Adding Another Solar Panel.

[launboy]

Currently I have 3 solar panels on my garage roof, all of them 2x20. One is a SunHeater brand panel with the inlet and outlet on the same side. The other two are SunGrabber panels with Inlet and outlet on opposite sides. Last summer I had the inlet and return piping all on the same side. The Sunheater was on it's own, and the 2 SunGrabber panels were in series.

We just went and picked up another panel that I found on Craigslist for $40.00. It's a 4x10 Sunheater(inlet and outlet on the same side. I was just outside measuring and determined they won't all fit on the garage. The 4x10 panel will have to go on the shed which sits right next to the garage, but is about 3 1/2ft lower. This solar setup gives me three different types of panels, at two different elevations.

I'm thinking of drilling out the disc in the header of the 2x20 SunHeater panel so it's like the SunGrabbers. Then I'll plumb then all in Parallel so the flow is fairly even between the three panels on the roof.

The panel on the shed will be Tee'd off the input pipe where it runs vertically up the garage wall. I'm going to put a valve here so I can adjust the flow if necessary. The return from this panel will then run up and meet the return pipe for the panels on the garage roof at the highest point. Is this part necessary, or can I just run it to the vertical section of the return pipe on the garage wall? I'm thinking of putting a valve on the input for all of the panels. I've already got one on the 2x20 SunHeater, and the 4x10 SunHeater came with it's own, so I'd only have to add two more.

The biggest problem I can see here will be getting the all of the panels to have an even flow rate, any tricks to this one?

Any and all thoughts, comments, ideas, questions, etc. are very welcome!

Here are some pics...
This shows the plumbing(right is TO solar, left is return FROM solar), the garage, and the shed.

Shows shed and garage from the shed.

Shed with 4x10 laying on it.

Solar panel setup from last year. I might change the piping on the roof for it though, opinions on this?

Thanks,
Adam

 

[mas985]

The panel on the shed will be Tee'd off the input pipe where it runs vertically up the garage wall. I'm going to put a valve here so I can adjust the flow if necessary. The return from this panel will then run up and meet the return pipe for the panels on the garage roof at the highest point. Is this part necessary, or can I just run it to the vertical section of the return pipe on the garage wall? I'm thinking of putting a valve on the input for all of the panels. I've already got one on the 2x20 SunHeater, and the 4x10 SunHeater came with it's own, so I'd only have to add two more.

The biggest problem I can see here will be getting the all of the panels to have an even flow rate, any tricks to this one?

From the pictures, I don't see a vacuum release but I would recommend that you design them to be self-draining. Also, I see a few local low spots where you may get trapped water. You should try and avoid that.

Plumbing multi-level solar panels can be a bit tricky and depends on where you are going to place the vacuum release valve. I would recommend having a single release valve at the upper most point of the upper panels and then having the return of the lower panels connect to the main return at a point slightly higher than the lower panels upper most point. However, it is not necessary to connect to the upper most point of the upper panels but just to a point that is slightly higher than the lower panels upper most point. The supply of the lower panels should be connected to the main supply at a point lower than the lowest point of those panels. This will ensure that all panels drain downward and avoid any trapped water.

Have I confused you enough yet.

The main idea is to make sure there are no locations where water can get trapped.

As for equal flow, what you are doing should be good enough. Having exactly equal flow is not really necessary as long as you have "enough" flow for each panel to maintain efficiency. The lower panels will have slightly higher flow rate because the pipe lengths are a little shorter but there are less panels so this may equalize out some.

 

[launboy]

... I would recommend having a single release valve at the upper most point of the upper panels and then having the return of the lower panels connect to the main return at a point slightly higher than the lower panels upper most point. However, it is not necessary to connect to the upper most point of the upper panels but just to a point that is slightly higher than the lower panels upper most point. The supply of the lower panels should be connected to the main supply at a point lower than the lowest point of those panels. This will ensure that all panels drain downward and avoid any trapped water.

Have I confused you enough yet.

I had to read it twice, but I think I got it. LOL The reason I asked about connecting the lower panel's return to the top of the upper panels was because I thought I'd read somewhere that this will help equal out the flow because the water still has to be pushed up to the same height as the higher panels. That, and it will ensure water fills all of the panels, and not just the lower one(I think that part is for lower banks with multiple panels though).

I didn't have a vacuum breaker last year, but one of my connections, right at the very top must have had a small leak in it. I could hear air being sucked in when the pump was off, but oddly, no water came out when it was on. So by the next morning, the panels were almost all the way drained. I'll probably add a vacuum breaker this year though.
This vacuum breaker might pose a problem though. I'm going to add a solar control to the setup this year and how will the panel sensor know if there's enough heat in the panels to open the valve if there's no water there to get hot?

One last thing, the guy I'm planning to buy the controller from has offered to customize the temp differentials at which it will switch the flow to the panels on and off... if that makes any sense??? Basically, he can set how much warmer the water in the panels has to be than the water in the pool before the controller will send water to the panels. He can also set the temp. at which the controller will shut off the flow to the panels. This can be anywhere from about 0-10°F, but it needs to be at least 3°F between on and off. At least, I think that's what he meant. :lol: I was thinking maybe 3°F more then pool to turn on, and 1°F to turn off. Should I make the turn on temp. higher? I hope that made sense.

