A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requiring a continuous source of fuel and oxygen (usually from air) to sustain…

A solar cell, also known as a photovoltaic cell (PV cell), is an electronic device that converts the energy of light directly into electricity by using the photovoltaic effect. It is a type of photoelectric cell, a device whose electrical characteristics (such as current, voltage, or resistance) vary when it is…

This is a list of notable photovoltaics (PV) companies. Grid-connected solar photovoltaics (PV) is the fastest growing energy technology in the world, growing from a cumulative installed capacity of 7.7 GW in 2007, to 320 GW in 2016.

A power purchase agreement (PPA), or electricity power agreement, is a long-term contract between an electricity generator and a customer, usually a utility, government or company. PPAs may last anywhere between 5 and 20 years, during which time the power purchaser buys energy at a pre-negotiated price.

A feed-in tariff (FIT) is paid by energy suppliers in the United Kingdom if a property or organisation generates their own electricity using technology such as solar panels or wind turbines and feeds any surplus back to the grid. The FIT scheme was imposed on suppliers by the UK government, and applied to…

An energy transition (or energy system transformation) is a major structural change to energy supply and consumption in an energy system. Currently, a transition to sustainable energy is underway to limit climate change.

NRG Energy, Inc. is an American energy company, headquartered in Houston, Texas.

Geothermal energy is thermal energy extracted from the Earth's crust. It combines energy from the planet's formation and from radioactive decay.

Constellation Energy Corporation is an American energy company headquartered in Baltimore, Maryland. The company provides electric power, natural gas, and energy management services.

Open energy-system models are energy-system models that are open source. These models can also be known as open energy models or open-source energy-system models or some combination thereof.