Glossary: General Energy / Electricity
When learning about energy efficiency, it may be useful to
have a basic understanding of terms related to energy and electricity.
Alternating current (AC): An alternating current means that the electrical current’s direction is reversed in cycles (120 reversals or 60 cycles per second in the U.S.). AC is used in electricity transmission and distribution because its voltage can be easily controlled.
Chemical energy: Chemical energy is generated from chemical reactions in which the chemical bonds of a substance are broken and rearranged to form new molecules that can provide energy. Chemical energy can be transformed into thermal energy, mechanical energy, and electrical energy. Respective examples of these conversions include burning wood, digestion of food, and the chemical process used in nuclear power plants.
Direct current (DC): A direct current means that electrical current flows in a single direction through a conductor. DC must be converted to alternating current (AC) to be used for a typical 120-volt or 220-volt household appliance. DC is used directly in industrial applications and appliances that use battery power.
Electrical circuit: The path followed by electrons from a power source such as a photovoltaic (solar) panel, through an electrical system to create light, motion, battery power, and other power. The circuit is completed when the electrons return to the power source, creating a continuous flow of electricity.
Electrical current: The flow of electrons through an electrical wire, or transmission or distribution line. Current is measured in amperes.
Electrical energy: Electrical energy is the flow of electrons along a circuit. The movement of electrons creates an electric current which can be connected to an end use like lighting or appliances. Electrical energy can also be transformed into mechanical energy (using an elevator) or thermal energy (by using a space heater). Conversely, mechanical, thermal, and other forms of energy can be converted to create electricity, as in wind turbines and biomass facilities respectively. Electrical energy is usually measured in kilowatt-hours (kWh) or megawatt-hours (MW).
Electricity: See electrical energy.
Electron: A negatively charged particle that is part of an atom. When electrons move among atoms to balance charges, an electrical current is created.
Energy: The ability to do work or the ability to move an object. Energy occurs in two primary states, potential and kinetic. This energy can occur in a number of forms including electrical, thermal (heat), chemical, radiant, and mechanical energy.
Kinetic energy: Kinetic energy is the release of potential energy to create motion, ultimately to do work. An example of kinetic energy is the energy carried by wind.
Mechanical energy: Mechanical energy refers to an object that is doing work by being in motion. Mechanical energy can be transformed into electrical energy or thermal energy. Examples include wind turbines and refrigerators, respectively.
Photon: A particle of light that acts as an individual unit of energy.
Potential energy: Potential energy is stored energy, waiting to be released. An example of potential energy is the energy embodied in ocean waves, which can be captured through ocean energy technologies to produce kinetic energy.
Power: Power is the rate at which work is done. The ratio of work and time determines the amount of power used. For example, imagine that two people start at the bottom of a mountain with the goal of reaching the top. The first person hikes to the top in a short amount of time. The second person scales the rocks to the top which takes a much longer amount of time. The same amount of work was done by both (they reached the top of the mountain), but the hiker has more power since the distance traveled was completed in a shorter amount of time. Power is expressed in Watts.
Radiant energy: Radiant energy comes from a light source, such as the sun. Energy released from the sun is in the form of photons. These tiny particles, invisible to the human eye, move in a way similar to a wave. Radiant energy can be transformed into electrical energy using solar panels.
Thermal energy: Thermal energy is the use of heat as a source of energy. Thermal energy can be used directly or can be transformed into mechanical energy (using a steam engine) which can then be transformed into electrical energy. Thermal energy is usually measured in British thermal units (Btu).
Work: Work is the transfer of energy to move an object a certain distance, such as a horse pulling a plow from one side of a field to another. Work is expressed in Joules. The rate at which work is performed is power.