform. A pile of tek screws and you are away.

__________________
Hare today, goon tomorrow!
Register to Reply
Guru

Join Date: Oct 2006
Location: 44.56024"N 15.307971E
Posts: 7806
Good Answers: 264
#9
In reply to #7

Re: Solar In Ground Pool Heater

01/30/2025 8:45 AM

Before you connect anything electrical to or near a swimming pool, observe the local and national electrical code rules on this. A voltage gradient can develop across the water, even from one fingertip to another on outstretched arms. A very small difference in potential can be very dangerous on a wet or submerged body; From a metal handrail to the water, or the concrete surrounding the pool are just two examples.

Be VERY careful!

An alternative method to heat the pool is to use the pool as a heat sink for your heat pump in the summer, and using the stored heat extracted from the pool in the winter to heat your home. A 3ton unit is 36000 BTU per hour, and you could switch it to air exchange mode if the water became too hot in the summer. Is there a pond or lake nearby that could be used as a heat sink/source? Consult a local HVAC expert for guidance on this method.

It takes 1 BTU to increase the temperature of 1 pound of water by 1degree F.

Water weighs about 8.34 pounds per gallon, so you have 23000 gallons X8.34= 191820 pounds of water.1BTU per pound per degree will take 191820 BTU.

A 3ton heat pump will take about 5.3 hours to raise temperature 1 degree F. Actually it will take longer considering system losses.

Now you have an idea of how much heat it will take to heat your pool. to your desired temperature.

__________________
"A man never stands so tall as when he stoops to help a child." "Never argue with a stupid person.They will drag you down to their level and beat you with experience" "Homo homini lupus"
Register to Reply Score 1 for Good Answer
3
Guru

Join Date: Apr 2010
Location: About 4000 miles from the center of the earth (+/-100 mi)
Posts: 9725
Good Answers: 1118
#8

Re: Solar In Ground Pool Heater

01/30/2025 8:40 AM

My wife has been bugging me for years about finding a cheap way to heat our in ground pool.

Why not go directly from sunshine to heat?

Register to Reply Good Answer (Score 3)
Guru
Engineering Fields - Manufacturing Engineering - New Member Hobbies - Target Shooting - New Member United States - Member - New Member Hobbies - Hunting - New Member

Join Date: Dec 2006
Location: Charlotte, NC USA
Posts: 785
Good Answers: 17
#12
In reply to #8

Re: Solar In Ground Pool Heater

01/30/2025 11:08 AM

I have one, but they are bulky, hard to store, takes time putting it on and off and heats the pool about 10 degrees F for a week of covering. I also have fountains on the side making a rolling storage impossible.

But thank you for your response.

__________________
Be careful of what you wish for .....
Register to Reply Score 1 for Good Answer
Guru

Join Date: Apr 2010
Location: About 4000 miles from the center of the earth (+/-100 mi)
Posts: 9725
Good Answers: 1118
#13
In reply to #12

Re: Solar In Ground Pool Heater

01/30/2025 11:45 AM

My parents had a pool in the backyard with a gas heater. (This was long before solar panels.) They had a plastic bubble over the pool, which kept the temperature inside good for swimming, even in the wintertime.

Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#10

Re: Solar In Ground Pool Heater

01/30/2025 8:55 AM

The pv solar panels have a low conversion rate, better efficiency can be achieved with direct thermal transfer...

..."When comparing the efficiency of photovoltaic (PV) solar panels to solar thermal systems, solar thermal panels are generally considered significantly more efficient at converting sunlight into usable energy, with typical efficiencies around 70% compared to PV panels which usually reach only 15-20% efficiency. "....

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply Score 1 for Good Answer
Member

Join Date: Mar 2018
Posts: 7
#11

Re: Solar In Ground Pool Heater

01/30/2025 8:56 AM

Solar thermal panels are significantly more efficient than solar photovoltaic (PV) panels, with an efficiency rate typically ranging from 70% to 80% at converting sunlight into heat, compared to the 15-20% efficiency of PV panels which convert sunlight into electricity.

