I purchased and installed my first solar electric panel—technically known as a photovoltaic module—in 1980. The PV module, an Arco model 16-2000, was rated at 33 watts. Installed on the roof of my house in Vermont, the panel has been exposed to the weather for 40 years.
A decade ago, I temporarily removed the panel from my roof and performed a series of tests to determine the panel’s electrical output. I reported the results in a May 2010 article called “Testing a Thirty-Year-Old Photovoltaic Module.”
Those tests revealed that after 30 years, the PV module was exceeding its original factory specifications. Now that the solar panel is 40 years old—significantly older than the presumed lifespan of a PV module—it is time to once again bring the panel down to the ground for another round of testing.
Here’s the short version of the test results: The solar panel’s electrical output has measurably declined. My imperfect test method shows that, compared to ten years ago, the solar panel has experienced a decrease in electrical output of between 3% and 8%.
If we assume the worst, the panel’s output has declined 8%. In other words, after 40 years of service, the PV module has an output equal to 92% of its output when new. Few homeowners would place such a PV module in a dumpster; after 40 years, the panel still belongs on my roof.
In my first test, the panel was connected to a 35-watt incandescent light bulb. (This incandescent bulb is rated for 12 volts DC.) The PV panel was connected directly to the lamp, with no intervening battery. The test occurred at about 11:00 a.m. on a sunny June day; the air temperature was in the mid 60s.
Under these conditions, the light bulb was drawing 1.948 amps—about 3% less than the same light bulb…