Tidal power, or tidal energy, is a form of hydro power that exploits the tidal movements of the ocean as water flows back and forth. Tidal power can be harnessed in a couple of ways: kinetic energy that powers turbines as the water moves between full and ebb tide, and; potential energy in which barrages are used to exploit the difference between high and low tide.
When there’s a substantial amount of water that rushes in and out of some rivers and inlets it’s possible to harness the energy created to drive generators to produce electricity. To tap this energy a barrage is built across the mouth of the river. Water turbines sit in the barrage wall and as the water rushes through, the turbines generate electricity.
The effectiveness of the installation to produce significant levels of electricity depends entirely on the range of the tide and the volume of water that is pushed through the barrage. In order to make the process worthwhile the tidal range must be at least 4 metres.
There are only a handful of places in the world where the conditions are suited to a tidal system that generates sustainable power. One of these is the Bay of Fundy in Canada which has the largest tidal range in the world with an annual average of 10.8 metres.
Tidal plants are similar in mechanics to hydropower plants with the obvious difference being that the flow of water driving the turbine in a tidal plant comes from purely natural forces.
The Case For Tidal Power
When a suitable site has been found and established, tidal power is more predictable than wind and fluctuates less drastically than solar insolation.
It’s a reliable producer of electricity.
Once built and running, there are virtually no costs associated with the production of electricity.
The Case Against Tidal Power
Appropriate sites for building a tidal power plant are scarce globally, particularly sites with a nearby requirement for electricity which would save on transport or storage costs.
Tidal power can have a significant effect on local biodiversity just as a large dam across a river does with the possibility of significant silt build up because of the reduced tidal flow.
Cost of Tidal Power
The cost of setting up a tidal power station can be very high, although once in place the operating costs are low. As an example of the cost of setting up, a proposed 8000 MW tidal power plant and barrage system on the Severn Estuary in the UK has been estimated to cost US$15 billion, while another in the San Bernadino strait which would produce 2,200 MW as a tidal fence in the Philippines will cost an estimated US$3 billion. (Source:Australian Institute of Energy)
Tidal Power By the Numbers
There are 2 large commercial scale tidal power sites in operation around the world. The first is a 240 MW bulb turbine at the mouth of La Rance estuary in France. That site powers a city of 300,000 people. The second is the previously mentioned Bay of Fundy plant in Canada which generates 16 MW powering around 4500 houses in the area.