sunny day, clear skies, lower output

rosythfifer

Hi

As the title really im just trying to understand why. Today is sunny again, warmest so far and clear skies. However my panels all in direct light are only putting out 1.7 Kw. Now in less clear days I have my panels maxed out at over 2. What could cause the drop. Is it possibly lack of cloud causi g no reflections back to the panels?

Andy_WSM

Warmer temperatures cause a drop in output, but not to that degree this time of year I wouldn't have thought.

Maybe there is high level cloud or a lot of pollution, so while it may look sunny it's not as bright as it's been when we had the colder air around?

rosythfifer

I think your right with high level as there is some light whispy streaks. I also never considered the clocks going forward when I was comparing times.

nobby1963

Also when the panels become too hot themselves they can not perform to their optimum.

KevinG

nobby1963 wrote: »

Also when the panels become too hot themselves they can not perform to their optimum.

Absolutely, my highest daily generation figures have always been in April and May when temperatures are lower. Obviously monthly generation is higher in the summer due to the generally longer and sunnier days.

nobby1963

I have found that a clear sunny day but with an odd couple of clouds coming along at regular ish intervals to allow the panels to cool has given us our best generation figures.
Having said that, down here in sunny Devon we have had a cracking couple of days with good generation- 24.36kwh - over a tenner for us - yesterday.
That will do nicely!
Nobby.

jimjames

Andy_WSM wrote: »

Warmer temperatures cause a drop in output, but not to that degree this time of year I wouldn't have thought.

Maybe there is high level cloud or a lot of pollution, so while it may look sunny it's not as bright as it's been when we had the colder air around?

You'd be surprised how much a panel heats up in the sun even on a day in April.

The calcs normally show a 0.5% drop in output per degree increase in temperature.

http://uk-solarpanels.blogspot.co.uk/2012/05/temperature-solar-panel-electricity.html

This shows the difference between 2 days with different temperatures.



I also did an experiment with cooling the panels with water and the output jumped considerably as a result.

http://uk-solarpanels.blogspot.co.uk/2012/08/cooling-solar-panels-increase.html

gazapc

As mentioned above, you get x% drop in power for every degree above standard test conditions. That standard test condition is 25 degrees C. For a typical Trina module they give -0.41%/degree increase and can expect a roof top module to get to 45-50 degrees in prolonged direct sunlight (roof top heat up more due to lack of air circulation when compared to ground mount).

So a 20 degree increase over standard test conditions gives just over an 8% drop. 2kW x 0.92 = 1.84 kW, so much closer to your actual generation stated.

Combine that with haze and perhaps dust from a dry day and output can easily drop.

Other countries suffer heat losses much more.