Treehugger: One Man’s Case for Residential Solar.

The upshot? Someone worked out that they’d save USD$40/mth adding solar power to his house and using it to power both the house and an electric car. He didn’t include the cost of a new car in his calculations.

Although this approach probably wouldn’t be applicable to every situation, it does demonstrate that even current-day technologies can be cost competitive. As the price of oil increases, a price is placed on carbon emissions (increasing the cost of burning coal for power), and renewable energy technologies increase in efficiency and drop in cost, the equations will make even more sense.