RW ,, that was excellent. I am printing your posting.. I will use it as I
look for panels on ebay, etc.

====================


"RW Salnick" wrote in message
...
Benning Wentworth inscribed in red ink for all to know:
I started out ... a trickle charge for my batteries. Then I looked on
the internet and many solar sites recommended a solar panel in the
80 watt scale. These sites said that the trickle charge panels like the
ones West has are pretty useless.

And so ... rather than put something on the boat that is more look that
effective ,,

I will hopefully be able to get enough power out of the panel to run
lights, and a couple of other items.

Mika-

You need to do a little research and planning. If you can answer these
two questions:

How many amps do my lights draw?
How many hours each day will I run my lights?

then you are making progress towards sizing a solar panel. I do not know
if you are 12V or 24V, so I will assume 12V because that is what my
systems are. Suppose you have 2 lights that draw 3 amps each, and you
expect to run them from 18:00 - 22:00 every night. Then you will be
comsuming 2 * 3 amps * 4 hours * 12 volts = 288 watt-hours each day.

To keep your battery from running down, you need to be able to put 288
watt-hours back into it each day. If you have an 80 watt panel, then
first you must de-rate it a little, to (others will give better figures,
but assume) say 85% because it never operates in the absolutely ideal lab
conditions at which panels are rated. So, your panel is realistically a
80 * 0.85 = 68 watt panel, and will produce 68 watt-hours for each hour
that it is in full, unshadowed, bright, overhead sunlight. To get your
288 watt-hours, you would need about 4.2 hours. But the sun is not
overhead 4 hours each day. My rule of thumb is to derate the panel by
another 50% to account for the rising/setting sun effect. So, your 80
watt nominal panel would need about 8 hours to replenish the power used by
your lights. On cloudy or rainy days, or when the days are short like in
northern lattitude winters, your battery would run down eventually,
because each day you take more out of it to run the lights than you put
back the next day with the solar panel.

Does that help?

bob