We are always interested in providing our readers with information concerning sustainable, renewable energy alternatives. This guest post about tidal stream energy comes from Liz Tyler.
Wind. Solar. Hydro. While all of these renewable sources are being looked at as viable replacements for fossil fuels, tidal stream energy presents one of the most exciting emerging forms of renewable energy to date. Unlike many other forms of renewable energy, tidal stream energy relies on a consistent source of kinetic energy caused by regular tidal cycles.
As you might guess, consistency is important and highly attractive for grid management – removing the need for fossil fuel backup power. Tidal turbines are installed on the seabed at locations with high tidal current velocities, or strong continuous ocean currents, to extract energy from the flowing water. One key to making tidal stream energy feasible and successful is placement. Because of the need for consistency, there is a need for skillful offshore geotechnical engineering.
How Tidal Stream Energy Works
Tidal stream power is a form of hydro-electric power that converts energy from tides into electricity. While it’s not in widespread use yet, it may be the wave of the future in alternative energy. Historically, tide mills are very old. They were once used to turn waterwheels used to mill grain.
Modern plants, however, make use of the kinetic energy of moving water to move turbines. These turbines are connected to a generator that works off of well-established technology to generate electricity.
In order for a tidal stream generator to work, it’s often necessary to use a tidal barrage. The barrage makes use of the potential energy in the difference in height between high and low tides. Special dams are erected to capture this potential energy. When the sea level rises, the water flows into a large basin. This basin holds the water until the tide recedes. When the tide does recede, the water is sent through large turbines that convert tidal forces into mechanical energy – thus generating electricity.
Current projects include the Rance tidal power plant – the first plant ever built utilizing tidal stream generators. It was built in 1960 (to ’66), and is still in operation today. It has a 240 MW capacity. More recent plants include the Ocean Renewable Power Corporation’s TidGen system – installed in Cobscook Bay, near Eastport, Maine in the U.S. It has a current capacity of 180 kW. The major advantage of the Cobscook Bay turbines over the Rance plant is that the TidGen system doesn’t require a barrage.
Tidal energy has many advantages that make it an attractive energy source:
- Tidal energy is the only technology that draws on the orbital characteristics of the Earth-Moon system. It is not dependent on current weather, which makes it more predictable and reliable than other sources like wind and solar.
- From an engineering perspective, the plants are easy to build, reliable, and very straightforward. They’re built on existing principles of turbine design.
- The environmental impact on marine life for newer turbine systems is minimal.
- Some estimates place the 20-year payback at 40 times the cost to build, install, and maintain the system.
It’s not all rainbows and sunshine, however. There are still some seriously limiting disadvantages to using tidal energy, including:
- Turbines are site-specific.
- To operate effectively, a minimum tidal range of 2 meters a second (3.9 knots) is required.
- The negative impact of some of the older, more established, tidal barrages is well-documented.
- Some argue that tidal energy is inherently inefficient at producing energy over the long term and that it effects on marine life aren’t well studied, even though no significant impact on the ecosystem has been noted as of yet.
Tidal Energy’s Future
In order for tidal energy to be a viable option, it needs the expertise of geotechnical engineers. These engineers need to be able to find tidal currents that are strong enough to deliver sustainable, significant power. Not only that, engineers need to assess the complexities of building plants in potentially remote locations or on the seabed, if needed. Finally, salt water causes corrosion of metal parts. It can be difficult to maintain a tidal stream generator because of this, and because generators are typically located in deep water. Mechanical lubricants can also leak into the ocean which might harm the marine life. These design challenges still need to be sorted out before tidal energy can become widespread.
Author: Liz Tyler is a full-time student working towards an advanced degree in geophysical engineering. She loves writing about various aspects of the subject as it relates to “the real world” for a number of different websites, including FugroGeoConsulting.
Photo: Tidal wave at Saltstraumen in Norway from Shutterstock