Solar Panels for Auto Applications

[RedDevil]

I was looking for a fitting thread to post this, but found nothing better than this one that has been dead for 6 years...

So RAISE, ye olde thread!

Cause I got myself a small 5 Watt(ish) solar panel and attached it under the top of the trunk window, where the rear view mirror can't see it:



I wired the positive lead under the roof liner to the map lights, where there's a permanent +. The negative lead goes to the central ground just below the hatch lock catch.

I bought it cause my 12V battery is always reading below 12V if the engine does not run. I suspect one cell is mostly depleted, but the others are brimmed and prevent it from getting charged. So my panel will do that now, very gradually indeed.

I bought it at amazon.de.

[oil pan 4]

Expect to only get 20 to 40% of name plate rating when putting them inside the vehicle, behind glass.

[RedDevil]

I tested it; it got just over 200 mAh in free air early afternoon, clear sky; and some 30 mAh in the fading evening light behind glass.
We'll see if it does tend the battery enough to raise the voltage to a healthier level.

The panel is meant for indoor use btw. That's why it can be very light, that's why I got it.

I already have a 9W outdoor panel, but couldn't mount it in or on the car in any reasonable way. It now charges our emergency torch. Behind glass...

[California98Civic]

Seems almost like it could replace a sunvisor behind the windshield.

[Xist]

Originally Posted by Fat Charlie

I wish that I had seen a picture like this while I was in the Army. I never heard of battery tenders on military vehicles. In the Guard I always PMCSed my truck and then made sure someone had slave cables and a HMMWV.

Every month there were several dead trucks. We ran them until the battery was charged, turned off the battery switch, and probably slaved them again the next month.

[RedDevil]

Originally Posted by California98Civic

Seems almost like it could replace a sunvisor behind the windshield.

It could, it even has elastic straps for that purpose. But my sun visors are too far back. Then, the hatch window is almost horizontal and the top is completely invisible in the mirror. It is the best possible location in my car.

I hadn't properly tested the charge current in situ. So this morning I hooked it up to my Fluke.

The weather could have been better:


But even under cloud cover (no shades) it produces 30-40 mA:


And in the gaps between the clouds things get better:


It had been higher than that (> 150 mA), but camera apps, handheld connectors and clumsy me conspired against capturing the moment.

Ah well. Good enough for its purpose. It will even charge a tiny bit on an overcast day. Voltage was up to 18 Volt unhooked, full cloud cover, and over 23 when the sun peeped by.

[freebeard]

This is mine, an OEM VW part. I use it on the Dasher because it's battery is weak.

[RedDevil]

I had my car serviced yesterday and forgot to unplug the solar panel.

The battery had been disconnected and during a test drive my UltraGauge could not find the OBDII signal. The car seemed to drive just as well, but one minute into the drive it threw a christmas tree of lights, alarms and warnings. The CVT control module had thrown an error which triggered all other systems to respond in style.
The dealer reset the codes and all was fine again.

I think the power from the solar panel kept some systems in zombie mode instead of properly shutting down, triggering error codes that threw off the rest.
Sure enough, since the reset no errors reappeared.

Lesson learned. Always unplug the panel before even coming near a dealership

[boxtruck_camper]

if you have the solar panels flat their output is going to be reduced by about 1/3rd

Not sure if this was the case with older panels, but I calculated a 14% reduction from flat to sloped. Not the worst.

[freebeard]

Corrective optics from Fresnel lens recycled from dead big screen TVs?