Solar hot water troubleshooting

I've got 20 evacuated tubes on my roof oriented NW, and I'm wondering if my system is working or not.
It's connected to a Resol DeltaSol BX controller.

The controller is saying that at peak sun my controller is only registering 31 deg C (89F) at the tail end of summer.  It's 20C today outside.

I went on the roof to check if there were any obvious damage, and there wasn't.  But feeling the tubes, only 5 of the 20 were cold, and 15 were warmish.
We don't really get below 0C most years so I doubt the tubes have ruptured inside.

Does this mean it's likely that 15 of my STS Sunsaver tubes have failed?

I guess evacuated tubes are old tech so no one knows these about things anymore.  Even the supplier has moved out of the business and only does PV these days.  No one left in the company that knows how these systems work.    The collectors are still under warranty so they need to find anyone who knows how to troubleshoot them.

Graham Chiu wrote:I've got 20 evacuated tubes on my roof oriented NW, and I'm wondering if my system is working or not.
It's connected to a Resol DeltaSol BX controller.

The controller is saying that at peak sun my controller is only registering 31 deg C (89F) at the tail end of summer.  It's 20C today outside.

I went on the roof to check if there were any obvious damage, and there wasn't.  But feeling the tubes, only 5 of the 20 were cold, and 15 were warmish.
We don't really get below 0C most years so I doubt the tubes have ruptured inside.

Does this mean it's likely that 15 of my STS Sunsaver tubes have failed?

I think you have your answer... lost their vacuum bad batch maybe?
There are a lot of types of evacuated tubes... do yours have a metal top piece that fits into a metal sleeve at the manifold? Or are they built into the manifold?
The troubles with moving water to the roof and back and the huge drop in the price of solar electric have taken their toll on the solar thermal industry...
Good luck   David

Does this help?

Graham Chiu wrote:Does this help?

Cam you remove each tube individually without draining the system?

So what type of system is it. Does the water stay in the manifold or does it drain back to a reservoir when the controller tells it to? I ask because I've seen a few where the thermostat reading from the roof is bad and it never sends the signal to fill the line. Here they do either glycol filled and heat 3xchanged or tanked with a drain back feature running straight water

The installation documents say it's an Open-loop system using water as the heat transfer fluid type.

When I heat the water up in the cylinder using the 3kW element, the temperature in the collector also goes up which I thought was odd.  It was setup to pump only if the difference in temperature between the collector and the bottom of the tank sensor was greater than 6K.  So, why would it pump hot water up to the collector?

Graham Chiu wrote:The installation documents say it's an Open-loop system using water as the heat transfer fluid type.

When I heat the water up in the cylinder using the 3kW element, the temperature in the collector also goes up which I thought was odd.  It was setup to pump only if the difference in temperature between the collector and the bottom of the tank sensor was greater than 6K.  So, why would it pump hot water up to the collector?

Yup, Where about are you Graham? you need a warm weather guy. We don't do systems like that up north. The way you are set up Think of your collector as an extension of your hotwater tank. Water sits in the collector until the controller tells it the temperature in the tank in less then the temperature in the collector.  Click pump turns on and the hot water from the collector is exchanged for the cooler water in the hot water tank. So either the water in the collector never gets up to the right temperature so there is never a call for the pump to turn on due to dead tubes, the thermostat reading on the collector is wrong so the pump never gets the signal to turn on or the pump is dead so can never turn on... I would suspect the controller or the tubes.

I'm in Wellington, New Zealand.  We don't have freezing in our pipes.

I think the controller is fine.  If I set the delta low enough for the conditions the pump starts working  ie. collector sensor is greater than bottom tank sensor + 6K.  Could the water from the bottom of the tank thermosiphon back to the collector when I apply power?
Seems unlikely.

I'm not sure how to remove the glass tubes.  Never got shown how to do it.

Graham Chiu wrote:I'm in Wellington, New Zealand.  We don't have freezing in our pipes.

I think the controller is fine.  If I set the delta low enough for the conditions the pump starts working  ie. collector sensor is greater than bottom tank sensor + 6K.  Could the water from the bottom of the tank thermosiphon back to the collector when I apply power?
Seems unlikely.

I'm not sure how to remove the glass tubes.  Never got shown how to do it.

hard to say it sure seems like it if you can heat up the collector. Ok so you are most of the way there. Tou know the controller works and the pump... leaving the tubes.

I've installed 7 of these systems. If the tubes are warm to the touch then the vacuum has failed. Usually the tube has a silver color at the bottom which is a oxygen absorption chemical. If the silver is gone the tube has failed. The tube will collect solar energy but will radiate it back out as soon as the temperature gets much higher than the outside air temperature. My system has a copper heat pipe and no water inside that plugs into the manafold  at the top. You loosen the connection at the bottom of each tube and wiggle and rotate and pull down to get the tube out of the  manifold. With my system you don't have to drain the water to replace the tubes. I don't know what is in your system so,if water comes out as you start to,remove a tube then you will have to drain the water. Chris

That sounds like what I have. I did examine the bottom of the tubes but didn't observe anything special but didn't know what I should be looking for. Maybe I need to remove a tube to see the bottom clearly?

I would guess it is a drain back system, if the collector loop is open. The can top right of the collector could be an auto air vent, but is likely a vaccum breaker for drainback.

A photo of the tank and mechanicals would help. If someone put a check valve in the feed to the collector loop. Also there is no way to tell what is going on with how heat is exhcanged to dhw. It could be drainback to a non pressurized tank with an external or internal HE or other. If the collector loop is open to atmosphere (technical not a bowl of water) then there are likely two tanks, or a tank within a tank........

The evacuated tubes should detatch at the bottom and slide out of the cups up top. If a bunch of water comes out (doubtfull, but possible with dip tubes) they are non heat pipe tech... if there is a copper bulb at the top and a dry fitting you have heat pipes. Thats a place to start determining what type of system and you will then see the barium on the bottom, if silver, all is well, if opaque white, the vaccum is lost.

Solar thermal hydronics since 2002.

It could be topped up with water..... i dont know why someone would do that it loses too much heat. But if you heat the tank at night and the collector gets warm it could be steam or it could be full of water. The only way for that to not heat the tank is for it to not circulate when heat is available at the collector. You should see high temps, up to 180 deg f.

I've found the plumber who was originally contracted to install the system so he's coming to have a look later this week.
I could go onto the roof again to examine the bottom of the tubes but will wait until spouse is home to hold the ladder for me !

I'm now wondering if that's one of the causes of my high electricity use if the hot water in the cylinder is thermosiphoning back to the panels at night.

I guess I could measure the night time temperature and see if the sensor is the same or lower.  If the sensor at the collector reads higher than ambient it must be thermosiphoning back upwards.

Sorry, I never finished this thread .. but all the tubes were deemed faulty and were replaced under warranty.

I guess I'll have to replace them again at the 10-15 year mark.

Good to know it was a problem that could be found and fixed. Have you had any sunny days to see if there's an improvement in performance?