Don't think solar system is operating as it should

[FED565]

New member, first question. My house has a fully hydronic boiler system for heating with a combo water heater that uses the boiler plus 4 solar panels. We replaced the whole hydronic portion last year with Locknivar products for some energy savings as the old system was 12 years old or so. Everything has been working fine but I always hear my boiler come on during the day even during nice days and I started wondering why so I started looking at the inlet temperature from the solar side into the hot water heater and it was never above 100 degrees. I do not know much about solar so I started checking the system and ended up purging a bunch of air from the valves at the top of the system on the roof and it seemed to help with the temperature getting a little hotter but not near the 125 degrees the hot water tank is set at. Also, the pump that pumps the solar system is a 12v pump that operates off of a solar panel next to the water solar panels so it only operates during the day but pumps all day long (and has been pumping cool water into the hot water tank causing the boiler to reheat it all day long).

So the panels I have came on the house when it was built in 2000 and they are starting to look a little worn out. So my thoughts on this was to get some kind of temperature switch that will only pump the solar when it gets to the required temperature. So my question is are my panels still good, can I repaint them black again? Should I get new panels (can you suggest brand/model), do I need to purge my system more? I would like to try some possible fixes before I call a plumber. Any suggestions are appreciated.

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thanks for your time
Scott

[peakbagger]

Those SHW panels look beat. Were they designed without glazing or did it disappear over the years?. Most SHW systems have differential controllers that only run the pump when the roof temp is higher than the tank temp.

If you are looking at lots of money to replace major components, the current cost effective way to heat hot water is with a heat pump hot water heater with enough solar panels to run it.

[FED565]

I thought they looked beat myself. Hoping to do a possible fix or just get a few more years out of these as I have just spent a mint on a new boiler and water heater. I think the panels look home made myself but I have no prior experience with solar. Looks like a lot of the black paint/coating is peeling off or totally gone where the tubes run through so I was thinking about redoing the black to hopefully increase the heat exchange. Not sure if even trying anything is futile or I just need to get new panels as I would like to go with the setup I already have.

[LucMan]

The piping to the panels is incorrect. The return line (top pipe) should be connected on the other side of the panels opposite the inlet.
The panels look unglazed from the picture and homemade, but look like they are built like a tank.
You could install a 115v differential controller and pump, this would switch the pump off if the water in the tank was higher than the temp of the panels. This would prevent you from heating the outdoors, and keep the boiler off more. Set the t stat for the upper coil at 120.
Keep using the panels until they no longer work, and make sure you bleed all the air out after repiping.

[Amy@altE]

I bet those are used panels they got for a discount (or free) because the tempered glass was broken. I have a few of them myself in my backyard, waiting for me to fix them. You can order tempered glass at a local glass shop and they will perform much better.

To control the pump, you have 2 options, one much cheaper than the other. 1. cheap option. The PV panel is oversized, so it is pumping water early in the morning and late in the afternoon when it shouldn't. You can, through trial and error, block off part of the panel to make it not put out so much power, so it will need more sunlight to to run, thus turning on later in the day once the collectors have time to heat up, and will turn off earlier in the day when the collectors have cooled down. 2. better option. There are 2 companies I know of who make 12V PV Differential temperature controllers (DTC). IMC Eagle2 http://www.solar.imcinstruments.com/Home/Eagle2-D2.pdf and Art Tec http://www.arttecsolar.com/

I did a video on the IMC one several years ago, go to YouTube "IMC Eagle 2 Differential Temperature Controllers - Overview" if you want more details. We don't carry SHW anymore, but I'm sure you can find a source for both of them.

[J.P.M.]

As Lucman wrote, it looks like the flow arrangement to the collectors is incorrect, probably short circuiting a significant portion of the collectors' area/risers.

Besides no glazing - a major problem if any significant performance under elevated temps. is to be expected - it looks like there is not a whole lot of insulation, if any, on the back and sides of the collectors, further limiting potential or actual performance.

To me, at least, the collectors appear not of DIY origin. If factory made, they're probably orphans by now as those material thicknesseses and other things seem to have the mark of age as well as limited knowledge of thermal design of solar collectors, reinforcing my hunch that they are now orphans - any co. designing like that won't last long.

I'd start by correcting the flow arrangement and insulating the panels with something that won't outgas when the collectors are glazed (regular fiberglass batts and poly foam can outgas a far amount). There is insulation avail. for solar thermal collectors. Johns Manville used to make some, but I've been away from that end of things for some time. Next, I'd glaze the collectors with tempered glass. Low iron tempered glass would probably be overkill and costly for these units, but tempered glass is essential. Don't forget some small vent holes top/bottom w/ bug screens on the backside to help vent any moisture that does get in. Finally, I'd scrap the pv pumping arrangement for an ac pump and a differential controller. Not as elegant as PV pumping, but more reliable and flexible, provided the power stay on most of the time.

