TIDAL ENERGY – LATEST DEVELOPMENT
Posted June 23, 2008on:
The oldest technology to harness tidal power for the generation of electricity involves building a dam, known as a barrage, across a bay or estuary that has large differences in elevation between high and low tides. Water retained behind a dam at high tide generates a power head sufficient to generate electricity as the tide ebbs and water released from within the dam turns conventional turbines. Though the American and Canadian governments considered constructing ocean dams to harness the power of the Atlantic tides in the 1930s, the first commercial scale tidal generating barrage rated at 240 MW was built in La Rance. This plant continues to operate today as does a smaller plant constructed in 1984 with the Annapolis Royal Tidal Generating Station in Nova Scotia, rated at 20 megawatts (enough power for 4,500 homes). Other tidal generating station operating today, is located near Murmansk on the White Sea in Russia, rated at 0.5 megawatts.
These first-generation tidal power plants have all withstood the rigours of the marine
environment and been in continuous pollution-free operation for many years. But due to the very high cost of building an ocean dam to harness tidal power, and environmental problems from the accumulation of silt within the catchment area of the dam (which requires regular, expensive dredging), engineers no longer consider barrage-style tidal power feasible for energy generation.
Engineers have recently created two new kinds of devices to harness the energy of tidal currents (AKA ‘tidal streams’) and generate renewable, pollution-free electricity. These new devices may be distinguished as Vertical-axis and Horizontal axis models, determined by the orientation of a subsea, rotating shaft that turns a gearbox linked to a turbine with the help of large, slow-moving rotor blades. Both models can be considered a kind of underwater windmill. While horizontal-axis turbine prototypes are now being tested in northern Europe (the UK and Norway). A vertical-axis turbine has already been successfully tested in Canada. Tidal current energy systems have been endorsed by leading environmental organizations, including Greenpeace, the Sierra Club of British Columbia and the David Suzuki Foundation as having ‘the lightest of environmental footprints,’ compared to other large-scale energy systems.
Vertical-axis tidal turbine – Canadian connection
A Canadian company – Blue Energy Canada Inc. – has completed six successful prototypes of its vertical-axis ‘Davis Hydro Turbine, named after its inventor, the late Barry Davis. Barry Davis got trained as an aerospace engineer, worked on the renowned Canadian Avro ‘Arrow’ project, as well on the equally-remarkable ‘Bras D’Or’ hydrofoil project of the Canadian Navy. Barry, then decided to apply his knowledge of hydrodynamics in creating a tidal energy generator. Barry received support from the Canadian National Research Council and successfully tested 5 turbine prototypes in the St. Lawrence Seaway and on the eastern seaboard. Blue Energy is presently raising funds for a commercial demonstration project of the Davis Hydro Turbine.
COMPARATIVE ENERGY DENSITY (kWh/m2)
SOLAR (PV) 1051 kWh/m2
WIND 1000 kWh/m2
WAVE 35-70,000 kWh/m2
BLUE ENERGY 192,720 kWh/m2
Horizontal-axis tidal turbine
Although, such tidal turbines were proposed during the oil crisis of the 1970s, the first tidal turbines began operating in the mid-1990s when a 15-kilowatt horizontal-axis tidal turbine was installed in Loch Linnhe on the west coast of Scotland, north of Glasgow. Now, two companies in the United Kingdom are planning to initiate horizontal-axis tidal turbine demonstration projects while another demonstration project has begun off the coast of Norway. A US company has also designed a working prototype. Horizontal-axis tidal turbines closely resemble wind turbines, except that the turbine and blades are completely submerged in water.
Like the ocean dam models of France, Canada and Russia, vertical and horizontalaxis tidal current energy generators are fueled by the renewable and free forces of the tides, and produce no pollution or greenhouse gas emissions. As an improvement on ocean dam models, however, the new models offer many additional advantages:
– As the new tidal current models do not require the construction of a dam, they are considered much less costly.
– As the new tidal current models do not require the construction of a dam, they are considered much more environmental-friendly.
As the new tidal current models do not require the construction of a dam,further cost reductions are realized from not having to dredge a catchments area.
– tidal current generators are also considered more efficient because they can produce electricity while tides are ebbing (going out) and surging (coming in), whereas barrage-style structures only generate electricity while the tide is ebbing.
– Vertical-axis tidal generators may be stacked and joined together in series to span a passage of water such as a fiord and offer a transportation corridor (bridge), essentially providing two infrastructure services for the price of one.
– Vertical-axis tidal generators may be joined together in series to create a ‘tidalfence’ capable of generating electricity on a scale comparable to the largest existing fossil fuel-based, hydroelectric and nuclear energy generation facilities.
– Tidal current energy, though intermittent, is predictable with exceptional accuracy many years in advance.
In other words, power suppliers will easily be able to schedule the integration of tidal energy with backup sources well in advance of requirements. Thus, among the emerging renewable energy field, tidal energy represents a much more reliable energy source than wind, solar and wave, which are not predictable.
– present tidal current, or tidal stream technologies are capable of exploiting and generating renewable energy in many marine environments that exist worldwide. Canada and the US, by virtue of the very significant tidal current regimes on its Atlantic and Pacific coastlines
– proximal to existing, significant electro transportation infrastructure – is blessed with exceptional opportunities to generate large-scale, renewable energy for domestic use and export.
Tidal energy power systems are expected to be very competitive with other conventional energy sources, and excellent cost advantages arise from there being no pollution or environmental expenses to remediate nor are their fuel expenses (the kinetic energy of tidal currents is free). Further, ongoing maintenance costs are expected to be modest, as they are with other large-scale marine infrastructures, e.g. bridges, ships, etc., and a non-polluting tidal energy regime will qualify for valuable carbon offset credits. A 2006 feasibility report on tidal current energy in British Columbia by Triton Consultants for BC Hydro stated, “Future energy costs are expected to reduce considerably as both existing and new technologies are developed over the next few years.
Assuming that maximum currents larger than 3.5 m/s can be exploited and present design developments continue, it is estimated that future tidal current energy costs between 5C / kWh and 7C / kWh are achievable