Hydroelectric is the use of water flow and the difference in potential energy to drive a turbine generator directly in order to produce electricity. The larger amount of water flow or a large difference in potential energy can result in a larger amount of electricity being generated. However, the application of hydropower is also limited by its geographical location. It can only apply in the big river such as the Yangtze River.
Wave energy utilizes the energy provided by the movement of sea waves to generate electricity and pump water. This technique is not very common due to two reasons. First, noise is produced during operation thus affecting the ecosystem. Secondly, the efficiency of converting electricity from wave energy is quite low.
Tide is formed by gravity from the Moon. There are two tides in one day including high tide and low tide. In high tide, the water level of storage reservoir is lower than sea level. Seawater enters the reservoir through turbines which leading to the rotation of turbines and the electricity is then generated. In low tide, the water level of storage reservoir is higher than sea level. Water from the reservoir can go back to the sea and result in turning the turbine. Electricity can then be produced. For example, the Rance tidal power plant is one of the commercial utility in the world.