GLOSSARY OF TERMS PART A

GLOSSARY OF TERMS
PART A (Certification)

Glossary

AC/AC interface: An interface between the inverter output and the AC load. It may include AC/AC voltage conversion and connection to an auxiliary power supply.

acceptance test conditions (ATC): Reference values of ambient temperature, in-plane irradiance and spectral distribution, specified for power rating of photovoltaic (PV) arrays. [IEC 1829, p. 19]

air mass (AM): The length of path through the earth's atmosphere traversed by the direct solar beam, expressed as a multiple of the path traversed to a point at sea level with the sun directly overhead. The value of Air Mass is 1 at sea level with cloudless sky when the sun is directly overhead and the air pressure P=1.013105 Pa (1.013 bar or 760 mm Hg). At any point, the value of the air mass is given by: AM=(P/P0)(1/sin) with Plocal air pressure in Pa.; P0 = 1.013105 Pa (1.013 bar) = solar elevation angle. [IEC 904-3, p. 17]

ambient temperature (Tamb): The temperature of the air surrounding the photovoltaic (PV) generator as measured in a vented enclosure and shielded from solar, sky, and ground radiation. [IEC 904-3, p. 23]

ampere-hour efficiency: This refers to the ratio of discharge amount to charge amount, which is calculated by: ampere-hour efficiency = [(discharge current x discharge time)/(charge current x charge time)] x 100 (%).

angle of incidence: The angle between the direct irradiant beam and the normal to the active surface. [IEC 904-3, p. 25]

array: A mechanically integrated assembly of modules or panels together with support structure, but exclusive of foundation, tracking apparatus, thermal control, and other such components to form a DC power-producing unit. [IEC 1277, p. 39]

array field: The aggregate of all solar photovoltaic arrays within a given system. [IEC 1277, p. 39]

assumed non-sunshine period: A period during which a system equipped with a battery but with no auxiliary power supply can be continuously operated with the battery only for the load estimated by specifications from a fully charged state.

azimuth: The projected angle between a straight line from the apparent position of the sun to the point of observation and due north, measured from south in the northern hemisphere, from north in the southern hemisphere, and negative to the east, positive to the west. [IEC 1194] Unit rad.

blocking diode: A diode connected in series with module(s) or panel(s) to prevent reverse current in such module(s) or panel(s).

cell temperature (Tj): Temperature measured by a thermal sensor in contact with the cell or derived from Voc measurement or thermal balance calculations. [IEC 904-3, p. 23]

charging efficiency: A generic term to express the ampere-hour efficiency and the watt-hour efficiency, but is more often used to mean the ampere-hour efficiency.

common load system: A system structured and designed to meet unspecified loads in a certain range.

conversion efficiency: The ratio of maximum electrical power output to the product of generator area and incident irradiance measured under defined test conditions and expressed as a percentage. [IEC 904-3, p. 21]

current temperature coefficient: The change of the short-circuit current of a photovoltaic (PV) device per unit change of cell temperature . [IEC 904-3, p. 25] Note: This coefficient varies with irradiance and, to a lesser extent, with temperature. Unit A-1.

current-voltage characteristic (I=f(V)): The output current of a photovoltaic (PV) generator as a function of output voltage at a particular temperature and irradiance. [IEC904-3, p. 21]

DC conditioner: A device which changes the PV array output voltage into a usable DC voltage.

DC/DC interface: An interface between the PV power generating system DC voltage and the DC load. It may include DC/DC voltage conversion and to connect an auxiliary DC power supply.

DC maximum voltage: Vmaximum DC input voltage of the power conditioner at specified operating conditions, such as Voc of the PV array. Unit V

DC voltage operating range: DC input voltage range of the power conditioner which can operate stably.

dependence on solar energy: In the case of a system equipped with an auxiliary power supply, the ratio of output energy of the PV system to the sum of the output energy and the supplementary electric energy. Note 1: Dependency on solar energy may be classified into measured data and estimated data. The shortest period is a month (30 days). Note 2: The supplementary electric energy means the backup electric energy from an auxiliary power supply.

depth of discharge (DOD): A value to express the state of discharge of a battery. The ratio of the discharge amount to the rated capacity is generally used.

diffuse irradiance: The radiant power from the whole of the sky, incident upon unit area except that contributing to the direct solar irradiance. [IEC 904-3, p. 17] unit Wm^-2.

diffuse irradiation: Diffuse irradiance integrated over a specific time interval. [IEC 904-3, p. 19]

dispersed system: A system to serve like a single station by way of a power system connecting many small- and medium-size power generating points. It can be classified into the following two types: 1) Multi-PV System: A system for parallel operation of dispersed multiple PV system units (PV array, inverter, etc.), through distribution lines; 2) Dispersed PV Array: A system with dispersed multiple PV arrays connected with each other in parallel, and with its inverters installed intensively.

