I think hydroelectric power is one of the oldest renewable energy technology. A hydroelectric power plant constitutes a dam and a reservoir. The potential energy of stored water can be used to drive a water turbine. The turbine will be coupled with an AC generator. There is a long pipe from the reservoir to the power house. It is known as penstock, which is used to contest potential energy of in to pressure energy. At the end of penstock nozzles are provided to convert pressure energy of water into kinetic energy. The energy of a water is actually comes from the sun. Sun is the driving force behind water cycle. There are different types of hydroelectric dams classified according to the power of water, applications etc.
Biomass refers to all the materials that constitute and originate from plants and animals. When biomass burns, it liberates heat energy. The heat energy liberated can be used for cooking, heating rooms, lighting and electrification of rural house hold etc.
Another energy source from The Ocean- Second Largest Renewable Energy Source. When wind blows cross the sea waves are produced. Thus wind power is transformed to wave power. This wave power can be effectively harnessed by underwater water tubines. Those wave turbines are designed in such a way that can harness maximum possible power from the wind.
There are places where high pressure steam is exhausting from the earth crust without any heat supply. This natural steam generators are powered by hot magma. When magma reaches under water reservoirs through weak earth crust water boils and steam is produced. The steam generated can be used to drive a steam turbine coupled with a generator to produce power.
There is a large difference of temperatures between deep ocean and surface. Near to equator this temperature difference is maximum. This difference in temperature can be used to generate power. This is known as ocean thermal energy. Ocean thermal energy harnessing can affect the ocean environment and ecosystem.
Hydrogen– hydrogen is a promising energy source. It is possible to generate energy from hydrogen by direct combustion or fuel cells.
Fusion energy – fusion of light elements like hydrogen can generate heat energy.
Cold fusion– It is a fusion reaction taken place in low temperatures.
Bubble power– it is similar to a cold fusion reaction. Hydrogen nuclei can fused together by tiny bubbles imploded by round water
Fuel cells– it directly converts chemical energy in a fuel to electrical energy without the application of burning.
Magnetohydrodynamic energy– MHD will convert thermal energy and kinetic energy directly in to electrical energy. This energy generator have no moving parts.
Osmotic power– it is also known as salinity gradient power. Power generation is possible when there is adequate difference in salt concentration.
Ocean thermal energy– there are ocean thermal energy converters which are used to produce power from the temperature difference between deep sea and surface.
Concentrated solar power– By using lenses concentrated solar energy can be used to generate power.