Image Credit: Noah Manning Backyard test. The PV module's electrical output was measured with a multimeter as the module was supplying power to two loads — first to a light bulb, and then to a blower.
Image Credit: Martin Holladay Test one: a 35-watt incandescent light bulb. The PV module easily illuminates a 35-watt incandescent light bulb. The voltage under full load is an impressive 14.89 volts DC.
Image Credit: Martin Holladay Drawing full amperage. The 35-watt light bulb draws 2.015 amps — equal to the full specified output of the PV module when new.
Image Credit: Martin Holladay Test two: a heavy load. The old Arco module didn't hesitate when it was hooked up to a heavy load — a 12-volt blower. The PV panel powered the blower at 2.5 amps — better than factory specs.
Image Credit: Martin Holladay
In 1980, after living in the woods of Vermont without electricity for five years, I bought my first photovoltaic (PV) module. Responding to a small ad in Mother Earth News, I sent a check to Joel Davidson, a back-to-the-land urban refugee who was facilitating a bulk purchase of PV panels. From his off-grid acreage in Pettigrew, Arkansas, Davidson was selling 33-watt Arco Solar modules for $275 each.
Many people ask, “How long do solar panels last?” To mark the 30th anniversary of my first PV module, I decided to climb up on my roof and bring it down for testing.
My Arco Solar panel (model 16-2000) was manufactured at a plant in Chatsworth, California. The module was designed to charge a 12-volt battery at a maximum voltage of about 16 VDC. When new, the 33-watt module produced 2.0 amps in full sunlight.
After being exposed to the weather for 30 years, how’s the old Arco module working now?
Better than factory specs
I decided to test my old PV module by connecting it directly (with no intervening battery) to two different 12-volt loads: a 35-watt incandescent light bulb, and a blower rated at 4.5 amps (about 54 watts).
I ran the test in my backyard, on a sunny day at about 11:30 a.m. The outdoor temperature was about 50°F.
The old PV module passed with flying colors. It easily powered up the light bulb; my Fluke multimeter showed that under a full load of 2.015 amps, the module’s voltage was an impressive 14.93 volts.
Cranking out 2.5 amps in full sunlight
The next test was more challenging: I hooked up the 54-watt blower directly to the panel. Wow! The blower started spinning at a fast clip. According to the Fluke multimeter, the blower was drawing 2.5 amps from my ancient solar panel — more power than would be expected from the factory specs.
I described my test to Raju Yenamandra, the North American head of sales and marketing for SolarWorld, the current owner of the old Arco Solar factory in California. “That’s unbelievable,” said Yenamandra.
When I explained that the outdoor temperature was rather cool, and the sky was unusually clear, Yenamandra did some quick math. “Well, it’s possible for you to get a 10% boost in performance due to the cool temperature. So, 33 watts times 1.1 is 36.3 watts, divided by 14.6 volts is 2.48 amps. That explains your results. Your module is still performing to factory specifications — or perhaps a little better. That’s very good. We usually tell people to anticipate a performance degradation of 0.27% per year.”
When I told Yenamandra that the PV module’s serial number is 256387, he informed me that it was manufactured in 1979, during the very early years of Arco’s PV manufacturing history.
Joel Davidson, the PV dealer who sold me my solar panel, now lives in California. When I called him up, he was happy to reminisce about the early days of PV. “I was selling to a range of people: back-to-the-land hippies, right-wing extremists and survivalists, engineers, hobbyists, and Christian missionaries on their way to Africa,” said Davidson. “Most of my customers were back-to-the-landers on the West Coast.”
It should be good for a few more decades of service
PV manufacturers have made several improvements since I bought my first module three decades ago. While my old Arco panel has simple electrical lugs on the back side for wiring, newer modules have sturdier junction boxes. Manufacturers have also improved the encapsulants and the lamination material. (Early modules used polyvinyl butyral, or PVB; manufacturers have since switched to ethylene vinyl acetate, or EVA).
My old module shows no signs of browning, electrical corrosion, or water intrusion. It certainly looks as if it’s ready to perform for another decade or two.
“A PV cell is a rock that makes electricity,” said Davidson. “Unless something corrodes the electrical contacts, it will still keep working.”
Last week’s blog: “A Leaky Old House Becomes a Net-Zero Showcase”