> I'm curious why anyone would install a solar panel for anything? Put in an
> aux battery, and run the engine for 15 minutes or so every day, which will
> produce about as much juice as a panel would all day

Not true!

even with a robust wire connection to an auxiliary battery (I have 4 gauge)
you will only get about, say, 20 amps going into the  aux battery (less if
the battery is not discharged very much)... with the less robust set ups
like the Hella that Busdepot sells or using the stock wiring you would get
maybe 8 or 10 amps...

even considering the 20 amp possibility that would be only 5 amps hours into
the aux battery in 15 minutes...

I have a 3 amp hour solar panel which means in the summer when the sun is
high it will charge something like 24 amp hours in a day (3 x 8 = 24, but
probably more like 20 due to sun angles, etc.)...

You would have to run the engine about an hour each day to get the same
amount of charge even with a robust aux battery set up (with the wimpy set
up it would take more like two hours)....

If I used two 3 amp hour solar panels it would take about 2 to 4 hours of
engine time to equal the daily charge of the solar panels...

also...personally I don't like the sound of my engine running when I'm
camping... or the exhaust fumes...

also... if your battery is dead you can't start your engine... but a solar
panel will recharge the battery so you can start the engine :)

Bill