diy solar

diy solar

Yield with low irradiation

Tidemo

New Member
Joined
Nov 7, 2022
Messages
3
Hi all,

I have a question about a lower irradiance and the yield of a solar panel.
From winter time I know, the voltage will increase a few voltages because of the Temperature Coefficient. (with colder tempature)
But how about the irradiation?
The STC is measured by an irradiance of 1000W/m2, but what if the irradiance is only 400W/m2.

Approximately how much % will this differ in yield?

Thank you in advance for all advice!
 
@Supervtech, thanks!
Can you also substantiate why?

With temperature coefficient, it it not the same.
For example, half of the tempature (12,5 degrees), is not half of the yield.
Is the calculation different with irradiance?
 
That's assuming it's not cloudy. Where I live the winters are cloudy, I average about 10 per cent production compared to the rest of the year.
 
In winter there are several factors affecting output.

Assuming winter in northern hemisphere.

1) low sun maximum elevation in sky at solar noon and shorter hours of daylight.

2) Greater attenuation of sun due to greater amount of atmosphere at or below vapor pressure. (haze, fog, clouds)

3) Cold temp is a benefit as it produces greater Vmp for panels, but typically does not offset the reductions due to first two items.

If practical to your setup, it is good if you can at least adjust panel tilt for seasons.

In the graph, the difference from illumination dot and slightly greater red line output is due to some diffusion panel pickup from off-direct-facing angle.
solar-intensity-vs-incidence to horizon.png
At very low illumination level, typically below about 200 watts per square meter, the panel shunt resistance has greater degradation to yield. Typical shunt resistance for a 300-400 watt panel of 72 series cells is 300-400 ohms, but it can be as low as 100 ohms for poor quality cells, and over 1000 ohms for high quality cells used in panel construction. Typical series resistance of panels, Rs, is 0.15 to 0.4 ohms, again higher quality panels have lower series resistance.

Panel illumination current, Isc, is almost a straight linear function of sun illumination level.

Bifacial panels make some reasonable sense if you have a ground mounted PV array and a lot of surrounding snow on ground around perimeter of array to reflect illumination to back of panels.
 
Last edited:
Back
Top