And the profits grow

[kandrathe]

"By the time it reaches Earth's surface, the energy in sunlight has fallen to about 1,000 watts per square meter at noon on a cloudless day. Averaged over the entire surface of the planet, 24 hours per day for a year, each square meter collects the approximate energy equivalent of almost a barrel of oil each year, or 4.2 kilowatt-hours of energy every day."

Assuming only 10% efficiency, that would be 0.42 kWh per day. To supply 877 kWh in 30 days, the required amount would then be 69.6 square meters. Small enough to fit easily on most roofs, I'd say.

"The average home uses about 877 kWh per month ... Each home would therefore require a solar panel covering about 365 square meters"

Is this how you come to your conclusions, Kandrathe?

Sure. I'll check my math.

Let's look at a real solar panel.

Sanyo 200 watt solar panel for $1050. It's dimensions are 51.9" x 35.2" x 1.4" and in optimum conditions it will generate 200 watts. 1826.88 (square inches) = 1.1786299 square meters -- So 200 watts / 1.1786299 square meters is 169.69 watts per square meter per second of sun. Again let's optimistically assume 8 hours of sun per day, 8 hours x 360 seconds per hour = 2880 seconds in 8 hours. 200 watts x 2880 seconds = 576000 watt seconds (Joules) or 1.6 kWh for the 8 hour period. So, 4.2 kWh / square meter is overly optimistic with this model of solar panel.

Back to the example of our Sanyo 200 watt panel. Let's see how many of these solar panels we need to supply our 877 kWh per month. We have 30 days of bright 8 hour sunny days to work with, so 1.6 kWh per day x 30 days gives us 48 kWh per month, or 877/48 means we need 18 or 19 of these to power our home. Yes, 18 x 1.1786299 = 21.22 square meters. This doesn't jive with my number of 365 square meters, so I'll go back and find my math error. If only we had more places that gave 100% optimum solar conditions for 30 days a month.