QUALITY OF SOLAR PANELS IS IN THE MATHS

NO WHERE TO HIDE: CALCULATING TRUE SOLAR PERFORMANCE

We have read many websites advertising caravan and 4WD solar panels at lower prices. They nearly always brag about having the “high or even highest efficiency solar panels in the market”.

We simply do the maths to find out the “pork pies” and its “porkies” on nearly every occassion.

How is this done?

It’s very easy you see. Sunpower publish the Voc of their solar wafers. Simply take the number of wafers on the panel and then divide the panel Voc by this number to get the Voc per wafer. Then look up the tables above to determine the quality.

There is a slight complication: If the panel has bypass diodes then the forward voltage loss has to be taken off (one reason whigh high voltage panels have an advantage as the loss is a much smaller pecentage). There will also be a very small voltage loss on the junctions themselves of say 0.1V. We use a 0.8V Diode loss.

Lets look at an example.

Safiery’s highest grade panels are 190W. They have a Voc of 38V. There are 54 wafers in a panel. The Calculation is:

Voltage of Wafers before Diode: 38V + 0.8V +0.1V = 38.9V.

 38.9V/54 Wafers = 0.7203V/Wafer

Looking up Chart above these wafers are Maxeon III Bin Le1 which is 0.721 per wafer. This shows the diode and junction drop to be a little more than 0.9V.

Checking the power against the same chart:

54 Wafers x 3.62 Wp per wafer = 195.48 Watts

Loss of 0.9V x 6.15Isc Loss on Diode/Junction = 5.535 W

195.48 – 5.535 = 190.013Wats

The Maths Check out. No Porky Pies here!

To check out your own panels follow this proceedure. If the wafers are not Sunpower, use the above as a guide. Here is the Summary of Sunpower Wafers/Cells.