Proper psi for solar panels?

[tmobileguy]

Split from P.s.i after solar installation. - Page 2 Zea3

The potential problem here is over pressurization of the solar panels not the filter, these panels when heated by sunlight become somewhat prone to pressure damage, so it is important to take precautions to make sure they do not see excessive pressures.

I'm building a solar panel system as we speak. Do you think water pressure is the number one cause of reduced life in a solar panel? And what pressures do you think are ideal when using a solar heating system. I am going to go with 2" headers to reduce pressure. Anything else I can do besides making sure the panels are wired parallel, output headers are higher then input (and on opposite side) to relieve air bubbles, and the use of a vacuum relief valve, as well as check valve on the return down from the panels? I was going to put a check valve on the way up as well (near the bottom).

Thanks and sorry to hijack.

 

[Isaac-1]

In my personal opinion the big killers of solar pool heaters are, freeze damage, abrasion due to daily expansion / contraction cycles across sharp / rough surfaces, water being trapped in panels not draining and exposed to sunlight / heat and over pressurization. Severity of each is relative, and I would not want to try to rank them in a particular order. Freezing is almost always fatal to these style panels, but is easily prevented, abrasion is often not considered, and over pressurization and over heating go hand in hand with each other. If you want a number, I would tend to say less than 1 PSI at the top of the panels is a good goal, this usually requires you to move the VRV to the bottom corner to prevent sucking air, the danger in aiming for less than 1 psi is the potential to get a negative pressure, and collapse the tubes which is easy to do with any negative pressure. There is some good information on this topic at the h2ot sun solar web page, particularly in their case studies.

Ike

 

[gwegan]

The number one cause is freeze damage. Hands down. Buts that's with professionally installed systems. With DYI install the numbers are small.

 

[tmobileguy]

I plan on using a solar controller that will recirculate the water when temps on the panels reach 5 degrees higher then pool water temps...but once it reaches it target temp, the water will just be cooking in those panels, and that worries me.....

I live in FL so we don't see freezing temps very often down here, but I plan on using the freeze recirculation on the controller which should eliminate the freezing water in the panels problem...

As far as the abrasion problem due to contraction and expansion, has anyone every thought about (or actually tried) putting some type of soft waterproof material under the panel to protect from that? I'm guessing its the underside of the panel that takes most of the abuse from this issue...

 

[tmobileguy]

I plan on using a solar controller that will recirculate the water when temps on the panels reach 5 degrees higher then pool water temps...but once it reaches it target temp, the water will just be cooking in those panels, and that worries me.....

A thought I had was to wire a 24v timer to the control valve from 12pm-4pm and set my 2 speed to pump to high during this same period also, so that water is always flowing through the panels during peak times to eliminate any potential overbuild up of heat....and then using the nocturnal function on the solar controller to bring down the temp of the pool water at night to cool it back down in case the water temps start getting much higher then desired temps... Thoughts???

 

[Isaac-1]

As long as you have the panels mounted correctly, a vacuum relief valve and an appropriate low pressure activating check valve installed the panels should automatically drain when the solar controller valve switches them off. The solar controller will sense when potential heat is available, not so with a simple timer which could allow substantial cooling to occur during the common summer thermal thunderstorms that are seen along all of the gulf coast. The key here is to not have water trapped in the panels, air in the panels is not nearly as big of issue as it conducts heat MUCH slower than water, therefore the importance of a properly located VRV to allow draining when the controller turns the solar valve off.

 

[tphaggerty]

I plan on using a solar controller that will recirculate the water when temps on the panels reach 5 degrees higher then pool water temps...but once it reaches it target temp, the water will just be cooking in those panels, and that worries me.....

I live in FL so we don't see freezing temps very often down here, but I plan on using the freeze recirculation on the controller which should eliminate the freezing water in the panels problem...

As far as the abrasion problem due to contraction and expansion, has anyone every thought about (or actually tried) putting some type of soft waterproof material under the panel to protect from that? I'm guessing its the underside of the panel that takes most of the abuse from this issue...

With a correctly set up system, the panels drain when not running.

 

[tmobileguy]

As long as you have the panels mounted correctly, a vacuum relief valve and an appropriate low pressure activating check valve installed the panels should automatically drain when the solar controller valve switches them off. The solar controller will sense when potential heat is available, not so with a simple timer which could allow substantial cooling to occur during the common summer thermal thunderstorms that are seen along all of the gulf coast. The key here is to not have water trapped in the panels, air in the panels is not nearly as big of issue as it conducts heat MUCH slower than water, therefore the importance of a properly located VRV to allow draining when the controller turns the solar valve off.

What psi would you recommend to have the check valve open at to make sure that the water drains down?

Also, with the outlet side being higher then the input side and the input side being closed by a 3 way valve, how does the water drain out of the panels?

And my last question, the solar controlling has a temp sensor that is supposed to be placed near the panels to detect the water temp to turn the unit on.... If you drain the system up top every time the controller is turned off, then how can the sensor detect the proper water temp to turn the unit back on if there is no water in the pipe to detect from....

 

[mas985]

A vacuum release valve is used for solar panels so when the pump shuts off, any negative pressure opens the valve and the panels drain. You only need one entry point of air for all sides of the panel to drain. The lower the elevation of the VRV, the less pressure is needed to keep it closed. This can be useful for VS pumps so you can lower the RPM as much as possible although you still have to prime the panels at higher RPM.

The water temperature sensor should be installed right after the filter but before the solar panels and solar valve. You want to measure the water temperature before it is heated by the panels because it is more representative of the true water temperature. Having the sensor before the solar valve means it will measure water temperature with or without solar engaged.

Also max pressure of the solar panels depends on the panel type and manufacture. I have EPDM panels and have run them at over 15 PSI without any issue. But this is not true for all panels. You have to consult manufacture recommendations and specs.

 

[tmobileguy]

The water temperature sensor should be installed right after the filter but before the solar panels and solar valve. You want to measure the water temperature before it is heated by the panels because it is more representative of the true water temperature. Having the sensor before the solar valve means it will measure water temperature with or without solar engaged.

Sorry, I should have clarified. I was referring to the temperature sensor that is reading the temp of the water in the solar panel area.

 

[mas985]

You don't install a water temperature sensor near the panels.

However, you do install a solar temp sensor near the panels that only measures the sun's incident energy.

 

[tmobileguy]

You don't install a water temperature sensor near the panels.

However, you do install a solar temp sensor near the panels that only measures the sun's incident energy.

Yep, that's what I was missing. I was assuming since the kit came with two of the exact same sensors, that they were installed the exact same way. I just re-read the manual for the controller and it stated....

"Solar Sensor: Use a screw or silicon adhesive to attach the sensor near the solar collector array.The sensor does not have to be attached to the collectors. It is only important that the sensor beexposed to the same sunlight as the collectors. Additionally, the underside of the sensing elementmay be covered with silicon to minimize wind cooling."

 

[mas985]

Although I would not cover the sensor with silicon because if the wind is cooling the sensor, it is also cooling the solar panels and you want the exposure to be the same.