Energy Generation from Building Roof Heat Dissipators

Back in 2009, within a few months after 2GreenEnergy announced that it would conduct a no-charge review of any renewable energy business plan, someone showed me the very idea shown at left: converting the energy from spinning heat dissipators into electricity.  I told him that he should begin by measuring the total amount of power available in the best of conditions, and determining the value of the energy they would produce in the course of the hottest day of the year.

I told him to get on a ladder and see how much effort it took to stop such a device in his bare hand, and asked him to use his best thinking to determine if that was a great deal of power or very little. Perhaps stop it slowly with friction from your hand applied for a few seconds, and see if the heat is uncomfortable.

I also suggested that the power associated with such a device would be equal to the power output of an electric motor that would cause the device to spin with that angular velocity.  Hunting around online, I’m guessing that couldn’t be more than 10 Watts.  So a 10-hour day of sun, neglecting losses, would generate  0.1 kWhrs, worth, in the average U.S. retail market, $0.01, or one cent.  Doesn’t sound like a bonanza here to me.

Fast forward 11 years, and I came across this precise concept, shown in this presentation (caution: Spanish ahead).