The balance of system encompasses all components of a photovoltaic system other than the photovoltaic panels. This includes wiring, switches, a mounting system, one or many solar inverters, a battery bank and battery charger.

The Baghdad Battery or Parthian Battery is a set of three artifacts which were found together: a ceramic pot, a tube of copper, and a rod of iron.

Bagasse is the dry pulpy fibrous material that remains after crushing sugarcane or sorghum stalks to extract their juice.

Backward erosion often occurs in non-plastic soils such as fine sands. It can occur in sandy foundations, within the dam or levee, or in cofferdams under high flood pressures during construction, causing unravelling at the downstream face.

Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources.

Backfeeding is the flow of electric power in the direction reverse to that of the generally understood or typical flow of power.

An azimuth is an angular measurement in a spherical coordinate system.

An axial turbine is a turbine in which the flow of the working fluid is parallel to the shaft.

An aviation biofuel or bio-jet-fuel or bio-aviation fuel is a biofuel used to power aircraft and is said to be a sustainable aviation fuel.

The mean wind speed over a specified period of time.

Seasonal average versus peak Energy Efficiency Ratio (EER) or Coefficient Of Performance (COP).

An avalanche photodiode (APD) is a highly sensitive semiconductor photodiode that exploits the photoelectric effect to convert light into electricity.

Hydrogeology is the area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust (commonly in aquifers).

A hydrogen vehicle is a vehicle that uses hydrogen fuel for motive power.

A hydrogen turboexpander-generator or generator loaded expander for hydrogen gas is an axial flow turbine or radial expander for energy recovery through which a high pressure hydrogen gas is expanded to produce work that is used to drive an electrical generator.

Hydrogen sulfide is the chemical compound with the formula H2S.

Hydrogen storage is a term used for any of several methods for storing hydrogen for later use.

A hydrogen station is a storage or filling station for hydrogen.

Hydrogen production is the family of industrial methods for generating hydrogen gas.

Hydrogen pipeline transport is a transportation of hydrogen through a pipe as part of the hydrogen infrastructure.