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Balance of System |
Those components other than the PV module that compose the complete PV operating system, including the inverter (in a grid-connected system), array mounting structure, cables and connectors. Off-grid systems include a charge controller and battery for electricity storage. |
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Balance of system (BOS) |
All the parts of a PV system excluding the solar module. |
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Ballast |
A circuit used to stabilize an electric current; for example, in a fluorescent light. |
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Battery |
A system in which stored chemical energy is converted directly into electrical energy. Can be either rechargeable or non-rechargeable. Different from a fuel cell in that it contains a fixed quantity of stored chemical energy rather than a continuous supply of fuel. |
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Battery capacity |
The total number of ampere-hours (Ah) that a fully charged battery can output. |
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Battery cell |
An individual unit of a battery that can store electrical energy and is capable of furnishing a current to an external load. For lead-acid batteries the voltage of a cell (fully charged) is about 2.2 volts DC. A battery may consist of a number of cells. |
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Battery charger |
A device used to charge a battery by converting usually AC voltage to a DC voltage suitable for the battery. Chargers often incorporate some form of regulator to prevent overcharging and damage to the battery. |
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Battery cycle life |
The number of times a battery can undergo a cycle of discharge and recharge before failing. Cycle life is normally specified as a function of discharge rate and temperature. |
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Battery self-discharge |
Energy loss by a battery that is not under load. |
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Battery state of charge (SOC) |
Extent of battery charge status as a percentage of full charge. Also 100% minus the depth of discharge. |
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BEOL |
Back-end-of-line. |
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BIPV |
Building Integrated Photovoltaics. As the name suggests, this is where PV modules are integrated in to the building construction materials as on integrated unit. |
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Blocking diode |
A diode used to prevent current flow in an undesirable direction; for example, from the rest of the PV array to a failed module or from the battery to the PV array when current generation is low. |
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British Thermal Unit (BTU) |
The amount of heat energy required to raise one pound of water from a temperature of 60 degrees F to 61 degrees F at one atmosphere pressure. One Watt hour equals 3,413 BTU. |
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Bypass diode |
A diode connected across one or more solar cells in a photovoltaic module such that the diode will conduct if the cell(s) become reverse biased. [UL 1703] |
