Tidal Energy

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.

 

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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.

Are There Any Tidal Power Plants In Operation?

There are a few sites around the world that are generating electricity directly from tidal power. These early power plants produce their energy by means of a tidal dam that spans a section of water and harnesses the energy that is generated when the water passes through.

They have each created a significant impact on the environment in their own way with erosion, silting and ecological problems all linked to them. For the most part, they are not considered to be the most favourable method of electricity creation although there are some exceptions.

Tidal Power Plants (Barrage)

 Power Station Name Capacity
(MW)
Country Year
Commissioned
 Rance Tidal Power Station 240 France 1966
 Kislaya Guba Tidal Power Station 1.7 Russia 1968
 Jianxia Tidal Power Station 3.2 China 1980
 Annapolis Royal Generating Station 20 Canada 1984
 Sihwa Lake Tidal Power Station 254 South Korea 2011
 Uldolmok Tidal Power Station 1.5 South Korea 2009

The preferred method of generating tidal energy is through the use of tidal devices that can be placed individually in the water. These devices come in a variety of guises and may be mounted on the sea floor or tethered so that the device can move to better capture changes in the current.

These types of devices are preferred over the barrage system for a number of reasons. Firstly, the impact to the surrounding environment is minimal. Secondly, it is easy to scale up a project by adding extra devices to the area. Thirdly, the devices can be removed from their position for repair and other maintenance tasks if required.

The technology is still very much in the early stages of development with a number of proposed tidal devices still going through pilot tests. Listed below are a couple of projects that have been successful in producing commercial quantities of electricity that feed into the local grid. Note that the capacity quoted represents the unscaled capacity.

Tidal Power Plants (Tidal Device)

 Power Station Name

Device Name

Capacity
(MW)

Country

Year
Commissioned

 Maine Tidal Power Station

TidGen

1.7

USA

2012

Shetland Tidal Project

Nova 30

0.3

Shetland Islands

2014

Strangford Lough Power Station

SeaGen

1.2

UK

2008

 

As well as the tidal power plants and devices that are currently in use producing commercial electricity there are some exciting developments in the works that could dramatically increase the impact that tidal energy has around the world. Possibly the largest is the development of Dynamic Tidal Power which has the potential of adding numerous gigawatts of electricity sourced from tidal currents.

As yet Dynamic Tidal Power is yet to be tested in ocean waters but there are developments that could see it brought to commercial reality in the next 5 – 10 years.

Read more about Dynamic Tidal Power here.

As more tidal devices are brought online they will be added to these tables.

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 a number of large commercial scale tidal power sites in operation around the world. The largest tidal power station in the world was commissioned in South Korea in 2011 and has a maximum generating capacity of 254 MW. It is known as the Sihwa Lake Tidal Power Station and is an interesting construction because it retrofitted an existing seawall with ten 25.4 MW submerged turbines to produce electricity from the tidal flows. The next largest is a 240 MW bulb turbine at the mouth of La Rance estuary in France. That site powers a city of 300,000 people. Another of the older barrage tidal dams is the Annapolis Royal Generating Station which is located on the Annapolis River in Nova Scotia, Canada. With a generating capcity of 20 MW the power station was commissioned in 1984. It has the capability to power around 4500 houses in the area.