The tides of the oceans held vast amounts of energy that were relatively untapped. Tidal generators could be used to harnes this energy.
(Note: The background section of this page uses most of the same words as the river current power page of Terra Futura to save time.)
The waterwheel was invented in ancient Greece. It was used for irrigation and as a power source. The technology spread quickly. Even during the Middle Ages, the waterwheel was very important. As the Industrial Revolution began, the waterwheel started to be used to power factories. As time went on, the waterwheel was replaced with the water turbine. The water turbine became one of the main components of the hydroelectric dam.
The first use of dams for hydroelectricity was in 1882. The water went into the dam and turned a water turbine which, in turn, turned a generator. This created electricity. As dams got larger like Hoover Dam, they started being used for flood control, irrigation, and even navigation. Authorities such as the Tennessee Valley Authority were created to build dams during the Great Depression. Dams continued to be used into the 21st century. By the 2020s, hydroelectric dams were even being used as arcologies with all the dam's non-support structure used as living and arcology space. Meanwhile, a new source power was being used: Tidal Power.
Tech Level: 10
Tidal generators were in limited use in some areas. They only worked for 10 hours a day and only the tide came in and out. One concept for attaining cheap tidal power was the surface tidal barrage. There were huge environmental problems caused by possibly placing a dam like this on the mouth of a river. This problem was overcome in some cases by a circular tidal barrage. It was like a coral reef very close to a delta, but just off-shore. Thus, they would not interfere with the environment. A more common solution was the tidal turbine. Tidal turbines were like upside down wind turbines. They were also very similar to water turbines used in dams. The blades were smaller than those of a wind turbine due to the density of water. In the 2010s, they worked well economically at 4-5 knots. In the 2020s, they would go faster. At the same time, a new source of water power had come: Wave Power.