The Anthropocene is a proposed geological epoch dating from the commencement of significant human impact on Earth's geology and ecosystems, including, but not limited to, anthropogenic climate change.

Anthracite, also known as hard coal, is a hard, compact variety of coal that has a submetallic luster.

An anode is an electrode through which the conventional current enters into a polarized electrical device.

Annualized geo-solar enables passive solar heating in even cold, foggy north temperate areas.

Defined to be the difference between the annual amount of heat rejected to the ground heat exchanger in the cooling mode and the annual amount of heat extracted from the ground heat exchanger in the heating mode.

In aerodynamics, angle of attack specifies the angle between the chord line of a foil and the vector representing the relative motion between the foil and the atmosphere.

Anisotropic energy is energy that is directionally specific.

Fitted to a wind turbine, measures the wind speed and transmits wind speed data to the controller.

Ancillary services are the services necessary to support the transmission of electric power from generators to consumers given the obligations of control areas and transmission utilities within those control areas to maintain reliable operations of the interconnected transmission system.

Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen.

Anaerobic decomposition is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen.

An ampere hour or amp hour (Ah) is a unit of electric charge, having dimensions of electric current multiplied by time, equal to the charge transferred by a steady current of one ampere flowing for one hour. The energy content of a battery is usually expressed indirectly by its capacity in ampere-hours;

The ampere, (often shortened to "amp"), is the base unit of electric current in the International System of Units (SI).

Ampacity is defined as the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating

Amorphous silicon is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCDs.

An amorphous metal transformer (AMT) is a type of energy efficient transformer found on electric grids.

An ammeter is a measuring instrument used to measure the current in a circuit. Electric currents are measured in amperes (A).

American Wire Gauge, also known as the Brown & Sharpe wire gauge, is a logarithmic stepped standardized wire gauge system used since 1857, predominantly in North America, for the diameters of round, solid, nonferrous, electrically conducting wire.

The American Petroleum Institute (API) is the largest U.S. trade association for the oil and natural gas industry.

The American National Standards Institute is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States.