Solar Panels - What controller and how many GMP to run through the panels?

DjEclipse

Well-known member
Jun 27, 2016
87
Ontario
Hello,

I just finished installing 4 - 2' x 20' panels on my roof. I initially installed them on the North side of the house as that is where my back yard is but found them not to produce much heat. I moved them to the be south facing on a 5/12 roof pitch to get more sun. I am still not getting much heat coming out of the jets in the pool. Should they have warm water coming out?

What GMP should I be sending through the solar panels? I built in a bypass valve so I can modulate the amount of water going through the panels and currently have it closed (100% going through the panels).

The solar panels are about 60' away so the water is running through roughly 120' of pipe round trip. Pump pressure is 12 or so not going through the panels and 17psi going through the panels. They are above the garage so one story roof.

I was expecting a little more performance out of these. My pool is 16 x 40 (lazy L shape).

Also what controller is everyone using? I read there are some that put the probe on the roof and inside the return and use that to open and close the 3 way valve. The only issue is I read the probe lead for the roof can only be 20' away which won't bring me to where the solar panels on the roof are located. It will just make it to the other side of the roof.

Any help would be appreciated.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,629
Pleasanton, CA
No, the water should not feel hot coming out of the panels. The objective is to maximize heat transfer and not water temperature coming out of the panels. If flow rate is too low, the water will heat up more in the panels but it will also lose more heat to the environment. If you keep the flow rate about 16 GPM (0.1 GPM/sqft), the heat rise should be below 3 degF and will maximize heat transfer.

The length of the probe wire should not matter that much to make a difference. However, if there is a closer location that has the same view to the sun, then you can also use that. It is better to have the probe close to the panels but not completely necessary. Having an identical exposure to the sun will suffice.

As for the controller, there is no favorite that I know of. There are many different ones used by the members on the forum. Any one should do.
 

DjEclipse

Well-known member
Jun 27, 2016
87
Ontario
No, the water should not feel hot coming out of the panels. The objective is to maximize heat transfer and not water temperature coming out of the panels. If flow rate is too low, the water will heat up more in the panels but it will also lose more heat to the environment. If you keep the flow rate about 16 GPM (0.1 GPM/sqft), the heat rise should be below 3 degF and will maximize heat transfer.

The length of the probe wire should not matter that much to make a difference. However, if there is a closer location that has the same view to the sun, then you can also use that. It is better to have the probe close to the panels but not completely necessary. Having an identical exposure to the sun will suffice.

As for the controller, there is no favorite that I know of. There are many different ones used by the members on the forum. Any one should do.
Thank you for the detailed reply.

It's good to know it's normal for the water out of the jets not to be warm.

I am going to have to buy a flow meter and stick it on the check valve for the return line from the solar pannels and see what gpm I am at.

I am able to have the probe on the same roof as rhe solar pannels but it will be roughly 30' from the actual pannels themselves. It should be close to the same sun though.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,629
Pleasanton, CA
You don't really need flow meter. You can just go by the pressure rise of the panels and the temperature of the returns. As long as the water is not hot coming out of the returns, you have enough flow rate. Also, you should limit the pressure rise of the panels to less than 5 PSI. This is usually done by the solar bypass valve.
 
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DjEclipse

Well-known member
Jun 27, 2016
87
Ontario
You don't really need flow meter. You can just go by the pressure rise of the panels and the temperature of the returns. As long as the water is not hot coming out of the returns, you have enough flow rate. Also, you should limit the pressure rise of the panels to less than 5 PSI. This is usually done by the solar bypass valve.
I don't have way of measuring the temp in the returns yet, I still am shopping for a controller that has the probes. What is the theory regarding the pressure rise and temp of the returns form the panel?

Is it possible to have too much flow through the panels where it cools the panels too much?

I currently have about a 5psi raise when going through the solar now, but some of that is all the extra bends and the 15' rise isn't it? I used 2-45's instead of 90deg bends to help flow.

I do have a bypass valve already installed, I a currently running with it closed so all the flow goes through the panels.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,629
Pleasanton, CA
What I meant is if you put your hand in the water and feel it coming out of the returns, it should not feel hot. A slight temp difference is fine.

As for the pressure rise, it is in relation to head loss and flow rate. This is another way to determine how much flow is going through the panels. Typically, most panels will have about 4 PSI of pressure loss when they are run at 0.1 GPM/sqft. Adding 1 PSI for dynamic head of the plumbing and you have about the correct pressure rise for the given flow rate. This is especially true when the flow rate requirement of the panels is fairly low (i.e. 16 GPM) and the head loss through the solar plumbing at that flow rate is fairly low.

