Harvesting the sunlight for energy has been a growing method and a renewed natural alternative to other energy sources. Solar cells are devices that convert sunlight energy into electricity using the photovoltaic effect. The efficiency of a solar cell is a measurement of the amount of sunlight converted into electricity using a particular solar cell module. Higher efficiency means higher electricity production. The efficiency can be calculated from the measurement of four parameters: quantum efficiency, thermodynamic efficiency, fill factor and Voc ratio; therefore, if the area of the cell and the wattage are known, the efficiency can be derived.
Things You'll Need
 Basic calculator
Instructions

Determine the area of the solar cell in meter squared (m Sq). For example, if the dimensions of one solar cell is 200 mm Sq x 200 mm Sq, then the cell area is 40,000 mm Sq. Converting mm Sq to M Sq: 40,000 mm sq x .00001 = 0.40 m Sq.

Divide the wattage (W) of the solar cell by the cell area to get the efficiency percentile. For example, if the wattage of the given solar cell is 5 Wp (price per Watt Peak), then 5 Wp / 0.40 m Sq = 2% efficiency.

Round the answer to three significant digits. For example, 2% efficiency rounded into three significant digits will yield 2.00% efficiency.
References
 Photo Credit solar cells image by Albert Lozano from Fotolia.com