Max temp for Solar Panel

DriveSkill

So having a bit of an issue with our Solar panels and the good weather! You would think we would have a plentiful supply of hot water but in fact we have very little....

I think I know what is happening ... basically the system is configured to turn on the pump when the temp at the panel is > 40C and <150C but it appears that once the sun starts hitting it by early in the morning we get to the 150 by perhaps 9am and then the pump shuts off so we get no more hot water for the day.

End result is we get a tank full of about 35-40C water.

Question is whether 150C is a good threshold or can I put it higher ?

Markcheese

That sounds odd... It should be pumping until it reaches your upper limit in the tank.... If only to cool panels...

DriveSkill

So I think it makes sense that there are thresholds where the pump doesnt work but I agree that the 150 upper limit seems relatively low and is easily achieved in this weather. As you say it might be more beneficial to try and cool down the panel.

At the moment the limits were the pump will stop are :

• If the panel temp is < 40C, this seems to make sense, heat transfer at that point would be minimal
• If the panel temp is > 150C, this is the one that seems to be kicking in....is it safe to run it higher ?
• If the water temp in our tank is >70C, again seems to make sense

Then there are settings also if the water in the tank is the same as the panel (within I think 5C) the pump wont go which also makes sense.

John.G

DriveSkill wrote: »

So having a bit of an issue with our Solar panels and the good weather! You would think we would have a plentiful supply of hot water but in fact we have very little....

I think I know what is happening ... basically the system is configured to turn on the pump when the temp at the panel is > 40C and <150C but it appears that once the sun starts hitting it by early in the morning we get to the 150 by perhaps 9am and then the pump shuts off so we get no more hot water for the day.

End result is we get a tank full of about 35-40C water.

Question is whether 150C is a good threshold or can I put it higher ?

There is something seriously wrong with your system or the way its configured, the > 40c figure is the collector enabling temperature, once the panel temperature reaches 40C (in your case, I've mine set at 25C) AND as long as there is a differential temperature of say 6c to 10c ( this is settable as well , mine is 7C) between the panel and the store temperature (this probe is located just above the solar coil in the hot water cylinder) the the solar circ pump should start and will continue to run until the differential temperature falls to its switch off point of around 3C to 6c (mine is 3C) ......so the water in the cylinder should continue to rise until the maximum cylinder temperature is reached (settable between say 60C and 95C, I've mine set at 85C) OR until the maximum solar panel temperature is reached (again settable, mine is set at 105C) the circ pump will then stop and the solar panel temperature will then rise very rapidly and in the case of evac tubes can go well in excess of 250C and will eventually cause serious damage to your system, solar fluid degradation, perished sealing washers etc).
I would advise you to get someone to look at your system ASAP as you should have lashings of hot water now, my cylinder temperature is at 77C right now after taking two showers. I have 2 flat plates/150 litre hot water cylinder.

If you wish you might post the controller make/model and also what system you have ie evac tube/flat plate and cylinder capacity and we might be able to suggest a few settings to help you while you are awaiting "expert" help.

There is a pressure gauge located at the solar expansion vessel, what pressure is this showing just now?? it should normally read around 1.5 bar to 3 bar.

Hopefully this should give you some idea of your system

dathi

[QUOTE=DriveSkill;107377810.

Ibut it appears that once the sun starts hitting it by early in the morning we get to the 150 by perhaps 9am and then the pump shuts off so we get no more hot water for the day.
?[/QUOTE]

sounds more like a flow rate issue with the solar fluid either the pump is not circulating the fluid fast enough or you have had a fluid leak as steam through a joint while the panel was at 150 and have lost volume

Tow

Trevor Sargent knows all about too hot solar panels: https://www.independent.ie/irish-news/sargent-gets-his-fingers-burnt-by-solar-panels-26440053.html

John.G

dathi wrote: »

sounds more like a flow rate issue with the solar fluid either the pump is not circulating the fluid fast enough or you have had a fluid leak as steam through a joint while the panel was at 150 and have lost volume

Correct, probably, either the circ pump isn't starting or the solar fluid level is low and that's why I'm asking what the system pressure is. In a correcly operating/configured system, the panel temperature should never be higher than 10c to 20C higher than the water temperature and the maximum cylinder temperature should be reached well before the maximum (switch off) panel temperature is reached.

