Clean Energy

Clean energy generally encompasses forms of energy that have minimal environmental impacts and produce minimal or no greenhouse gas emissions.  Clean energy refers to renewable energy, and has also been used to refer to energy conservation and energy efficiency -- increased conservation and efficiency being the cleanest "sources" of additional energy capacity available.¹  As such, the development and growth of clean energy as an alternative to conventional, carbon-intensive energy sources has been identified as a critical factor in climate change mitigation efforts, particularly in light of projections that global energy demands may grow by more than 50% by 2030 compared to 2004 levels.²

Renewable energy sources are sustainable within a short timeframe relative to the Earth' natural cycles, and many of them produce provide energy with low or no greenhouse gas emissions.³  Renewable energy sources include solar, wind, geothermal, ocean thermal, hydropower, tidal, ocean wave, and biomass and biofuels energy. 

Clean energy sources such as wind, solar, geothermal, tide and wave energy are projected to grow 7.2% annually through 2030, bringing non-hydro renewables up from 1 to 4% of total global energy generation. Hydropower energy generation is expected to increase as well, although as a percentage of total energy it is expected to decrease two percentage points to 14%.⁴

Because of the seasonal, intermittent, and otherwise fickle nature of most renewable energy sources, storage of renewable energy when it is generated--so it is available when there is energy demand--is seen as an essential component to making renewables practical.  Energy storage options being invested in include hydrogen fuel cells, supercapacitors, and batteries.

By reducing demand for energy, energy conservation and energy efficiency decrease the total greenhouse gas emissions produced associated with energy production.  Energy conservation and efficiency are especially important energy solutions because they are significantly easier, quicker and cheaper to implement than solutions involving the production of energy from new or improved processes.  They are also areas where huge energy savings have been identified.  According to the International Energy Agency (IEA), "energy efficiency gains since 1990 have led to annual energy saving of more than 16 EJ in 2005 and 1.3 Gt of avoided CO2 emissions" among IEA countries.⁴  By applying proven technologies and best practices globally, another 1.9-3.2 Gt of CO2 emissions could be saved in industry alone.⁵  In public power generation, another 1.8-2.5 Gt in CO2 in annual saving is possible.⁶

Enhanced conventional energy refers to technologies that reduce the greenhouse gas emissions of conventional fossil fuel technologies. Whether enhanced conventional energy sources can be named clean energy is debated. While they are cleaner than conventional sources, they are by no means carbon neutral. Enhanced conventional energy sources include 'clean coal' technologies, such as coal washing, liquiditation, gasification, carbon capture and storage, and improved combustion technologies, including gasification, the Integrated Gasification Combined Cycle, Fluerized Bed Combustion and Supercritical and Ultrasupercritical Boilers.  Nuclear power is also labeled clean energy by some proponents, although it's excluded by others because of its environmental impacts other than greenhouse gas emissions.

Energy conservation describes behavior that results in the use of less energy, and thus frequently a decrease in greenhouse gas emissions.  Conserving energy can be as simple as turning of the lights or biking to work instead of using a car. It can also be achieved through the use of energy efficient technologies and insulating buildings.

Energy efficiency is the "ratio of energy output of a conversion process or of a system to its energy input."IPCC Energy efficient technologies require less energy to perform the same than regular technologies. Improving energy efficiency, for example in buildings, appliances, transport and industry, as well as end-use applications such as lighting, leads to large emissions cuts. The energy saved through energy conservation, including through energy efficiency, is often refered to as negawatts.