This is the fifth 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.
Economic Analysis
The economics of tidal power generation are very complicated. The barrage style tidal power plants have gone through extensive testing and La Rance has demonstrated that it is an economically viable way of generating power. However, barrage style tidal power plants require massive initial capital and extensive construction time. Due to these limitations, there has been no significant interest in barrage tidal power since the early 1980s and it seems that nothing will disturb this trend.
On the other hand, tidal stream generators have the attraction of being small devices that can be installed on a piecemeal basis, thereby reducing their initial costs. This allowed for the creation of the first major tidal generation project in the U.S., Verdant Power. It also generated interest in tidal power throughout the north east and west of the U.S., as well as the U.K.. As studies of various designs, notably in the U.S., U.K., Canada, Japan, etc., are concluded, the long-term economic potential of stream turbines will become clearer. At this point, the cost of tidal stream power generation is a great unknown. Depending on which advocate is speaking, a very different conclusion can be drawn. For instance, a proposed 35 megawatts tidal stream facility beneath the Golden Gate Bridge in San Fransisco has user energy costs ranging from 6.6–7.6 cents per kilowatt hour from Electric Power Research Institute’s (EPRI’s) feasibility study [21] to 0.85–1.40 dollars per kilowatt hour from a feasibility study prepared by URS for the San Fransisco Public Utilities Commission.
One thing certainly undermines the value of the EPRI’s feasibility study, tidal power generation will be more expensive in the future than either wind or solar power, currently priced at 7 and 10–40 cents per kilowatt hour respectively. Tidal power is behind in development and a great deal of money and time needs to be spent on engineering and assuaging concerns about the environmental impact. Verdant Power claims it will spend more than five years and $2 million on environmental research, monitoring the impact of its turbines on fish and migratory birds before it will get to the final stages of obtaining the necessary permits to install more turbines and be capable of producingelectricity on a larger scale of ten megawatts. Wind and solar advocates have already spent much time on these issues, giving them a leg-up on development.
An attempt to compare the initial capital investments is presented in table 2. The numbers for tidal power are estimates, as only one “commercial” facility has been constructed and projecting unknown numbers into the megawatt scale is difficult. Table 2 indicates that with tidal power’s advantage of predictability over other renewable energy sources, it is not far from being an economically viable way to produce energy. Although, if a tax is not levied on carbon-dioxide and equivalents emissions, coal and natural gas will continue to be the only economic options.
Table 2: Estimated initial capital cost in dollars per peak kilowatts installed.
When considering renewable energy sources like tidal, solar, or wind, further economic consideration must be made. A variable power source affects the grid as a whole. There is an inherent inability for thermal energy sources to adjust their power output instantaneously when renewable energy becomes available or disappears. Either inefficiencies from the start-up costs of thermal energy sources will need to be accounted for in the grid or some form of storage will need to be added. Both of these options come with costs and consequences. Eventually someone will pay have to for this and it certainly won’t be the utility company. No plant built recently, all outside the U.S., has been built for less than $2, 000 per kilowatt of generating capacity.
An additional economic variable that must be addressed for any renewable energy is what form of subsidy is available to that energy source. Unfortunately, there are currently no U.S. federal subsidies available for tidal power, although it is a renewable energy source and one would hope that the government will begin to see it as a viable alternative. There are some states, MA, CA, RI, HI, etc., that have provided support for tidal power, either through low interest funding or subsidies and, therefore, they are the areas where development of tidal power plants is occurring. On the other side of the Atlantic, tidal power generation is receiving more significant support. SeaGen, for instance, is benefiting from U.K. support where it is receiving three times the subsidies or Renewable Obligation Certificates per megawatt hour than onshore wind farms. The extra incentives in the U.K. are helping tidal power catch up to the existing renewable energy developments.
Be sure to keep following this series, the next portion of this paper will focus on the future of tidal energy generation.