distributed multi-load system: A system to interchange generated power for the load other than those required in the premise of the same facility where a PV system is located through installation of small-scale distribution lines.

effective efficiency: The ratio of output energy to input energy during an identified period.

fixed voltage operation: A control whereby system operation is always at constant voltage near the maximum power voltage of the PV array.

high-frequency isolation inverter: An inverter with the high frequency transformer for electrical isolation between the input circuit and the output circuit of the inverter.

inverter: A device which changes DC input into AC output (82(CO)19, p. 20)

irradiance: Radiant power incident upon unit area of surface. [IEC 904-3, p. 17] unit Wm^-2.

irradiation (H): Irradiance integrated over a specified time interval. [IEC 904-3, p. 19] unit Jm^-2.

islanding operation: A state in which a part of the power system connected with non-utility power generating facility generates power locally with a group of non-utility power generating facilities, being isolated from an interconnected power source, and supply power to line load.

isolated operation: A state in which a non-utility power generating facility is paralleled off from a power system and is being operated solely in the customer's generating facility.

lead-acid battery for photovoltaic application: A generic term of lead-acid batteries used in solar power generating systems. In the narrow sense, it refers to lead-acid batteries designed to meet the quality requirements of a solar power generation system.

load current (IL): The current supplied by the photovoltaic (PV) generator at a particular temperature and irradiance into a load connected across its terminals [IEC 904-3, p. 23] Unit A.

load power (PL): The power supplied to a load connected to the terminals of a photovoltaic (PV) generator at a particular temperature and irradiance. PLVLIL [IEC 904-3, p. 23] Unit W.

load voltage (VL): The voltage appearing across the terminals of a load connected to the terminals of the photovoltaic (PV) generator at a particular temperature and irradiance. [IEC 904-3, p. 23] Unit V.

master control and monitoring (MCM): Logic and control circuitry which supervises the overall operation of the system by the interaction between all subsystems. (82(CO)19, p. 20)

maximum power (Pmax): The point on the current-voltage characteristic where the product of current and voltage is a maximum. [IEC 904-3, p. 21] Unit W

maximum power current (Ipmax): The current corresponding to maximum power. [IEC 904-3, p. 21] Unit A

maximum power tracking (MPT): A control strategy whereby system operation is always at or near the maximum power point of the PV array. (82(CO)19, p. 20)

maximum power voltage (VP_max): The voltage corresponding to maximum power. [IEC 904-3, p. 21] Unit V

mismatch loss: Equivalent power loss produced when the power conditioner is operating in a different input voltage or current from the maximum power voltage or the maximum power current of the PV array.

module: The smallest complete environmentally protected assembly of interconnected solar cells. [IEC 904-3, p. 21; IEC 1277, p. 39]

module surface temperature: The mean temperature of the back surface of the module. [IEC 904-3, p. 23]

monitor and control subsystem: Logic and control circuitry that supervises the overall operation of the system by controlling the interaction between all sub-systems. {IEC 1277, p. 39]

nominal operating cell temperature (NOCT): The equilibrium mean solar cell temperature within a module in a standard reference environment (SRE) of 800 Wm^-2 irradiance, 20 ambient air temperature, 1 ms^-1 wind speed, electronically open-circuit and open-rack mounted at normal incidence, at solar noon. [IEC 904-3, p. 25]

nominal system output (power): System's DC output which is obtained on SOC when connected with the load determined by a prescribed solar cell array. Note 1: Unit = [V]; Note 2: On the nominal system output conditions, nominal system output current by output current. Their unit symbols are represented by [V] and [A], respectively.

on-site system: A system to meet the load installed in the same plant where a PV system is located; the produced power is consumed within the premise of that plant that generates the power.

open-circuit voltage (Voc): The voltage across an unloaded (open) photovoltaic (PV) generator at a particular temperature and irradiance. [IEC 904-3, p. 21] Unit V

optional test conditions: Test irradiance as measured with a reference device of 1000 Wm^-2 and cell temperature at any conveniently measured ambient conditions. [IEC 904-3, p. 23]

output energy of PV system: The output energy obtained during a specified period of time. Note: Output energy may be classified into measured data and estimated data. The shortest period is a month (30 days). Unit = Wh per month or year, as the case may be.

ozone content: The volume of ozone at standard temperature and pressure in a vertical column of the atmosphere 110-4 m2 in cross section. [IEC 904-3, p. 19] Unit m

panel: A group of modules fastened together, pre-assembled and wired, designed to serve as an installable unit in an array and/or sub-array. [IEC 1277, p. 41]

partial state of charge (PSOC): A state where a battery has not reach a fully charged condition.

