Tidal energy is most often produced in large amounts using a tidal barrage, similar to a dam. When built across a river estuary, the tide flows through this barrage and either spins a turbine directly, or compresses air through a pipe, which is in turn used to spin a turbine. Barrages rely on gravitational potential energy: a high tide will fall to a low tide. However, this method of energy production comes with several drawbacks: there are only around twenty sites globally that are suited to a barrage; and they are known to block the passage of sewage or other sediment, as well as fish and other marine life. There have been recent developments to the tidal barrage—for one, the tidal lagoon, which is similar to a barrage except it is not built fully across the river estuary. There is also the tidal stream generator, essentially a wind turbine that is not pushed by air but by the flow of a current. However, both the tidal lagoon and tidal stream generator are not yet fully developed, so they are not used in more than an experimental capacity.

The foremost advantage to tidal energy is the fact that water is a renewable resource. As it relies on the flow and ebb of the river’s tide, tidal energy is far more predictable and reliable than solar or wind energy, and comes without the pollution of greenhouse gases or waste.  Tidal plants have a low running cost as well. The main disadvantage to this type of energy is the extreme scarcity of sites to build a barrage. Furthermore, the initial fee is rather large. While tidal energy is ‘clean’ and renewable, it may damage the river’s ecosystem due to the building up of sediment and the impeding of fish. Also, tidal plants only provide energy at certain as they rely on the tides and when they change.

From a cost/benefit standpoint, tidal energy is rather risky. The initial construction fee of a tidal barrage is rather high; the 240MW tidal plant on the Rance River in France cost around 94.5 million Euros and took three years, and in modern times produces only 0.012% of France’s power consumption. However, the running costs of tidal plants are lower than many other means of energy production. The Rance tidal plant has recovered its initial costs over the thirty-some years since its production.

Tidal plants generally produce less energy than wind or solar plants, but are far more reliable as the tides are more constant than wind or exposure to sunlight. They are similar to geothermal plants in that although they have a high initial cost and must be built in one of the sparse specific locations, they boast a low running cost. As with most renewable energy, tidal plants are not viable as a replacement for conventional types of energy, but work well as supplemental energy or for small communities.