I have started experimenting with using a pair of small solar cells as a maintenance charger on my spare car.
Testing the cells open circuit shows they can easily produce a no load voltage of 18v on a reasonably bright but not cloudless day.
On a known good but partially discharged 60ah 600 cca battery fitted in a vehicle with a 60 ma parasitic on a grey late October day a single panel not pointed directly at the sun lifted the system voltage measured across the battery terminals from 12.04v to 12.20v . Adding the second panel in parallel further increased the system voltage to 12.36v.
I wouldn’t expect 12.36v to recharge a discharged battery but it suggests in average daylight in a northern latitude two panels are supplying enough ma and volts to counter self-discharge and parasitic drain.
Clearly I am going to do further investigation I have used a mains charger to bring the battery up a full charge and after the surface charge to dissipates I will start monitoring the battery voltage and current.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
After just a few days the results are proving interesting
5 days after bringing batteries up to full charge
Weather conditions clear skies temperature freezing overnight, 3c at time of voltage readings.
Solar cells not pointing directly at the sun.
Both in vehicle battery and out of vehicle battery had full charge and showed the same voltage at start of test.
Control Battery Out of Vehicle 12.6v
Battery in car with solar cells connected 12.84v
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
I've been looking at some of the solar cells commercially available, cheap ones obviously
I think it's a great idea for anything going into temporary storage like a motorcycle or boat for the winter.
Thanks for posting this
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