[VAC] Re: Solar panel mounting ideas

[Jim Dunmyer <jdunmyer@xxxxxxxxxxx>]

Vanessa,
 The simple explanation is this:

Solar panels are usually rated in watts. The conversion is: Watts =
Volts X Amps, so Amps = Watts/Volts.

However! Panels are rated at their open-circuit voltage, which is 17-18
in the case of a crystalline 36-cell panel (the most common and most
desirable). This means that a "75-watt" panel will give about 4 amps
maximum. It also means that in actual use, where it's operating at
battery voltage (14 volts while under charge), the output is only 56
watts. Your panel is apparently a "40-watt" unit that will yield 32
watts under actual operating conditions.

All of that technical BS aside, here's the deal: 

Convert everything to one unit of measurement, preferably Amps and
Amp-Hours. An AH is one amp of draw for one hour time, 4 amps for 15
minutes, etc. You need to convert to AH because we don't use POWER per
se, we use power over a period of time.

If your panel is rated in Watts, convert as above, a 40 watt panel gives
2.3 amps, 50 watts = 2.7, 75 watt = 4, 100 watt = 5.5.

On a bright, sunny day, a solar panel will operate at maximum output for
about 4 hours, half output for another 4, IF it's pointed directly at
the sun at solar noon. That means that your "40-watt" panel will give
you about 14 AH/day. That's the calculations that I use, which are
probably conservative. If you're actually getting 23 AH/day, you're
doing very well, indeed.

Once again, if you're looking at solar panels first, you're going at it
backwards. You absolutely, positively, MUST calculate your usage before
doing anything else. Convert to AH. Then, figure out what size panel(s)
to buy so you can make that much electricity every day. Realize that if
you're into long-term camping w/o hookups, you need some reserve
capacity for cloudy days, in both your batteries and your panels.

RE: inverters: most are very inefficient under light loads, so don't
rush out and buy the biggest one you can find just ro run your TV rig.
My little 300-watt inverter draws .5 amps with no load, or 12AH/day if I
were to leave it on all the time. It'll hit nearly 30 amps under full
load, of course. An inverter like mine should run your TV set in fine
shape.

                                      <<Jim>>