Register to Reply
3
Guru
Hobbies - DIY Welding - Wannabeabettawelda

Join Date: May 2007
Location: Annapolis, Maryland
Posts: 7860
Good Answers: 452
#14

Re: Solar In Ground Pool Heater

01/30/2025 5:48 PM

One of my co-workers here in Maryland added a flat-plate heat exchanger to his air-conditioning condenser unit and heats his pool while he air-conditions his house. I believe he has a separate pumped loop, not part of the filtration system. Not only does it heat his pool for little extra energy consumption, he increased the efficiency of his central A/C.

Register to Reply Good Answer (Score 3)
Guru
Hobbies - DIY Welding - Wannabeabettawelda

Join Date: May 2007
Location: Annapolis, Maryland
Posts: 7860
Good Answers: 452
#28
In reply to #14

Re: Solar In Ground Pool Heater

02/03/2025 11:01 PM

It looks like I may have been mistaken about my co-worker's pool heater. It doesn't look like a flat-plate heat exchanger (first error) and the heat exchanger does appear to be in the filtration loop (second error). I should have talked to him first before running my mouth.

He told me this was the kit was used for his pool. He has been using it for 10 years and is a happy customer.

https://www.hotspotenergy.com/pool-heater/

Cheers !

Register to Reply
Power-User

Join Date: Apr 2007
Posts: 236
Good Answers: 13
#15

Re: Solar In Ground Pool Heater

01/30/2025 11:48 PM

I've been battling pool heating for years. Never bothered with the idea of photovoltaic cells, too inefficient.

Heating black poly pipe works well, but has some problems:

1. It requires a lot of space. The amount of heat gain in your pool will depend upon the ratio of the pool surface area to the surface area of your poly pipe layout (of course, pool depth is a factor, but you can't change that). Pipe size doesn't really matter; water moving slowly through a large pipe vs water moving quickly through a longer small pipe, it still comes down to the surface area of pipe that is exposed to sunlight.

2. The direction of the sunlight plays a role. If you put your pipe on a roof, it helps if the roof is angled toward the sun (facing south in the northern hemisphere.

3. The poly pipe will work more efficiently if you can enclose it under glass or clear acrylic sheet. However, this means that you'll have to clean it and it would be subject to damage from hail (both significant problems where I live).

4. The biggest problem with poly pipe is movement. It expands and contracts a lot. If you put it on a roof, it need to be secured or it will 'walk' right off the roof. Even if secured, it will ruin shingles (ask me how I know). I ended up putting mine on the ground, which allowed for movement, but the barbed connectors that were available at the time were always coming apart. At least once a week I'd come home from work to find half my water drained out in the yard. Another problem with putting the pipe on the ground is that you have to mow (weed eat) grass and weeds that grow up through the pipe coils.

My next attempt will include putting a poly pipe grid on the metal roof of my barn. It's pretty flat, and I've figured out a way to secure the pipe that will allow some movement, but keep it from walking very far. I think the new SharkBite connectors will provide a more secure connection than the old barbed ones.

My plan will incorporate a large black poly tank(s) with about 2000 gallons capacity. I will operate the solar collector in a loop to heat water in the tank during the day. I typically swim in the late afternoon or evening, so I would reset the valves to circulate the hot water into the pool before use.

Register to Reply
Active Contributor

Join Date: Jun 2019
Posts: 15
#18

Re: Solar In Ground Pool Heater

01/31/2025 5:10 PM

Some interesting answers in there but I have one thought. How about putting some black cover (plastic/bed sheets/whatever in the bottom of the pool to absorb heat. Then cover at night to reduce heat loss. Could roll it up to one side if you want the normal color.

Still have the problem of not a lot of gain per day but much less hassle and cost. Not pretty either but you could pretend you are swimming in space.

Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#20
In reply to #18

Re: Solar In Ground Pool Heater

01/31/2025 6:05 PM

I had a buddy once that painted the bottom of his pool flat black, he claimed it worked, but in all honesty it was not attractive at all...

