Hydroelectric power is another source of clean and renewable energy.
It can be harnessed by controlling the natural outflow of water with different methods. The most popular is through dams, which, unfortunately, are no longer considered environmentally friendly. Most of the hydroelectric dams in the world are historically recent, but all reservoirs eventually will fill up with mud and require very expensive excavation to clear them up to become useful again. Biomass energy derived from plant and animal matter is still another renewable source being considered as a standby replacement for fossil fuels. Organic waste in the form of dead trees, leaves, animal corpses and food processing waste exists in abundance and can be used to produce energy. However, there is no way to ventilate the direct burning of biomass as fuel without diffusing carbon dioxide and other greenhouse gases into the atmosphere.