Tidal power

Tidal power is the process of capturing energy from the Earth's oceanic tides. This energy is converted into useful forms of power, primarily electricity. Unlike solar or wind energy, tidal power is highly predictable. This predictability comes from the consistent patterns of the Earth's rotation and the Moon's orbit. While it is not yet widely used, tidal energy has massive potential for future electricity generation. It is classified as a renewable resource because it is practically inexhaustible.

The mechanism behind tides involves gravitational forces from celestial bodies. The Moon and the Sun exert gravitational attraction on the Earth. These forces create periodic motions or currents in the world's oceans. As the Earth rotates, these forces cause regular changes in sea levels. The magnitude of these changes depends on the positions of the Moon and Sun. Local geography, such as the shape of the seafloor and coastlines, also affects the tides.

There are four main methods used to generate tidal power. The first is the tidal stream generator. These use the kinetic energy of moving water to spin turbines. They function similarly to wind turbines but operate underwater. The second method is the tidal barrage. A barrage is a large dam built across a tidal estuary. It uses potential energy created by the height difference between high and low tides.

A third method is the tidal lagoon. This involves building circular retaining walls to create artificial reservoirs. These lagoons capture potential energy without using a pre-existing ecosystem. A fourth theoretical method is dynamic tidal power, or DTP. DTP proposes building very long dams, perhaps 30 to 50 km, extending from coasts into the sea. These dams would create tidal phase differences to produce strong, oscillating currents.

Humans have a long history with tidal energy. During the Middle Ages or even Roman times, people used tide mills. These mills used incoming water to fill storage ponds. As the tide receded, the water turned wheels to mill grain. In the 19th century, technology advanced to use falling water and turbines for electricity. The first large-scale tidal power station was the Rance Tidal Power Station in France. It became operational in 1966 and remained the largest for 45 years.

Modern tidal installations have reached massive scales. The Sihwa Lake Tidal Power Station in South Korea opened in August 2011. It is now the world's largest tidal power installation. It uses 10 turbines and has a total power output capacity of 254 MW. This surpassed the Rance station, which has a capacity of 240 MW. However, tidal power can be expensive. A project in Snohomish County, Washington, began in 2007. Its budget grew from $10 million to $38 million before it was cancelled in 2014.

Tidal energy is unique among renewable resources. Most other energies, like wind, solar, or even fossil fuels, originate from the Sun. Nuclear energy uses mineral deposits, and geothermal power uses Earth's internal heat. Tidal power is the only technology that draws energy from the orbital characteristics of the Earth–Moon system. Using this energy causes a tiny loss of mechanical energy in that system. This process actually slows the rotation of the Earth very slightly. Over the last 620 million years, the Earth's day has increased from 21.9 hours to 24 hours. This effect is negligible and will not be noticeable to humans in the foreseeable future.