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply
Guru
Hobbies - DIY Welding - Wannabeabettawelda

Join Date: May 2007
Location: Annapolis, Maryland
Posts: 7860
Good Answers: 452
#21
In reply to #20

Re: Solar In Ground Pool Heater

01/31/2025 11:44 PM

Most of the sun's energy is absorbed by the water. If the water were very shallow, then the black paint might help some.

https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water#/media/File:Absorption_spectrum_of_liquid_water.png

Register to Reply
Guru
Hobbies - DIY Welding - Wannabeabettawelda

Join Date: May 2007
Location: Annapolis, Maryland
Posts: 7860
Good Answers: 452
#22
In reply to #20

Re: Solar In Ground Pool Heater

02/01/2025 12:03 AM

https://sunwindsolar.com/blog/solar-radiation-spectrum/

Here are some graphics that illustrate the issue pretty well.

And then the spectral absorption of water:

Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#23
In reply to #22

Re: Solar In Ground Pool Heater

02/01/2025 12:49 AM

He's in North Carolina, not going to have enough solar heating without some assistance...

..."In Raleigh, for example, the noon solar elevation is 78° on June 21, whereas it is only 31° on December 21..."

..."Solar insolation in Raleigh, NC, peaks around 800 W/m² during the summer solstice and drops to 300 W/m² during the winter solstice, with moderate levels around 600 W/m² during the equinoxes."...

It would help to have the solar thermal array facing the Sun directly, and also to be an area probably 1.5 times the surface area of the pool, so a bit larger than here in the south....

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply Score 1 for Good Answer
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#24
In reply to #23

Re: Solar In Ground Pool Heater

02/01/2025 10:06 PM

It takes 49.4 watts to heat a gallon of water by 20 degrees Fahrenheit in one hour....

340 watts would be about 7 gallons...however that is maximum output in ideal conditions and ignoring losses....we could assume 1/2 that in reality....

13,000 gallons divided by 3.5 = 3714

Yeah I'd go with a heat pump...or you could go with a waste oil heater or diesel heater or wood burning heater...

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply Score 1 for Good Answer
Guru
Hobbies - DIY Welding - Wannabeabettawelda

Join Date: May 2007
Location: Annapolis, Maryland
Posts: 7860
Good Answers: 452
#25
In reply to #24

Re: Solar In Ground Pool Heater

02/03/2025 10:33 PM

Or a tire burning heater from TCMtech?

Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#29
In reply to #25

Re: Solar In Ground Pool Heater

02/03/2025 11:41 PM

Ha ha sure...

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply Score 1 for Good Answer
Guru
Hobbies - DIY Welding - Wannabeabettawelda

Join Date: May 2007
Location: Annapolis, Maryland
Posts: 7860
Good Answers: 452
#30
In reply to #29

Re: Solar In Ground Pool Heater

02/04/2025 4:14 PM

Register to Reply Off Topic (Score 5)
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32049
Good Answers: 838
#32
In reply to #25

Re: Solar In Ground Pool Heater

02/05/2025 10:15 AM

...or KrisDel?

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Power-User

Join Date: Apr 2007
Posts: 236
Good Answers: 13
#27
In reply to #20

Re: Solar In Ground Pool Heater

02/03/2025 10:57 PM

I also had a friend with a black bottom pool. Well, it started that way, but after a year or two is was just an ugly gray.

Forgot--on the solar covers, they are not nearly as effective as many people think. They heat the water at the surface, but after you get down about 6 inches, the water is cold. They also blow off in windy areas. I had to retrieve mine from the neighbor's yard a number of times.

Register to Reply
Register to Reply 32 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

Brave Sir Robin (6); DinosaurDad (1); HiTekRedNek (2); Labyguy (2); PWSlack (2); rgupta36 (1); Rixter (2); rwilliams (1); SolarEagle (10); Stef (1); steve45 (4)

Previous in Forum: Caption This.   Next in Forum: LV Cable

Advertisement