Strange Result

[Kontiki]

I used the http://re.jrc.ec.europa.eu/pvgis/apps3/pvest.php site to estimate my solar panel performance. What I don't understand is the daily performance
May 14.3 kw
June 13.8 kw
July 13.9 kw

I would have expected June to be the highest performing month as the days are longer. Maybe it knows something we don't & we are in for a rubbish June this year

[kenneal - lagger]

What roof slope did you use? If your roof is steep you will get a better angle to the sun early and late in the year and a higher peak output. this could counteract the extra day length.

[adam2]

As above, and also higher temperatures slightly reduce output.

[biffvernon]

Maybe it knows something we don't & we are in for a rubbish June this year

That'll be it. It's rained every day since the Government declared a drought.

[kenneal - lagger]

We've had about 20mm so far today and it's still coming.

[Kontiki]

Roof angle is 25 degrees. Worst day today for quite a while only 4.5 kw

[kenneal - lagger]

With that rood angle the output should get higher the higher the sun. It must just be historic changes in cloud cover each month.

[An Inspector Calls]

I would have expected June to be the highest performing month as the days are longer. Maybe it knows something we don't & we are in for a rubbish June this year

The June minima is confirmed here:
http://www.transitioncambridge.org/thew ... AQ#shading

and explained in this paper:
http://www.bfrl.nist.gov/863/bipv/docum ... _Final.pdf

[RenewableCandy]

The rig in the paper are vertical panels, so the angle of incidence is going to be less in the summer (at the most-relevant time of day at any rate). I assume they were rigged in the USA so they'll have very different weather patterns to us.

The London figures probably are to do with cloud cover: I've read of a theory that the UK has a "monsoon" in mid-June, not checked the cloud-cover figures to confirm this, mind.

However, by the middle of August Chateau Renewable will have a set of figures to investigate...and so far at least, the June ones have been positively lethargic compared to other summer and spring months. Of course, you miss a lot of that "extra" sun in June, because it's shining on the North side of the house first and last thing in the day.

[An Inspector Calls]

In London (latitude 50 N), on a roof exceeding a slope of 27 degrees, the sun will go over the vertical for a roof-mounted solar panel at the summer solstice.

[RenewableCandy]

Point taken but the effect must be tiny (cosine law and all that) and on our roof (nearly 54 degN, 30 deg slope) it won't be happening, yet our June figures are still a bit lethargic. 'Course that's just the one year though.

[An Inspector Calls]

54 N, so the limit is a 31 degree slope roof. Yours is far steeper than that.

[Kontiki]

We are at 53 degrees north, our June figures up to yesterdays reading was 245.2 kw giving a daily average of 17.51 kw up to the 14th June. Working on the data I got from the solar prediction site I need another 168.8 kw to meet the monthly target that means I have to get a daily average of 10.6 kw weather forecast not looking good for this weekend though .