All the above comes at a price. If that price approaches the cost of replacing the collectors, or makes the solar portion of the heating system non cost effective, it may be throwing good money after bad.

As for covering part of the PV array to slow down the flow, with all that's wrong with this system, I'm not sure the pv is oversized or not. I'd decide if a rehab is worth it before I started screwing around with the pumping system. I suppose changing the pumping rate can't hurt, but with all that's wrong with this system, changing the flow rates just adds another level of uncertainty to the solution matrix. I'd get the flow arrangement and the equipment right before farting around with flow rates. I will say that, within reason and with some economic considerations aside for the moment, I'm not sure it's possible to oversize any pump - that's one reason why God made throttling valves. On the other hand, even if designed well and run correctly, the flow in this system will be so deep in laminar flow that knocking it back by, say, 20 - 30 % or so probably won't do much except increase the mean plate temp. some and decrease efficiency some.

If I kept the PV pumping at all, before I'd cover a portion of a PV panel, I'd rather change the panel orientation (probably more horizontal) for less output farther from solar noon - something I did on a system back in the day that seemed to be adequate to some degree.

[LucMan]

The proper glazing for thermal panels is extremely expensive and I would not waste the money on it for these panels.
Basically they are pool panels at this point, but with reconfiguring the piping (in Nevada) you should not have a problem getting 120 - 140 degree water this time of year.
There may be a problem with over heating this summer, so a dump zone may have to be added in the future if the need arises.

[J.P.M.]

I wonder I this system ever froze and if not, what prevented it.

[pleppik]

So the panels I have came on the house when it was built in 2000 and they are starting to look a little worn out. So my thoughts on this was to get some kind of temperature switch that will only pump the solar when it gets to the required temperature. So my question is are my panels still good, can I repaint them black again? Should I get new panels (can you suggest brand/model), do I need to purge my system more? I would like to try some possible fixes before I call a plumber. Any suggestions are appreciated.

One quick experiment you can do to determine for sure if the panels are cooling rather than heating the water: disconnect the circulation pump and see if your energy consumption goes up or down.

[FED565]

Thanks everyone for the replies as they are all very helpful on understanding on what I currently have.

They system has never froze as long as I have had it as it does have antifreeze in the system, when I had the new boiler and water heater installed the plumber refilled the solar part with enough antifreeze for out climate.

My plan now is to turn off the solar portion of my hot water completely by unplugging the pump and I also have a shutoff valve on the inlet and outlet of the system that goes into the water heater. So I will have no flow and can see if my propane bill goes down. I would definitely like to keep the solar portion of my system but it looks like I made need to bite the bullet and get a correctly configured system installed.

[J.P.M.]

Thanks everyone for the replies as they are all very helpful on understanding on what I currently have.

They system has never froze as long as I have had it as it does have antifreeze in the system, when I had the new boiler and water heater installed the plumber refilled the solar part with enough antifreeze for out climate.

My plan now is to turn off the solar portion of my hot water completely by unplugging the pump and I also have a shutoff valve on the inlet and outlet of the system that goes into the water heater. So I will have no flow and can see if my propane bill goes down. I would definitely like to keep the solar portion of my system but it looks like I made need to bite the bullet and get a correctly configured system installed.

If you do that, as a safety precaution, maybe overcautious, cover the panels. They probably won't overheat and the H2O/glycol probably has a relatively high boiling point, but covering the collectors won't hurt.

You didn't mention, or I missed that the collector is a closed loop. Maybe another problem is with the HX portion of the system.

[FED565]

Yes I believe it is a closed loop system.

[FED565]

I have been looking online for new panels and it looks like there are few very popular brands. What would any of you suggest as far as good for price and quality? Also, would you suggest buying local or from an online retailer and if so which one?

From turning the solar completely off I have noticed that the boiler is not coming on as much.

thanks again for your help
Scott

[LucMan]

I have been looking online for new panels and it looks like there are few very popular brands. What would any of you suggest as far as good for price and quality? Also, would you suggest buying local or from an online retailer and if so which one?

From turning the solar completely off I have noticed that the boiler is not coming on as much.

thanks again for your help
Scott

AET & Sunearth flat plate panels.
Stay away from evacuated tube.

[Amy@altE]

I have been looking online for new panels and it looks like there are few very popular brands. What would any of you suggest as far as good for price and quality? Also, would you suggest buying local or from an online retailer and if so which one?

thanks again for your help
Scott

AET is great, so is Heliodyne. Heliodyne is in CA, so shipping may be better than AET coming from FL. I'm not sure who is selling them online anymore (we stopped selling SHW last year), you can call either of them and ask if they have a local distributor.