Tidal Energy

Tidal energy is one of two utility scale electricity generation technologies that are not ultimately a result of the sun (can you guess the other?). Tides on earth are caused by the gravitational pull of the moon. As the moon orbits and gets closer or farther from the earth, its pull on the materials on the earth’s surface is different. This causes the easily observable high and low tides that people in NB are very familiar with. It should be noted that extracting energy from waves is also possible and will be discussed in this section.

At this point in time, there are no clearly dominant forms of tidal or wave energy generation technologies. There are large, commercial facilities up and running in Canada, France, and South Korea, but most installations are in the pilot stages. Three main classes of technologies will be discussed here.

The Annapolis Generating station in Nova Scotia uses a tidal barrage which is basically a dam across a bay in the ocean that uses the flow of water into and out of the basin to spin a turbine (see Figure 1).

Figure 1. Power house of the Annapolis royal generating station. http://www.gulfofmaine.org/times/summer2006/gulflog.html

There are also free-sitting turbines that can be placed on the ocean floor and are spun by sub-surface tidal currents.

Lastly, there are some technologies being developed that generate electricity by the gentle rocking of waves. These machines sit on the surface and as they move up and down (with wave motion), a fluid is compressed with is used to operate an electric generator.

Tidal and wave energy generators are sized to fit the geography they will be utilizing and so don’t come in any prescribed sizes, although a 1000 MW facility would be considered very large.

• Upfront costs – The lack of maturity of the technology makes the costs of tidal and wave energy quite high, with amounts of $4,000,000 to$10,000,000 per MW being common.
• Fuel Costs – Free!
• Flexibility– The amount of power from tidal and wave facilities can’t be increased or decreased as needed, which can be challenging for electric grid operators. However, due to the cyclical nature of tides, the amount of power that will be generated (and when!) can both be predicted to a decent level of accuracy, this is a useful fact to electric grid operators and is different from most other renewable technologies.
• Capacity Factor -
• Environmental impacts – No CO2 emissions from operation, the only emissions come from manufacturing and construction and end up being around 10 g CO2 per kWh. Other environmental impacts, like interference with sea creatures, sea bed erosion, and underwater noise are still being studied.