Reclaiming forgotten power.

I just had an enjoyable email exchange with a friend who asked me about something he’d been wondering. (These are generally the best kinds of email exchanges to have.) He’d been driving past a Scottish wind farm and starting wondering about the rain.

Why aren’t they building generators that capture the power of falling rain drops? Stick one on a roof and get what’s essentially free energy. For that matter, you could use a similar system to harness the power of people’s feet on sidewalks. And once the rain washes off the roof, it usually drains somewhere – why not stick turbines in sewers?

At first, I thought, well, the amount of energy you could get from raindrops would probably be negligible, since they all impact at different times. But then I looked around a little. And what do you know….

They do have a way to harness power from rain:

“The recoverable energy depends directly on the size of the piezoelectric membrane, the size of raindrops, and their frequency,” Jager explained. “The available energy per drop varies between 2 µJ from 1 mJ depending on its size.

“The corresponding instantaneous converted power starts from a few µW up to 10 mW for a converter area of a several square centimeters. An interesting figure to keep in mind could also be the available rain power per year in common France regions with a continental climate: almost 1 Wh per square meter per year.”

They also have systems to harvest power from pedestrians’ feet:

For two architecture students at the Massachusetts Institute of Technology in Cambridge, Mass., the sound of footsteps is an echo of energy gone to waste. They figure that the stomp of every footfall gives off enough power to light two 60-watt bulbs for one second.

“Now imagine how many people walk through a train station each morning, or walk down the street in Hong Kong,” says James Graham, who, with fellow MIT graduate student Thaddeus Jusczyk, is helping to develop the growing field of “crowd farming.”

They devised a special floor of sliding blocks that can turn motion energy (such as from a footstep) into electrical energy. As commuters march across the floor, it would collect tiny flickers of power from each stride and channel that energy.

According to their design – which this summer won a prestigious award from the Holcim Foundation for Sustainable Construction in Zurich, Switzerland – 28,527 footsteps could power a train for one second – 84,162,203 paces could launch a space shuttle.

And someone’s even patented a sewer-based turbine system:

All that water moves through the sewer systems of every community in this nation and all the nations of the world. The present invention places a turbine generator 30 in the outflow pipes 10 of every sewer system to generate electrical power from this unused and overlooked source of flowing water. Every sewer system must pump the wastewater from their systems and dump the excess water in the streams and rivers. Often the systems must pump the water under pressure to make sure the community system continues to operate without backing up….

Regardless of whether the wastewater is pumped or allowed to drain using gravity, the tremendous volumes of water produced by every community can be a new source of generating electrical power. A small community of 10,000 people produces over 1-¼ million gallons of wastewater on a daily basis. Electricity produced from this water flow could generate millions of watts of power….

I want to see these everywhere.