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Combiner box
A combiner box is a weatherproof enclosure in a photovoltaic system that connects several solar panel strings in parallel, with fuses, surge protection, and a disconnect.
Combustion
Combustion, or the combustion reaction, is a rapid exothermic reaction between a fuel and an oxidizer, usually oxygen, releasing heat and light, as in fires and engines.
COMESA electricity market
The COMESA electricity market is the framework for cross-border power trade among the 21 member states of the Common Market for Eastern and Southern Africa.
COMEX
COMEX (Commodity Exchange) is a United States futures exchange for metals, founded in New York in 1933, where the benchmark gold, silver, and copper futures contracts trade under CME Group.
Comgás
Comgás (Companhia de Gás de São Paulo) is a Brazilian piped natural gas distributor serving 177 cities in São Paulo state, privatized in 1999 and majority-owned by Cosan.
Comisión Federal de Electricidad
Comisión Federal de Electricidad (CFE), or Federal Electricity Commission, is Mexico's state-owned electric utility. Created in 1937, it supplies most of the country's electricity and was reconstituted by a 2024 constitutional reform.
Comisión Nacional de los Mercados y la Competencia
The Comisión Nacional de los Mercados y la Competencia (CNMC) is Spain's independent regulator for competition and key sectors including energy, telecommunications, and transport, created in 2013.
Comisión Reguladora de Energía
The Comisión Reguladora de Energía (CRE, Energy Regulatory Commission) was Mexico's federal regulator for natural gas and electricity, created in 1994 and replaced by the CNE in 2025.
Comissão Nacional de Energia Nuclear
The Comissão Nacional de Energia Nuclear (CNEN, National Nuclear Energy Commission) is Brazil's federal autarky for nuclear energy, created in 1956 and seated in Rio de Janeiro.
Commissariat à l'énergie atomique
The Commissariat à l'énergie atomique (CEA) is a French public research and technology organization created by General de Gaulle's ordinance of 1945 to pursue atomic energy research.
Commission de régulation de l'énergie
The Commission de régulation de l'énergie (CRE) is the French independent administrative authority regulating electricity and gas markets, established in 2000 as France opened its energy markets to competition.
Common cause failure
A common cause failure (CCF) is when two or more components fail together from a shared cause, defeating redundancy; it is central to nuclear plant risk assessment.
Common ethanol fuel mixtures
Common ethanol fuel mixtures, also called gasahol, are ethanol-gasoline blends named by ethanol percentage: E10 for any conventional vehicle, E15 for 2001 and newer vehicles, and E85 for flexible fuel vehicles.
Common rail
Common rail is a diesel fuel injection system in which a high-pressure pump feeds a shared rail that supplies electronically controlled injectors, introduced in 1997.
Common-mode leakage current
Common-mode leakage current is an unwanted current that flows between a photovoltaic array and the grid through parasitic capacitance, the defining safety problem of transformerless PV inverters.
Commonwealth Edison
Commonwealth Edison, known as ComEd, is an investor-owned electric utility serving more than 400 municipalities in northern Illinois, including Chicago, and operates as a subsidiary of Exelon.
Commonwealth Fusion Systems
Commonwealth Fusion Systems is an American private fusion company spun out of MIT in 2018 that is building SPARC, a compact net-energy tokamak, in Devens, Massachusetts.
Commonwealth LNG
Commonwealth LNG is a liquefied natural gas production and export terminal on the west bank of the Calcasieu Ship Channel near Cameron, Louisiana, permitted for 9.5 million tonnes per year.
Community choice aggregation
Community choice aggregation (CCA) is a program letting cities and counties become the default electricity supplier for their residents, while the incumbent utility delivers the power and customers can opt out.
Community Energy (company)
Community Energy, Inc. is an American renewable energy company founded in 1999 in Radnor, Pennsylvania, which began selling retail wind power and became a large-scale solar developer.
Community Offshore Wind
Community Offshore Wind was a US offshore wind joint venture of RWE and National Grid Ventures holding lease OCS-A 0539 in the New York Bight, canceled in 2026.
Compact fluorescent lamp
A compact fluorescent lamp (CFL) is a fluorescent lamp with a bent spiral tube designed to fit household fixtures, invented by Edward Hammer at General Electric in 1976.
Compact toroid
A compact toroid (CT), also called a compact torus, is a magnetically confined plasma torus with no center column, covering two configurations, the field-reversed configuration and the spheromak.
Compact transmission line
A compact transmission line is an overhead power line built with reduced phase spacing and shorter insulators, so more power flows through a narrower right-of-way than a conventional design allows.
Compagnie nationale du Rhône
The Compagnie nationale du Rhône (CNR) is a French joint-stock company created in 1933 to develop the Rhône river from Switzerland to the Mediterranean through hydroelectricity, navigation, and irrigation.
Companhia de Electricidade de Macau
Companhia de Electricidade de Macau (澳电) is the utility holding Macau's exclusive concession to transmit, distribute, and supply electricity since 1985, extended to 2040, with most power imported from Guangdong.
Companhia Energética de São Paulo
Companhia Energética de São Paulo (CESP) is a Brazilian electricity generation company owned by the Auren Energia group, founded by São Paulo state in 1966 and privatized in 2018.
Companhia Paranaense de Energia
Companhia Paranaense de Energia (Copel) is a Brazilian electric utility headquartered in Curitiba, Paraná. Founded as a state-owned company in 1954, it was privatized in 2023 and serves nearly all of Paraná.
COMPASS-U
COMPASS-U (COMPASS Upgrade) is a medium-size, high-magnetic-field tokamak under construction at the Institute of Plasma Physics in Prague, replacing COMPASS in 2021 to support ITER and address DEMO design challenges.
Competitive Power Ventures
Competitive Power Ventures (CPV) is an American independent power company headquartered in Silver Spring, Maryland. Founded in 1999, it develops natural gas, wind, and solar generation projects.