"Things that STILL Work!" Home Power tests an Ancient PV Panel We've been telling you that photovoltaics last a long time. Well, here's living proof that PVs can handle the LONG haul. This venerable PV panel has been in the sun for more than 10 years and still produces more than its rated output. Amazingly enough these silicon marvels don't seem to wear out. In the Spring of 1977 the US Energy R&D Administration spent one million dollars on a PV powered irrigation project in Mead, Nebraska. This venture was conducted by Lincoln Labs of MIT and the University of Nebraska- Lincoln. Their goal was to pump over 700,000 gallons of water daily using PV produced electricity. The system employed 100,000 photovoltaic cells costing $22 per Watt in 1977. The resulting array produced 25kW during peak sunlight periods. Well, the experiment ended after 10 years (successfully, I must say) and the facility was disbanded. The PVs were sold on the surplus market. We at Home Power couldn't pass up the chance to get one of these working antiques and test it. Was it still working well after 10 years in the Sun? Or had the cells degraded and lost their power producing capacity? Here's the straight storyÉ The PV Panel The panel we tested was made by Sensor Technology in Chatsworth, CA in 1977. It is composed of 44 round, 2 inch diameter, single crystal PV cells. The panel is rated at 8 Watts output. Its part number is 20-10- 1452 and its serial number is 3045. The panel is 11.375 inches wide, by 22.875 inches long, and 1 inch thick. Physically it is unique. The cells lay within an aluminum tray. The cells are electrically isolated from the tray by a nylon wire mesh. The entire works is potted in silicon RTV compound. This module uses no glass in its face. The aluminum case and the absence of any glass makes this panel very light in weight- only 8 pounds. The electrical terminals are ring connector types and located on the back of the panel. How this PV Panel has survived in the Sun I was amazed that the RTV compound is still in perfect condition after 10 years in the sun. When we got the panel it had a fair amount of dirt and grunge covering its face. A little soap and water cleaned it up. The panel's face, made of special UV transmissive silicon RTV, is still clear and flawless. The panel is still sealed and shows no sign of weather degradation or moisture infiltration. We used a Fluke 77 Digital Multimeter (DMM) to test the panels electrical operation. We measured the open circuit voltage of the panel at 24.65 VDC. We hooked the panel up to a small lead-acid battery, including a blocking diode. The battery was just about full already and its voltage quickly went to 14.4 VDC. At 14.4 VDC, this panel was delivering 0.76 Amperes to the battery. Since Watts is Volts times Amps, this panel was producing 10.94 Watts (14.4 VDC times 0.76 Amperes equals 10.94 Watts). Not bad for an 8 Watt rated panel that's been working hard for ten years. Not bad at allÉ Out to Pasture? Not hardly. The very thought of a PV panel that's not in the Sunshine gives me the shakes. We installed the Sensor Tech panel on our rack and wired it into our system. Here it happily produces electricity right along with our more modern Kyocera poly crystalline PV panels. One big happy solar family. Eventhough this ten year old panel has seen some service, it's still going strong and will charge our batteries for years to come. Own a working part of Solar History These government surplus panels are being sold by Solar Electric Engineering, 175 Cascade Court, Rohnert Park, CA 94928 ¥ tele: 707-586- 1987 or 1-800-832-1986. The price of a single Sensor Tech panel like the one we tested is $69. Two to three panels cost $65 each, four to nineteen panels $50. each and twenty or more $36. each and that's about $4.50 per rated Watt! Gary Starr, CEO of Solar Electric, tells us these panels are finding new homes quickly, so if you want your own part of Solar History better hurry. Conclusion When someone tells you that PV panels are a lifetime investment, he's telling you the truth. While we can estimate their lifetimes in decades, the proof of the pudding can only be found over time. This particular panel has spent over 10 years working its silicon heart out. And it's still producing more power than its original rating! Very few things in this Life offer the steadfast reliability and performance of photovoltaics. Lifetimes of energy from the Sun! Use PVs and will them to your children and your children can will them to their children andÉ RP