Cumulus Support

A couple of years ago I was tempted to buy a sunshine recorder that was discussed here. In the event I didn't go for it mainly because of access issues and the need for regular maintenance.

I'm currently looking at having solar panels installed and with the software that some inverters have allowing you to read the output it occurred to me that it might be possible to use that data to measure hours of sunshine.

Does anyone know if this might be possible?

I'm interested in this too. I use PVOUTPUT for the solar logging - http://pvoutput.org/list.jsp?sid=1627

Only issue for me would be i'm not south so lose daylight readings earlier than dusk.

Hi,

The output should give a reasonable indication of the "Sunlight", but not (IMHO) a "perfect" measure of the "Meteorological" Watts/square metre. That's because the panels are (presumably) sloping, whilst a solar radiation sensor should be (usually) flat and horizontal.

During the Summer months, the sun will rise and/or set behind the plane of the panels (assuming that they are facing reasonably southwards). So you are likely to get a lower reading than is "correct" during the early/late hours of the day and perhaps too high a value at noon. In principle it can be mostly corrected with appropriate "maths" (three-dimensional geometry, etc.), but it's not trivial.

Cheers, Alan.

Thanks for your reply Alan. I appreciate it's not a straight-forward problem to solve. My house faces ESE (120 degrees) so that aspect would capture the dawn or soon after as the horizon isn't too bad. That direction would be okay until around noon when the SSW facing roof (210) would take over. During winter that would capture the day's remaining sunshine.

During the other seasons a few panels on the WNW facing roof (300) would capture the late afternoon and evening sunshine.

If it was possible to nominate one panel from each side it should in theory be possible to record most of the day's sunshine albeit with the drawbacks you have mentioned.

Assuming all that is technically possible might some type of software be capable of recording sunshine hours?

Hi Ray,

I had this thought too, when I had my PV array installed. I suppose it [sunshine hours]could be derived from the array output but I find the PV system generates even when there is indistinct sunlight!

I haven't tried to fathom-out how pvoutput uses the API feed from my Wunderground data to determine the conditions. Certainly the results differ significantly from my observations

Hi Mike,

The problematic part is deciding what's sunshine and what isn't. I think it would be quite hard making that decision from the output on a pv array. Probably why no-one has made anything that makes pv panels into a sunshine recorder. Ho hum.

Yes, indeed. Taking today as an example, we've been overcast all day with the exception of some very short spells of sunshine around midday. The PV array has, despite the absence of real sunshine, generated 4.295kWh.

That's very encouraging Mike. I will have some news for you next week hopefully.