Geoff Greene saw the power of water currents up close 15 years ago, when a 25-foot boat he was riding in the Mississippi River was nearly dragged underwater when its anchor snagged on the bottom and pulled down on the back of the vessel.
A question then popped into Greene's brain: How can I harness that underwater energy?
"A lot of power there, I've got to look into this," Greene recalls thinking. "It evolved into this wonderfully simple wheel."
Using water's movement to generate energy is certainly not an original thought — dams and hydroelectric power plants fill that role. But Greene's challenge was to create a new way to produce clean energy and avoid the costly and time-consuming effort of building a dam or power plant.
Enter the Greene Turbine, a 15-year labor of science, engineering and love that will be exhibited starting Monday at the University of Memphis. Greene, a 46-year-old high school graduate with no college degree who earns his living as a handyman, has a vision of installing his turbines in rivers and oceans to add juice to the nation's electrical grids.
The invention looks a bit like a windmill encircled by a rim. It has a sealed middle structure and concrete blades that harness ocean or deep river currents to turn it. As the device moves like a Ferris wheel, large water tanks at the end of each "spoke" fill up. When a tank reaches the top of the wheel, water pours down to the center of the wheel through the "spokes," which are actually pipes.
The rush of water continuously spins the turbine inside the enclosed middle, generating power that then is transferred into a generator. The tanks are refilled as the wheel turns and dump the water at the wheel's highest point, over and over again. So, unlike a dam, no reservoir is needed, because the tanks refill on their own.
"This is an engine; its fuel source is moving water," Greene said.
Since the turbine uses only water and gravity to create renewable energy, it is pollution-free — a big selling point for people, companies and governments dealing with the effect that burning fossil fuels has on the Earth's atmosphere.
The apparatus, which would be 250 feet in diameter, works underwater and would be built using materials that already exist. Greene, who estimates that one turbine could power 1,000 homes at a time, needs money to research and build a prototype.
Seeking help, he approached mechanical engineering professor John Hochstein at the University of Memphis. After speaking a few times with Greene, Hochstein realized the idea's potential. Hochstein and Greene have been working together on the hydrokinetic energy turbine for about a year and have asked the Department of Energy for funding to produce a turbine that would be installed in the Mississippi River.
"Renewable energy is obviously a hot topic, but an advantage that hydrokinetic energy has is that it's available 24-7," Hochstein said, adding that other sources like solar and wind power can't work around the clock because they depend on the sun being up and the wind blowing hard enough.
Hochstein says the turbine does not need traditional gear boxes or transmission shafts to harness the energy, eliminating problems with torque and stress that could doom turbines as large as Greene's.
Were Greene to use gears and a shaft, the shaft would have to be up to 40 feet in diameter to prevent it from snapping.
"It avoids a mechanical nightmare," Hochstein said. "Where his idea sells is with size. As you get bigger and bigger, the conventional design becomes harder and harder to implement. Whereas the bigger his gets, the better sense it makes."
In an e-mail responding to questions from The Associated Press, the Energy Department said there are more than 100 marine and hydrokinetic devices under development in the United States and the world. These devices harness the energy of waves, currents, tides or free-flowing rivers, but most are in the early stages of readiness, the Energy Department said.
The Energy Department said it is currently evaluating how to use water resources to produce energy and expects some challenges, such as designing devices that resist harsh marine environments and are environmentally safe, will be overcome. It wouldn't comment directly on Greene's device without knowing the engineering details of his design.
"The Department is optimistic that marine and hydrokinetic resources can provide another valuable option to our nation's portfolio of clean renewable energy sources," the department's e-mail said.
Greene wants $100,000 to get started on a prototype. He found a couple of investors who have leased office space and created a corporation. But getting the Department of Energy funding this year is key.
The hope is to have a working Greene Turbine in the Mississippi in two years.
"It can be a huge benefit to everybody," Hochstein said. "It has the ability to generate a significant amount of power with zero carbon footprint."
The exhibit, "Greene Power: A New Twist on a Turbine," runs through Sept. 24 at the Ned R. McWherter Library at the University of Memphis.