Current Status of Tidal Power Generation Part IV: Issues Surrounding Tidal Power Generation

Current Status of Tidal Power Generation

This is the fourth part of the first portion of a multi-part series featuring papers on OE-related topics by students from the 2.65 class. The series is intended to raise interest and awareness of ocean energy research at MIT and in the world. This portion is on Tidal Power generation and is written by James Modisette, a graduate student in course 16. His sources and the full-text with citations are available upon request.

Issues


Tidal-power generation, like all renewable energies, has its own set of limiting characteristics. Like wind and solar, tidal power cannot provide the constant power generation of a coal-fired power plant. A double-effect barrage or a tidal stream turbine will only produce peak power over four periods of several hours each day. There is also a variation, due to lunar and solar cycles, in the amplitude and period of the tides. However, these variations are predictable whereas wind and solar resources are at the whim of the weather. Scientists already know all the future variations in the tidal cycle. So a tidal power plant may add complexity to managing the power grid but it will not cause unexpected loss or creation of power.

Another limitation of tidal power plants is that along with the long construction times and massive amounts of capital necessary for installation of tidal barrages, they also require specific geographic coastal configurations. This leads to potentially large impacts on ports and shipping lanes and ends up with a case of NIMBY that may never be resolvable. Imagine if Jim Gordon had attempted to take over Nantucket Harbor for Cape Tidal as opposed to putting 130 turbines over thirteen miles away from Nantucket for Cape Wind. Even if they make environmental and economic sense, tidal barrages demand such a significant amount of coastal real estate that it is nearly impossible to conceive of having them in the U.S.

Tidal stream generators address this problem directly by being smaller, local units that can be placed underwater so that they are not visible and do not affect boat traffic. Tidal power generation has an environmental impact much like any other source of energy. There is no way that the construction of a tidal barrage will not alter the ecosystem of a living tidal basin, as demonstrated by La Rance. With the barrage tidal system there is a loss of seawater exchange. This loss leads to a change in the salinity of the water which can cause wholesale changes in ecosystems. The original ecosystem of the estuary where La Rance was installed was almost completely destroyed. It took the restocking of the estuary and ten to fifteen years before a new biological equilibrium
was reached.

Another environmental impact that both tidal barrages and tidal stream generators present, is a danger to fish. Tidal barrages benefit from existing hydro-power plants which also face this challenge and are being forced to develop new turbines that can operate without hurting fish. One possible solution for tidal barrages is to wait and allow standard hydro-power to solve the fish problem. Stream turbines, on the other hand, do not have that luxury. Verdant Power has already been delayed five years in the permitting process and has spent more than $2 million on environmental research.

Another limiting characteristic is that tides aren’t always close to urban populations where there is a high demand for power. For instance, there are large tides in Newfoundland but the population density is negligible. Transferring tidal power generated in Newfoundland to the urban regions of southern Canada or the Northeastern U.S. is infeasible. The capital to create the power lines to transfer the power is outrageous and by the time the power reached the cities a significant amount of energy will have been wasted in transit canceling out any benefits of generating the renewable energy.

Be sure to keep following this series, the next portion of this paper will focus on an economic analysis of tidal power generation..