Problem with Temperature Reading on Solar Panel

fitzie79

Hi,

I have had an issue with the temperature reading on the solar panel controller pretty much since the day it was installed. The guy who installed it turned out to be a bit of a cowboy (I didn't hire him - it was through the plumber who was actually quite good otherwise).

Basically the temperature reading on the control panel for the solar panels will intermittently give a false high reading - this turns on the pump when it shouldn't. If I go into a menu on the control panel and then back out of it it seems to reset the reading and the problem disappears. Similarly, if i turn on and off the pump it resets itself.

I had the guy who installed it out a couple of times to look at it (he was due to come out on 12 seperate occassions but actually only turned up twice - always some last minute family business....).

He tried to blame the electrician's wiring initially - saying that the cable the electrician used had too high a resistance because it was an outdoor shielded type of cable that was used, when he asked for a 3 core cable. When I pointed out to him that the cable was thicker than what he requested, and therefore had less resistance he tried to bluff his way around it. The other thing that I noticed with the wiring was that he had incorrectly used the alarm cable to connect the solar panel temp sensor to the 3 core cable. The solar panels are mounted on the garage with the control panel in the utility. The electrician had ran 2 cables to the garage, one for the alarm system and one for the solar panel. However, even though this cable probably isn't ideal and may have more resistance I would have thought that a resistance issue would give a continuous false reading?

On the second visit he then tried to change the control panel but this didn't resolve the issue either.

Since his last visit he has gone out of business and there is no way of contacting him (it would probably be a waste of time getting him back anyway). Does anyone have a suggestion as to what could possibly be causing the problem? I asked him about the possibility of a faulty temperature sensor on the panels but he reckoned that was very unlikely????

PS Sorry for the long winded description!

ccsolar

Hi Fitz79
Is it possible to replace the sensor cable from the panels to the controller with out much hassle, or is the cable buried under ground.
What part of the country are you in?
You could run a new sensor cable above ground for a temporary fix and see if this solves the problem.
What make of controller is it, ?

Cc

fitzie79

I am based in Cork

The cables are buried under the ground but i could possibly run a test cable from the solar panel to the control panel. I would have thought if the resistance is the issue then it wouldn't be an intermittent problem - is there something else that could be going on?

There is no brand on the control panel. It has 4 grey buttons on the front, a red LED that comes on when the pump is on and the backlight on it is bluey. Sorry the description is poor but hopefully it might ring a bell with someone?

freddyuk

Does this happen when the sun is out?? Or when the panel is obviously cold.
Could you have air in the system which causes a hot spot in the panel system? Is there an AAV by the sensor on the panel? Start with the easy options first.
The sensor cables are not particularly special as you can use bell wire and get a satisfactory reading but I am not an electrician. Failing that swop the sensors over and see if the problem persists (after bleeding).

fitzie79

it always happens with the sun out. on sunday the reading was 35 then suddenly shot up to 115! i've noticed that the reading fluctuates up and down quite a bit as well - constantly moving up/down within a 3 degree range. the readings at the top/bottom of the tank are pretty constant - only varying within +- 0.1 degrees.

the air in the system theory is interesting - what is an aav?

fitzie79

managed to find the controller model. it's this one

http://www.seitron.it/en/products/details.php?sectionid=37&itemid=464&pag=1&pathtype=sectiontree

ccsolar

Hi Fitzie79
An aav is the automatic air vent
Any chance of an up date ?
Cc

fitzie79

thanks for that. i'll have a look for that on the panels. haven't been able to do much with it over the past week - waiting for someone to come out and give me a hand debugging it. had to turn off the pump last night as the sensor was reading 75 at 6pm last night when it had been cloudy all day. weather for next few days is poor so going to leave it off.

hoefully over the weekend will get a chance to look at it properly

fitzie79

got to look at this issue a bit more this morning. it was a bit eventful to say the least. we took the cover off the panel so that we could get access to the probes. i had an ohmeter with me so the plan was to measure the resistance reading from each of the probes to ensure it made sense. however, when taking off the cover there was a big bang and smoke..... the supply cables to the pump shorted as there was a loose strand from the neutral that touched the live. we should have turned off the power to the panel first but if the wiring wasn't so shoddy it wouldnt have mattered. the short blew the relay for the output from the panel so now the pump won't work.....

anyway we verified the signals from the probes are not a problem. i measured the resistance of the probes and based on the delta resistance of 3.85ohm/deg was able to calculate the temperature at each sensor. all 3 sensors made sense. the reading from the solar panel sensor was rock solid - previously the display would show this fluctuating constantly up and down by 1 degree.

now that i am satisfied that the sensors are working ok i think the problem was with the control panel (it certainly has a problem now anyway!). looking through the manual there is a configuration for 2 solar panels (setup 15 in the manual link above). i am going to try to hook it up like this and use the output from the 2nd relay to drive the pump (assuming this hasn't been damaged). however, i need to get a 1k resistor as at the moment the panel gives an alert saying that sensor 1 is open as it has no feed. by connecting a 1k resistor across this channel it should think that the temperature on the panel is 0degree and the 2nd panel input should function ok.

however, in the worst case scenario that the panel wont work does anyone have a recommendation for a new control panel? i'd like one that monitors the amount of energy that has been gained from the solar panels (just to see how much they are producing). are these control panels simple to configure yourself?

