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PV terms
Terms for Photovoltaic installation
59
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04/28/2009

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Term
Insolation
Definition
The solar radiation incident on an area over time.  Equivalent to energy and usually expressed in kilowatt hours of power per square meter.
Term
Irradiance
Definition
The solar power incident on a surface.  Usually expressed in kilowatts per square meter. (Irradiance multiplied by time equals Insolation)
Term
I-V Curve
Definition
The plot point of the current versus the voltage characteristics of a PV cell, module, or array.  Typically measured at 1000 watts per square meter of solar insolation at a specific cell temperature.  The shape of the curve characterizes cell performance.
Term
Maximum Power Point
Definition
Also called Peak Power Point-that point on an I-V curve that represents the maximum power output, measured in watts, for a particular cell or module. (Vmp x Imp = MP)
Term
Maximum Power Point Tracking
Definition
A power conditioner which continuosly controls PV source voltage in order to hold it at its maximum power output current.
Term
Open Circuit Voltage (Voc)
Definition
The maximum voltage produced by an illuminated PV cell, module or array with no load connected.  This value will increase as the temperature of PV material decreases.
Term
Short Circuit Current (Isc)
Definition
The current produced by an illuminated PV cell, module, or array when its output terminals are shorted.  The maximum current on an I-V curve, which is he operating point for a PV device under no load or short-circuit condition and no voltage output.  Isc increases as irradiance increases.
Term
Solar Cell
Definition
Individual PV unit designed to harvest sunlight energy via the photvoltaic effect.  Photons of sunlight produce electrical current.
Term
Solar Modules
Definition
Individual modules containing multiple mono and/or polycrystalline solar cells mounted in an aluminum frame and covered with tempered glass.
Term
Panels
Definition
Modules are grouped together to form a panel. For example, a series string of modules would equal one panel.
Term
Solar Array
Definition
All of the panels in a system are interconnected to form an array.
Term
String or Series String
Definition
Panels that are aligned in series.  When modules are wired in series the voltages are added from module to module.  For example, if there were ten 24v modules wired in series the total voltage of the string would be 240v
Term
Source Circuit
Definition
Each series string is a source circuit, or a circuit that produces electricity.
Term
Inverter
Definition
Converts D/C power to A/C.  The array produces D/C power but household current is A/C. An inverter is needed to use the power created by an array.  Inverters also condition power to match the utility grid.
Term
D/C Disconnect
Definition
Lockable, accessible disconnect that is fused.  Wired between the combiner box and the inverter.
Term
Azimuth
Definition
Angle between true south and the point directly below the location of the sun.  Measured in degrees east or west of true south in northern latitudes.
Term
Polycrystalline
Definition
PV wafer composed of MANY silicon crystals.
Term
Bypass Diode
Definition
Directs current around a malfunctioned or shaded module.  It protects solar cells from thermal destruction in case of total or partial shading of individual solar cells while other cells are exposed to full light.
Term
Langley
Definition
Unit of solar irradiance. 1 gram calorie per square centimeter.
Term
DC
Definition
Direct current
Term
Grid
Definition
Electric utility distribution network.
Term
P-N Junction
Definition
The interface between the P & N layers of a cell.
Term
Deration Factor
Definition
The rate that output capacity of a cell decreases over time.
Term
N-Type Silicon
Definition
Phosphorous doped cell layer with free electrons.
Term
Cell Efficiency
Definition
% of sunlight converted to electricity.
Term
Fixed Tilt Array
Definition
Is mounted in one permanent position.
Term
Main Enemies of Solar
Definition
Hard Shading and Heat
Term
Hybrid Inverter
Definition
Used for PV systems that are grid tied but also have battery and/or generator backup.
Term
Kilowatt Hour (kWh)
Definition
1000 watts over a 60 minute period of time.  One thousand watt hours.
Term
MPP
Definition
Located on the I-V curve--MAXIMUM Power Point, also called Peak Poer Point, the point on an I-V curve that represents the MAX power output, measured in watts for a particular cell or module.
Term
Rectifier
Definition
Converts A/C to D/C and is used in hybrid or stand alone alone systems with backup.
Term
Orientation
Definition
Location of a structure or array in relationship to North, South, East & West.
Term
Resistance
Definition
The property of a conductor which opposes the flow of an electric current resulting in the generation of heat in the conducting material. The unit of resistance is measured in ohms.
Term
Module
Definition
An encapsulated unit containing a number of interconnected photovoltaic cells that generates DC power under concentrated sunlight.
Term
Series String
Definition
When modules are wired in these the voltage adds and the amps stay the same.
Term
Solar Noon
Definition
Half way between sun up and sun down, the moment when the sun is HIGHEST in the sky.  To determine solar noon, calculate the length of day from the time of sunset and sunrise and divide by two. 
Term
Volt (V)
Definition
A unit of measure of the force, or "push" given the electrons in an electric current.  Also referred as the electromotive force.
Term
Watt Hour
Definition
A quantity of electrical energy when one watt is used for one hour.
Term
Kilowatt
Definition
1000 watts
Term
Crystalline Silicon
Definition
Composite semiconductor used in PV.  A type of PV cell made from single crystal or polycrystalline slice of silicon.
Term
Main Service Panel
Definition
Load center for resistance.  Power from the inverter back feeds the panel through a conventional double pole circuit breaker.  electricity from the array is fed to household circuits through the service panel.
Term
A/C Disconnect
Definition
Mounted between the inverter and the electrical panel.  Code requires a fusible, lockable, disconnect.
Term
P-Type Silicon
Definition
Semiconductor grade silicon doped with the element boron giving it a positive bias.
Term
Load
Definition
Any device that consumes electricity.  i.e. lights, heaters, pumps, electronics, etc...
Term
True South
Definition
Solar South
Term
Altitude
Definition
The angle of the sun above the horizon.
Term
How many peak sun hours in L.A.?
Definition
5.5 hours
Term
Watt (P)
Definition
The unit of electric power, or amount of work.  One ampere of current flowing at potential of one volt produces one watt of power.
Term
Watt's Law
Definition
W=A x V or P(Watts) = I(Amps) x E(Volts)
Term
Name 4 Resistance Factors?
Definition

1. Length

2. How thick is wire (guage)

3. Material (Copper, Aluminum, etc...)

4. Temperature

Term
Work
Definition
It's the transfer of energy from one form to another.
Term
Insulation
Definition
Materials that reduce the rate or slow down the movement of heat.
Term
Semi-Conductor
Definition
Any material that has limited capacity for conducting an electric current.
Term
Blocking Diode
Definition
A Semi-conductor device connected in series with a PV module and a storage battery to prevent reverse current discharge of the battery through the module when there is no output, or low output from the cells.
Term
Angle of Inclination
Definition
The angle that an array is mounted in relationship to horizontal.
Term
Angle of Incidence
Definition
Angle which references the sun's radiation striking a surface.  A "normal" angle of incidence refers to the sun striking a surface at a 90 degree angle.
Term
STC
Definition
Standard Testing Conditions-Conditions under which a module is typically tested in a lab.
Term
PTC
Definition
Practical Test Condition-when a module is tested under Real world conditions.
Term
BTU
Definition
British thermal unit--the quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit.
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