This is a 20 w. 12 v. poly crystalline PV panel, the dimensions are roughly 14×36 (inches). The two story, flat roof building provides an ideal location for the solar panel. The panel is slightly elevated to provide air flow across the bottom, to prevent overheating. An 18 AWG wire is fed to the backyard of the building, where it charges a 12 volt battery during daylight hours.
The battery above is an 18 volt lith-ion, salvaged from a Ryobi cell that went bad. I’m able to make use of the cells because the problem was in the circuitry. Although it’s rated at 18 V., it stills charges to near full capacity with the 12 V solar panel. I always have the option to remove a a cell to bring the rating down if it fails to hold a charge satisfactorily. The V. rating was recorded during overcast; in full sunlight it peaks at 22 V.
This LED snake light was a freebie. No one else wanted it because the base was cracked. I installed a new base from a salvaged piece of limestone. With a little bit of drilling, and some simple hardware, I managed to retrofit the lamp to accommodate a 12 V battery. (I removed the original circuitry which rectified house hold AC current to DC current. After that I was good to go.) This battery is a 12 V. nickle-cadmium, with 2 A. capacity.
After a few initial experiments, I realized I needed to add a current limiting diode to the positive lead on the desklight, due to extensive overheating. The 12 V. battery actually melted the plastic shroud clear off the lamp, but with the limiter in place, I can even use the 18 V. cell without further damage from excessive heat.
I’ve had the system together for a few weeks, and am very satisfied with the results. On a sunny day, the batteries power the lamp for approximately half the time it takes to charge them. Ten hours charge equals five hours of light. Although it’s a crude system that surely lacks tight efficiency, the charge rate is greater than I thought it would be.