PV 301
Glossary of Terms

Alternating Current (AC) - Electric current in which the direction of flow oscillates at frequent, regular intervals.

Altitude - The angle between the horizon (a horizontal plane) and the sun, measured in degrees.

Amorphous Silicon - A thin film PV silicon cell having no crystalline structure.

Ampere (Amp) - Unit of electric current measuring the flow of electrons per unit time.

Ampere-Hour (Ah) - The quantity of electrical energy equal to the flow of current one ampere for one hour.

Angle of Incidence - 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 (or perpendicular) angle.

Array - A mechanically integrated configuration of modules together with support structure, designed to form a DC power producing unit.

Azimuth - Angle between true south and the point directly below the location of the sun. Measured in degrees.

Battery - Two or more "cells" electrically connected for storing electrical energy. Common usage permits this designation to be applied also to a single cell used independently as in a flashlight battery.

Battery Capacity - Generally, the total number of ampere-hours that can be withdrawn from a fully charged cell or battery.

Battery Cell - A galvanic cell for storage of electrical energy. This cell, after being discharged, may be restored to a fully charged condition by an electric current.

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 Self Discharge - Self-discharge is the loss of otherwise useable chemical energy by spontaneous currents within the cell or battery regardless of its connections to an external circuit.

Battery State of Charge - Percentage of full charge or 100 percent minus the depth of discharge (see depth of discharge).

Blocking Diode - A semi-conductor device connected in series with a module and a storage battery to prevent a reverse current discharge of the battery through the module when there is no output, or low output from the cells.

Bypass Diode - A semi-conductor device connected in parallel with a series block of parallel strings to prevent current from flowing back through any shaded or failed modules in the same block.

Cell Junction - The contact zone between two layers of a photovoltaic cell. Also referred to as the P/N junction.

Charge Controller - A device that controls the charging rate and/or state of charge for batteries.

Charge Rate - The current applied to a cell or battery to restore its available capacity. Concentrator - An optical component of a photovoltaic array used to direct and increase the amount of incident sunlight on a solar cell.

Conversion Efficiency (Cell) - The ratio of the electricity energy produced by a photovoltaic cell (under full sun conditions) to the energy from incident sunlight on the cell.

Crystalline Silicon - A type of PV cell made from a single crystal or polycrystalline slice of silicon.

Current - The flow of electric charge in a conductor between two points having a difference in potential (voltage).

Days of Autonomy - the number of consecutive days a stand-alone system will meet a defined load without solar energy input.

Deep Cycle Battery - Type of battery that can be discharged to a large fraction of capacity many times without damaging the battery.

Depth of Discharge (DOD) - The amount of ampere-hours removed from a fully charged cell or battery, expressed as a percentage of rated capacity.

Design Month - The month having the combination of insolation and load that requires the maximum energy from the array.

Diffuse Radiation - Refers to solar radiation that reaches the earth is directly due to reflection and scattering.

Diode - Electronic component that allows current flow in one direction only. See Blocking Diode, Bypass Diode.

Direct Current (DC) - Electric current flowing in one direction.

Discharge Rate - The current removed over a specific period of time from a cell or battery.

Disconnect - Switch gear used to connect or disconnect components in a PV system.

Duty Cycle - The ration of active time to total time. Used to describe the operating regime of appliances or loads in PV systems.

Efficiency - The ration of output power to input power. Expressed in percent.

Electric Circuit - A complete path followed by electrons from a power source to a load and back to source.

Electric Current - Magnitude of the flow of electrons.

Electrolyte - A conducting medium in which the flow of electric current takes place by migration of ions. The electrolyte for a lead-acid storage cell is an aqueous solution of sulfuric acid.

Energy Payback Time - The time required for any energy producing system or device to produce as much energy as was required in its manufacture.

Equalization - The process of mixing the electrolyte in batteries by periodically overcharging the batteries for a short period.

Grid - The network of transmission lines, distribution lines, and transformers used in central power systems. Insolation - The solar radiation incident on an area. Usually expressed in watts per square meter or Btu's/per hour. Inverter - A solid state device which changes a DC input to an AC output.

IV Curve - The graphical representation of the current versus the voltage of a photovoltaic cell, module or array as the load is increased from zero voltage to maximum voltage. Typically measured at 1000 watts per square meter of solar insolation at a specific cell temperature.

Kilowatt (kW) - One thousand watts.

Kilowatt Hour (kWh) - One thousand watt hours.

