Solar Plumbing Questions

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D

Dale.s

0
Feb 12, 2010
82
Blessing, Tx (South of Houston)
This year i will be adding a 2 2X20 solar panels to my pool, as well as redoing the whole equipment pad. My origanal plan was to have a 3 way valve to direct the flow either direct to return line, or loop through panels first.

I just received the panels and while reading the instructions it says they work best at 1-4gpm flow. So now my question is can i stick with origanal plan and divert all flow through panels (at best i belive max is 30gpm) or should i just divert a portion of the flow, if its just a portion can i just turn the 3way a little to acheive this? Would a check valve be needed to make the flow accually go through panels?

My origanal plan did not include a check valve, the panels will be rack mounted next to the pool, on the ground.
 
Most people put a check valve between the filter and the solar panels. That check valve is only there to prevent debris from being washed out of the filter and into the pool when the panels drain down when the pump is off, which could force water to go backwards through the filter. The panels will work even without the check valve, and the check valve isn't required at all if you have a sand filter or if the panels are below the level of the filter.
 
Wouldn't you want a check valve after the panels and before they connect to the return pipe to keep water from flowing back to the panels when you bypass them? Sure the pressure would build and fl
 
carlscan26 said:
Wouldn't you want a check valve after the panels and before they connect to the return pipe to keep water from flowing back to the panels when you bypass them?
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No, that is not commonly done. Most designs allow the panels to be pressurized via the panel return flow line any time the pump is running. The advantages of not pressurizing the panels are minimal; not sufficient to justify the small additional back pressure of adding a check valve there.
 
I could see where the back presssure is not an issue if the panels are near or below the equipment pad but if they're on a roof then aren't you creating an additional load that the pump has to push against? I'm thinking some water goes into the panels backwards until pressure builds since there is no exit path and this load of water will flow back down when the pump is off but while it's running the pump has to keep pushing against that load right?
 
First, the OP stated that this will be a ground installation. Second, for a ground installation without a vacuum release valve, the return and filter check valves are not really required. Water will remain in the panels at all time and the pressure in the panels will be nearly the same with or without a check valve if the solar valve shuts off during the pump operation.

Even on a roof installation, the load on the pump would be no more with than without a check valve. Where it helps on a roof mount is when there is a vacuum release valve and air is involved. The check valve prevents the water from flowing backwards into the panels and compressing the trapped air which, like a filter, can create large bursts of pressure release when the pump is shut off.
 
I thought I referenced the OPs situation with my comment that this wouldn't matter for a solar system at ground level...

mas985 said:
Even on a roof installation, the load on the pump would be no more with than without a check valve. Where it helps on a roof mount is when there is a vacuum release valve and air is involved. The check valve prevents the water from flowing backwards into the panels and compressing the trapped air which, like a filter, can create large bursts of pressure release when the pump is shut off.
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Yeah that's what I was getting at; the compressed air essentially acts like a compressed spring. And without a check valve for a roof system (I thought they all have vacuum release valves) you'd create stored energy that will be released once an opening becomes available - i.e. when the pump stops holding it back. Since the pump would be the energy source that "charged" the air spring and maintained it, there would be an additional load for the pump.
 
The pump spends energy to pump up the pressure in the panels when it first starts up, but once everything is running there is no additional load on the pump. The pressure in the pipe leading to the panels will be the exact same pressure the water would be applying to the side of the pipe, if there was pipe there instead of an opening to the panels. So it is all the same to the pump.
 

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As Jason pointed out there is no difference in the load to the pump. There is extra load placed upon the pump only when filling the pipe but once equilibrium is reached, there is no longer an "extra" load on the pump. The pressure in the pipe keeps the water/air under pressure but no extra energy is required to maintain that pressure since it would be the same with or without the solar system, of course without water flowing throught it. Think it of this way, it requires energy to bring the water up to pressure but not to maintain pressure unless it is lost somewhere like dynamic head.

The only factor that could come into play is compressed air which would release quickly after the pump is shut off. I don't think it would be a huge issue although it could cause water hammer in the plumbing system.
 
JasonLion said:
Most people put a check valve between the filter and the solar panels. That check valve is only there to prevent debris from being washed out of the filter and into the pool when the panels drain down when the pump is off, which could force water to go backwards through the filter. The panels will work even without the check valve, and the check valve isn't required at all if you have a sand filter or if the panels are below the level of the filter.
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I have a sand filter 3 foot below the waterline and am hoping to put panels 6 foot above the waterline. Will I still not need a check valve ? I'm curious as to why a sand filter wouldn't need one. I'd be happy if this is the case as the good check valves are quite expensive here.
 
In a sand filter there is a substantial vertical separation between the debris on the bottom and the water inlet at the top. In order to wash debris backwards out of the filter there needs to be enough water flow to push the debris all the way to the top of the filter and out the inlet. Obviously this is possible, since that is exactly what happens during backwashing, however that takes a substantial water flow for a period of time. The brief, relatively slow, flow from the panels draining down is not normally sufficient. This is a "your milage may vary" situation. Some specific setup could provide enough water flow.

DE and cartridge filters are quite different, with very small distances between trapped debris and the input. Even very small reverse water flows are usually enough to send some debris, and/or DE, out the input.
 
Thanks for all the information guys! One more question though. If you don't fully open the 3 way, then you have water going to the panels, and past the panels. Without a check valve on the return line from the solar before it gets to the main return, wouldn't water try flowing backwards through the solar system? Would you still get flow through the panels?
 
The water pressure is always higher at the three way valve than it is where the returns join back up after the solar panels, so water will never flow backwards through the solar system (at least as long as the pump is on).
 
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