Photovoltaic Cells: A Brief Technical Explanation

The PV cell acts like an electron pump. There is no storage capacity in a PV cell; it’s simply an electron pump. Each cell makes just under half a volt regardless of size. The amount of current is determined by the number of elec- trons that the solar photons knock off. We can get more electrons by using bigger cells, or by using more efficient cells, or by exposing our cells to more intense sunlight. There are practical limits, however, to size, efficiency, and how much sunlight a cell can tolerate.

Since 0.5-volt solar panels won’t often do us much good, we usually assemble a number of PV cells for higher voltage output. A PV “module” consists of many cells wired in series to produce a higher voltage. Modules consisting of about 36 cells in series have become the industry standard for large power production. This makes a module that delivers power at 17 to 18 volts, a handy level for 12-volt battery charging. In recent years, as PV modules and systems have grown larger, 24-volt modules consisting of 72 cells have also become standardized.

The module is encapsulated with tempered glass (or some other transparent material) on the front surface and with a protective and waterproof material on the back surface. The edges are sealed for weatherproofing, and there is often an aluminum frame holding everything together in a mountable unit. A junction box, or wire leads, providing electrical connections is usually found on the module’s back. Truly weatherproof encapsulation was a problem with the early modules assembled 20 years ago. We have not seen any encapsulation problems with glass-faced modules in many years.