PV Gap

Emily Said:

how many watts dose solar light panels put out?

We Answered:

The output depends on how bright the sun is, how efficient the panels are, how big they are, and how directly they are pointed at the sun. For most of the day, the sun shines with an intensity of about 1000 watts per square meter on a surface directly facing the sun.

For a smooth photovoltaic surface where the peaks of the cell surface do not cast shadows on the valleys, you can figure on a multiplier of cos ?, where ? is the angle off straight-on between the flat surface of the cell and the sun.

Most solar panels today are about 5-30 percent efficient, with the higher efficiencies for really expensive technologies. For the kinds of cells you see on garden solar lights, you can figure about 8-15 percent efficiency.

If A is the active area of the panel in square meters, ? is the sensor's efficiency, and ? is the angle of incidence of the sun with respect to the normal to the surface of the panel, then its power output is

P = 1000 W/m² * A? cos ?

If A is a 5 x 5 cm (2 x 2 inch) square, A = 0.0025 square meters. Take ? to be ten percent (0.1) and the angle of incidence ? to be 45 degrees, for which cos ? will be about 0.71. In this case, the power output will be

P = 1000 W/m² * 0.0025 m² * 0.10 * 0.71
or 0.18 watts.