Hydroelectricity, or electricity generated from hydropower, is a highly efficient form of energy. It is considered to be one of the most efficient and cost-effective forms of renewable energy, as it can generate electricity with an efficiency of up to 90%.

The efficiency of hydroelectricity depends on the design and size of the hydroelectric power plant, the flow and height of the water, and the type of turbine used. In general, large hydroelectric power plants tend to be more efficient than small ones, and plants that use high-head turbines (which use a large drop in water level to generate electricity) tend to be more efficient than those that use low-head turbines.

There are many large hydroelectric power plants around the world. Some of the largest hydroelectric power plants include:

1. Three Gorges Dam – Located on the Yangtze River in China, the Three Gorges Dam is the largest hydroelectric power plant in the world in terms of installed capacity, with a capacity of 22,500 MW.
2. Itaipu Dam – Located on the Paraná River between Brazil and Paraguay, the Itaipu Dam is the second-largest hydroelectric power plant in the world, with an installed capacity of 14,000 MW.
3. Xiluodu Dam – Located on the Jinsha River in China, the Xiluodu Dam is the third-largest hydroelectric power plant in the world, with an installed capacity of 13,860 MW.
4. Guri Dam – Located on the Caroní River in Venezuela, the Guri Dam is the fourth-largest hydroelectric power plant in the world, with an installed capacity of 10,200 MW.
5. Tucuruí Dam – Located on the Tocantins River in Brazil, the Tucuruí Dam is the fifth-largest hydroelectric power plant in the world, with an installed capacity of 8,370 MW.

Hydroelectricity is a clean, renewable, and reliable source of electricity that can be used to power homes, businesses, and communities. It has a relatively low environmental impact compared to other forms of electricity generation, and it can help to reduce greenhouse gas emissions and combat climate change.