Ocean - Energy Policy Analysis: A Conceptual Framework - page 182

Figure 11.1 TidGen™ Power System
Source: Ocean Renewable Power Company 2011c.
run between 3.6 and 4.9 knots (4 to 5.5 mph). In currents of that speed, a 49.2-foot (15-meter)
diameter tidal turbine can generate as much energy as a 197-foot (60-meter) diameter wind tur-
bine. Ideal locations for tidal turbine farms are close to shore in water 65.5 to 98.5 feet (20 to 30
meters) deep (USDOI 2011a).
A recent innovation is a tidal turbine that uses rotating foils with the appearance of a manual
reel lawn mower, as illustrated in Figure 11.1, manufactured by Ocean Renewable Power Company
(Sharp 2010). A sixty-kilowatt prototype tidal power generator mounted on a barge was successfully
tested in tidal currents at Eastport, Maine, by Ocean Renewable Power Company (ORPC) in 2010.
In the TidGen™ Power System, each side of a central hub features four helix-shaped foils wrapped
around spacing rings and pierced by the turbine shaft. The turbines turn slowly, roughly sixty revolu-
tions per minute in a seven-mph current. The slow speed and wide foil spacing are intended to allow
marine life to move through the turbine unharmed (Turkel 2010). The ORPC design may also be
useful in rivers and estuaries and possibly even using large ocean currents described below.
Dams used with hydroelectric facilities and other energy technologies often cause considerable
harm to fish and ocean mammals, and silt builds up behind them. Because it does not require use
of a dam, the ORPC unit does not entail ecosystem change from buildup of silt behind a dam.
The TidGen™ Power System unit tested in 2010 produced grid-compatible electricity; underwater
video cameras and sensors indicated there was no harm to fish, which appeared to go out of their
way to avoid the unit (Sharp 2010).
The ORPC TidGen™ Power System unit self-starts when the current reaches two knots and
produces increasing amounts of electricity as tidal currents reach six knots. All told, the unit
produces power for twenty to twenty-one hours per day as the tides come in and go out. ORPC's
design consists of stackable power units tethered to the ocean floor, where ship traffic may pass
overhead without harm (Sharp 2010).
ORPC plans to install a larger, 150-kilowatt unit off eastern Maine that will deliver power to
Bangor Hydro Electric Company's grid, with additional future units increasing capacity to 3.2
megawatts by the end of 2014 (ORPC 2011b; Sharp 2010). Additional units to be installed by 2015
will bring capacity to a total of more than five megawatts (Woodard 2011). ORPC has permits for
three sites off Eastport, one of the world's best tidal sites, where twice a day the tide rises and falls
about twenty feet (Sharp 2010). ORPC is developing tidal power sites in Maine, Alaska, and Nova
Scotia, with combined potential to generate more than 300 megawatts (ORPC 2011a).