Cadmium telluride thin film photovoltaic cells (CdTe PV) - Type of thin film solar cells based on the cadmium telluride chemical compound.

Capture and use of coal mine ventilation air methane - Process of capturing and then using the methane that is contained in the exhaust air from underground coal mines.

Carbon capture and sequestration (CCS) - System that captures carbon from fossil fuel, either prior to or after combustion, and sequesters it for long-term storage underground.

Carbon dioxide equivalent (CDE) - For a given amount of greenhouse gas, it is the amount of carbon dioxide (CO₂) with the same global warming potential (GWP), assuming it remains in the atmosphere for 100 years. For example, the GWP of nitrous oxide is 320 times that of CO₂, thus one ton nitrogen oxide equals 320 tons CDE.

Carbon monoxide (CO) - Odorless, colorless, poisonous gas produced by the incomplete burning of fossil fuels (e.g., gasoline, oil, natural gas). Produced primarily by vehicles and industrial processes.

Cassava bioethanol - Bioethanol produced from cassava crop.

Cellulosic bioethanol - Bioethanol produced from wood, grasses or other plants.

Centralized energy generation model - Energy is generated in large-scale centralized power plants and distributed to the end user via the power grid.

Certified emissions reductions (CER) - Refers to carbon and/or climate credits issued by the Clean Development Mechanism. CERs are utilized by participating countries (and projects) in order to comply with established emission limitation targets. They can be temporary or permanent depending on the duration of its benefits, and can be acquired or traded on the market.

Chemical wastewater treatments - Treatment methods that use substances such as chlorine, ozone or hydrogen peroxide to remove pollutants.

CIGS thin film photovoltaic cells (CIGS PV) - Type of thin film solar cells, based on the copper irridium gallium selenide chemical compound.

Circulating fluidized bed combustion (CFBC) - Combustion application that uses fluidized beds, which is a device that causes the solid components of a fluid to act like a liquid. It then suspends solid fuel over streams of hot air during the combustion process thereby resulting in more efficient chemical reactions.

Civil heat - Burning of biomass to generate heat to be used for civil purposes.

Clean Development Mechanism (CDM) - Mechanism by which countries that are signatories to the Kyoto Protocol can invest in emission reduction projects in developing countries instead of implementing similar projects in-country.

Cleaner aircraft fuels - Aircraft fuels that produce considerably less air emissions than conventional aircraft fuels while delivering equal or better performance.

Cleaner ship fuels - Ship fuels that produce considerably less air emissions than conventional ship fuels while delivering equal or better performance.

Coal bed methane (CBM) - Methane originating in coal seams in a near liquid state that is drained from surface boreholes before mining takes place

Coal blending - Process of combining various types of pulverized coal to take advantage of their different combustion and emission properties.

Coal briquettes - Small rectangular blocks of compressed coal used in limited industrial applications, primarily smaller scale chemical plants and blast furnaces. Utilization of briquettes can reduce emission resulting from combustion.

Coal liquefaction - Process that converts coal into liquid fuels.

Coal mine methane (CMM) - Methane contained in gases captured in a working coal mine by methane drainage systems.

Coal screening and scrubbing - Processes that reduces impurities (such as ash or sulfur) contained in coal prior to burning, normally at or close to the coal mine.

Coal water slurry - Coal-based liquid fuel consisting of fine coal particles suspended in water. It consists of 55-70% of fine dispersed coal particles and 30-45% of water.

Coal water slurry technology - Technology and application that transforms coal water slurry into a viable energy product. The use of slurry saves substantial amounts of heavy oil in the electricity generating process and emits fewer pollutants.

Coke - Dense, almost completely pure form of carbon that burns at very high temperatures. Used in a variety of industrial applications, including steel production.

Combined cycle - A technique, employed by power producing plants or engines, that uses more than one thermodynamic cycle so as to further utilize waste heat generated from initial combustion.

Combined heat and power (CHP) - System that simultaneously generates electricity and usable heat by capturing heat that would normally be lost.

Commissioning and efficient operations - Assuring that all systems in a building are installed, tested, operated and maintained as originally intended.

Composite materials cables - Transmission and distribution line cables made from compostive materials that are specifically engineered to reduce losses.

Compost - Biodegration or decay of organic matter, such as agricultural and food waste. Compost, a high quality fertilizer, is the main byproduct of the process.

Compressed air energy storage (CAES) - System that can store energy by compressing air in a compartment, such as airtight underground cavern, and then generate electricity by releasing the air from storage through a combustion turbine.

Compressed natural gas (CNG) - Fossil fuel substitute for gasoline, diesel or propane made by compressing natural gas and stored in special compressed gas cylinders.

Concentrating photovoltaics (CPV) - Devices that concentrate sunlight onto photovoltaic surfaces to produce electricity.

Concentrating solar power (CSP) - Whereas concentrated photovoltaic uses photovoltaic surfaces to generate electricity, CSP uses lenses or mirrors and tracking systems to concentrate a large area of sunlight into a small beam. The heat produced by the small beam of light will then be used to generate electricity.

Control systems - Systems that monitor and control the behavior of other devices or systems to ensure optimal operation of the wind turbine.

Conversion efficiency - Ratio between input and output after an energy is converted from one form to another. The calculation of this ratio also figures in the usefulness of the output amount. Specifically for photovoltaic cells, conversion efficiency is the proportion of sunlight energy that the cell converts to electrical energy.

Conversion technologies - Devices that convert electricity received from a set of wind turbines to the standard required by the power grid before feeding the electricity onto the grid.

Copper rotor motors (CRM) - Motor technologies that offer increased electrical energy efficiency, lower operating temperature, extended motor life and reduced weight and size.

Crystalline silicon photovoltaic cells (cSi PV) - Type of solar cell made from a single crystal or a polycrystalline slice of silicon; it was the first type to be widely commercialized.

Cylinder deactivation - Automobile engine technology that can reduce fuel consumption and emission of an engine during light load operation by keeping the intake and exhaust valves closed for a particular cylinder.