In Maine, the tides of Passamaquoddy Bay and Cobscook Bay average eighteen feet and range from twelve to nearly twenty-six feet during neap and spring tide conditions, respectively. Historically, the energy contained in the tides gained attention since settlers first realized the value of this renewable resource for the development of mechanical power and eventually for the potential to generate electricity.
Tidal mills were common-place along the Maine coast during the nineteenth and early twentieth century. By selecting sites capable of impounding tidal waters with substantial tidal ranges, a mill operator could store potential energy for transformation to kinetic energy with the receding tides. Other sites without substantial tidal ranges used the currents combined with river flow, when available, to turn paddle wheels to develop mechanical energy to operate pulleys or to turn gears. This source of energy was free and renewable and fueled part of the industrial revolution.
Starting around the second decade of the twentieth century, developers started assessing the tides for the generation of electricity. Dexter Cooper, an engineer with a summer home in Campobello (New Brunswick), designed a power scheme utilizing the tides of Passamaquoddy Bay and Cobscook Bay. For one mode of development, Cooper proposed an international project capable of continuously generating electricity with a two-pool mode of operation; i.e., using Passamaquoddy as a high pool and Cobscook as a low pool with the installation of power plant and barrages (dams) between the two bays.
In the 1930s, the United States under President Franklin Roosevelt appropriated funds to construct an “All-American” project based in Cobscook Bay and intrinsically connected to Passamaquoddy Bay. In this case, Cobscook Bay was defined as the high pool and the generation of electricity would have started shortly after high tide once an adequate elevation differential was established between impounded waters in Cobscook Bay and the receding waters of the Bay of Fundy. After two or three years of construction activity, the project was suspended due to concerns associated with economic feasibility and the inability to fully integrate electricity into a regional grid. Other factors included opposition from private utilities for public power and political complications.
President Kennedy brought back the Cobscook Bay project in the 1960s while combining tidal power with a pumped storage (hydro-electric) project at Dickey-Lincoln (Aroostook County – Maine) for the generation of continuous power. Once again, the scale of the project and concerns associated with public utility integration combined with environmental issues with Dickey-Lincoln resulted in a decision against development.
During the energy crisis of the 1970s, large scale tidal power for Cobscook Bay and Passamaquoddy Bay was resurrected in terms of an International and all-American project. During this period, the Passamaquoddy Tribe at the Pleasant Point Reservation proposed the construction of the Half-Moon Cove project as both a demonstration project and a decentralized source of energy. Dr. Normand Laberge was hired to develop plans for Half-Moon Cove which eventually led to the filing a license application with the Federal Energy Regulatory Commission (FERC). The project was deemed technically feasible but marginally viable on economic grounds due to the fee structure established in Maine for renewable energy projects during the early 1980s.
The driving mechanism in the 1970s was based primarily on the assumption that the price of fossil fuel would continue to escalate due to geo-political issues and from a belief of a limited supply. The price of fossil fuel remained relatively constant from the 1980s until several years ago. Today, interest in renewable sources of electricity has been rekindled due to rising fuel costs. On a parallel track, serious concerns about the adverse impacts associated with global warming have also increased interest in tidal power as an acceptable source of electricity.
Interest in tidal power is presently focused on current driven (hydro-kinetic) devices which do not require the construction of barrages. European countries have taken the lead in the development of hydro-kinetic devices with prospects for the commercialization of a one megawatt (MW) unit by 2009-2010. At least two hydro-kinetic devices in the hundred of kilowatt (kW) range have been successfully tested in European waters along with an assessment of environmental factors. In the United States, interest in these devices has also increased in such places as San Francisco and New York City. In this case, the key parameter is current velocity along with adequate depth and not tidal range. Oddly, a high tidal range complicates the installation of large scale hydro-kinetic devices due to the need to adjust the location in the vertical plane for the varying elevation of the sea level.
Tidewalker Associates under the direction of Dr. Normand Laberge recently completed a three year preliminary permit from FERC (2007-201) to study Half-Moon Cove as a site for a tidal barrage with the potential to utilize hydro-kinetic devices as a primary and / or secondary source of power. Tidewalker Associates are also investigating other sites with the potential for tidal power development as a regional source of electricity with desirable environmental objectives. Tidewalker Associates possess the qualifications to determine environmental, technical, and economic feasibility and continues to attract investors for expanding the scope of operation. Tidewalker submitted an application with FERC for a successive preliminary permit in April 2010. A second company, Eastport Tidal Power LLC, has filed a competing application for the same site with a proposal to use reversible turbines with pumping capability. FERC will soon decide on the competing applications for a preliminary permit.
As an important side note, energy derived from a current-driven device is directly proportional to the current velocity to the third power. Generally, a current of five knots is a pre-requisite for the installation of such devices which emphasizes the importance of site selection. A difference of two in the ratio of average current velocity translates to an eight-fold difference in the energy capable of being derived from a suitable site for hydro-kinetic devices. In order to match the output of the tidal barrage at the entrance to Half-Moon Cove, approximately three hundred hydro-kinetic devices with a diameter of sixteen feet would be required.
Tidewalker Associates is proposing a “run-of-the-tide” mode of operation which will not result in a reduction in the tidal range within Half-Moon Cove. During the past year (2010), Tidewalker’s focus has changed by concentrating on the use of the Gorlov Helical Turbine (GHT) designed by Dr. Alexander Gorlov. Tidewalker is also considering the use of a flexible dam to reduce material and construction costs and to enable more leeway in addressing environmental concerns. Tidewalker continues working on the development of tidal power in Cobscook Bay (Maine) for the reasons outlined above.
For additional information on Tidewalker Associates and tidal power development, please contact placecove@gmail.com.
