Throughout history, humans have used renewable energy, but large-scale development has only occurred recently. Tidal energy converts tidal movements into electricity and was first harnessed in the Middle Ages through tide mills. Today, tidal power is still in its early stages, but it has great potential for the future. There are two main technologies for generating tidal energy: tidal ranges and tidal streams, which can be implemented using different methods. One key advantage of tidal energy is its high predictability compared to other renewable sources.

Tides are regular changes in sea level caused mainly by the gravitational pull of the Moon and the Sun, with additional influences from Earth's rotation, seabed topography, and atmospheric pressure. Isaac Newton correctly explained this phenomenon using his law of universal gravitation.

Tides can be classified as high or low, depending on sea level, and occur twice daily in most locations. Their amplitude varies, from being barely noticeable in enclosed seas to reaching up to 15 meters in places like Canada's Bay of Fundy. Tidal currents include flood tides (rising water) and ebb tides (falling water).

Tide mills, also known as sea mills, have been used for centuries to harness tidal energy, primarily for grinding grain or spices. These mills collected water during high tide and released it during low tide to rotate a waterwheel, generating mechanical energy. The oldest known tide mill, dating back to A.D. 619, was discovered at Nendrum Monastery in Northern Ireland.

Tide mills were especially common in England, France, and the Iberian Peninsula, with some still preserved today. They were strategically built in estuaries where tidal range was sufficient but waves would not disrupt the process. The system operated by trapping rising water in a pond and releasing it through a sluice to drive the waterwheel. While their use declined after the Industrial Revolution, they served as a foundation for modern tidal energy plants, which are still in early development stages.

Tidal stream structures are placed underwater in areas where tidal currents are strongest, often due to topographical features. This technology harnesses the kinetic energy of moving water to generate electricity, typically using turbines, though some designs operate without them. Tidal stream devices can be installed individually or in groups, with larger arrays capturing more energy but increasing costs.

Tidal barrages function similarly to ancient tide mills by utilizing the water level difference between high and low tides to generate electricity. These installations require a dam, typically built in an estuary, equipped with gates and hydraulic turbines. Water flows freely into the basin during rising tides, and once the tide recedes, the trapped water is released through turbines, generating electricity via a generator.

The energy transfer is crucial: after generation, electricity is transmitted to a substation, where voltage is increased to reduce energy loss during transportation.

Tidal barrages have been in operation since 1966, with the La Rance tidal power plant in France proving their longevity and efficiency. They are the most effective form of tidal energy, generating significantly more power than tidal stream devices. However, barrages require specific locations, have high construction costs, and pose environmental challenges such as disrupting ecosystems and altering water salinity. Efforts to reduce these impacts include developing fish-friendly turbines.