For technical glossaries, visit the Renewable Resource Data Center.
A
Amps (I)
The unit of measure that indicates how much electricity flows through a conductor. It is like using cubic feet per second to measure the flow of water. For example, a 1,200-watt, 120-volt hair dryer pulls 10 amperes of electricity current. (amps = watts/volts)
B
Balance of System (BOS) Components
The parts of the photovoltaic system other than the PV array: switches, controls, meters, power-conditioning equipment, supporting structure for the array and storage components, if any.
Batteries, see Storage
Batteries are often sold with a PV system. The primary purpose is to store the electricity not immediately used, which could be used at some later time. With net metering, the value of batteries is less because the utility grid basically acts as a storage facility. For a reliable generation system that can function independent of the utility grid, however, batteries may be a viable component to the total system. Back-up generators may be included in a system to provide power when the PV system is not operating, and are generally included when systems are not grid connected. Neither batteries nor generators are eligible for rebate money.
Building Integrated Photovoltaics
A term for the design and integration of PV into the building envelope, typically replacing conventional building materials. BIPV often integrates PV cells into vertical facades, such as in window glazing; into roofing systems, replacing traditional roofing materials and into shading structures that cover windows.
D
Data Acquisition System (DAS)
A key part of the DATA COLLECTION SYSTEM which has the function of collecting analog and digital signals, converting the analog signals to digital, multiplexing the signals, doing arithmetic and logical operations, and storing measured and calculated values. Depending on the specific manufacturer's model, the DAS may have its own display and printing devices built in (e.g., data loggers).
Data Collection System
A complete system for collecting, analyzing, storing, and displaying measured and calculated data. It consists of sensors, signal conditioning, cabling, and the DAS.
F
Flat Plate Array
A PV array using non concentrating modules with a flat surface for collecting solar energy.
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G
Gigawatt
One billion watts or one million kilowatts
Grid
The network of ac power transmission lines and transformers used in central power systems. Grid power means utility power.
Grid-tied System
Grid-connected or utility-interactive PV systems are designed to operate in parallel with and interconnected with the electric utility grid. The primary component in grid-connected PV systems is the inverter, or power conditioning unit (PCU). The PCU converts the DC power produced by the PV array into AC power consistent with the voltage and power quality requirements of the utility grid, and automatically stops supplying power to the grid when the utility grid is not energized. A bi-directional interface is made between the PV system AC output circuits and the electric utility network, typically at an on-site distribution panel or service entrance. This allows the AC power produced by the PV system to either supply on-site electrical loads, or to back feed the grid when the PV system output is greater than the on-site load demand. At night and during other periods when the electrical loads are greater than the PV system output, the balance of power required by the loads is received from the electric utility This safety feature is required in all grid-connected PV systems, and ensures that the PV system will not continue to operate and feed back onto the utility grid when the grid is down for service or repair.
H
Hybrid Power Systems
A PV system that includes other sources of electricity generation, such as wind, microturbines or diesel generators.
I
Interconnection Agreement
An agreement entered into with the local utility (PG&E) allowing for net-metering a photovoltaic, wind or fuel cell system to the utility grid.
Inverter
A power conversion device which changes dc voltage input to an ac voltage output. A power conversion device which changes dc voltage in Grid-connected or utility-interactive PV systems are designed to operate in parallel with and interconnected with the electric utility grid. The primary component in grid-connected PV systems is the inverter, or power conditioning unit (PCU). The PCU converts the DC power produced by the PV array into AC power consistent with the voltage and power quality requirements of the utility grid, and automatically stops supplying power to the grid when the utility grid is not energized. A bi-directional interface is made between the PV system AC output circuits and the electric utility network, typically at an on-site distribution panel or service entrance. This allows the AC power produced by the PV system to either supply on-site electrical loads, or to back feed the grid when the PV system output is greater than the on-site load demand. At night and during other periods when the electrical loads are greater than the PV system output, the balance of power required by the loads is received from the electric utility. This safety feature is required in all grid-connected PV systems, and ensures that the PV system will not continue to operate and feed back onto the utility grid when the grid is down for service or repair or put to an ac voltage output.
K
Kilowatts
1000 watts (equal to 1,000 watts). A unit of measure of the amount of electricity needed to operate given equipment. For example, one kW is enough power to illuminate 10 light bulbs at 100 watts each. (volts x amps = watts)
Kilowatts AC (or Peak KW)
Maximum generating capacity of photovoltaic system. Term used in performance rating of PV cells, modules, and arrays, usually at sunlight intensity of 1000 W/m2 with an average cell temperature of 25°C.
Kilowatts DC (nameplate)
Size of the photovoltaic system, based on the sum of the nameplate module wattages. The power of a PV system will be lower than the kilowatts DC due to dust and dirt, ambient temperature, conversion losses (going from DC to AC), wire losses, orientation, tilt and shading.
Kilowatt Hours
The amount of kW produced over a period of time, or one kilowatt of electricity supplied for one hour. For example, a one kW system, if operating at full capacity for 5 hours will produce 5 kWh of electricity.
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M
Megawatt
One thousand kilowatts or one million watts. One megawatt is enough to power 1,000 average California homes per day.
Mounting Systems
Roof, Ground, Pole.
N
Net-metering
Net Metering is a billing arrangement between Pacific Gas & Electric and customers who generate their own electricity with photovoltaic or wind systems, by which the excess electricity produced using your own generating equipment is fed back onto the utility grid and is deducted from your electric bill.
O
Off-grid System
System installed in households, typically in remote areas, that are not connected to the utility grid. Requires a means to store electricity (most commonly a lead-acid battery). Also called "stand-alone photovoltaic power system".
Output (of a PV system)
The amount of electricity a PV system produces. Dust and dirt, ambient temperature, conversion losses (going from DC to AC), wire losses, orientation, tilt and shading all effect the output of a PV system.
P
Photovoltaic Cell
A device that produces electricity from light. Cells are the building block for modules.
Photovoltaic Module
A number of PV cells connected together, sealed with an encapsulant, and having a standard size and output power; the smallest building block of the power generating part of a PV array.
Photovoltaic Array
A group of photovoltaic panels.
Polycrystalline Silicon
Silicon which has solidified rapidly enough to produce many small crystals which are arbitrarily arranged. This type of cell has grain boundaries, randomly oriented, visible on the active surface. Compare to Monocrystalline Silicon and Amorphous Silicon.
S
Stand Alone PV System
A type of PV system that is not connected to an auxiliary power source or a PV system that operates independently of the electric utility lines. It usually contains one or more batteries, but many pumping systems comprise only the PV array and the inverter. Also known as an "off-grid PV system"
Storage
Storage refers to saving surplus electricity produced by a PV system. Generally batteries are used as storage devices.
T
Tilt Angle
The angle which the plane of a PV module makes relative to the horizontal plane.
Tracking Equipment
Structure that houses PV modules and that can automatically follow the sun across the sky throughout the day to maximize output.
Turn-key photovoltaic Products/Services
Typically refers to a solar contractor that handles most/all of the stages of a photovoltaic installation, including design, engineering, product supply and installation.
V
Volts (V)
A unit of measure of the force, or 'push,' given the electrons in an electric circuit. One volt produces one ampere of current when acting on a resistance of one ohm.