Is it possible to have too much flow through the panels where it cools the panels too much?
No. There are just diminishing returns. The real issue is pressure differential across the panels which is why the pressure rise is important.

I currently have about a 5psi raise when going through the solar now, but some of that is all the extra bends and the 15' rise isn't it? I used 2-45's instead of 90deg bends to help flow.
Yes it is but most of the loss is going to be through the panels. The 15' rise does not add to the head loss because there is a 15' fall as well. Assuming the plumbing is fully primed.

But it is surprising you have only 5 PSI rise with the panels on vs off. Are you sure there is not another bypass built into the plumbing? Sometimes a separate pipe and valve is used as a bypass. Also, is the pump a VS being operated at lower RPM?
 

DjEclipse

Well-known member
Jun 27, 2016
87
Ontario
What I meant is if you put your hand in the water and feel it coming out of the returns, it should not feel hot. A slight temp difference is fine.

As for the pressure rise, it is in relation to head loss and flow rate. This is another way to determine how much flow is going through the panels. Typically, most panels will have about 4 PSI of pressure loss when they are run at 0.1 GPM/sqft. Adding 1 PSI for dynamic head of the plumbing and you have about the correct pressure rise for the given flow rate. This is especially true when the flow rate requirement of the panels is fairly low (i.e. 16 GPM) and the head loss through the solar plumbing at that flow rate is fairly low.
Wouldn't the number of panels in the system have an effect on the overall pressure loss as well? I am running 4 - 20' x 2'

But it is surprising you have only 5 PSI rise with the panels on vs off. Are you sure there is not another bypass built into the plumbing? Sometimes a separate pipe and valve is used as a bypass. Also, is the pump a VS being operated at lower RPM?
I put the system together myself, there is not another bypass in the system I currently have it running 100% through the panels through the diverter valve (when the panels are on). I built in a bypass that is after the T going up to the panels, this is closed.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,629
Pleasanton, CA
Wouldn't the number of panels in the system have an effect on the overall pressure loss as well? I am running 4 - 20' x 2'
Not if the same flow rate per panel is maintained. As long as each 2x20' panel has 4 GPM going through it and all the panels are plumbed in parallel, it doesn't matter if you have 4, 8 or 16 panels, the pressure loss is the same. However, total flow rate would need to change in order to maintain that 4 GPM per panel so the total head loss in the rest of the plumbing would change accordingly.

I put the system together myself, there is not another bypass in the system I currently have it running 100% through the panels through the diverter valve (when the panels are on). I built in a bypass that is after the T going up to the panels, this is closed.
Ok but if you don't mind, I would like to dig a little deeper into your setup to help me understand what is going on.

What is your current pump model?

Are all the panels plumbed in parallel?

Do you have a VRV installed and at what location?

You mentioned the plumbing to solar, how about to and from the pool? All 2" as well and what is the distance between pool and pump?

Are these the Sungrabber solar panels?

Any chance you could post a picture of the pad with solar plumbing?
 

DjEclipse

Well-known member
Jun 27, 2016
87
Ontario
Not if the same flow rate per panel is maintained. As long as each 2x20' panel has 4 GPM going through it and all the panels are plumbed in parallel, it doesn't matter if you have 4, 8 or 16 panels, the pressure loss is the same. However, total flow rate would need to change in order to maintain that 4 GPM per panel so the total head loss in the rest of the plumbing would change accordingly.

Ok but if you don't mind, I would like to dig a little deeper into your setup to help me understand what is going on.

What is your current pump model?

Are all the panels plumbed in parallel?

Do you have a VRV installed and at what location?

You mentioned the plumbing to solar, how about to and from the pool? All 2" as well and what is the distance between pool and pump?

Are these the Sungrabber solar panels?

Any chance you could post a picture of the pad with solar plumbing?
Thank you for all the help.

I attached a diagram of the piping set up from the filter with the valves etc.

What is a VRV?

The panels are in parallel on the roof. I do have Watts Vacuum breaker just before the pipes go into the bottom of the solar panels, inlet side. Is there any benefit to running the panels in series?

All piping that I can see is 1.5" piping. I used 1.5" to and from the solar panels as well. After the solar it goes into the chlorinator and then to the 3 jets in the pool. Pool is roughly 33' away from the pump, first jet is roughly 75' away.

