Tidal Energy
Overview
Global Highlights
What’s Happening in BC?
What Does it Cost?
Environmental Matters
Technical Matters
Price, Policy and Political Matters
Can I Use it at Home?
Links
Overview
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 world’s 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.
Global Highlights
- On Nov.13, 2003, the world’s 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.
What’s Happening in BC
BC Hydro’s 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.
Environmental Matters
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.
Technical Matters
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.
Links
Credits
Written by Bo Martin for the BC Sustainable Energy Association.
Text updated December 16, 2004
Links updated September 14, 2007
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