Undersized Pool Solar...Is it worth it?

joeprunc

Active member
Apr 26, 2021
41
Discovery Bay, CA
Pool Size
20000
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
We are building a pool and have our PB add plumbing for future pool solar (and automation). Pool size is 16 x 35 (with a 8x7 spa and 400kBTU heater). We live in Northern California and have significantly warm days from May-Sept (90s-100s). Most of our neighbors pools warm up sufficiently without any heating to mid to upper 80s by July.

I'm handy and plan on installing plumbing and pool solar myself, the problem is most of my desired roof space is already slated for future "electric solar". Is it worth installing (2) 4'-10' panels on a roof that gets high exposure in the afternoon and early evening (when temps and sun exposure are the hottest)? That is only 7% surface area exposure (absolute minimum recommended by installers is generally 20-25%). I would also couple this with a cheap solar pool cover for spring and fall (to minimize heat loss through the night).

My thoughts are it would only cost be a few hundred dollars and a weekend worth of work. I have to believe any solar heat is better than no solar heat....to help extend my pool season. Currently my neighbor is averaging a 8°F drop through the evening without a cover.

Would you recommend going forward with an undersized system, or just scrap the idea?
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
14,735
Pleasanton, CA
Pool Size
20000
Surface
Plaster
Chlorine
Salt Water Generator
The heat gain is proportional to the surface area of the panels. So if the panels are 80 sq-ft in area, then assuming 1500 BTU/sq-ft (optimistic), the gain per day would be 120k BTU/day. In a 20k pool, that would be about 0.7 deg F. Not much gain. Over the course of several days, that might double on average (heat loss increases too). So it might raise the average temperature of the pool but as much as 2F. Again, not a lot.

However, a cover could boost temps by as much as 10F.
 

joeprunc

Active member
Apr 26, 2021
41
Discovery Bay, CA
Pool Size
20000
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Thank you, yeah 1°F gain per day will not be worth the expense. I'd probably be better off just using the NG heater to extend the pool seasons.

If I do decide to work this, is there any difference in putting panels on a East vs West roof face?
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
14,735
Pleasanton, CA
Pool Size
20000
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Plaster
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West is usually better from the simple fact that the air temperatures are warmer afternoon vs morning so between the two, the efficiency will be higher with western exposure vs eastern exposure.
 
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1poolman1

In The Industry
Jul 14, 2014
170
Sacramento
Anything less than 50% of your total pool area, with conventional solar panels, will be disappointing at best. Conventional sizing says you need 80% even with a good Southern exposure. If you only put in the 2 panels and keep a solar blanket on at all times you may be happy with the result. If you're going to do this yourself, try to leave room for additional panels at a later date.

In Northern California we can gain, with a properly sized array, 5-7 degrees per day and lose 3-5 at night with the nights as cool as they are right now. I installed solar for 10 years before an accident ended that. That was my experience then and the physics hasn't changed.
 

joeprunc

Active member
Apr 26, 2021
41
Discovery Bay, CA
Pool Size
20000
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Thank you for the additional help. I'm looking at my roof and think I can get two groups of 4'-10' panels with a bit of extra plumbing.
I might start out with just the two which will be very simple to run, but leave tie ins for two in the future.

Do the "glazed panels" significantly increase efficiency and worth the extra price tag if undersizing? Looking at SwimLux glazed panels (although they are more than double the price....ouch)
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
14,735
Pleasanton, CA
Pool Size
20000
Surface
Plaster
Chlorine
Salt Water Generator
The glazed panels work better in cold weather but worse in warm weather. They are really meant for winter use. Not worth it IMHO.

Note to get a larger area, you can pretty much put panels where ever there is a flat surface even if it is vertical (with reduced efficiency).
 

mrjetson707

Well-known member
Sep 7, 2021
57
Martinez, California
Pool Size
11000
Surface
Plaster
Chlorine
Liquid Chlorine
We are building a pool and have our PB add plumbing for future pool solar (and automation). Pool size is 16 x 35 (with a 8x7 spa and 400kBTU heater). We live in Northern California and have significantly warm days from May-Sept (90s-100s). Most of our neighbors pools warm up sufficiently without any heating to mid to upper 80s by July.

