Guys,
A few days ago there was a short thread about cheap solar panels.
In case any of you are interested, this morning I took a quick look
and found some cheap panels at:
http://www.jademountain.com/usedpv.html
They probably have limited quantities of the "used" and "off-spec"
units, so remember that the early bird gets the worm.
Of course, the cheapest buy per watt is going to be the larger panels
and the used panels. Remember, You need at least 14.5 volts at the
voltage/current "knee" in order to charge lead-acid batteries. This
does not mean you can connect these panels straight to batteries and
then forget them. See my previous notes for details or send me a
note if you need more info.
73,
Lyn, W4WDN
LYN WILLIAMS wrote:
> joel malman wrote:
>
> > Folks,
> > But the thing that interested me most was an item called "One Sunny Foot".
> > It's a 1 square foot solar panel. Puts out 12v at 166ma. I seem to remember
> > a bit of chat on this list about 6 months ago re: "The Sunny Foot", and
> > how someone was using it to recharge gell cells and/or lead acid batteries.
>
> Joel,
> Notice that the ad says "Up to 12v" at 166ma.
>
> You can not charge a "12v" lead-acid storage battery with 12v. A "12v"
> lead-acid storage battery which was fully discharged yesterday and has been
> sitting disconnected on the bench for the last 24 hours should still measure
> 11.6 to 11.7 volts. You would only have a driving force of .3 to .4 volts.
>
> If the same battery were fully charged yesterday and left disconnected for the
> last 24 hours, it should now read only 12.7 volts. Connecting your 12 volt
> panel across this would certainly not charge it! Proper charging of a 12v
> lead-acid storage battery requires a multi-step process in which the charging
> voltage may need to vary from 11.6 volts to 14.22 volts.
>
> Most photovoltaic panels these days are silicon based and the voltage from
> each cell is approximately 0.5 volts under full sunlight. I recommend that you
> have 36 silicon cells wired in series to produce 18 volts. This will leave a
> few volts to spare for voltage drop across regulators, wires, etc, although
> you can "make do" with as few as 29 cells, which would produce 14.5 volts.
>
> You could use two of these panels in series, but that would waste a lot of
> energy as heat in dropping resistors or regulators in order to keep from
> burning up the batteries. So the panels just don't have the right number
> of cells in series for 12v lead acid batteries.
>
> Also, at $20.00 for 1.99 watts (more than $10.00 per watt), these panels are
> fairly high priced if you need a substantial amount of solar energy. You should
>
> be able to get a more convenient number of cells at a better price if you look
> around some.
>
> Hope this helps.
>
> Lyn, W4WDN
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