Producing water that’s fit to drink, or clean enough to recycle back into streams or rivers, is tremendously energy-intensive. Up to 7% of the world’s electricity is consumed in water production of one form of other, including desalination. And in some places, where water has to be pumped over long distances from its source to your faucet--like in California--the usage is even higher, perhaps as much as 20%.
There is, though, a neat way of offsetting some of that cost: using the natural pressure of the water supply to generate electricity.
Frank Zammataro, founder of a New York start-up called Rentricity, notes that we currently waste much of the energy from gravity-fed water distribution. To make sure that water doesn’t burst metropolitan pipes, managers cut the pressure at different points--from something like 150 pounds per square inch when it arrives from reservoirs at receiving stations, to less than a quarter of that. The simple idea of Rentricity is, rather than wasting that energy, to use it generate power instead.
"There’s lots of pressure reduction and regulation that could sustain energy generation," says Zammataro. "There are points in the system where you can take advantage of pressure that’s already being dissipated through valving."
Rentricity’s equipment includes a reverse pump linked to a generator, which it can install at different points of the water system. It currently has three working projects that are offsetting some of the cost of water production. Zammataro claims that a 62 kilowatt system installed at a plant in Keene, New Hampshire, is the "the first energy-neutral water treatment plant in the world that’s being powerd by its own water supply".
The company has another two projects in Pennsylvania, and a bigger 350 KW system that’s set to start running in California, in September. And, Rentricity is also working with New York’s Department of Environmental Protection to see if it’s possible to generate electricity at three of the city’s 14 wastewater treatment plants. Up to 1.6 billion gallons of water flows through New York’s pipes every day, creating a big potential opportunity, according to Zammataro.
While the amounts of electricity involved may not be huge, Rentricity’s model has advantages. The power is dependable, and ongoing, making financing the projects easier. And the equipment involved is not particularly sophisticated (Zammataro calls it "off-the-shelf"). So water managers shouldn’t be too concerned about using it.
"There is no doubt in my mind that this will be an important addition to water infrastructure in the future," Zammataro says.