Three versions of the same activity are explained in this writeup intended to investigate the energy conversion efficiency of your school's photovoltaic system. The first requirement then, is access to a solar system. You also need ammeters, voltmeters, incandescent light fixtures, Vernier units, graphing calculators, or calculator-based lab units depending on which alternative you choose to use. You must be familiar with the use of the equipment as the lesson plan does not explain in detail. Because of the materials required, implementing this activity is not feasible for everyone.