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Thinking small with tidal power

Why put a 1.2MW turbine in the ocean when you can get away with smaller ones that cost less?

A lot of wave and tidal power systems being proposed these days will be capable of generating megawatts of power.

Puget Sound Tidal Power is aiming for 10 to 15 kilowatts with its turbine--barely enough for five homes--but the lower power output also means a lower price tag, according to company President Burton Hamner. The total cost of a single turbine from Puget Sound in mass manufacturing will come to around $10,000 or so, he said. The budget on larger turbines often runs into the millions of dollars.

"We think you could get payback in five to eight years," he said during a meeting a the Dow Jones Alternative Energy Innovations Conference taking place in Redwood City, Calif., this week. "We have devised a turbine that is small enough to be mass produced."

Micro power production is a growing theme among energy start-ups. Hawaii's Sopogy is promoting systems for producing electricity from solar thermal energy that would go on a house. Now, solar thermal systems are mostly huge engineering projects taking up hundreds of acres of desert land.

Similarly, Rentricity has come up with a hydroelectric turbine for generating electricity from municipal water plants. Now, hydro power comes from erecting massive dams on rivers.

Puget Sound has essentially created a scaled-down version of a tidal turbine. Overall, the unit stands about 15 feet high. In these systems, ocean tides or current from a river turn a turbine, which in turn generates electricity. Wind turbines do the same thing, but they aren't under water. Water is far denser than air, and tides are more predictable than the wind, so the potential to generate electricity from tides is enormous.

On the other hand, inserting mechanical equipment into the open ocean or a river comes with risks. Thus, most tidal and wave power devices are still in the testing or conceptual stages.

The smaller size has a few advantages, Hamner asserted. For one, Puget Sound's turbine can fit into more places than larger systems. He estimated that there are 500,000 sites worldwide and 10,000 in the U.S. that could be equipped with one of the company's turbines.

The turbines can also be lashed together to mimic the performance of a larger system. The company is currently analyzing the tidal power sites controlled by Tacoma Power, a local utility. One location could be equipped with 175 of the small turbines.

Environmental issues, of course, will have to be analyzed. Putting too many in a river could become a hazard. Puget Sound is also studying which type of turbine blade to use. Ideally, the company wants something that will turn in almost any conditions but also turn slowly enough not to harm fish.