Larry wrote in
:

Geoff Schultz wrote in
:

I must be confused by what you wrote. You're stating that solar
cells turn brown if they're loaded?!? What solar arrays have you
seen that aren't loaded? And if so, why where they installed? I've
rarely seen
a
case where the entire output of an array hasn't been needed/used
other than when a boat was at dock.

Personally I use a diversion controller since it handles both my wind
generator and solar panels and the wind generator has to have a load
to
keep it from free-wheeling.

I've been very happy with my Morningstar Tri-star controller, but
have nothing but bad experiences with Xantrex C-40 controllers.



Wind generators need shunt controllers to keep them from freewheeling
and throwing the blades off. We're talking, here, about SOLAR PANELS
and I'll stick to that.

Any solid state device, including solar panels, have one enemy, HEAT!
They fry from the heat. This causes doping migration across the
junction. A solar panel is simply a 2-pole diode exposed so photons
can drive electrons across the junction. It's why you always have a
blocking diode because it will conduct like a diode the other way
discharging the battery at night or in clouds.

Heat cooking common solar panels is easily seen in the area of each
cell where the current flows through the device, leaving the area
around the edges where no current flows its original metallic blue
color. The current area of the cell gets browner and browner as it
ages and the heat causes the cell's fundamental chemistry to change,
lowering output. Look at any old solar panel that's been pumping out
the amps for a few years and you can see it.

Now, the batteries are charged and the solar array in the hot noonday
sun is attempting to crank out its 19V open circuit voltage. The
common shunt regulator simply loads down the solar cell with a shunt
resistance to cause the array's inherent series resistance to absorb
the difference between the array's open circuit voltage, around 19V
and the desired float voltage of 14.2V for 12V lead-acid house
batteries. Let's do some simple math...19 - 14.2 = 4.8 volts dropped
inside the series of cells x whatever total current the array is
cranking out in the hot, direct sun say 10A for simplicity = 48 WATTS
of heat MORE than what the natural no- current temperature rise of the
panels is with no load current. 48 watts is a fairly good amount of
heat when concentrated in that little circle that's turning brown in
the middle of the cells. Don't think so? Try this. take a contact
thermometer or an infrared thermometer that can measure the temp of
the cells UNPLUGGED in that hot sun. Now, plug it into the
combination of shunt controller/battery in its normal connection.
Watch the temperature of the cells rise with that 48W of heat across
the panels. It's a serious amount. Leave that running a few years at
6-7 hours on sunny days.

Why go to all that when it's SO easy to put in a SERIES controller
that will simply SWITCH OFF the power at 14.2V and switch it back on,
again, at 13.2V just like a good battery charger? Why make the cells
so HOT?! Unlike the windcharger which NEEDS the load current to slow
it down from overspeed....solar cells DON'T!

http://www.solazone.com.au/Regulators.htm
Why not install a multistage series regulator that charges up the
house batteries EXACTLY like your multistage AC charger does?

http://www.arrid.com.au/?act=Solar%20Regulators

http://www.marinewarehouse.net/blueskyenergy.html

http://www.wirefreedirect.com/mornin...ontrollers.asp
"These products are well known for their reliability and ability to
extend battery life and capacity through their PWM - Pulse Width
Modulation technology - the battery is continually poled (pulsed) so
maintaining the battery in a fully topped up state and ensures the
voltage remains constant. This method ensures that the battery
receives maximum charge, whilst preventing overcharging. The
Morningstar range range of solar controllers charge controllers are
famous for their superior quality of construction reliability. "

Constant voltage, PULSED charging....just like your AC charger at the
dock.

I understand how the various types of regulators work. What amazed me
was your statement about utilizing a type of regulator to avoid placing a
load on the solar cells to keep them from turning brown.

You've spent too much time at a dock if you think that's a problem for a
cruising boat or any household system, as the demands typically outstrip
generated supply and you're sucking every watt that the panels can make.
If you're not using them, why waste the money installing them?

For me, my panels get disconnected when I pull into dock for extended
stays, and for short stays the excess power goes to heating water, so I'm
being "green."

-- Geoff
www.GeoffSchultz.org