I left this out, most current commercial panels have an open circuit voltage of around 20V in full sun for 12V charging. Similar to a wind genny, as the conditions improve, you will produce more voltage and current. From what information I have read and measurements from my panels, I believe that maximum power occurrs not far (a couple of volts or so on a 12V system) below the opencircuit voltage, and that lowering the voltage across the load beyond that does not increase the current greatly, and in fact reduces the power (P=IV) output. However I suspect this may vary somewhat with different cell types. The reason for matching the current of the cells in the string is that like a chain, the string of cells will only be as good as its weakest cell. If you put a .25 amp cell in a string of 1 amp cells, the output of the whole string will be brought down. You can see this by hooking a bad or weak cell and a good cell in series and measuring the short circuit current. Also, some people use 1/8" steel for backing, for my simple panel, I used glass, commercial manufacturers often laminate high strength plastics to the pack of their panels. Have fun building the panel and keep us updated. Rich Hagen