Battery-Driven Tanis

BDS wrote:
Well, it looks like they are out there and available as you've pointed
out. When I looked at websites that offered them as battery chargers
I only found the smaller ones meant to keep an already charged battery
at full charge.

Those are popular because they're cheap - the solar cell itself is much
cheaper, and the control gear is much simpler - usually just a simple
diode to keep the battery from discharging through the solar cell at
night. Unless you hook one of those 10-20 W cells up to a tiny battery,
it'll never overcharge the battery, even in full sunlight at the equator
on the longest day of the year. They work pretty well for vehicles that
have to be parked in remote areas for long periods of time.

Bigger cells need a charge controller, both to regulate the charging
current to the battery, and to maximize the power output from the solar
cell. A 150 W nominal solar cell might actually give you full output
at 15 V, 10 A. If you draw 11 A you might drag it down to 13 V (143 W
output) and if you draw 9 A it might only go up to 16 V (144 W output).
The charge controller can "learn" the characteristics of the solar cell
and adjust how much power it's trying to draw. They are usually easy
to hook up - they are basically a box of electronics with terminal
strips on it and maybe a dial to adjust the battery charging rate - but
they aren't particularly cheap.

Still, this is much more expensive than a small generator would be,
and depends on things like sunny days and being kept clear of ice and
snow.

True. At the moment, solar seems to be a win if the other options are a
lot more expensive or impractical for some reason - if you have a cell
site on the side of a mountain somewhere, few people want to pay to
string a power line to it, nor do they want to pay somebody to drive a
fuel truck up there every so often. Solar cells are also quiet and have
no moving parts, which can be an advantage in some applications. Their
efficiency seems to be improving similarly to that of internal
combustion engines - probably nobody is going to triple the efficiency
of either device overnight, but with lots of work, it can get a percent
or two better a year, and if you keep at it, it gets more and more
practical.

I'm not an attorney either but I don't think you would get into any
trouble building one for yourself for your own use - who is going to
hire an attorney to sue you for $1,000 (the cost of pursuing it would
be orders of magnitude higher than that) and what attorney would be
interested in such a case?

That's why I included the disclaimer "[if] the guy isn't an attorney
himself". If his time is "free" he can sue you for fun.

Matt Roberds