Clean coal is a concept for processes or approaches that mitigate emissions of carbon dioxide (CO2) and other greenhouse gases that arise from the utilization of coal, mainly for electrical power generation, using clean coal technology. Currently, the term clean coal is used in the coal industry primarily in reference to carbon capture and storage, which pumps and stores CO2 emissions underground, and plants using integrated gasification combined cycle (IGCC). IGCC involves coal gasification, which provides a basis for increased efficiency and lower cost in capturing CO2 emissions. Prior to the current focus on carbon capture and storage, the term clean coal had been used to refer to technologies for reducing emissions of NOx, sulfur, and heavy metals from coal combustion.
**Source: Wikipedia, the free encyclopedia**
Renewable energy is generally defined as energy that is collected from resources which are naturally replenished on a human timescale, such as sunlight, wind, rain, tides, waves, and geothermal heat. Renewable energy often provides energy in four important areas: electricity generation, air and water heating/cooling, transportation, and rural (off-grid) energy services.