Tomo87

fitzie79 wrote: »

got to look at this issue a bit more this morning. it was a bit eventful to say the least. we took the cover off the panel so that we could get access to the probes. i had an ohmeter with me so the plan was to measure the resistance reading from each of the probes to ensure it made sense. however, when taking off the cover there was a big bang and smoke..... the supply cables to the pump shorted as there was a loose strand from the neutral that touched the live. we should have turned off the power to the panel first but if the wiring wasn't so shoddy it wouldnt have mattered. the short blew the relay for the output from the panel so now the pump won't work.....

anyway we verified the signals from the probes are not a problem. i measured the resistance of the probes and based on the delta resistance of 3.85ohm/deg was able to calculate the temperature at each sensor. all 3 sensors made sense. the reading from the solar panel sensor was rock solid - previously the display would show this fluctuating constantly up and down by 1 degree.

now that i am satisfied that the sensors are working ok i think the problem was with the control panel (it certainly has a problem now anyway!). looking through the manual there is a configuration for 2 solar panels (setup 15 in the manual link above). i am going to try to hook it up like this and use the output from the 2nd relay to drive the pump (assuming this hasn't been damaged). however, i need to get a 1k resistor as at the moment the panel gives an alert saying that sensor 1 is open as it has no feed. by connecting a 1k resistor across this channel it should think that the temperature on the panel is 0degree and the 2nd panel input should function ok.

however, in the worst case scenario that the panel wont work does anyone have a recommendation for a new control panel? i'd like one that monitors the amount of energy that has been gained from the solar panels (just to see how much they are producing). are these control panels simple to configure yourself?

There are solar controllers available that take an SD card so you can record and see temperatures over the year displayed on a graph, however if you want a proper heat metering solution where you can see the energy contribution from the solar then you'll need to fit a flow meter that will allow the controller to give a Kilowatt hour reading and also additional sensors on your flow and return lines, The sensor in your panel may have to be swapped if the new controller uses a different kind of sensor, Pt1000s are the sensors i'm more familar with, they work fine with .75mm sq. cable up to 50m. other than that another controller would be easily fitted and quite straight forward to configure.

fitzie79

i don't want exact figures for the energy contribution - just an approximate idea is enough. what controllers use the sd cards? can you recommend some of them - if recommendations are against the forum rules can you pm them to me.

thanks

championc

Hi Fitzie

I have a Kingspan SC300 (a badged Steca TR 0603mc). It records all data to an SD Card and it can be reviewed on a PC with Steca Software. It's perfect for looking at problems to get a good idea as to what's going on.

On mine, I can see the temperature at the roof, the bottom of the store and the top of the store. I can also see when the pump runs. So I can see the roof temperature rise and when it's more than 8 deg C higher than the bottom of the store, the Pump kicks in. You can then see the roof temperature initially being lowered as it transfers it's heat into the store and certainly, during early morning when the sun is just hitting the panel, you can see the pump kicking in and out a few times until the greater intensity of the sun generates enough constant heat to keep the pump running and the store temperature begins it's climb upwards.

You can really see it in this zoomed in display of my data from 26 March 2011 just gone


In your case, it sounds like the pump was not kicking in early enough and so it was allowing your panel to essentially overheat. So this could have been a bad wiring connection for the pump or the temperature sensor. I too agree that bellwire is perfectly OK for PT1000 type sensors.

Hope this helps


C

quentingargan

I agree with all the posts here, though for the sake of it, I would avoid bell wire - I have come across a few electrical errors with this because it is solid copper and can break if stretched, or if it gets a knock in the loft space. For the sake of I would use stranded wire if doing a refit. 0.75mm or above is fine for up to 50m of wire run.

macnab

Unusually high temperatures at the panels can indicate air at the top of the system, this can be accompanied by fluctuations in the system pressure. Air being a gas will expand much more than fluid and thus you get pressure fluctuations. This can be caused by a leak or more likely a dodgy AAV, either caused by poor performance in general or poor location (not at the highest point) This problem will also result in poor heat transfer so your vessel will not have as much hot water as you would expect. I have just had to refill my system due to a dodgy AAV. The results were obvious yesterday with 70 Degrees Celcius at the bottom of the vessel and 74 at the top. Where as last week on a day with similar weather I had 27 Degrees at the bottom and 56 Degrees at the top.