Chris Becker for The New York TimesLooking down the shaft of a tidal turbine being readied for operation. It will be lowered to the bottom of Cobscook Bay off Eastport, Me. 
As my colleague Jess Bidgood reported in Friday’s paper, a tidal energy project is moving ahead in Maine, with high costs but high hopes too. But the 180-kilowatt unit that the Ocean Renewable Power Company hopes to put under water next week is really just a first step. The big question is, how well will it withstand the force of the rushing water?
The region, the Bay of Fundy, is famous for strong tides, but the company has picked a spot called Cobscook Bay, where the current is relatively slow, an average of 5.8 knots, or 6.7 miles an hour. That is the speed at which the hardware will produce 180 kilowatts.
If the equipment performs well there, the next step is for the company to put a similar piece of hardware in water moving at 8 knots, or 9.2 miles an hour. In that water, the same equipment would produce 498 kilowatts, or 2.8 times as much.
If the water speed is greater by only about one-third, why does power nearly triple? Because the energy in the passing water rises with the cube of its speed; that is, the ratio of the energy in a 5.8 knot current to an 8 knot current is the ratio of 5.8 x 5.8 x 5.8 versus 8 x 8 x 8.
But “the increase isn’t free,” as a spokeswoman for the company, Susy Kist, put it. The stresses on the structure also increase, so it has to be made stronger, she said.
Still, the higher energy of passing water could allow production of far more electricity per dollar than is spent on hardware. And unlike wind power, tidal power is predictable.
And unlike mountaintop wind, the generating site is near the grid because there is always transmission capacity near the shoreline.
Ocean Renewable’s plan is to expand the project to about three megawatts, about 17 times larger than what the first piece of equipment will produce.
An even better nexus of energy and load was a tidal installation in New York City, in the East River between Roosevelt Island and Queens. But its turbines, using a different design than the ones in Maine, could not cope with the strong tides. The company behind that project, Verdant Power, got a license from federal regulators in January to try again.
The Verdant turbine was unlike Ocean Renewable’s, which looks like an eggbeater turned sideways.
“This is not a very good term to use, but it looks like a windmill in the water,” said Glenn M. Smith, Verdant’s chief executive.
The company has no hardware in the river now but plans to try
again next year, in water with a speed of 3.9 to 5.8 knots.