Cameron Harris Posted over 4 years ago A conversation with GE: What are the best ideas for alternative energy management at home? How much is one hour of sunlight on three square meter worth? Let’s see, if we’re talking about electricity and we say that electricity is worth $0.10 per KWH than 3KWH’s are worth $0.30. The problem is that PV panels have a radiant energy conversion rate of about 20% or less so three hours of sunlight on one square meter of a solar panel is worth less than $0.06 How about heat? How much is 3 hours of sunlight on one square meter of a solar collector worth if we’re talking about heat? Well 1KWH = 3400 BTU so 3KWH = 10,200 BTU. Since one gallon of fuel oil contains 150,000 BTU 10,200 BTU’s are the equivalent of .07 gallons of fuel oil. Now if fuel oil is selling for $2.00/gallon which it soon will be the value 10,200 BTU’s is about $0.14. You might think this is an unfair assumption since we're not taking into account the heat conversion efficiency factor like we did with the solar panel. I’m glad to see you’re paying attention and you are right about this. The heat transfer efficiency of a solar hot water system is between 50% and 70% the same as oil burner heat transfer efficiency. Since the heat transfer efficiency for an oil burner is about the same as solar collector and the price of oil is $2.00/gallon than the value of 3 hours of sunlight on one square meter is worth actually $0.14. How about the value of heat energy over the period of one year on a roof (20’ x 50’) tilted south at a steep pitch designed to maximize heat gain? The surface area of the roof is 1000 sq ft or 95m2. The solar energy available (for north central USA ) over the period one year on one square meter is 1500KWH. So on 95m2 we’d have:95x1500 or 142,500KWH or 484,500,000 BTU or the fuel oil equivalent of 3,230 gallons of #2 fuel oil. At $2.00/gallon our solar roof could save us as much as $6,460/yr. If half this energy is used for heating and half is used for electric power we could meet the residential requirements for energy independence.