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.