Life-Cycle Cost - An estimate of the cost of owning and operating a system for the period of its useful life; usually expressed in terms of the present value of ail lifetime costs.

Load - The amount of electrical power being consumed at any given moment. Also, any device or appliance that is using power.

Maximum Power - For a photovoltaic cell module or array, this refers to the power at the point on the current-voltage curve where the current-voltage product is a maximum.

Maximum Power Point - The operating point on a PV array I-V curve where maximum power is delivered.

Module - A predetermined electrical configuration of solar cells laminated into a protected assembly.

NEC - An abbreviation for the National Electric Code which contains safety guidelines for all types of electrical installations. Article 690 pertains to solar photovoltaic systems.

Nominal Operating Cell Temperature (NOCT) - The reference cell (module) operating temperature presented on manufacturer's literature. Generally the NOCT is referenced at 25ºC, 77ºF.

Nominal Voltage - A reference voltage used to describe batteries, modules, or systems (i.e., a 12-volt or 24-volt battery, module or system).

N-Type Silicon - Refined semiconductor grade silicon. Contains the element phosphorus giving it a negative bias.

Ohm - A unit of electrical resistance measurement.

Open Circuit Voltage - The maximum possible voltage across a photovoltaic array.

Open circuit voltage occurs in sunlight when no current is flowing.

Orientation - Placement according to the directions, N, S, E, W; azimuth is the measure in degrees from true south.

Panel - A configuration of modules fastened together, l and wired, and designed to provide a field installable unit.

Parallel Connection - The method of interconnecting electricity-producing devices or power consuming devices, so that the voltage is constant but the current is additive.

Peak Load - The maximum load or electrical power consumption occurring in a given period of time.

Peak Sun Hours - The equivalent number of hours per day when solar irradiance averages 1000 w/m2. Peak Watt - The amount of power a photovoltaic device will produce during peak insolation periods when the cell is faced directly at the sun.

Photon - A particle of light, the basic packet of light energy.

Photovoltaic Cell - A cell that generates electrical energy when incident solar radiation falls on it. This term distinguishes it from a photoconductive cell (photoresistor) which changes its electrical resistance when light falls on it.

Photovoltaic System - An installed aggregate of solar array, power conditioning and other subsystems providing power to a given application.

Polycrystalline Silicon - Silicon which has solidified rapidly enough to produce many small crystals which are arbitrarily arranged.

Power Conditioning - The electrical equipment used to convert power from a photovoltaic array into a form suitable to meet the power supply requirements of more traditional loads. Loosely, a collective term for inverter, transformer, voltage regulator, meters, switches, and controls.

P-Type Silicon - Semi-conductor grade silicon doped with the element boron giving it a positive bias.

Remote Site - Site which is not conveniently located near a utility grid.

Resistance (R) - 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 Ohms.

Semiconductor - Any material between an insulator and conductor which has a limited capacity for conducting electricity.

Series Connection - A method of interconnecting electricity producing devices or power-using devices so that the current remains constant and the voltage is additive.

Short Circuit Current - Current measured when a PV cell (module) is not connected to a load or other resistance.

Silicon - Semiconductor material commonly used in photovoltaic cells.

Single-Crystal Silicon - A material formed from a single silicon crystal.

Solar Cell - Photovoltaic cell.

Solar Thermal Electric - Method of producing electricity from solar energy by concentrating sunlight on a working fluid which changes phase to drive a turbine generator.

Stand-Alone System - A photovoltaic system that operates independently of the utility lines. It may draw supplementary power from the utility but is not capable of providing power to the utility.

State-of-Charge - The available capacity in a cell or battery expressed as a percentage of rated capacity. For example, if 25 ampere-hours have been removed from a fully charged 100-ampere-hours cell, the new state of charge is 75 percent.

Surge Capacity - The ability of an inverter or generator to deliver high currents momentarily required when starting ac motors.

Temperature Compensation - An allowance made in charge controllers set points for changing battery temperatures.

Tilt Angle - Angle of inclination of collector as measured in degrees from the horizontal.

Uninterruptible Power Supply (UPS) - The designation of a power supply providing continuous uninterruptible service.

Volt, Voltage - A unit of measurement of the force given to electrons in an electric circuit; electric potential.

Wafer - A thin slice of semiconductor material used in photovoltaic cell manufacture.

Watt, Wattage - A measure of electric power.

Watts = Volts x Amps Watt Hour - A quantity of electrical energy when one watt is used for one hour.

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