Page 361 - Handbook of Energy Engineering Calculations

When the sunlight strikes a typical photovoltaic or solar cell, Fig. 18,
photons are absorbed and electrons are freed to flow as shown. Each cell
consists of a thin layer of phosphorus-doped silicon in close contact with a
layer of boron-doped silicon. By chemically treating silicon in this manner, a
permanent electric field is created. The electrons freed when sunlight hits the

cell flow through metal contacts to generate electricity.

FIGURE 18 Electron flow from the array generates electricity. (U.S.
Department of Energy.)

Photovoltaics, defined as electricity produced solely from the energy of the

sun, is modular in design. It can grow with the electrical demands placed on
it. An individual cell will produce only a small amount of electricity, but
placing several cells together increases the amount of electricity produced.
Groups of cells are mounted on a rigid plate and are electrically

interconnected to form a photovoltaic module which produces a nominal 12
V. Then, groups of modules are mounted together on a permanently attached
frame to form a panel. Panels are interconnected to form a photovoltaic array
for differing power levels, Fig. 19.