On the relationship between duration of sunshine and solar radiation on the earth's surface: Ångström's equation revisited

Suehrcke, Harry (2000) On the relationship between duration of sunshine and solar radiation on the earth's surface: Ångström's equation revisited. Solar Energy, 68 (5). pp. 417-425.

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Abstract

The paper presents a relationship between the relative sunshine duration and solar irradiation on the earth's surface. Following a review of the literature on Ångström's equation and the properties of instantaneous solar radiation, the sunshine–radiation relationship is derived from monthly average values of daily beam radiation which are used as a measure for the fraction of clear sky, ƒ[clear]=H̄[b]/H̄[b,clear]. The resulting (non-linear) relationship, ƒ[clear]=(K̄/K̄[clear])^2, unlike the Ångström–Prescott relation, does not contain empirical constants and only requires the monthly average clear sky atmospheric transmittance to account for the climate of a particular location (K̄[clear] is typically between 0.65 to 0.75). The relationship is verified for monthly intervals for Perth and Townsville, Australia and compared to existing Ångström–Prescott equations for a wide range of climates and locations. The excellent agreement of the proposed relationship with the average value of data in the latter comparison suggests that it may be universally valid and that the Ångström–Prescott equation is a local (linear) approximation of the derived relationship. For daily time intervals the sunshine–radiation relationship changes to ƒ[clear]=(K/K[clear])^3. The paper closes with a discussion on applications of the new relationship including the performance prediction of solar energy systems.

Item ID: 13025
Item Type: Article (Refereed Research - C1)
Keywords: Ångström's equation; solar radiation; sunshine duration
ISSN: 0038-092X
Date Deposited: 22 Jul 2012 13:24
FoR Codes: 09 ENGINEERING > 0913 Mechanical Engineering > 091399 Mechanical Engineering not elsewhere classified @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970101 Expanding Knowledge in the Mathematical Sciences @ 100%
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