In December 2010, the Federal Energy Regulatory Commission (FERC) awarded a three year preliminary permit to Tidewalker Associates from Trescott, Maine to study the feasibility of tidal power development in Cobsook Bay. The entrance to Half-Moon Cove which borders Perry and Eastport (Maine) is the focus of this interest due to its narrow and relatively deep cross-section which would enable the harnessing of the tides for the production of electricity. In this case, the investigation will concentrate on the construction of a barrage (dam) to maximize production by utilizing tidal exchanges which average 18 feet during a typical lunar cycle. Tidewalker Associates will also investigate the use of current driven (or hydro-kinetic) devices as a secondary / supplementary and less effective manner for tapping the energy resources of downeast Maine.
In the case of the tidal barrage, the project with a capacity of 9 megawatts (MW) will generate approximately 40 million kilowatt-hour (kWhr) in a normal year which is equivalent to the annual demand of electricity for roughly 8,000 consumers. In comparison, a current driven turbine with a diameter of 16 feet installed at the entrance to Half-Moon Cove would generate approximately 120 thousand kWhr per year for a unit with an installed capacity ranging from 0.10 - 0.20 MW. In terms of equivalency, nearly 300 current driven turbines or hydro-kinetic devices would be needed to match the production of the tidal barrage.
For the tidal barrage, the production of electricity would be intermittent but predictable and would range in availability from 70-80 % of the time. The environmental impacts associated with the desired mode of operation will be studied on an on-going basis. The benefits of the project will be compared with the costs at the end of the investigation to determine technical, environmental, and economic feasibility. As anticipated, a decision will then be made to apply for a FERC license before 2012 for the most acceptable mode of development.
In terms of societal objectives, the project represents a commitment towards energy independence and the utilization of a clean, renewable source of electricity. For tidal power, the annual cost of generation over the lifetime of the facility is relatively constant since the project does not depend on a highly inflationary component (e.g., price of fossil fuel) to produce electricity. Residential consumers in Maine pay approximately 18 cents per kWhr for electricity (2010) from public utilities with nearly 50% of this cost comprised of distribution and transmission charges. Since 2000 to 2007, the service price of electricity for Maine customers has nearly doubled which equates into a 10% annual increase over the period of interest. By considering the life cycle cost of electricity, tidal power represents a sound investment for the present by developing a regional source of energy which would have dramatic benefits on reducing the future costs of electricity. Tidewalker also has the objective of using the maximum amount of electricity within the surrounding region by considering resistance heating for homes as a way to reduce fossil fuel dependence and by encouraging the development of an industrial / commercial base within the service area; e.g., glass fabrication / recycling plant.
In summary, the construction of the Half-Moon Cove project would stabilize the regional supply of electricity, encourage economic development through tourism and other mechanisms (e.g., attraction of lower priced electricity), and improve global and local environmental conditions. In the case of the tidal barrage, the dam might allow for the construction of a second route into Eastport which would divert traffic from the Pleasant Point Reservation. The roadway across the barrage would reduce traffic through the Passamaquoddy Reservation and establish a second thoroughfare to and from Eastport, an island connected to the mainland by a causeway constructed in the 1930s as part of the Quoddy Tidal Project which was never completed under President Roosevelt. The placement of a roadway across the barrage is not an integral part of the design but will be considered as determined by local preferences.
As a final note, any form of project construction represents an impact on the environment. When assessing the value of a project, the operational benefits have to be weighed against costs in order to determine acceptability. With respect to other alternatives, Half-Moon Cove represents an effective utilization of a renewable resource compatible with regional demands and consistent with national objectives. By modifying our mode of operation in response to stakeholder interests, Tidewalker has proposed a tidal barrage project without affecting any changes in the tidal range of Half-Moon Cove.
Tidewalker Associates is also investigating an other site for the development of tidal power in Cobscook Bay (Trescott / Carryingplace Cove). In this case, the possibility of linking the two projects together through a delayed production schedule high would generate continuous power by properly timing periods of operation. In brief, high pool operation is based on detaining tidal waters after high tide until a sufficient hydraulic head is created for release through turbines. In the case of low pool operation, production occurs after low tide after the creation of a sufficient head before releasing tidal waters through the turbines as enhanced kinetic energy. By combining the two outputs and using a one hour phase difference, a dependable and continuous output of electricity could be generated for regional consumption.
The option of using current-driven (hydro-kinetic) devices at discrete sites for residential or cluster housing is also being investigated for small-scale applications. In this case, small generators located on small rafts or anchored to the sea bottom could be inserted into a tidal stream to generate renewable energy. Due to the nature and periodicity of tides, this form of energy generation could produce intermittent but predictable energy at remote sites. Economic justification for utilizing this technology exists today for specialized applications. With an expectation of regularly increasing energy costs and with a realization of the benefits of renewable resources as a way to protect the environment, the economic feasibility of tidal power as a competitive source of electricity becomes more attractive when considered as an investment in this type of development in order to more quickly reap the long-term benefits during a volatile period of energy availability and environmental accountability.