Solar Installation

[stever]

It's been a month and we have started to use the solar. I have two banks -- high roof and low roof -- both facing south. The lower bank has 4-4x8 panels and is about 5 feet baove the pump level and the upper bank has 10 4x8 panels and is 8 feet above the lower bank. I think the panels are Solar Indsutries with raised tubes.

The solar installation company installed the two banks in series -- claiming it heats much better that way. My worry is that if I am running the solar heat at 40 gpm as they set up that the lower panels are getting 10 gpm each -- much too high in my opinion. I seem to be limited to maybe 25 gpm if I read the specs correctly (to hit about 6 gpm each). The upper panels will and up with 2.5 gpm at this rate -- if I did my numbers correctly.

Should this be plumber in parallel? If it was, would water get to all the panels equally (given the upper has more panels and is higher)?


I have only 70 to 75% pool area in panels, under the 80% I was told i should have, but still expected more heating. I can feel hot water coming out of the returns, but the temperature only raises about 4 degrees in a day (would have raised 2 w/o solar anyway) and then gives it all back overnight. This is with full sun. How is this supposed to extend the swimming season? When the water is down to 76, it won't make it to 80 by the end of the day.

I understand a cover would help a lot overnight... but...?

Thanks,
Steve

 

[meatloaf]

What is the outside day time air temperature? I can raise my pool temp 5-6* per day with my homemade system. Something doesn't sound right. I would expect quite a bit more from your system. And yes, a solar cover applied at night would definitely retain the heat.

 

[JohnT]

IMO, they should have separate feeds, then the outlets of each should connect together at the highest point in the system. Two reasons for this: First is flow. Each bank can have its flow regulated independently. Second is plain old physics. The rate of heat transfer between two materials is dependent on the temperature difference between the two, so running the water through one bank then the other reduces the efficiency of the second bank.

 

[mas985]

As John pointed out the heat transfer is directly related to the temp difference betweent the water and the incident solar energy. So plumbing the panels in parallel would be more efficient however, it is difficult to say if you would see a large jump in temperature with that change alone. There could be other factors involved.

Water flow rate is also very important. Increasing the flow through the panels can also make them more efficient. The faster the water travels the more efficient the panels are however, there are diminishing returns to this so once you reach the optimum flow rate, more won't help that much. So even if the panels are in series, there could be enough flow rate to compensate for that.

Another factor is the angle of the panels to the sun. This time of year, the sun is very high in the sky so if you have a 60 degree roof, you could loose close to 30% of the sun's energy at your latitude.

Still another factor is wind speed. Solar loses efficiency with higher wind speed so if you are close to the water and get the ocean breeze all day long, that could also explain it.

Also, the pool itself is responsible for close to half of the heat gain that you might see so if the pool is in shade most of the day, you will get about half the heat gain that you would get with the pool and solar in the sun all day.

I have about 80% solar coverage for my pool and can get over 8 degrees of gain during the hotest days of summer. Even on moderately warm days, I can still expect 6 degrees of gain. Now my pool is in the sun most of the day so about half that gain is from the pool alone. Without solar, I can usually expect about 3 degrees of gain during the day.

I would expect more heating than what you are seeing but again it could be explained by any one of the factors above. 4 degrees is what I would expect from the pool alone so it doesn't look like the panels are adding much unless the pool is in shade most of the day, then what you are getting is probably close to what I would expect.

 

[Rockcrawler]

IMO you cannot expect to keep the heat you gain unless you have a pool cover, I live in El Paso with most of the summer in the 90s, you can expect to lose a lot of heat from the pool at night especially if the low temp dips down to the 70s, I have found the perfect medium for me, because its so hot here I only cover half of my pool and with 8hrs of solar run time in the day my water temp is steady at 90 degrees and that is when temps are averaging 95 in the day


Southern Cal, you are already in the low 70s at night so you can not expect the solar to recover that much heat loss in one day, bottom line, you need a cover to retain the heat at night.

I agree with mas, my pool is in full sun all day and that also has to be factored in to the (recovery) temp gains

 

[dayhiker]

Do you cover the shallow end or deep end? It seems like you would cover the shallow. The deeper would have more thermal mass to hold on the heat? The water current created by the temp diff may make this a moot point and you just cover whichever end you want.

 

[Rockcrawler]

Day hiker, never really thought about it, but out of conveinance I cover the deep end, so when I get home from work and just want to dip in the pool, I don't have to remove the cover, that makes sense about the mass on the deep end, but the pump is running during the day for solar so the water is circulating

 

[stever]

Thank you all -- all good ideas.

The pool is in the sun from 8:30 until 5:00 with no trees, etc shadowing it. There has been only light breezes and the high temperatures have been 90. At night it has been in the 70s. I do not cover the pool, but understand I should (don't know what to do with the bubble cover once it's out of the box).

In the morning the pool is 78 and by evening w/o solar it's 82. Solar may add 2-3 degrees. I may not retain any heat overnight (understandably) but would like to see the 78 become 86 by the end of the day with sun on the pool and solar.

I understand that the colder the water is the more heat transfer there will be, thus it's better to have a high flow rate and panels in parallel. The solar company swore that series would heat better. I can only assume this is because if a regulating valve is not installed the high panels may not get any water at all.

I can't raise the GPM because all of the flow goes through the first 4 panels first. I am limited to that maximum flow (say 6 gpm/panelx4=24GPM). Then unfortunately that flow continues on to the 10 upper panels at only 2.4 GPM. I'm kind of locked in to these flows. The lower panels are not adding too much heat to the system before it gets to the upper panels, so I'm probably not losing too much there, but I'd like more than 2.4 GPM/panel for the upper 10.

The roof is 4:12 south facing - roughly 30 degrees. If I add more panels I'd add them to the east side of the house to get the pool warming up ASAP in the morning. What's the point of West facing and adding the heat right before the sun goes down and it gets lost? Oh yea -- the cover.....

I upper the GPM (over-drome the lower panels) and the water seemed to not be hearly as hot coming out of the returns. I understand it wasn't, but that there was more of it -- more than compensating -- but it didn't seem much warmer than the pool itself. I'll experiment a little.

Steve

 

[Rockcrawler]

IMO with a 22,000 gal pool 2-3 degrees a day is good, and if you could retain the heat overnight the temp would keep going up, but on the other hand if you have had 90 degee days I would think you should get more than 2-3 degree a day.

My panels face west, I would of installed then south but my roof faces the wrong way,here in El Paso the hottest part of the day is from 3pm to 7pm, my solar turns on about 1 pm and runs until 7 pm. IMO im not sure adding panels to get the morning sun will do much improvement, as the morning temps are low.

yeah the cover, besides its cheaper :lol:

 

[launboy]

FWIW, I have 3-2x20 panels on a south facing roof totalling 120 sq. ft. This is only 47% of our 18' round AG pool. When I installed the panels I plumbed them in parallel and all of the exits converge at the top of the highest panel and are Tee'd into one pipe that goes back to the pool.

With this setup I can gain 8-10 degrees a day with a full sun. We also leave the solar cover on whenever we're not in the pool. I keep it around 90* and if it gets their or hotter I just take the cover off. The pool is in the sun from 8 a.m to about 3 p.m. but the solar panels get sun(and are on) from 9 a.m. to 6 p.m..

Also, my panels get 10 GPM each(in parallel and the pump produces 30 GPM with solar on).

HTH,
Adam