Solar Panels

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B

BPet

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Sep 8, 2015
25
Wellington
I have 11 solar panels on a two story roof. The gutter is approx 22' off the ground and then the roof slants upwards so that top of the solar panels are at least 27'+ from the ground. The pool & solar was installed approx. 1 year ago and I noticed that when the solar is running, I would feel very hot water coming into the pool from the outlets or water features, but it was not continuous. The water would be extremely hot for a few minutes and then go back towards a normal temperature...and then a few minutes later it would be very hot again. Now, as I think about it, and learn about solar, it occurs to me that shouldn't the temperature be consistent coming from the solar panels? If the solar is running, why would the temperature vary?

My variable speed pump runs at 2350RPM when the solar kicks in via the Pentair system. My solar installer actually had it set to a lower speed, but his method of determining the proper speed was based on feeling the solar panels on the roof and figuring that as long as they were not too hot, then there was good flow.

I'm wondering if I should be increasing the RPMs until the water returned to the pool is just slightly warmer than the pool water?
 
If you are getting intermittent flow, id increase the speed to see if that resolves the issue.

If your water temp sensor is downstream of the solar, the heated water may be causing the solar to cycle on and off. If you are getting flow from solar, it will be initially very warm then should only be a few degrees warmer than the pool water after the latent heat in the panels is first adsorbed into the water.

Can you provide a few pics of the system?
 
There is a water temperature sensor after the Pump, but before the solar. From the looks of it, it seems to me that the water goes to Pump, Water Sensor, Filter, Solar, Chlorinator, back to Pool. I know that there is another sensor up on the roof, but I can't get to that to take a picture.

Here are some Pics of the Pump area.
IMG_3928.jpgIMG_3927.jpgIMG_3926.jpg
 
Does the water enter the solar panels on the lower header and exit the upper header on the opposite side? It sounds like gravity is pulling the water down out of the panels faster than the pump is pushing it up. It is definitely worth a try to raise the pump rpm to see if it solves the problem.
 
Two questions

1) What is the filter pressure at 2350 RPM

2) Where is the VRV installed?


If the VRV is installed at the top of the panels (i.e. 27') the filter pressure should be more than 14 PSI to keep it closed. Otherwise, it will open and reduce flow which could be why it is cycling.
 
The pressure at 2350RPM is around 9PSI. Is the VRV the bulb looking device? If so, it is installed where the pipe from the solar returns from the roof down by the pump level - in the last of the pictures posted...I just increased the RPM to 2550 and the pressure went to 14PSI.

My wife seems to think that it was not cycling, but I was just noticing how hot the solar was when it first kicked in...which is possible. I'm still thinking that the RPM should be higher so that I am sure to be taking all of the heat from the solar panels. The Pool Temp is 79 degrees and I could feel an easily noticeable difference in the water temp that is returning from the solar. I guess I'll keep it at 2550 and see if I notice the pool heating up better...
 
The water from the panels will be hot when first turned on and should cool off as time progresses. For maximum heat transfer, you actually don't want to feel much of a temp rise. 3 degrees or less is optimal. But if the water gets hot again in the middle of the run, then something is wrong. Is the solar temperature sensor in direct sunlight on the panels themselves (not in the pipe)?
 
I'm not sure where the solar temperate sensor is located, I can't see it since it is on the 2nd Story roof. I think the water returning from the solar now seems consistent in temperature and so the only current issue is whether the RPM is high enough for optimal heating. I have been nudging the RPM up to see when it feels like a 3 degree difference in Temp...currently I'm at 2650RPM & 15PSI reading on filter. The water coming back from the Solar still feels warm. I'm thinking that a 3 degree difference in temperature would only feel just a slight bit warmer than the surrounding water? What do you think? I guess I could turn on the Scuppers and have them fill up a gallon or two into a 5 Gal bucket and try to check the water temperature that way? Not sure how accurate that would be? Any other suggestions for testing the post solar heat water to determine how much warmer it is compared to the pool water? Thanks for your help! :)
 
I can estimate the flow rate from the pump RPM and wattage (need this) with the filter PSI. Also, what is total size of the solar panels in sq-ft? But you could do the bucket method too.
 

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Flow rate is around 70 GPM at 2650 RPM. For 560 sqft panels, I would target around 56 GPM so you could drop to 2150 RPM.

I noticed that you have the Intellichlor SWG. Does the screenlogic show the cell temperature and is the cell installed post panels? If so, you can use that along with the pool temperature to determine the heat gain of the panels.
 
Thanks again. ScreenLogic does not show the cell temperature. I see that the Intellichlor shuts off when temperature gets below 59 degrees and so the temperature data is somewhere, I just don't know how to access it or if it is accessible?

Lets say I measure the water temperature post solar, at the pool scupper, and it is 5+ degrees hotter than the pool water when running 2150RPM. Would I be better running at 2650RPM if they gave me a 3 degree difference or do I risk damaging the solar at the higher GPM? (Even at 2650RPM it seem like more than a 3 degree difference to me, but I have not measured yet to be sure)

Thanks again for all of your assistance with this!
 
At 2650 or even 2150 RPM, I wouldn't expect much more than 3 degrees of heat gain.

As for panel pressure, you need to check the manufactures specs. Some are not so sensitive to pressure so it may not be an issue. But even so, 15 PSI filter pressure is less than 3 PSI at the panels so that should be fine.
 
I just tested the temperature difference by putting the Thermometer in the stream from the jet in the side of the pool and it seemed like a 4 degree difference. Then, I filled a 5 Gal bucket halfway up from the scupper and it looks like only a 2 degree difference. That was at 2650RPM and so I guess I'll reduce the RPM. Thanks again.
 
Best solution is to determine the reccomended flow rate for your panels and adjust to that- that way you get the most effective heat transfer. True, water will be warmer when flow is decreased, but the thermal mass (volume of heated water) will be smaller, which will offset most of the gains from higher water temp (if the flow is below the mfg recommendations). The mfg determines what flow is optimal to capture the most heat so would go with that.

for example, fafco recommends 5gpm flow to each panel so as to achieve a 0.85 efficiency factor. Reducing flow to 2gpm reduces efficiency to 0.7. If you have fafco panels, you should be running your variable speed pump to achieve 55gpm to get the most efficient heating.
 
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