Thanks,
Adam

 

[JasonLion]

There doesn't need to be any water in the panels to get the roof mounted temperature sensor to work. The roof mounted sensor isn't normally touching the panels, or the water, at all. It simply records what the temperature is inside an appropriately thick piece of plastic exposed to the same sunlight and wind as the panels.

You do want the total length of the water path to be the same. The return from the lower panels should not go straight back down to the pool, but instead should head up to the top of the system. It can however join a pipe that already exists and share that pipe for as much of the distance as possible.

Adjusting the on and off temperatures for the controller can provide small optimizations. Still, the factor settings are a fairly good place to start.

 

[mas985]

I had to read it twice, but I think I got it. LOL The reason I asked about connecting the lower panel's return to the top of the upper panels was because I thought I'd read somewhere that this will help equal out the flow because the water still has to be pushed up to the same height as the higher panels. That, and it will ensure water fills all of the panels, and not just the lower one(I think that part is for lower banks with multiple panels though).

Actually, the raising in height is compensated for by the falling on the other side so height is only relavent to draining of the panels. The flow rate through the panels is determined by the pressure difference on each side of the panel. As Jason pointed out, to acheive equal flow the pipe lengths/fittings need to be the same although like I said before, a few feet of pipe isn't really going to make all that much difference. Hooking the panels in parallel is the most important thing you can do and try to avoid any water traps.

I didn't have a vacuum breaker last year, but one of my connections, right at the very top must have had a small leak in it. I could hear air being sucked in when the pump was off, but oddly, no water came out when it was on. So by the next morning, the panels were almost all the way drained. I'll probably add a vacuum breaker this year though.
This vacuum breaker might pose a problem though. I'm going to add a solar control to the setup this year and how will the panel sensor know if there's enough heat in the panels to open the valve if there's no water there to get hot?

As Jason pointed out, the temp sensor is usually mounted in the direct sun. The point of this sensor is to capture the incident sun's temperature with wind and not the water flowing through it. Mine will sometimes read well above 110 degrees. You can either put the sensor in a spare piece of solar panel which is mounted separately from the real panels or you can just attach it to one of the pipes in clear view of the sun and the sensor in mid air (this is the way mine is attached). Once the direct sun's temperature drops below the water temperature (measured with another sensor near the pad), the solar controller will turn off the solar.

One last thing, the guy I'm planning to buy the controller from has offered to customize the temp differentials at which it will switch the flow to the panels on and off... if that makes any sense??? Basically, he can set how much warmer the water in the panels has to be than the water in the pool before the controller will send water to the panels. He can also set the temp. at which the controller will shut off the flow to the panels. This can be anywhere from about 0-10°F, but it needs to be at least 3°F between on and off. At least, I think that's what he meant. :lol: I was thinking maybe 3°F more then pool to turn on, and 1°F to turn off. Should I make the turn on temp. higher? I hope that made sense.

Thanks,
Adam

The on/off temperature differential is only important when the sun and air is not so hot and close to the water temp. As water temp approaches the sun's incident temperature minus any wind loss, the heat transfer from the panels to the water slows down quite a bit. So to get the last degree of water temperature rise takes forever and not really worth it. 10 degrees is probably way too much and 1 degree is way too little. My solar turns off when there is less than 3 degrees difference between the water temp and solar temp which may be a little on the small side. I notice that my solar stays on even though the water temp gain is very little. I can tell because I have a water temp sensor before and after the solar so I know exactly what my solar gain is.

My guess is that somewhere between 3-5 degrees might be close to ideal but it is hard to say. Having it adjustable would be really nice so you could experiment some. You might ask him if it is easy to change later.

But if you want to be safe, I would make it 3 degrees or less. Having the panels on a little longer is certainly better than having them turn off too soon.

 

[launboy]

Thanks for all the help guys. I may end up running the return from the lower panel to the top of the others just because of the way the plumbing will run.

I can certainly ask how hard it is to adjust the temp. differential part later on. My thinking behind the 1-3, or 2-5 range was based on the assumption that the sensor would be sensing outgoing water temp. I know(well, read) that these panels, when running near peak efficiency only raise the water 2-4 degrees each time it goes through.

Here's a link to the auction for the control.
http://cgi.ebay.com/SOLAR-HOT-WATER...5|66:2|65:12|39:1|240:1318|301:1|293:1|294:50

I believe the sensors on this unit are intended to take the reading of the water temp.
From the seller... "There is a good possibility that my control sensor could be taped to the upper-most output pipe, and insulated from the wind, and provide an adequate indication to the controller. If this does not work well, then you need to find a way to install a water-proof sensing tube into the upper output pipe so that the control sensor can be inserted to a point that is centered in the water flow of the pipe. This would be naturally insulated against wind interference and give the control accurate information."

The problem is the auction ends tomorrow while I'm at school and I haven't decided what differentials I want the unit to use. Does anybody know the temps. the Goldline or similar units use?

Thanks,
Adam