Pool solar on a north facing roof nor-cal

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CaptainCannonball

CaptainCannonball

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May 18, 2016
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Woodland, Ca
So we just completed our second pool build and we have basically committed to installing solar for pool heating. Unfortunately, or fortunately, depending on how you look at it, our only available roof space is north facing due to our PV solar on the south roof. I've taken a close look at the roof angle (~23deg) and sun angles through the months where we would actually need the heat and am fairly confident in the benefits.

I do worry that this may end up being a waste of money compared to a traditional gas heater or even a heat pump. My pool builder balked at the heat pump idea stating "our humidity is too low for it to be effective." When I looked at the trends for early spring and late fall the humidity was much higher than middle of the summer.

Anyway, on to what has me a little hesitant. I have determined that the best fit for us is the Heliocol panels and as I'm reading the installation manual, it very specifically says not to instal on a north facing roof. The pool is about 550sq/ft and the proposed solar is 550sq/ft.

Does anybody have have any experience with this?

Thanks in advance for any help, advise or comments you have.
 
Welcome to TFP :)
Installing on north facing roof will not work like you want it to... Really the only thing it will pick up is ambiant air temp, so if the roof is 100 degrees it might pick up some of that heat.. they need direct sunlight just like you PV cells on the south side...

I don't know if you have the room but some use pergolas or a pool house to place them on or even the ground will work, you need direct sunlight on them and the longer it stay's in the sun the better.

I hope this helps :)
 
Unfortunately that north roof is really my only option. The panels will get sun, as the roof isn't in shade. As an example, in the middle of April, the panels would be in sun from 8am-4pm. Now granted in the early and late hours it would only be a few degrees, but from 10am-1pm the sun is at 60deg or greater elevation while the panels are at -23deg giving almost 40 degree exposure.

I am am pretty far from an expert on this, but that would seem to suggest about half the exposure of a panel placed +23deg. I dunno, I thought I read somewhere on the interwebs that with pool solar the angles weren't as critical as with PV systems.

I appreciate you taking the time to reply and thanks for for the welcome to the site, I've actually been quite an avid reader in the past with my last pool and decided it was time to "ante up" with a supporting membership.
 
The energy capture of the panels is proportional the cosine of the incident angle. So if the roof angle is 23 degrees and the sun's elevation is 60 degrees (30 from ground normal), the incident angle on the panels would be 53 degrees off panel normal and the effective loss of area is 40%. But if the panels were on the south side of the house, the angle would be 7 degrees and very little loss of area. So your 550 sq-ft of panels would be about the same as 330 sq-ft of panels on the south of the house. Still not bad.

I used to have 440 sq-ft of panels on the front of the house (SSW), and for a couple reasons, I just moved them to the NWW side of the house and dropped the size down to about 140 sq-ft of panel and yesterday my water was 86F. Of course we had two days of really hot weather too but still, not bad performance. My point is that you don't need all that much area to add heat to the pool, especially in your location. But the key is to use a solar cover, especially in CA. The higher water temps increases evaporation and with water restrictions, you will need to have a cover.

It is a little involved but I have a heat transfer spreadsheet (in sig) that can be used to compare installation locations.
 
mas985 said:
I used to have 440 sq-ft of panels on the front of the house (SSW), and for a couple reasons, I just moved them to the NWW side of the house and dropped the size down to about 140 sq-ft of panel and yesterday my water was 86F. Of course we had two days of really hot weather too but still, not bad performance. My point is that you don't need all that much area to add heat to the pool, especially in your location. But the key is to use a solar cover, especially in CA. The higher water temps increases evaporation and with water restrictions, you will need to have a cover
Click to expand...

On our last pool, in a similar geographic location, we had four 2x20 Fafco panels mounted to our fence along with a cover. The results were pretty obscene with consistent mid 90's throughout the summer. We aren't really looking for that, in fact our primary motivation was to eliminate the cover.

Thank you you very much for your expertise. I appreciate you dumbing it down for me with the 330sq/ft comparison. At that, it seems to be sized close to the 60% that all the solar folks recommend. If you don't mind me asking, why did you decide to reduce the size and move your panels? We have been around 82 with these warm days but dear wife expects 85 minimum for her swimming pleasure.
 
I moved the panels because

A) They were on the front of house and bit of an eye sore.

