Hi Ghurd.
Your dead right that I meant bypass... not blocking.
Thats the agreeing part over....
I am not talking about panels affecting other panels, I am concerned with a cell within a panel
The panel is made up of current sources ( cells). Their voltage per cell is dictated by the material and doping to make the diode.
The electric field is fixed at a set temperature.... ... (even though the cells terminal voltage is controlled by the internal resistance/impedance we'll ignore this for now)
The current is a function of the number of incident photons incoming.
Now I suspect you have measured a battery in a string that was weak, and showed signs of lower voltage than the others in the string. If we let this go on, or increase the load, the weak cell will lower in voltage while the goodies stay high. At a point, the battery reverses polarity, and destruction is soon to follow.
The cells in the panel behave the same. Shorting them out, only gives a terminal voltage of zero... inside the panel, the voltage over any point or points is the function of the Isc x the resistance/impedance of the circuit under test.
As the system has resistance, and the internal impedance of the cell appears to wane in less light, our voltage in any part of the circuit is measurable if you had access to the junctions.
This pic is the one of interest in that article.
Look at it, and then guess what happens to the left hand cell, when you have cells that can do 11amps Isc ( I have panels that I have seen those figures on... 6x6 poly panels)... and the circuit will pull in in high light conditions rather than low light I suspect. Panels can easily do 30% more power in the right light conditions.
When the shaded/weak cell cops all that current from it's brothers... things happen.
The proof is in the cooked panels....
The blocking diodes you have pictured only isolate the bank from the panels and each other ( to stop pyrotechnics when you short the panels but not the batteries), so is not in question here.
I am bothered by the reverse biasing in the weak cell too as it may permanently harm the cell, but the heat is something else. It melts the solder, and breaks the heat treated glass in the bigger panels.
Thats my point. Use the same circuit, but isolate the panels rather than shorting them....
It is impossible to heat the whole panel by shorting, as that breaks a few rules.... but we can direct the energy of the panel to a specific place, and cause havoc.... bit like using a magnifying glass to burn paper, you can only do it over a tiny area, not the whole looking glass, and still stay inside the thermodynamics envelope.
..................oztules
