How much energy does a green roof save?

According to the Center for Climate Systems Research, a comparison of a standard black tar roof and a green roof showed these results:

One square meter of black tar roof produced 500 kWh per year.
One square meter of green roof produced 140 kWh per year.

Con Edison currently charges an average of $0.192 per kWh, which means that according to this study, a green roof saves a difference of $ 68.40 per square meter, or $6.40 per square foot.

On average, for one story structures, a green roof saves $4.50 per square foot on an annual basis.