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Reliability - PV Panels

So what's wrong with buying cheap panels ?  Why isn't " dollars per watt " a good way of measuring the value of a solar array ?

We have been testing PV Panels from many manufacturers - we put them all on the same roof, at the same angle, exposed to the same sunlight, and record the results.  Some of what we found surprised even us.  Please continue reading to learn some of what we discovered.

1 - Performance

Sad to say, all PV panels aren't born equal. Because they are not all made to the same quality standards, some panels just don't generate as much electricity as others.

To be sure, two panels may be advertised as the same capacity ( given a nameplate rating of something like 170 watts ), but that does not actually mean they will both produce the same amount of electricity ( or revenue ) per day.  Some of the panels we tested actually delivered far less than their Nameplate Rating - for example, one panel rated at 170 watts seldom delivered more than 140 watts ( even at times when the better panels were delivering electricity at their full rating )

Additionally, some panels perform very poorly in 'less than perfect' light.  That is, they may work well at high noon on a clear day, but if there is some cloud cover, or it is early or late in the day, their performance dropped off dramatically.  As you know, most places on earth ( and Ontario is a perfect example ) have widely varying light conditions, and are rarely fully illuminated.  Fortunately, we have found panels that work extremely well ( Day4 panels deliver an average of 13% more energy per day than even panels that cost more ).

2 - Degradation

Solar panels generally have a build-in degradation.  The manufacturers will offer guarantees that after ( for example ) 5 years, the panel will still produce 98% of its rating, and after 10 years will produce 95%, and so on.  This is in recognition that the physical structure of the panel changes year after year.

Now, we know that in space, solar panels have been operating with zero degradation for half a century, so what's going on ?  What's happening is similar to what you might see in your home if you have double-pane windows.  After a few years, the atmosphere 'leaks in' and there is mist or cloudiness in the windows.  In PV panels, the same thing happens, and the air actually causes the connections within the panel to corrode.

Depending on the manufacturing processes, some panels are much more susceptible to this degradation than others.  The best panels have an extra layer in the back, specifically to keep out oxygen ( we know of two panel manufacturers that do this ) .  One panel manufacturer ( Day4 ) use a unique process that replaces the easily-oxidized solder connections with a proprietary technology that can't corrode.  Apparently, they have 'force aged' their panels and are seeing little or no degradation for over a hundred years.

  If you are paying for the panels and receiving the revenue, you obviously want to own panels like this , that will maintain their performance for the lifetime of the array.

3 - Back to the Numbers

So, to repeat, what's wrong with "dollars per watt" .  Simply put, that's a good measurement is you are being paid by the watt, but in jurisdictions like Ontario, you will be paid by the KiloWattHour, and that's a measurement that is totally driven by performance.  The PhotoVoltaic array that produces more KiloWattHours will earn more money.