RV-409 is the panel that I have. Sorry, I thought that was the link I provided.
I ordered RV-419 (two panels), but received RV-409. That $35 controller looks like a good deal. I didn't order/install a controller because I was under the impression that it wasn't needed under 40-45 watts...this was my first solar
energy experiment. I haven't had any overcharging problems, but I might be the exception because my electric system is in daily use.
Since my panel is flat-mounted, the seasons do make a difference. On a summer day, when the sun is high, full charge usually means about 13.3 volts. On a short winter day, that would be more like 12.8 volts, still pretty good, especially considering that that's when I'm using the furnace
fan practically all night. A big benefit is that I rarely, if ever, see voltage go below 12.2...a battery
will last much longer if it is never discharged below about 50-60%, right about 12.2 volts. After killing several batteries pre-solar, my current battery
is 2 years old, and I expect it may last 5 years.
Cloudy days might shave .1 or .2 volts off your full charge...that is, hardly any difference. The shade will knock off a little more, but you will still be charging throughout the day.
I've had a lot of fun monitoring the voltage and seeing how much charge I get under different conditions and seasons. I don't have any maintenance...sometimes I get on a ladder and wipe the thing off with window cleaner, just for kicks. If I were in a shady campsite, I would try to find a sunny-ish spot to prop up the panel. Based on my summer vs. winter readings, the closer to perpendicular to the sun's rays, the better. For instance, in winter, I try to park a little bit tilted to the south. When I'm parked for the night, I unplug from the truck, so I'm not draining that battery at night. When plugged in during the day, the panel is charging both batteries. I've noticed little things - for instance, watching a DVD movie (laser) seems to use more power than the equivalent amount of time of plain TV. I've always got plenty of power in the mornings for a shower (water pump), even after using the lights
, etc. at night.
The one thing my system can't really keep up with is charging my power-hungry laptop through an inverter. I use shore power or another location generally for the computer.
If I knew 2 years ago how well this thing would perform, I would have paid $1000 for it.
ps That's not an endorsement for any particular brand or distributor. The ones mentioned just happen to be what I bought after shopping around.
Here's a picture of it (in action!):