Homebrewed Electricity > Solar

Why 36 Cells per panel?

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Subman:
Hi I am going to try my first DIY solar panel. I am having some confusion thou. This maybe a stupid question but it bugs me.  Why do most so called 12V solar panels have 36 cells. Each cell is .5V therefore producing 18V. A 12V battery only requires 13.8V to charge, so why 18V???

ghurd:
Most people expect a FLA battery needs 14.4V to get 'full'.
More than 15V to equalize.

Blocking diode uses up 0.7V.  (edited typo)
Wire losses use some volts, as do physical connections (like terminal connection on the battery termial, both for the wire and battery post).
Hot panels make less volts, relative to peak power.
Less than perfect sun (1000W/m^2) moves the peak power graph to the left (toward 0) and down.

And the peak power is usually closer to 0.47V per cell, which in itself is a whole volt.

Might Google 'self regulating solar panels' which usually used 30, maybe 32 or 33 cells.
The idea was if they could not make amps at enough voltage, then they did not need a charge controller.
Problem was they could barely charge a battery, making them about useless.

Use 36 cells.
G-

Rover:

--- Quote from: Subman on May 19, 2010, 05:11:32 PM ---Hi I am going to try my first DIY solar panel. I am having some confusion thou. This maybe a stupid question but it bugs me.  Why do most so called 12V solar panels have 36 cells. Each cell is .5V therefore producing 18V. A 12V battery only requires 13.8V to charge, so why 18V???

--- End quote ---

Better off having a controller regulate something to regulate , as opposed to having not enough to worry about regulating.

Subman:
Thank you so much. Finally a straight answer that makes sense.

DamonHD:
I suspect that many people wonder about this so for now I've made the thread sticky, but maybe we can edit a link to it into a library thread / FAQ at some point...

Rgds

Damon

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