solar cells

[canis]

Ah, re-reading it seems like one of your chains is not producing any power.

It looks like each row of 9 cells is wired in series. Further, rows are then wired in series so that every cell is wired in a big long series circuit. See if you can find a wiring diagram on the panel somewhere to confirm this.

Thus, with each cell contributing about 0.5V, each row should produce 4.5V. 4 such rows should get you to ~19V (with some variance due to load etc).

Now, when you have a cell in series with others and you shade it, or corrode its leads somewhat, it not only stops producing power, but it also cancels another cell out as it acts like a diode (see my last post). It looks like you have some wiring issues or something.

Try the single-cell shading thingy I suggested and see if you can identify which cells are producing power and which cells aren't. Hopefully it should be fixable with a soldering iron.

If wiring or leads are bad, short circuit current will be lower than rated or no current will flow at all. 9 cells will have to be shaded to drop voltage to 10 volts. Also 36x4x4=576 and 30x15=450.

 

[disappoint]

...I thought (and this is my big question) - isn't the voltage supposed to be roughly constant & only the current vary significantly depending on light intensity?...

I must be misunderstanding something here. What on earth would make you think that voltage would be constant? Not even theoretically would this be possible. Surely not practically or experimentally.

If V=IR what happens to V when R approaches 0? "I" is going to have to get impossibly large to keep a constant non zero voltage won't it? So yes, V will approach 0 when R does. So the more load you put on it the lower the voltage will go unless you can deliver much higher current. There is a limit to how much current you can draw from any practical device and hence a limit to how much load you can put on the system to keep a constant voltage.