User:Genevievenemeth/Notes

A tidal farm is a group of multiple tidal stream generators located under water used for the production of electricity. A tidal farm utilizes the same processes as a wind farm. Similar to a wind turbine, each tidal stream generator is composed of a tower with multiple turbines attached to it. Just as the movement of wind turns a wind turbine blade, the movement of seawater turns a tidal stream generator turbine blade, generating electricity. Each individual tidal stream generator unit collects electricity and then connects to a substation that sends the electricity to a central power grid. Tidal farm energy collection is a new technology that is currently beginning to test prototypes with various designs in regions like Northern Ireland, Scotland and Wales.

Design
A tidal stream generator is composed of a single tower with multiple turbines connected to it, located in a body of water. Tides are created in the water as a result of the moon pulling water toward it, or the moon pulling the Earth away from the water, with gravitational force. As the body of water moves due to the ebb and flow of the tides, the turbines crank, generating electricity. The distance between turbines is determined by wake interactions and maintenance needs. Tidal turbines perform best in coastal currents between 4 and 5.5 mph. A 49.2 ft diameter tidal turbine can generate the same amount of energy as a 197 ft diameter wind turbine in these conditions. There are also different types of turbines that can be used in a tidal farm. Currently, four different types of turbines have been created: Horizontal Axis Turbines, Vertical Axis Turbines, Linear Lift Mechanism, and Venturi Based System.

There are a number of specific requirements for the creation and placement of tidal farms:
 * The location of the tidal farm must be in an area with consistently strong waves.
 * The generators must be able to withstand rough weather.
 * Ideal locations are close to shore in 65.5-98.5 ft water depths.

Offshore Installations
Due to their high cost of construction, tidal farms are a rare find around the world. But, many countries are starting initiatives in planning and building tidal farms. These include: France, Northern Ireland,  Scotland, Wales, and England.

France
In 2011, The French electricity authority purchased tidal energy turbines from OpenHydro, to be installed near Brittany. This will be the world’s largest tidal energy farm when finished in 2012. These 2MW turbines will provide enough energy to power 4,000 homes.

Northern Ireland
In Strangord Lough, Northern Ireland, the world’s first commercial-scale tidal turbine was installed. This 1.2MW project will supply energy for 1,000 homes. A main issue in this project was observing how the turbines affected local marine life, mainly seals.

Scotland
Scotland is beginning to build 10 1 MW turbines off the coast of Islay. This will be the world’s largest tidal energy farm. This farm will provide electricity for more than 5,000 homes.

Wales
In early 2011, a lease was agreed that allows for the development of the first tidal farm in Wales, pending environmental consent from the Welsh government. This 10 MW farm, consisting of 7 turbines off the coast of Anglesey, will potentially provide electricity for one fifth of the island.

England
In May 2011, a two month trial tidal farm was installed in the Thames River. This farm would potentially contain hundreds of turbines, providing power to 35,000 homes. The turbines used in this project were designed to cost less in installation than a usual model.

Environmental Impact
Because the tide never stops moving water, electricity can theoretically be generated at any time. A significant amount of energy can be produced as a result. Though realistically energy supply is variable, tidal energy is more consistent than wind and solar energy. Also, like wind turbines, once they are made they do not produce carbon dioxide. No fuel is needed and no waste is produced. Tidal farms are also inexpensive to operate and maintain.

There is little known about the environmental impacts of tidal farms because it is such a new technology. At this time, there is mostly speculation about how tidal farms adversely affect local marine life. It is possible that the noise generated by the turbines underwater may affect marine animals that use auditory cues to communicate and navigate. In Northern Ireland, multiple forms of technology and certain agreements were made to observe the local marine life while installing the turbines. These include a sonar system that monitored seal movements and the agreement that the project would only operate during daylight, so to observe interactions with sea life.

In addition to potentially disrupting marine life and altering habitats, there are other disadvantages to tidal farms. The tidal farms are initially costly to develop, coming with a high price tag. Also, generation of energy by tidal farms is still a developing technology, so only a few models have been tested. Many are still in trial phase.