As a newbe to pv installations can anyone tell me how or where I can find information on checking out whether my installation is working correctly. I am sure the output is only 1/3rd of comparitable 3Kwh systems but I can not find any information on testing or even if it is possible to test panels outside of manufacturer testing.
I am aware of the effects that shading,cloud cover and angle of panels can make but even allowing for these generation has always been low with an ideal summer weather daily total generation of 5.8Kwh

PV systems are rated at typically 1000 W/m² insolation from the sun, so if your system is rated at 3 kWp (not 3kWh, BTW) then it should deliver that power in bright sunshine in mid-summer, when the sun is high in the sky (it may actually deliver a little bit more then). At this time of the year, with the sun low in the sky, limited daylight hours and quite a bit of cloud around you will get a lot less.

For example, where I am in the south of the UK the average daily insolation (power from the sun) is about 1.2 kWh per square metre per day for January, and an 18% efficient solar panel would only deliver about 0.2 kWh per square metre per day of useful power. By June/July the power of the sun will have increased to over 5 kWh per square metre per day, nearly five times more than the January figure.

Chaps, the OP did say "an ideal summer weather daily total generation of 5.8Kwh". That does seem to me like about a third of what you could expect from a reasonable installation.

First thing I'd want do is measure the open circuit voltage and short circuit current of each of the individual strings but that might not be practical for you for all sorts of reasons so I think we need to know a little more about the installation (grid-tie?, what inverter? what panels? how are the wired?) before giving any advice but the first questions I'd ask is what actually happened on a good day? What did the inverter report as to the peak output achieved? What was the output for the rest of the day, etc?

<blockquote><cite>Posted By: Ed Davies</cite>Chaps, the OP did say "an ideal summer weather daily total generation of 5.8Kwh". That does seem to me like about a third of what you could expect from a reasonable installation.

First thing I'd want do is measure the open circuit voltage and short circuit current of each of the individual strings but that might not be practical for you for all sorts of reasons so I think we need to know a little more about the installation (grid-tie?, what inverter? what panels? how are the wired?) before giving any advice but the first questions I'd ask is what actually happened on a good day? What did the inverter report as to the peak output achieved? What was the output for the rest of the day, etc?</blockquote>

Hi Folks thanks for your input

1)checking out what JSHarris put forward When you say 0.2Kwh per square metre per day would I be right in thinking that if I multiply the square area of my panels by 0.2 this would be an indication of what I could expect to generate on a reasonable day at this time of year?
I have 12 panels each measuring 1M x 1.3m including outer frame ,so say a total area of about 15 square metre
X 0.2 = 0.3kwh
Would this be my expected total daily generation or the peak output per hour ?

I am also in the south and over the previous four days my total daily generation each day has been 0.7 / 0.8 / 1.2 and 0.1 yesterday when it was wet & cloudy all day here.

2)Ed - Your right dont want to curl what little hair I have left,so would not want work on the system live myself.
My system is grid tied and consists of 12 Philadelphia 250Wp panels in one string connected to a 3kWGT(E) Enasolar Invertor.

Since April the highest spot output I have seen was at about 1.30pm in June when I got 2.19 Kwh and the total output for that day was 5.5Kwh.
The days highest total output since last April was 6.7

Sorry Ed thanks for putting me right.
Yes 3 kw and 2.19 kw

Previously when I contacted the installer I felt I was being fobbed off with jargan and various weather conditions affecting my system,possibly because they did not want to come back and check the system or did not know how to.
My Energy supplier has come back to me to check my readings as they consider them to be low for my size of system ,which has prompted me to try and find out more in advance of contacting them, in the hopes of being more positive in getting the sytem checked and understanding what they could be checking.

Well it could also be a wiring problem, it does happen! We had our 4KW Sanyo installation with PowerOne inverter live since 12th Dec but the output when the sun was bright was never more than 800/900W, it just didn't feel right. We have 3 strings, 2 with 6 panels together in parallel and then 5 panels on its own

After testing the output with a volt meter on wiring before the DC isolation switches and before the inverter, I determined that the + and - wires had been wired incorrectly coming out of the DC isolation switch for the 12 panel array so I was getting no output from 2/3 of the panels. Corrected it and output shot up to 2.1KW when sun came out, much happier :-)

Did your installer give you a installation test cert. ?
Have you contacted them with your concerns ?

Also there a UK online data base of uploaded PV output date , you could check it against tihs for similar local system. soory dont have a link though I'm sure someone will

Yes I got an instalation test cert.but it is mainly tick boxes on the schedule of items inspected with nothing ticked on the schedule of items tested.

Posted By: diydoctorThe wiring was a possibility I wondered about but was thinking more about the connection between panels than back at the invertor.

It's a bit odd that you seem to be getting some 2/3rds of the appropriate maximum power yet only get about 1/3rd of the expected energy per day.

My initial thought was that you had a problem like Phil.Chaddah-Duke's above and that's still possible. E.g., could they have just plugged the panels in such a way that a few panels are missing from the string completely? Alternatively, there could be something wrong with the configuration of your inverter or, as CWatters mentions, a mains voltage problem such that your inverter is dropping out for significant periods of time.

I can understand you not wanting to mess with the system too much but checking the voltage from the panels with the inverter on and off line (i.e., the actual Vmp and Voc values) when there's reasonably bright sunshine on all of the panels might give a clue and should be possible without doing anything very hair raising. Remember that the panel voltages shouldn't be too dependent on how bright the sun is - that mostly affects the current the panels can supply. If those are much less than 12 times the panel datasheet values it means the problem is probably in the panels otherwise it's likely an inverter problem.

Have finally managed to get my installer back to check my system out,which initially consisted of them looking at the trees around and declaring them to be the cause.Reluctantly they agreed to check the inverter output.
Unfortunately it was a dull and overcast day so there was not a lot of output.He said the readings were 401Vdc and 0.8amps which was consistent with the weather and the invertor output reading,so everything was o.k.
Two other comments he made which put some doubt back in my mind were :-

1] There are two ways of making the connections to the inverter and he usually does it the other way so has reconnected it the way he normally does it

2]Because the trees are shading some of the panels, some of the generation from those panels in the full sun is being used to power up the shaded panels.

I can understand loosing some power to the cables but I would have thought the shaded panels will still produce some power as the system generates even on overcast days albeit not very much in comparison to a sunny day.
It will be interesting to see on a decent day if there is any increase in generation from having the system connected up his way.

Colin, what is your nearest town and I shall see if I can get some solar data for it.

Just catching up with this thread. Having just got together the output data for February, herewith are the outputs in kWh per month for my 3.9 kWp system installed last April (location west Pembs):

Apr-11 386
May-11 405
Jun-11 491
Jul-11 411
Aug-11 333
Sep-11 253
Oct-11 140
Nov-11 78
Dec-11 33
Jan-12 54
Feb-12 103

I was interested to read that the OP could expect to get around 20% of the best summer output during the winter months. As you can see during December we achieved only approx 7% of the output we got in June and that's with an all singing, all dancing, microinverter jobbie! The 6 months from September to February have contributed just 24% of the total output. The old adage "make hay whilst the sun shines" comes to mind!

hi,

Your installer ought to be taking this more seriously IMO. My 0.9kWp little system peaked at somewhere between 5-6kWh last summer, yours is only generating around 1/3 of what it ought to on peak summer days.

The string voltage and output on the test look about right, so that's not the problem. I'm suspicious that you've got shading from eg a TV aerial, soil stack vent, chimney or tree that's causing huge problems with your system in summer. Can you post a picture of the system and surrounding roof, and any nearby trees etc please?

this is my day job btw.