HYDROELECTRIC ENERGY
水力
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.
水力發電是利用水的流量及位能差直接推動渦輪發電機而產生電力，水流量及位能差越大，所產生的電能越多。這是受地理環境所影響的，因此在大型河流如在長江興建的三峽大霸(右圖) 才適合發展水力發電。
Wave Energy
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.
海浪
海浪發電是利用海面波浪移動的能量去作其他用途，例如發電、泵水等。但技術並不被廣泛應用，因為此技術所發出的噪音會影響生態，而且電能轉換效率較低。
Tidal Energy
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.
潮汐
地球上潮汐的形成是由於月球的引力，一天有兩次潮汐，就是漲潮和退潮。漲朝時，儲水庫中的水位較海水水位低，因此海水會透過渦輪進入儲水庫，當渦輪轉動時，便會推動電機以產生電能。退潮時，儲水庫中的水位較高，因此水會經過渦輪回流到大海，渦輪的轉動令發電機產生電能。法國朗斯是世界其中一個力商業實用價值的潮汐發電站(右圖)。