Running a portable solar station for
a week, with the confidence not to bring a A/C battery charger, is
awesome. However there is much misinformation and some basics that must be
covered.
Solar panels can put out 18-21 volts
when in full sun. You cannot supply this to your radio directly! You
cannot leave a solar panel with a rating close to the rating of your
battery in the full sun either. You need a solar controller.
The typical solar controller has a
built-in battery disconnect which will shut down power to your radio when
the battery drops to 11.1 volts. This protects the battery. A good
solar controller also has a three step charging scheme built into it to
properly charge your batteries. With all of your expense in
equipment, a solar controller is a cheap investment.
If you read all of the tedious
detail on "sizing your battery", this is a snap!
After you have selected your battery size (8Ah in my previous example),
then you know that you want to charge that at no more than a 10%
rate. That means you want a charge rate of .8Ah or 800 mAh.
Lets round that up to 1A. 1A at 13 volts is 13 Watts. Always
add about 10% for inefficiency and we come close to a 15 watt solar panel
to supply just over 1A to our controller. The controller will do the
rest!
Now, consider that the panel is not
going to be near the radio. Since the panel is putting out up to 21
volts in FULL sun, lets put the controller, and the battery near the
radio. Voltage drop will occur between the panel and the controller.
Even at that, the wire should be a decent gauge and you should measure the
drop so that you are not surprised - I was!
Full sun is something that most of
us cannot commit to. I can operate, my style, for 4 hours day, five
days on one 8Ah battery and a 4 watt panel. With two cloudy days, I lost
>1volt in that 5 day period. The same is true for heavy usage at
field day for two years. However, if I was operating FD for five
days, my panel, or battery would have to be increased.
