B

BALANCE OF SYSTEMS (BOS) Parts or components of a photovoltaic system other than the photovoltaic array or other generating equipment.

BALLAST A circuit used to condition and stabilize an electric current, for example, in a fluorescent light.

BATCH SOLAR HOT WATER HEATER The simplest of solar hot water systems. A tank of water within a glass-covered insulated enclosure aimed at the sun. Water is heated in the tank and then flows to the load or an auxiliary water heater.

BATTERY Two or more electrochemical cells electrically interconnected in an appropriate series/parallel arrangement to provide the required operating voltage and capacity levels. Under common usage, the term battery also applies to a single cell if it constitutes the entire electrochemical storage system.

BATTERY CAPACITY The total maximum charge, expressed in ampere-hours, that can be withdrawn from a cell or battery under a specific set of operating conditions including discharge rate, temperature, state of charge, age, and cutoff voltage.

BATTERY CELL The simplest operating unit in a storage battery. It consists of one or more positive electrodes or plates, electrolyte that permits ionic conduction, one or more negative electrodes or plates, separators between plates of opposite polarity, a container for all the above, and posts or other terminals for electrical connection.

BATTERY CYCLE LIFE The number of cycles, to a specified depth of discharge, that a cell or battery can undergo before failing to meet its specified capacity or efficiency performance criteria.

BATTERY LIFE The period during which a cell or battery is capable of operating above a specified capacity or efficiency performance level. With lead-acid batteries, end-of-life is generally considered when a fully charged cell can deliver only 80 percent of its rated capacity. Beyond this state of aging, deterioration and loss of capacity begins to accelerate rapidly. Life may be measured in cycles or years, depending on the type of service for which the cell or battery is intended.

BETZ LIMIT The theoretical maximum energy that a wind generator can extract from the wind—59.6 percent.

BIOMASS Any organic matter available on a renewable basis, including agricultural crops, wastes, and residues; wood, wood wastes, and residues; animal wastes and municipal wastes; and aquatic plants.

BIOFUELS (BIOMASS FUELS) Biomass converted directly to energy or converted to liquid or gaseous fuels, such as ethanol methane, and hydrogen.

BLADE The energy-capturing, aerodynamically designed part of a wind turbine, which interacts directly with the wind.

BLOCKING DIODE A semiconductor connected in series with a solar-electric cell or cells and a storage battery to keep the battery from discharging through the cell when there is no output, or low output, from the solar cell. It can be thought of as a one-way valve that allows electrons to flow forwards, but not backwards.

BRAKE Device for stopping a wind turbine. This can be an electric brake that shorts the output of the turbine (dynamic braking), or a mechanical brake that physically stops the rotation, as with a brake drum and shoe.

BREAKER A manually operable switching device that also automatically opens a circuit in the event of over current.

BRITISH THERMAL UNIT (BTU) The amount of heat required to raise the temperature of one pound (one pint) of water, one degree Fahrenheit. 1 watt-hour = 3.413 BTU.

BULK CHARGE The initial phase of battery charging, when the largest amount of energy is put into the battery.

BUSS An electrical connection component that can accept multiple cables or wires. Also bus, bus bar, or bus bar.

BYPASS DIODE A semiconductor device connected in parallel with a series block of parallel PV strings to prevent current from flowing back through any shaded or failed modules in the same block.