DriveSkill

Thanks for all the replies. Perhaps you are on to something in terms of a leak of the solar fluid - had an issue with that last year and it was supposed to have been fixed but but they did have to come back 3 times! maybe there is another leak now.

The pressure gauge was quite low (< 1I think) this morning but I have seen it at 2-3 and generally it drops back again as the system cools.

Sounds like I might need someone to come look at it !!

dathi

john do you not have a heat dump to prevent over heating of the solar panel my one is dumping heat every afternoon at the moment

DriveSkill

So it does look like the pressure is low in my system, was just below 1 this morning - actually seemed to be even less last night and I actually turned off the pump.

Not sure what a heat dump is .... so not sure if I have one or not!

dathi

DriveSkill wrote: »

Not sure what a heat dump is .... so not sure if I have one or not!

sorry was asking other poster john.g, a heat dump is a system that diverts the solar flow into a dedicated radiator or central heating rads to dissipate the excess heat when your cylinder is up to max temperature

DriveSkill

So my system seems to be back working again which is odd as I didnt do anything apart from turn off the pump last night and turned it back on again this morning around 8am.

Came home this evening to find a full tank of water and the pressure around 3.5 - temp at the panel was 125C (6pm)

So now I dont know if I have a leak or not as the system definitely wasnt refilled but the pressure seems to have come back - at least when it heats up.

John.G

DriveSkill wrote: »

So my system seems to be back working again which is odd as I didnt do anything apart from turn off the pump last night and turned it back on again this morning around 8am.

Came home this evening to find a full tank of water and the pressure around 3.5 - temp at the panel was 125C (6pm)

So now I dont know if I have a leak or not as the system definitely wasnt refilled but the pressure seems to have come back - at least when it heats up.

What was the tank temperature?

DriveSkill

John.G wrote: »

What was the tank temperature?

Tank temp last night was around 70C so it basically was as expected.




However this morning its back on the blink again and now I'm thinking it could be the pump itself that has failed....


Pressure is around 2.5 Bar (for the solar fluid)


Temp at the panel is 155C.
Top of the tank is around 50C.
Pump is not running......



I changed the cutoff limit from 150C to 160C but the pump is still not kicking in! So I think that might be the problem


Dont know why it seems to work intermittently.


I've cut the power again in the hope that a reset might help (as that seemed to work the other day when I turned if off overnight) but seems unlikely!

John.G

DriveSkill wrote: »

So my system seems to be back working again which is odd as I didnt do anything apart from turn off the pump last night and turned it back on again this morning around 8am.

Came home this evening to find a full tank of water and the pressure around 3.5 - temp at the panel was 125C (6pm)

So now I dont know if I have a leak or not as the system definitely wasnt refilled but the pressure seems to have come back - at least when it heats up.

If everything was working to spec then that pressure should still be ~~ 2.5 to 2.7 bar when everything is cooled down. I think most (mine was at any rate) solar expansion vessels are pre pressurised to 2.5 Bar, then are filled to 2.7/2.8 bar to give a small reserve/buffer of ~ 1 litre of solar fluid.
If the pressure is falling to 1 bar or less when the system cools down then its more than likely that you have air in the system and also a loss of solar liquid.
The other only possibility that I can think of is that you have lost most of the expansion vessel pre pressure, you might just remove the plastic cover on the end of the expansion vessel and just press the little valve briefly with your thumb/finger nail and see if air comes out.

John.G

DriveSkill wrote: »

Tank temp last night was around 70C so it basically was as expected.




However this morning its back on the blink again and now I'm thinking it could be the pump itself that has failed....


Pressure is around 2.5 Bar (for the solar fluid)


Temp at the panel is 155C.
Top of the tank is around 50C.
Pump is not running......



I changed the cutoff limit from 150C to 160C but the pump is still not kicking in! So I think that might be the problem


Dont know why it seems to work intermittently.as


I've cut the power again in the hope that a reset might help (as that seemed to work the other day when I turned if off overnight) but seems unlikely!

I had posted before I saw this latest one, I wouldn't advise starting or attempting to start the pump with a panel temp of 150C you can get a lot of thermal shocking due to the big differential between the solar coil temp of 150C and the cylinder temp of 50C, I would wait until this evening and see if the pump starts automatically again when the collector temperature falls to whatever the controller setting is for restart.

I'm getting a bit mixed up in the different threads but can you see the make/model of your controller and post it please.