ORIGIN OF TECHNICAL TERMS
The term photovoltaics derives from the Greek word phos meaning light and the
word volt, unit for electrical voltage named by Alessandro Volta. Photovoltaics
is a science, which examines light-electricity conversion, respectively, photon
energy-electric current conversion. In other words it stands for light-current
conversion. As many other technical (and common) words even significant amount of
solar energy enginering terminology based on ancient greek language. Some words
were derived directly from greek language other indirectly from latin language.
Few words originate also in arabic language, they were overtaken from arabic
language in the early middle century.
Some important photovoltaic terms and symbols used in solar energy engineering and
in photovoltaics are presented in the tables below. Detailed information can be
found in technical report IEC/TR2 61836 Solar photovoltaic energy systems - Terms
and symbols.
BASIC UNITS AND MEASURES
Units and measures used in solar energy engineering are, with some exceptions,
used also in physics, mechanical engineering and some other branches of enginnering.
Basically units and measures can be devided into three major groups: terms related to solar radiation, terms related to
light transmission and terms related to sun-earth geometry.
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Global irradiance [1]
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G
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W/m2
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Beam irradiance
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Gb
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W/m2
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Diffuse irradiance
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Gd
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W/m2
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Spectral irradiance
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Eλ
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W/m2μm-1
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Global irradiation [2]
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H
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J/m2
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Beam irradiation
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Hb
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J/m2
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Diffuse irradiation
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Hd
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J/m2
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TABLE 1: Most common units and measures related to solar radiation
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Specific heat
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c
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J/kgK
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Thermal conductivity
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k
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W/mK
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Extinction coefficient
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Κ
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-
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Refraction index
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k
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-
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Absorptance
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α
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-
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Emmitance
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ε
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-
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Reflectance
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ρ
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-
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Density
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ρ
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kg/m3
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Transmittance
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τ
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-
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TABLE 2: Most common units and measures related to radiation (light) transmission
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Altitude (0 to ± 90°) [3]
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α
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degrees (°)
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Surface tilt angle
(0 do ± 90° tilt toward equator positive)
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β
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degrees (°)
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Azimuth of surface [4]
(-180° to + 180° toward W negative)
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γ
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degrees (°)
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Declination (0 to ± 23.45°) [5]
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δ
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degrees (°)
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Solar azimuth angle
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γs
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degrees (°)
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Incidence angle (0 to + 90°)
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i
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degrees (°)
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Zenith angle (0 to + 90°)
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θ
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degrees (°)
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Latitude
(0 to ± 90°, N from equator positive)
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Ψ
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degrees (°)
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Hour angle [6]
(-180° to + 180°, noon 0°, afternoon positive)
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ω
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degrees (°)
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TABLE 3: Most common units and measures related to
Sun-Earth geometry [3],
[7]
Notes
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[1]
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Common term meaning solar irradiance is also solar power.
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[2]
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The unit Wh/m2 (kWh/m2) is often used in technical practise in
Europe. Sometimes also term insolation (incident solar radiation) is used.
Please look for further information and additional symbols in
suggested literature.
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[3]
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In computer programmes all angles are usually expressed in radians.
One radian is equal to 180/π degrees.
One degree = radian⋅(180/π).
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[4]
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Azimuth angle can also be expressed in range from 0° to +360°, clockwise from
North positive. Such values are more common in architecture for example in
solar energy enginering azimuth toward south is usually 0° as presented in the Table 3.
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[5]
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Declination value calculated by Cooper's formulae, more precise methods are
also available. For details see site analysis section.
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[6]
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For description of Sun-Earth geometrical relations term solar geometry is also
sometimes used.
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[7]
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Hour angle is calculated by simple equation
h = ± 15°⋅number of hours from/to solar noon.
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ORIGIN OF TECHNICAL TERMS
Books
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Green, T.M.: The Greek & Latin Roots of English ;
Rowman & Littlefield Publishers, Inc.; 4 edition, 2007, ISBN 978-0742547803.
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Papaioannou, M., Papaioannou, P.: English and Greek Words of Hellenic Origin ;
Ellin, 2003, ISBN 978-9602867921.
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Konstantinidis, A.: Greek words in english language (greek language), Self published, ISBN 960-90338-2-2.
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Dictionaries
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Glare, P.W.G.: Oxford Latin Dictionary ;
Oxford University Press, 1983, 978-0198642244.
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Smith, W., Hall, T.D.: Smith's English-Latin Dictionary ;
Bolchazy-Carducci Publishers, 2000, ISBN 978-0865164918.
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Smith, W., Lockwood, P.: Chambers Murray Latin-English Dictionary ;
Chambers; Rei Sub edition, 1994, ISBN 978-0550190031.
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Liddell, H.G., Scott, R.: An Intermediate Greek-English Lexicon: Founded upon the Seventh Edition of Liddell and Scott's Greek-English Lexicon
Oxford University Press, 1945, ISBN 978-0199102068.
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UNITS, WEIGTHS AND MEASURES
Books
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Cardarelli, F.: Encyclopaedia of Scientific Units, Weights and Measures: Their SI Equivalences and Origins ;
Springer, 2003, ISBN 978-1852336820.
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Gupta, S.V.: Units of Measurement: Past, Present and Future. International System of Units (Springer Series in Materials Science)
Springer, 2009, ISBN 978-3642007378.
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Lindeburg, M.R.: Engineering Unit Conversions
Professional Publications, Inc., 1998, ISBN 978-1591260998.
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Websites
convert-me.com -
Here you will find interactive calculators for many measurement systems both
commonly used like metric and U.S. Avoirdupois and quite exotic like Ancient
Greek and Roman.
Website also available in:
Electropedia -
Electropedia: The World's Online Electrotechnical Vocabulary.
Electropedia also available in:
...
ADITIONAL INFORMATION
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IEC/TS 61836, Solar photovoltaic energy systems - Terms, definitions and symbols
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Units and Symbols in Solar Energy; Solar Energy, vol.71, number 1, 2001.
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Beckman, W.A et al.: Units and symbols in solar energy; Solar Energy, vol. 21, no. 1, 1978, p. 65-68.
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Rösemann, R.: Solar Radiation Measurement, From Sensor to Application; Gengenbach Messtechnik, 2004,
ISBN 3-936947-70-8.
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TCAEP: The Constants and Equation Pages.
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The NIST Reference on Constants Units and Uncertainty.
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English weigths and measures.
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Eric Weisstein's World of Science.
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