Martin Holladay, a green building designer, purchased his very first solar photovoltaic (PV) panel back in 1980 after living in the wood without electricity for 5 years. The Arco Solar panel (model 16-2000) was designed to charge a 12-volt battery at a maximum voltage of about 16 VDC. When new, the 33-watt panel produced 2.0 amps in full sunlight.
After being in the field for 30 years, Martin decided to test the panel in 2010. He first connected a DC 35-watt incandescent light bulb to the panel in his backyard, on a sunny day with temperature about 10°C. The bulb lit with his Fluke multimeter showed 2.015 amps and voltage of 14.93 volts.
He called up the manufacturer and described his experiment to them. According to the manufacturer the cool temperature could boost the panel output by 10%. So, 33-watt panel would get 36.3 watts, divided by 14.6 volts is 2.48 amps. That explains his results. The panel was definitely still performing to factory specifications - or perhaps a little better, even after 30-YEAR.
Solar panel warranties generally cover up to 20 to 25 years at 80% nominal output. Over the years, all panels will degrade somewhat. Even when some older panels may not reach that 80% mark of the rated peak output, they can continue to produce smaller amounts of energy for years after their warranties are up.
The Arco solar panel, however, far outlived its warranty and is certainly working well into its old age.
Image Credits: www.greenbuildingadvisor.com