Solar energy reaching the earth is about 1350 W/m 2 outside the earth’s atmosphere and 950 W/m 2 on earth’s surface normal to the sun on a clear day….. Solar energy reaching the earth is about 1350 W/m2 outside the earth?s atmosphere and 950 W/m2 on earth?s surface normal to the sun on a clear day. Someone is marketing 2m x 3m photovoltaic cell panels with the claim that a single panel can meet the electricity needs of a house. How do you evaluate his claim? Photovoltaic cells have a conversion efficiency of about 15%.