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Rentricity Uses Pressure in City Pipes to Make Electricity

Clean Energy: The Rentricity installation in Keene, NH. Photograph: Courtesy of Frank Zammataro

Most of the drinking water in Keene, N.H., flows from two reservoirs at an elevation several hundred feet above the city’s water treatment plant. It arrives there at a high pressure that needs to be reduced nearly tenfold for treatment. In February, Keene began using that excess water pressure to spin two turbines plugged into the pipe by a New York City startup called Rentricity, using small generators to make electricity from water pressure that was previously dissipated by a mechanical valve. “What we’re really trying to do is recover energy that’s just not being tapped into and use it to make [utilities] more efficient,” says Rentricity founder Frank Zammataro.

The 53-year-old former Merrill Lynch technology executive is one of dozens of entrepreneurs trying to capture so-called hydrokinetic power from moving water in rivers, oceans, or, in Rentricity’s case, pipes. Such projects are distinct from traditional hydroelectric power because they tap into existing flows, rather than dam rivers. Joe Sweet, a researcher at the Connecticut Center for Entrepreneurship and Innovation who co-authored a report on hydrokinetics last year, says the industry is young and “it hasn’t been really settled what’s going to be the best commercially applied technology.” Zammataro says the economics of Rentricity’s projects are more appealing than other types of clean energy because they can count on consistent and predictable water flows, unlike solar or wind generators that depend on the weather. The equipment has a 40-year life span, and energy savings will cover the cost in three to 16 years, depending on the size of the installation and the clean energy incentives in place, he adds.

Rentricity posted a small profit on revenue of almost $500,000 in 2010, Zammataro says. The 10-employee company doesn’t develop any unique technology. Instead, he says, Rentricity uses off-the-shelf equipment such as pumps that can run in reverse to keep project costs low. The generator in Keene can create about 62 kilowatts of electricity at peak flow, about the same amount of energy needed to power roughly 50 homes. It cost the city about $500,000, about half of which was paid for by a federal clean-energy grant under the 2009 American Recovery and Reinvestment Act, according to Kürt Blomquist, Keene’s public works director. The energy savings will pay for the city’s investment in eight to 11 years, he says.

In addition to the Keene site, Rentricity has a 30-kilowatt installation in western Pennsylvania and three more projects in development. The largest, a 325-kilowatt installation at a water transfer station in Palos Verdes, Calif., is scheduled to start operating later this year. Zammataro says the company can harvest energy anywhere a water system needs to reduce pressure, including in pipelines beneath the streets, at transfer stations, or at treatment plants for clean or waste water. The electricity can power the water system’s needs or be delivered back to the grid.


Many of Rentricity’s counterparts face substantial barriers from regulators and environmental advocates to prove that the equipment they want to place in water bodies won’t hurt ecosystems or interfere with ship traffic. “For a startup company, it’s very difficult to be going into a very long process before you even get into the ground,” Sweet says. By targeting pipelines rather than natural water bodies, Rentricity avoids much of the red tape that other hydrokinetic companies encounter. No fish swim through the water pipes it taps, though Zammataro says he still has to get projects approved by the Federal Energy Regulatory Commission.

His biggest hurdle is convincing wary water managers that his systems won’t interfere with their operations. Zammataro has testified twice before the New York City Council, recently joining executives from three other energy startups on June 20, to urge the city to evaluate the energy potential of its water system. The city’s Department of Environmental Protection is cautious. “It seems imprudent to experiment with these systems for marginal power benefit with real potential consequence to our service reliability,” the agency’s chief of staff, Anthony Fiore, said in prepared testimony opposing the plan.

Zammataro understands why water utilities hesitate. “This is a conservative lot for all the right reasons,” he says. Still, vast water systems like New York’s, mostly powered by gravity pulling water from sources upstate, represent tremendous opportunity for hydrokinetic outfits. Keene’s water treatment plant processes 6 million gallons a day at peak times. New York’s water, Zammataro estimates, might provide up to 1 percent of the city’s energy needs: “Over 1 billion gallons of water a day flow through this city,” he says.

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