Solar panels are SunPirate
Sunpirate Solar Pool Panels

Pump is Hayward Super Pump 2 speed power saver, 3450/ 1725rpm. part number 7-193727-02 I am running the solar panels on high speed only.

I think this answers all of the questions.

Any idea if my pump can be controlled with a solar panel controller to change speed when the valve opens to the solar panels? Or do I need a different pump to be able to do that?
 

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mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,629
Pleasanton, CA
VRV = Vacuum Release Valve

Panels should be plumbed in parallel so that is ok.

Some follow-up questions:

Is this an above ground pool?

How large is the pool (gallons)?

Does the pool have both a main drain and skimmer and do they have separate lines back to the equipment or do they combine at the skimmer?

What is the height of the pump relative to the pool water level?

In the picture, there are two valves, one labeled diverter and the second labeled 3-way. When solar is on, both of those are set to send 100% of the flow to the panels? Some manufactures use different handle positions on their valves so I just wanted to make sure that you have confirmed that water is flowing to the panels and not just bypass through that upper bypass.

A signature loaded with your equipment setup would be helpful: Read This BEFORE You Post - Trouble Free Pool

As for the controller, I am not sure there are any a solar "only" controllers that will control speeds of the two speed pump. Higher end full equipment controllers ($$) will do this. You may have to research this a bit more to see if there is a lower end one that will do this. The Pentair SolarTouch controller will control a Pentair VS pump.
 
Last edited:

DjEclipse

Well-known member
Jun 27, 2016
87
Ontario
VRV = Vacuum Release Valve

Panels should be plumbed in parallel so that is ok.

Some follow-up questions:

Is this an above ground pool?

How large is the pool (gallons)?

Does the pool have both a main drain and skimmer and do they have separate lines back to the equipment or do they combine at the skimmer?

What is the height of the pump relative to the pool water level?

In the picture, there are two valves, one labeled diverter and the second labeled 3-way. When solar is on, both of those are set to send 100% of the flow to the panels? Some manufactures use different handle positions on their valves so I just wanted to make sure that you have confirmed that water is flowing to the panels and not just bypass through that upper bypass.

A signature loaded with your equipment setup would be helpful: Read This BEFORE You Post - Trouble Free Pool

As for the controller, I am not sure there are any a solar "only" controllers that will control speeds of the two speed pump. Higher end full equipment controllers ($$) will do this. You may have to research this a bit more to see if there is a lower end one that will do this. The Pentair SolarTouch controller will control a Pentair VS pump.

Pool is 23,000 gallons In ground
Pump sits on the concrete pad at ground level so same level as the pool pretty much. All piping is under the concrete pad.
It has one skimmer and one main drain that is plumbed into the bottom of the skimmer with a flapper door to modulate how much "suction" the main drain sees. The skimmer line goes to the pump, the return line goes to the 3 jets. It is a pretty simple set up.

I just tested again and pressure increases 4-5psi when water is going 100% through the solar panels.

In the diagram when solar is on the 3 way valve is set to block off the pipe on the left and send 100% of the water up to the solar. The diverter valve is closed forcing 100% of the water up to the panels. I did this so I could automate the system via the 3 way valve controller and have the diverter valve set to what ever I needed it to be.

VRV is what I am calling the Vacuum breaker. It is installed just before the water enters the panels. I read putting it at the top of the panels may result in it opening as it may not see enough pressure.

I will do some research but it would be nice to have the pump on low speed over night and auto high rmp when panels open. All the controllers I am seeing are 300-400 for the solar 3 way valve control and 2 temp probes.

I need something as I am not sure when to open the panels and when to leave them closed. Yesterday it was cloudy but still hot. I left them off as I didn;t know how much sun/ heat they were seeing. Today is sunny but windy so again I am not sure if it's right to open them.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,629
Pleasanton, CA
Generally, if you are operating solar more than a couple hours per day, that is really all the run time you should need.

One way to operate without a controller is with a pool timer that turns on the pump approximately when the sun hits the panels and shuts off slightly before the sun leaves the panels. This should be enough time to chlorinate the pool and skim the surface. Basically solar only operation.

But doing some head calcs, I estimate a flow rate of about 54 GPM without solar and 44 GPM with solar so more than enough flow rate through the panels. You could probably bypass some of the water and still maintain panel efficiency.
 

DjEclipse

Well-known member
Jun 27, 2016
87
Ontario
Generally, if you are operating solar more than a couple hours per day, that is really all the run time you should need.