photovoltaic effect: Direct conversion of radiant energy into electrical energy. [IEC 904-3, p. 21]

photovoltaic (PV) system: An installed aggregate of components and subsystems that combine to use the photovoltaic effect to convert solar energy into electrical energy suitable for connection to an application load. In its simplest form, a PV system consists of a PV array with connections to the load, but it may also include power conditioning, monitoring and control equipment, energy storage, and power distribution units. Systems may be either stand-alone or utility-intertied.

photovoltaic (PV) system efficiency: The ratio of output energy of PV systems to the product of solar radiation on an inclined face and array area. Note: PV system efficiency may be classified into measured data and estimated data. The shortest period is a month (30 days).

power conditioner: The electrical equipment used to convert electrical power into a form or forms of electrical power suitable for subsequent use. [IEC 1277, p. 41] The electrical equipment consists of all or some of monitor and control subsystems. DC conditioner, DC/DC interface, Inverter, AC/AC interface, and utility interface used to convert DC electrical power of PV array out put into a form or forms of electrical power suitable for subsequent use.

precipitable water vapour content: The volume of precipitable water vapour in a vertical column of the atmosphere 110-4 m² in cross section expressed as the height of the corresponding vertical column of water. [IEC 904-3, p. 19] Unit m

primary reference solar cell: A reference cell whose calibration is based on a radiometer or standard detector conforming to the standard World Radiometric Reference (W.R.R.). [IEC 904-2, p. 7]

pyranometer: A radiometer normally used to measure global irradiance (or, with a shade ring or disc, diffuse irradiance) on a horizontal plane. Can also be used at an angle to measure the total irradiance on an inclined plane, which in this case includes an element due to radiation reflected from the foreground. [IEC 904-3, p. 19]

pyrheliometer: A radiometer, complemented with a collimator, used to measure direct irradiance (sometimes called Normal Incidence Pyrheliometeror NIP). [IEC 904-3, p. 19]

rated current (IR): The assigned value of current of a photovoltaic (PV) generator at the rated voltage under specified operating conditions. [IEC 904-3, p. 23] Unit A

rated power (PR): The assigned value of power output of a photovoltaic (PV) generator at rated voltage under specified operating conditions. [IEC 904-3, p. 23] Unit W

rated system output (power): System's AC output which is obtained when connected with rated load. [W] Note 1: Rated load is represented by load conditions required to realize the rated system output specified by the manufacturer. Note 2: Irradiance conditions are determined at random, provided that the irradiance conditions for systems with no batteries are desirably equal to SOC. But, if it is difficult to do so, a test can be done by adding the connected point of the solar cell array with power equivalent to an effective output of the solar cell array.

rated voltage (VR): The assigned value of voltage at which a photovoltaic (PV) generator is designed to provide near-maximum electrical power under specified operating conditions. [IEC 904-3, p. 23] Unit V

reference solar cell: A specially calibrated cell, which is used to measure irradiance or to set simulator irradiance levels in terms of a reference solar spectral irradiance distribution. [IEC 904-2, p. 7]

relative spectral response (S_rel): The spectral response normalized to unity at wavelength of maximum response. S_rel = S()/S_max. Note: The term response is commonly used, but responsivity is strictly correct. [IEC 904-3, p. 21]

reverse power flow: A power flow from a customer's generating facility to a power system side.

secondary reference solar cell: A reference cell calibrated in natural or simulated sunlight against a primary reference cell. [IEC 904-2, p. 7]

shadow cover rate: The ratio the equivalent area of the part covered by shadow on the array surface to the overall area of the array. Shadow cover rate = (equivalent area of part covered by shadow)/(overall area of solar cell's array).

short-circuit current (I_sc): The output current of a photovoltaic (PV) generator in the short-circuit condition at a particular temperature and irradiance. [IEC 904-3, p. 21] Unit A

single PV system: A system with PV stations installed intensively at a single place.

solar cell: The basic photovoltaic (PV) device, which generates electricity when exposed to sunlight. [IEC 904-3, p. 21]

solar elevation: Angle between the direct solar beam and the horizontal plane. [IEC 904-3, p. 17] Unit rad

solar (PV) array: see "array"

solar (PV) panel: see "panel"

solar (PV) subarray: see "sub-array"

specific load systems: A system structured and designed to meet known specific load demand only.

