Most people know what a solar panel is and what it does. And while they might not understand the
inner workings of how a panel produces electrical energy, they know that the higher the power
output, generally the better it is for their 4WD or campervan.
Unfortunately, many unscrupulous vendors know that customers want high-power panels but also
know that only a very small percentage of them will ever test the power output.
If you go onto eBay, you can find dozens of listings for panels like this.
Apparently, this panel has a size of 975*560mm and can be had for less than $120 including shipping.
Well, perhaps not quite. According to Clean Energy Reviews, the highest efficiency panel is the
SunPower Maxeon 6 440W with an efficiency of 22.8% (measured at an output of 1000W/m2 ).
Taking the non-descript eBay solar panel’s claimed power output at face value, we can calculate the
efficiency using the following formula.
Electrical power out is easy, that’s 300W. We know that solar radiation is 1000W/m2 but to convert
it to a power, we’ve got to get rid of the area term by multiplying it by its area.
So we get 52.2% efficiency! This is close to two and a half times the efficiency of the most efficient panel, so obviously something is not right.
The issue is of course that the 300W is just false advertising. They will be an actual 100W panels at
It’s very difficult for the average user to discern what panel rating is real and what panel rating is
made up, so we have created an easy tool that will tell you if your panel rating is likely correct or just
completely made up:
What should I do?
Customers frequently ask me about what panels to use and I tell them about this rampant lying
within the industry.
There is fortunately one thing you can do (other than using the calculator above) and that’s to buy a
residential solar panel.
Residential solar panels have to be accredited by the CEC (Clean Energy Council) in order to be
eligible for RECs (Renewable Energy Certificates). Because of this, vendors can’t just make up the
power ratings like they can for unregulated panels. So if you buy a 300W residential panel, it will be
a lot bigger and heavier than the falsely advertised panel, but it will also be capable of outputting
300W of power under the right circumstances!