One way to operate without a controller is with a pool timer that turns on the pump approximately when the sun hits the panels and shuts off slightly before the sun leaves the panels. This should be enough time to chlorinate the pool and skim the surface. Basically solar only operation.

But doing some head calcs, I estimate a flow rate of about 54 GPM without solar and 44 GPM with solar so more than enough flow rate through the panels. You could probably bypass some of the water and still maintain panel efficiency.
Thank you for the rough calculations. I may try bypassing in the future.

If I do bypass what psi increase should I be looking for? Right now it's 4 - 5, maybe bring it down to 3psi increase?

In the past I have used a timer turning the pump off for a fee hours at night and the pool ended up cloudy with chlorine levels dropping.

This season I have left it on almost 24 /7 low speed when the solar is not on and pool is very clear. I throw 3 pucks in the chlorinator once a week and every so often pH plumber and calcium plus when needed.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,629
Pleasanton, CA
You can probably halve the PSI rise and you should still be ok. PSI is proportional to GPM^2 so half the PSI rise would be approximately 30% less flow rate. So still well above the minimum required.

In the past I have used a timer turning the pump off for a fee hours at night and the pool ended up cloudy with chlorine levels dropping.
That isn't because of run time but because your FC levels are too low. When you reduce run time, you need add the same amount of FC within a shorter time period so you must adjust the puck feeder to add more FC.

Are you following the FC/CYA recommendations: Chlorine / CYA Chart - Trouble Free Pool
 

DjEclipse

Well-known member
Jun 27, 2016
87
Ontario
You can probably halve the PSI rise and you should still be ok. PSI is proportional to GPM^2 so half the PSI rise would be approximately 30% less flow rate. So still well above the minimum required.

That isn't because of run time but because your FC levels are too low. When you reduce run time, you need add the same amount of FC within a shorter time period so you must adjust the puck feeder to add more FC.

Are you following the FC/CYA recommendations: Chlorine / CYA Chart - Trouble Free Pool
When I open the diverter valve the psi goes down as it allows some water to take a less restrictive pass right to the pool instead of going up to the pannels.

I am talking about the pressure gauge on the filter. I don't have a pressure gauge on the pipes going to the solar pannels.

Thanks for the chart and video. It is very well put together.

The chlorinator is already set to 80%. I was told my stabilizer was high when I took in got a pool sample last week. I'll have it checked again this week.

I never knew there was a relationship between the chlorine and stabilizer.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,629
Pleasanton, CA
So I was referring to the filter pressure rise between no solar and solar. So if the pressure rise is 6 PSI with no bypass, a 3 PSI rise with bypass partly on is fine which means the filter pressure would be around 15 PSI with solar on and with a partial bypass. Even 14 PSI is probably ok.

High CYA will make a pool nearly impossible to maintain. You need to get your own test kit and measure it periodically. The pucks add nearly as much CYA as FC so it is a constant battle to keep CYA in check when using pucks. This is the reason the forum recommends other forms of chlorination.
 

DjEclipse

Well-known member
Jun 27, 2016
87
Ontario
So I was referring to the filter pressure rise between no solar and solar. So if the pressure rise is 6 PSI with no bypass, a 3 PSI rise with bypass partly on is fine which means the filter pressure would be around 15 PSI with solar on and with a partial bypass. Even 14 PSI is probably ok.

High CYA will make a pool nearly impossible to maintain. You need to get your own test kit and measure it periodically. The pucks add nearly as much CYA as FC so it is a constant battle to keep CYA in check when using pucks. This is the reason the forum recommends other forms of chlorination.
OK thanks agsin for the clarification.

Filter pressure is around 12psi not going through solar and 16- 17psi going g through solar. Good to know I can dial it down to 15ish psi with solar using the bypass.

I'll have to do a search on the other forms of chlorination. I have only been using pucks and liquid " shock" if I was low on chlorine. It has worked ok. Not too costly.
 

LFrankow

LifeTime Supporter
Sep 27, 2012
581
Medicine Hat, Alberta
I read that it is not accurate if you extend it.

What make / model solar pollen controller do you use? How do you like it?
I have the Pentair Solartouch controller works very well. It shuts down flow to the panels when a cloud comes over, also puts pump into low speed when solar is not available or viable.
My panels/sensor is roughly 75 feet from the controller, i haven't noticed any problems with probe readings, but if I want I can recalibrate the sensors. When the rooftop sensors reads 40+ C temp rise thru the panels is roughly 5 C. I have a laser temp reader.
 
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