Fundamentals: Quantities, Definitions, and Units

  • Jesús PoloEmail author
  • Luis Martín-Pomares
  • Christian A. Gueymard
  • José L. Balenzategui
  • Fernando Fabero
  • José P. Silva
Part of the Green Energy and Technology book series (GREEN)


Solar radiation is a generic term that refers to different magnitudes of the solar electromagnetic radiation. The quantification of solar radiation incident at the Earth’s surface is of high interest in many disciplines (radiative transfer in the atmosphere, meteorology and climatology, remote sensing of the atmosphere, solar energy studies, etc.). This multidisciplinary aspect of solar radiation sometimes produces duplication of names, definitions, or units. Moreover, different application-specific conventions for variable naming or units exist, which can be confusing. The solar irradiance that reaches a point at the Earth’s surface is basically dominated by (i) the geometric aspects of the Earth’s orbit around the Sun, and the inclination of its rotation axis in the ecliptic plane that determines the incident angle of the Sun rays; and (ii) the interaction mechanisms of solar radiation with various types of atmospheric constituents. This chapter intends to give the reader an overview of the basic definitions of the main variables that are commonly found in solar energy, and hence in this book as well. In addition, some basic aspects of solar geometry are briefly presented, followed by a concise description of the fundamentals of radiation-transfer modeling in the atmosphere. Detailed information on these topics, which is out of the scope of this book, can be found in many textbooks and the abundant literature on solar radiation, radiative transfer and atmospheric physics, to which the avid reader is referred for additional insight.



This work has been partially supported by the Spanish National Funding Program for Scientific and Technical Research of Excellence, Generation of Knowledge Subprogram, 2017 call, DEPRISACR project (reference CGL2017-87299-P). The authors wish to thank Dr Stefan Wilbert from DLR for sharing several useful comments and remarks on this chapter.


  1. ASTM (2012) Standard tables for reference solar spectral irradiances: direct normal and hemispherical on 37° tilted surface. Standard G173-03(2012). ASTM International.
  2. Balenzategui JL, Chenlo F (2005) Measurement and analysis of angular response of bare and encapsulated silicon solar cells. Sol Energy Mater Sol Cells. Scholar
  3. Blanc P, Wald L (2012) The SG2 algorithm for a fast and accurate computation of the position of the Sun for multi-decadal time period. Sol Energy 86:3072–3083. Scholar
  4. Blanc P, Espinar B, Geuder N et al (2014) Direct normal irradiance related definitions and applications: the circumsolar issue. Sol Energy 110:561–577. Scholar
  5. CIE (Commission Internationale de l’Éclairage) (1987) Methods of characterizing illuminance meters and luminance meters. CIE 69-1987. Vienna, AustriaGoogle Scholar
  6. CIMO (2017) Part I, Chapter 7 for solar radiation measurements. Part I, Chapter 16 for aerosols measurements. In: The CIMO guide. World Meteorological Organization. WMO guide to meteorological instruments and methods of observation (WMO-No. 8, 2014 edition, updated in 2017)Google Scholar
  7. Coddington O, Lean JL, Pilewskie P et al (2016) A solar irradiance climate data record. Bull Am Meteorol Soc 97:1265–1282. Scholar
  8. Fröhlich C, Brusa RW (1981) Solar radiation and its variation in time. Sol Phys 74:209–215CrossRefGoogle Scholar
  9. Garg HP, Datta G (1993) Fundamentals and characteristics of solar radiation. Renew Energy 3:305–319. Scholar
  10. Gueymard C (1995) SMARTS2: a simple model of the atmospheric radiative transfer of sunshine: algorithms and performance assessment. Rep. FSEC-PF-270-95. Florida Solar Energy Center, Cocoa, FLGoogle Scholar
  11. Gueymard CA (2001) Parameterized transmittance model for direct beam and circumsolar spectral irradiance. Sol Energy 71:325–346. Scholar
  12. Gueymard CA (2018a) A reevaluation of the solar constant based on a 42-year total solar irradiance time series and a reconciliation of spaceborne observations. Sol Energy 168:2–9. Scholar
  13. Gueymard CA (2018b) Revised composite extraterrestrial spectrum based on recent solar irradiance observations. Sol Energy 169:434–440. Scholar
  14. Gueymard CA, Myers D, Emery K (2002) Proposed reference irradiance spectra for solar energy systems testing. Sol Energy 73:443–467. Scholar
  15. IEC (International Electrotechnical Commision) (1987) International electrotechnical vocabulary, Chapter 845: lighting. IEC 60050-845. Geneva, SwitzerlandGoogle Scholar
  16. IEC (2016) Photovoltaic devices—Part 3: measurement principles for terrestrial photovoltaic (PV) solar devices with reference spectral irradiance data. IEC 60904-3:2016 RLV Standard. International Electrotechnical Commission, Geneva, SwitzerlandGoogle Scholar
  17. Iqbal M (1983) An introduction to solar radiation. Academic Press, CanadaGoogle Scholar
  18. Kasten F, Young AT (1989) Revised optical air mass tables and approximation formula. Appl Opt 28:4735–4738CrossRefGoogle Scholar
  19. Kopp G, Lean JL (2011) A new, lower value of total solar irradiance: evidence and climate significance. Geophys Res Lett 38:L01706. Scholar
  20. Lenoble J (1993) Atmospheric radiative transfer. Deepak Publishing, HamptonGoogle Scholar
  21. Liou K-N (2002) An introduction to atmospheric radiation. Academic Press, San Diego, USAGoogle Scholar
  22. Martin N, Ruiz JM (2001) Calculation of the PV modules angular losses under field conditions by means of an analytical model. Sol Energy Mater Sol Cells 70:25–38. Scholar
  23. McCluney R (1994) Introduction to radiometry and photometry, 2nd edn. Artech House, Boston, LondonGoogle Scholar
  24. Petty GW (2006) A first course in atmospheric radiation, 2nd edn. Sundog Publishing, MadisonGoogle Scholar
  25. Sengupta M, Habte A, Gueymard C et al (2017) Best practices handbook for the collection and use of solar resource data for solar energy applications. pp 1–233.
  26. Thomas GE, Stamnes K (1999) Radiative transfer in the atmosphere and ocean. Cambridge University Press, CambridgeGoogle Scholar
  27. Willson RC (1994) Atlas of satellite observations related to global change. In: Turner JL, Foster CLP (eds) Weather. Wiley-Blackwell, Hoboken, pp 5–18Google Scholar
  28. Young AT (1994) Air mass and refraction. Appl Opt 33:1108–1110. Scholar

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Jesús Polo
    • 1
    Email author
  • Luis Martín-Pomares
    • 2
  • Christian A. Gueymard
    • 3
  • José L. Balenzategui
    • 1
  • Fernando Fabero
    • 1
  • José P. Silva
    • 1
  1. 1.Photovoltaic Solar Energy Unit, Renewable Energy Division (Energy Department) of CIEMATMadridSpain
  2. 2.Qatar Environment and Energy Research InstituteHamad Bin Khalifa UniversityDohaQatar
  3. 3.Solar Consulting ServicesColebrookUSA

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