Tidal Power

Implementation

Tides are created by the Earth’s gravitational interaction with the moon, the sun, and its own rotation.  The oceans naturally lay over the Earth's solid surface because of gravity, and the gravitational attraction between the rotating Earth, the Moon and the Sun disturbs these motions and forces already at play, producing ebbs and flows that result in tides. ² Sites that are most attractive have a wide tidal range, a trait common to estuaries and some coastal areas. ³ Most typically, plants construct a barrier or dam that forces water through large turbines resembling those used for wind energy. ⁴ The turbines capture the kinetic motion of the ocean tides to power generators, producing electricity that can be used directly or put onto the grid.

As with other renewables like solar and wind, tidal energy itself is free, but power plants can be very costly to build. The main barrier is that tidal barrages are very expensive and may require years to construct, and no power can be generated until they are entirely complete. ⁵ Because plants take a long time to build investors must await long paypack periods. However, once the plant is running the operation and maintenance costs are low. ⁶

Advantages

Tidal power offers some key benefits. Tidal energy is a renewable energy resource that generates very few harmful emissions.  Tides provide a more reliable energy source than other renewables such as solar or wind, being less vulnerable to weather and seasonal variations.  Long-term operating costs and overhead are very low compared to conventional energy sources.

Drawbacks and limitations

There are few examples of large-scale tidal power plants today, largely because of some key limitations.  Putting barriers into waterways, particularly the highly diverse estuaries that are often most feasible for tidal power sites,  can have adverse effects on natural habitats by impacting sedimentation and erosion, water flow, salinity and overall water quality. ⁵

The optimal times of day for tidal power generation are not in sync with human demand. ⁶ In addition, the ideal tidal sites may not be located in areas where electricity demand is high. ⁷  Additionally, planners must also factor in the possible impacts of climate change that may increase the occurrence of such weather events as storm surges, tidal flooding and droughts that could change conditions for tidal operations. ⁸

Footnotes

¹: John Twidell et al., Renewable Energy Resources, Second Edition. New York: Taylor & Francis 2006, pg. 447.
²: Twidell et al., pg. 431.
³: Twidell et al., pg. 449.
⁴: EERE Consumer's Guide, Ocean Tidal Power. Retrieved on: 21 February 2009.
⁵: Twidell et al., pg. 449.
⁶: University of Strathclyde at Glasgow Renewables in Scotland project, "Tidal Power". Retrieved on: 21 February 2009.
⁷: US Department of the Interior, Technology White Paper on Ocean Current Energy Potential on the U.S. Outer Continental Shelf, May 2006. Retrieved on: 20 February 2009.
⁸: UK Environment Agency Website Copyright 2008, "Generating electricity from tidal power". Retrieved on: 21 February 2009.

Resources

• Tidal In Stream Energy Conversion Reports
• Alternative Energy:This page introduces tidal power technology. The main website also provides comprehensive information on renewable energy technology and news.