House fitted with 4KW of solar panels
In brilliant sunshine, such as we have had over the past couple of days,
what prevents solar panels producing the full permitted 4KW. Down to 2KW
A few days earlier, when not as hot, solar panels were producing 3.73KW.
Angle of the sun (time of day).
Dust on the panels (my car seems to have a thick layer of yellow
pollen or sand which has built up over a few hot days of non-use).
Of course, there's also the possibility of a fault.
Also, it's light, not heat, which generates electricity.
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And crucially heat decreases their efficiency although not normally by
factors of two. You should measure peak output when the sun is aligned
with the axis of your collectors (roughly same time each day).
Then you have a comparable number. It is possible you have a dodgy panel
that is misbehaving under thermal stress or they are covered in pollen
and dust at the moment.
Any partial shading of the array severely compromises output.
Temperature. The hotter they get, the less efficient they are.
I got peaks of over 4kW out of our 3.99kW system a few weeks ago when
the sky was clear but the temperature low. On similarly bright but warm
days now, the peaks are around 3kW.
Overall, with the longer days, I'm getting in excess of 25kWh each day.
Is the right answer. Panels have power TC of about -0.4 to 0.5% per
degree C, and the panels will get hot, maybe 45-50 C hence, on a hot
day, peak output can be 20-25% below peak output on a cool day wit
There's even a specification for it, NOCT - nominal operating cell
And he is factually wrong to boot. To get absolutely maximum output from
a solar array requires a clear blue sky path to the sun and the largest
amount of thin white cirrus cloud everywhere else. Enough to scatter
light that was destined to hit somewhere else onto your PV.
White clouds are *brighter* than blue sky in every universe but Harry's.
If you have the option since mirrors are cheap and solar PV device
expensive a 120 degree mirror assembly \_/ either side of the active
cells gives you about twice the output (but not flat plate). Tends to
get the PV cells a bit too warm and makes clear epoxy go yellow though.
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