The greatest advantage of tidal current energy is that it is completely predictable, free, and sustainable.
There are basically two types of tidal energy; dams and ocean currents.
The first type is based on using a barrage at a bay with a large tidal range. Power is generated primarily during ebb tides as the barrage creates a significant head of water, much like a hydroelectric dam. The technology is very well established and a 240 MW plant has operated at the Rance estuary in Brittany, France, since 1966. A 20 MW facility has also been in place since 1984 in Annapolis, Nova Scotia. However, estuaries are among the worlds most productive and sensitive ecosystems, and barrages cause large disruptions to their natural processes. We will therefore not further consider barrage based tidal power as a truly sustainable energy resource.
The second type is based on utilizing the fast-flowing marine currents caused by tidal action. While there are non-tidal based ocean currents such as the Gulf Stream, those are usually too diffuse to be a practical energy source. The tides cause water to flow inwards from the ocean twice a day during flood tides, and outwards during ebb tides. Additional monthly and annual cycles vary the strength of this current on a monthly and annual basis. Narrow and shallow constrictions produce the fastest and most powerful movements, whose energy can be captured using submerged turbines. This is a new and emerging technology, where only a few prototypes have been tested; up until 2003 no commercial grid-connected plant had been installed. Nevertheless, it is a truly sustainable energy source which is also very predictable. It is not subject to the vagaries of weather or climate change, and while the energy varies, it follows a predictable pattern that is known many years in advance.
- On Nov.13, 2003, the worlds first commercial grid-connected tidal current plant opened in Hammerfest, Norway. It is initially only a 300 kW plant generating 700 MWhrs/year, but the operators plan to install a much larger second-generation plant within 2 years. Norway now hopes to become to ocean current energy what Denmark has become to wind energy.
- The European Commission has estimated that the ocean currents around the UK alone could generate 48 TWhrs/year. (New Scientist, Sept.22, 2003)
- In May 2003, San Francisco decided to develop a 1 MW ocean current pilot project using the Hydro Venturi technology. (Mercury News, May 6, 2003)
- On June 16, 2003, Marine Current Turbines (UK) announced the successful installation and operation of a prototype 300 kW turbine off Devon.
Whats Happening in BC
BC Hydros 2002 Green Energy Study for BC estimated the realistic energy potential for tidal current energy generation in BC to be 20 TWhrs/year. The estimated cost was 11 cents/kWhr for a large (800 MW) site, and 25 cents/kWhr for a small (43 MW) site. The best sites are in the Strait of Georgia and Johnstone Strait, which are both relatively close to the main centers of consumption.
Blue Energy is a BC company that is one of the world leaders in this field. It has operated for 14 years, promoting the use of the Davis Turbine in a Tidal Fence. Most notable among its proposed projects is a longstanding proposal to build the 2,200 MW Dalupiri project in the Philippines. Blue Energy is currently pursuing the development of a 500 kW pre-commercial demonstration project off the BC coast.
What Does it Cost?
The cost of tidal energy is very site specific, and influenced by geography, distance to grid, and speed and volume of the current.
The 2002 Green Energy Study for BC estimated the cost to be 11-25 cents/kWhr, but if current design developments continue, costs are expected to fall to between 5 and 7 cents/kWhr.
The submerged turbines could damage fish and marine mammals, but carefully placed screens should be able to lead them around and away from the turbines. At 25 rpm the blades in the turbines turn quite slowly, further reducing the risk.
The installations must be carefully designed to avoid conflicts with marine transportation, especially since they will be located in constricted areas.
The submerged turbines are fundamentally similar to wind turbines, but since water is 835 times more dense than air, the blades can be much smaller and more compact.
Power generation varies significantly during each day, but because it does so in a regular and predictable manner, it can be more easily integrated into the grid and/or combined with hydrogen production.
The most urgent need for this new technology is for small to medium scale long-term demonstration projects. This would serve to help refine the technology, reduce costs and make it a practical reality.
Price, Policy and Political Matters
The greatest advantage of tidal current energy is that it is completely predictable, free, and sustainable. However, extracting the energy is still in the development stage, and it will need public support during the initial stages to refine the technology and bring the cost down.
Currently there is no government funding specifically for tidal current projects anywhere in Canada.
Can I Do at Home?
No, not unless you live on a house boat that is moored in a strong tidal current.
A Global View
Blue Energy Canada Inc
BWEA's Wave/Tidal Potential Map
Clean Current, North Vancouver
Ocean Renewable Energy Group (OREG)
Marine Current Turbines, UK
Underwater Electric Kite Corp., Maryland, USA
Written by Bo Martin for the BC Sustainable Energy Association, 2005.