spectral irradiance (E): Irradiance per unit bandwidth at a particular wavelength. [IEC 904-3, p. 17] Unit Wm^-2m-1

spectral irradiance distribution: Spectral irradiance plotted as a function of wavelength. [IEC 904-3, p. 19] Unit Wm^-2m^-1

spectral photon irradiance (Ep): Photon flux density at a particular wavelength. Ep=5,0351014E (in m). [IEC 904-3, p. 17] Unit cm^-2s^-1m^-1

spectral response(s): The short-circuit current density generated by unit irradiance at a particular wavelength, plotted as a function of wavelength. [IEC 904-3, p. 21] Note: The term response is commonly used, but responsivity is strictly correct. Unit AW-1

stand-alone PV system: A PV system to supply power1, being independent from a commercial power system. Note 1: Power may be supplied from other generation systems to meet load demand.

standard test conditions (STC): Reference testing values of cell temperature (25), in-plane irradiance (1000 Wm^-2), air mass solar reference spectrum (AM-1,5) for a PV module or PV cell testing. [IEC 1829, p. 19]

sub-array: The part of an array assembly that can be considered as a unit and whose output is some fraction of the array output. [IEC 1277, p. 41]

support structure for Solar (PV) panel: A support structure to install a module or panel.

system utilization factor: The ratio of output energy of the PV system to the product of standard solar cell array output and operating time. Note: System utilization factor may be classified into measured data and estimated data. The shortest period is a month (30 days).

test irradiance (Gt): Irradiance used for test purposes, as measured with a reference device. [IEC 904-3, p. 23] Unit Wm^-2

total irradiance (GT): Total radiant power incident upon unit area of a tilted surface. [IEC 904-3, p. 17] Unit Wm^-2

total irradiation (HT): The integrated total irradiance over a specified time interval on a tilted surface. [IEC 904-3, p. 19] Unit Jm^-2

transformerless inverter: An inverter without any isolation transformer.

turbidity (aD1): The reduced transparency of the atmosphere, caused by absorption and scattering of radiation by solid or liquid particles, other than clouds, held in suspension. As defined by ngstrom, the turbidity of the atmosphere is related to t, the extension coefficient as t a wavelength of 1000 nm and to , the wavelength exponent in the expression for the aerosol extinction function. t values less than 0,10 indicate a very clear condition, whereas values greater than 0,20 indicate a distinctly hazy condition. [IEC 904-3, p. 19] Unit m

utility backed-up system: A system to isolate demand from a PV system and switch to a commercial power system, only when the power of the PV system falls short. It can be classified into the following two types: 1) DC-side switch-over system: A system to switch to a commercial power system on the DC side of a PV system by converting AC into DC through a rectification circuit; 2) AC-side switch-over system: A system to switch to a commercial power system on the inverter power side (AC power) of a PV system.

utility-connected operation: A state of a non-utility power generating facility between a point of time that it is paralleled with a commercial power system and a point of time that it is paralleled off. Depending on the class and form of the voltage of the commercial power system interconnected, such an interconnected system may be classified into a low-voltage interconnection, a high-voltage interconnection, a super-high-voltage interconnection, a spot-network interconnection system, etc.

utility-connected PV system: A system to deliver and receive power, being connected in parallel with a commercial power system.

utility frequency isolation inverter: An inverter with the utility frequency transformer for electrical isolation at the inverter output.

utility interactive operating range: Range of utility voltage, frequency, or distortion of utility voltage wave-form where the power conditioner can operate stably during utility interactive operation.

utility interface: An interconnection interface between the inverter output and the utility grid, including specified protective functions. It may include an AC/AC voltage conversion.

valve-regulated lead acid battery: A sealed lead-acid battery of a system in which oxygen gas generated from positive plates is reactively absorbed into negative plates to make them chemically discharged, thereby suppressing generation of hydrogen gas. The battery is equipped with a valve to release gas outside the battery when pressure has built up in the cells.

voltage-temperature coefficient: The change of the open-circuit voltage of a photovoltaic (PV) device per unit change of cell temperature. [IEC 904-3, p. 25] (Note: This coefficient varies with irradiance and, to a lessor extent, with temperature.) Unit V-1

watt-hour efficiency: This refers to the ratio of a discharged power amount to a charged power amount, calculated by using the formula: watt-hour efficiency = [(discharge current x discharge time x average discharge voltage)/(charge current x charge time x average charge voltage)] x 100 (%) = ampere-hour efficiency x [average discharge voltage/(average charge voltage]. In this case, the average voltage to the specified final discharge voltage is often used, rather than that to the specified time.

weighted-average conversion efficiency: The method of estimating the effective efficiency that is calculated as the sum of the products of each power level efficiency and related weighting coefficient. When the system is a utility-interactive type, the weighting coefficients depend on a regional irradiance duration curve. When the system is a stand-alone type, with storage subsystems, the weighting coefficients depend on the load duration curve.