Undersized Pool Solar...Is it worth it?

joeprunc

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Apr 26, 2021
77
Discovery Bay, CA
Pool Size
20000
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Salt Water Generator
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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

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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

Well-known member
Apr 26, 2021
77
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

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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
2,908
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

Well-known member
Apr 26, 2021
77
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

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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
107
Martinez, California
Pool Size
11000
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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
2,482
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

Well-known member
Apr 26, 2021
77
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

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May 19, 2021
206
Charlotte, NC
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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.
 
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ccbill

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Jul 23, 2021
182
Atascadero, Ca
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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.
 

joeprunc

Well-known member
Apr 26, 2021
77
Discovery Bay, CA
Pool Size
20000
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Bringing this thread back up.

So we are enjoying our first season with our pool. I've had a solar cover on our pool since late March, and am quite happy with the $200 investment. In May our pool was reaching 85F-88F, and now mid June its getting too hot...so I need to remove the cover more often to keep the pool temps from crossing 90F. Unfortunately, I'm out of the house for work from 4:30AM till 5:00PM every so removing the cover for the day isn't an option. I'm finding with our late spring and summer weather, our pool gets hot enough on the hot days, but not enough on the cooler days (when the cover is off all day and night). Therefore my idea of installing 20% solar is back on the table, I already have plumbing, automation, and a intelli valve for solar setup., and I'm thinking the solar would allow me to maintain the desired 1F-3F bump in the peak season, control from getting too hot, and remove the ugly cover.

I've got a few projects around the house before I get to this, but wanted to see if my silly justification makes sense.
 

mas985

TFP Expert
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May 3, 2007
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Pleasanton, CA
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As long as you don't expect too much from the panels. My panels are currently, had more previously, about %20 of pool area and it is enough to add a couple degrees so a few more swim days.
 

joeprunc

Well-known member
Apr 26, 2021
77
Discovery Bay, CA
Pool Size
20000
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
<<<<HELP NEEDED>>>>

The panels arrived and I plan on starting the process of install.... however looking at the plumbing diagrams and need some guidance.

The pool builder installed an Intellivalve 3 way right after my filter with a stub & a stub return for me to plumb for solar. There is no room for a check valve between the filter and 3way without significant piping modifications. How am I going to make sure that my solar doesn't drain through my filter and into my pool?

Most Solar plumbing diagrams "online" recommend a check valve before the 3 way valve.
  1. With an automated valve, do I need the check valve between the filter and 3way valve? Do I need to wire or program this valve appropriately to "close solar" when the filter pump stops?
  2. Should I install a check valve between the 3 way valve and solar collector inlet to eliminate the back flow to filter from the inlet side?
  3. How will I keep the return of the panels from draining backwards when the pump stops?

(here's an early picture during our build)
1658325541623.png
 

mas985

TFP Expert
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You only need a check valve right after the filter and before the solar valve. This will prevent water from drain backwards through the filter from either the supply side or the return side.

Some also add a check valve on the return plumbing before it ties back into the pad plumbing. This check valve helps prevent the panels from filling with water when the solar valve is off.

Similar to this:

1658329895457.png
 

joeprunc

Well-known member
Apr 26, 2021
77
Discovery Bay, CA
Pool Size
20000
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
You only need a check valve right after the filter and before the solar valve. This will prevent water from drain backwards through the filter from either the supply side or the return side.

Some also add a check valve on the return plumbing before it ties back into the pad plumbing. This check valve helps prevent the panels from filling with water when the solar valve is off.

Similar to this:

View attachment 438147
I've seen that in multiple diagrams....I guess what I'm asking is can I omit this check valve, or put a check valves somewhere else (like between pump and filter), due to the fact that I do not have space for it....or do I have to rework all my piping?
 

1poolman1

In The Industry
Jul 14, 2014
2,908
Sacramento
Don't omit the check valve in the return-from-solar plumbing. While it should be as close the the equipment as possible, it can be virtually anywhere in the line coming off the roof. The big concern is that any water back-filling that line up to the check valve can freeze in winter. Without the valve, the panels can fill in reverse and they will freeze faster. That gets very expensive.
 

joeprunc

Well-known member
Apr 26, 2021
77
Discovery Bay, CA
Pool Size
20000
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Don't omit the check valve in the return-from-solar plumbing. While it should be as close the the equipment as possible, it can be virtually anywhere in the line coming off the roof. The big concern is that any water back-filling that line up to the check valve can freeze in winter. Without the valve, the panels can fill in reverse and they will freeze faster. That gets very expensive.
I will have a check valve from solar return to main piping, as well as manual jandy valves. However this will not restrict back flow when pump is off.

My existing plan was per below
1658352422583.png
 

tphaggerty

LifeTime Supporter
Jun 27, 2007
231
Poughquag, NY
I don’t have a check valve on the solar return, just on the pump side. And we didn’t put one on my neighbor’s system (3 4x12 panels for a 15k above ground so “undersized “ as well, but they love it, easily keeps their pool 5 to 8 degrees warmer). I air purge all of my lines when winterizing, so no concern about water freezing in them. I’m not sure how panels could fill in reverse if you have a properly operating 3 way valve.

Do make sure that the panels are slightly tilted so that the water flows to the highest point before returning. This ensures that all of the air is purged from the panels when they start up. Very important, if any of the panels get air bound, you don’t get any heat from them.

And cover the pool at night!!! This is key to solar happiness, especially in climates like NY that get colder at night and in drier climates to prevent evaporative cooling. If you don’t want to cover, it really isn’t worth doing solar (IMO !!).
 

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