B) They had come loose after a number high wind storms so they required repair anyway.

C) I found that the panels were on for only an hour or two each day, with a cover, so I really didn't need the full surface area.

D) I really wanted to try and run the panels on low speed of a two speed pump and lowering the elevation would help accomplish that although I could have done that by lowering the VRV but at the time I did not have a controller that supported priming at high speed and then running at low speed.

I would not have done it for any one of the reasons but for all four, I decided it was worth it and the results were better than I had expected. I lowered the panels to 6' above the ground and to a somewhat sheltered area so there is not as much wind heat loss as there is on top of the house so a bit better performance per sq-ft than I had before.


However, you really should reconsider a pool cover. Remember CA is still under drought restrictions and because of the elevated water temperatures with solar, without a solar cover, evaporation will be very high and you will lose a lot of water and may even cost you fine if your city does that. Plus without a cover, you will get 6-8 degree water temperature swings during the day because of the heat loss at night. Yes you can compensate with more panels but you need to run your pump longer and at higher speeds ($$$) to accomplish that. So for the sake of both energy and water conservation, a solar cover is really worth it.
 
A solar controller is also key to success with solar so that the valve is only open when solar heat is available. Your solar panels are also very efficient pool coolers if they run when there is no sun on the panels, in rain, wind, etc. The sun is at an odd angle for us right now and I need to do some tree trimming but my solar temp sensor was in the sun and most of the panels were in the shade and my water temp dropped something like 8 degrees in a few hours. Very annoying!

Welcome to TFP and thanks for supporting TFP!

+1 to 85° and higher water! :thumleft:
 
I live in Gold River so I'm close to woodland. Half my panels face north. Does it affect performance? Yes.

Keeping the pool covered is critical.

Towards the end of September no matter how hot the day the pool does not heat up as fast. So I don't get that much extra swim season. But if you like a warm pool they are fantastic.
 
mas985 said:
However, you really should reconsider a pool cover.
Click to expand...

I will, my neighbor actually gave me his new solar cover that he never installed. I'm starting to wish I would have just paid the 16k for an auto cover. Even if you have the money, it's hard to justify a cover that costs as much as a new car.:D

- - - Updated - - -

pooldv said:
A solar controller is also key to success with solar so that the valve is only open when solar heat is available.
Click to expand...

I definitely agree, from what I was told, my aqualink rs is capable of controlling the solar with the addition of a temp sensor and actuator. I'll pay close attention to sensor placement.
 

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Post number 4 by mas985 helped seal the deal for me and helped me pull the trigger. Given the information I provided about my roof angle he was able to predict about a 40% reduction in effectiveness. The numbers that Heliocol tout are close to the btus provided after factoring in 60% effectiveness of my system. I've spent more energy than I care to admit verifying this by accurately measuring flow and temp rise, especially since Mark nailed it almost exactly with a few strokes of the keyboard. :)

Take a close look at the angle of your roof vs. the angle of the sun. I strongly recommend the Heliocol panels because I believe they do a better job of absorbing not only direct solar energy, but also radiant energy given their separated tube design.

Since I'm no longer a shamed closeted non solar cover user, I can tell you that even with no cover and the "cold" spell over the last week, our pool is at 82.
 
mas985 said:
The energy capture of the panels is proportional the cosine of the incident angle. So if the roof angle is 23 degrees and the sun's elevation is 60 degrees (30 from ground normal), the incident angle on the panels would be 53 degrees off panel normal and the effective loss of area is 40%. But if the panels were on the south side of the house, the angle would be 7 degrees and very little loss of area. So your 550 sq-ft of panels would be about the same as 330 sq-ft of panels on the south of the house. Still not bad.

I used to have 440 sq-ft of panels on the front of the house (SSW), and for a couple reasons, I just moved them to the NWW side of the house and dropped the size down to about 140 sq-ft of panel and yesterday my water was 86F. Of course we had two days of really hot weather too but still, not bad performance. My point is that you don't need all that much area to add heat to the pool, especially in your location. But the key is to use a solar cover, especially in CA. The higher water temps increases evaporation and with water restrictions, you will need to have a cover.

It is a little involved but I have a heat transfer spreadsheet (in sig) that can be used to compare installation locations.
Click to expand...
Would you be willing to share that spreadsheet?
Thanks!
 
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