I'm handy and plan on installing plumbing and pool solar myself, the problem is most of my desired roof space is already slated for future "electric solar". Is it worth installing (2) 4'-10' panels on a roof that gets high exposure in the afternoon and early evening (when temps and sun exposure are the hottest)? That is only 7% surface area exposure (absolute minimum recommended by installers is generally 20-25%). I would also couple this with a cheap solar pool cover for spring and fall (to minimize heat loss through the night).

My thoughts are it would only cost be a few hundred dollars and a weekend worth of work. I have to believe any solar heat is better than no solar heat....to help extend my pool season. Currently my neighbor is averaging a 8°F drop through the evening without a cover.

Would you recommend going forward with an undersized system, or just scrap the idea?
Did you end up getting solar? I'm in a similar situation. also Northern California
 

sktn77a

Gold Supporter
May 16, 2010
2,225
Chapel Hill, NC
I see you are in the Central Valley. My in-laws live in Elk Grove, have a 35,000 gal pool and have solar with eight 4x10 panels. That sucker heats up the pool like nobody's business! In fact, they have to turn it off for 4 months of the summer to prevent the pool getting too warm (mid 90s). They use the pool year round.

I think two 4x10 panels should be sufficient in the shoulder months and maybe beyond (your pool is half the size of their).

Oh, and trust me, you'll quickly get tired of covering and uncovering the pool with a solar cover every day!
 

joeprunc

Active member
Apr 26, 2021
41
Discovery Bay, CA
Pool Size
20000
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Thank you for the insight. My friend who has a 17000 gal pool had (6) 4'X10 panels installed. You are right he had to turn his off for multiple months as well. But now that its getting into the 50s at night his solar during the warmer days is extending his swimming season into Oct.

With all the discussions and threads I've read, I know understand that more panels you put on the longer your season...you can further help with a solar cover, but like you said the cover will be a PITA. With two panels I may be able to extend the swimming season by 2 months, and having the panels really really help in the tail end of the season when the days isn't too hot, and the evening are much cooler (and longer).

I've been looking more and going to see if I can get creative and install a total of 4 panels on two different roof surfaces. Its just the desired roof space on my house will be used for electric solar, and since I'm doing it on my own, I preferred not to have multi sections. Maybe a winter project.
 

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Tcadwall0

Gold Supporter
May 19, 2021
137
Charlotte, NC
Pool Size
12900
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-20
Just to temper the Solar Cover part. With or without solar (or any type of) heat, a solar blanket really helps to keep the heat in the pool overnight. I purchased a solar cover reel on Amazon, and it makes it incredibly easy to put on / remove the cover. Literally, less than 5min for either operation.

My reel has wheels on one end, so that I can move it wherever I need to when not in use, and it spends the summer behind a fence near my pool equipment. I did make a modification for covering the pool. I wrapped a piece of PVC with a pool noodle, and attached it to the 'free' end of the cover. A small rope is used with that to pull the cover onto the pool in one smooth motion.

I know, not every pool has a layout that works well with a solar cover or a solar reel, but the reel does make this a very quick and easy process for many pools.
 

ccbill

Well-known member
Jul 23, 2021
140
Atascadero, Ca
Pool Size
23000
Surface
Plaster
Chlorine
Liquid Chlorine
With regard to the solar cover: I don't find it onerous to remove it but then I've been doing it for 30+ years, cutting it in pieces helps a lot; never tried a reel for it.
Currently my neighbor is averaging a 8°F drop through the evening without a cover.
I currently experience a two degree drop overnight with temps in the high 40's - this cover is the thinnest and on its last legs it will be replaced before spring, I keep the cover on 24/7 it helps quit a bit with evaporation loss and chemical consumption. I'm south of you by about 175 miles.

Boy if I could get 2-3 degrees in the shoulder months I would take it but I haven't looked at costs. I did see some panels on craigslist a couple months ago, I should have snagged them.
 
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