Sky type classification in Central England during winter

• Published in: Energy (Oxford) Vol. 30; no. 9; pp. 1667 - 1674
• Main Authors: Markou, M.T., Kambezidis, H.D., Bartzokas, A., Katsoulis, B.D., Muneer, T.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 01-07-2005; Elsevier Science
• Subjects: Applied sciences; Energy; Exact sciences and technology; Natural energy; Solar energy; Solar radiation; England; United Kingdom; Great Britain; Europe; British Isles, England; British Isles, England, South Yorkshire, Sheffield; Horizontal; Daylight; Diffuse solar radiation; Winter; Classification; Zenithal lighting; Solar radiation; Standards
• ISSN: 0360-5442
• DOI: 10.1016/j.energy.2004.05.002

In the present work, we studied the exterior daylight conditions in Sheffield in Central England (53.38° N, 1.50° W) during winter. The study makes use of the 15 standard sky types defined by Kittler et al. These sky types are presented as diagrams of the ratio of the zenith luminance (
L
z) to the diffuse horizontal illuminance (
D
v) against solar altitude (
γ). The illuminance parameters used are time series of half-hourly values of
D
v,
L
z, global (
G
e) and diffuse (
D
e) horizontal irradiance and
γ for the period from November 1, 1993, to February 10, 1994.
This study shows that the most frequent winter sky types in Central England are: (i) I.2 (overcast, with steep gradation and slight brightening towards the sun), with a frequency of occurrence of 19.5%, (ii) I.1 (overcast, with steep gradation and with azimuthal uniformity) (10.5%) and (iii) II.1 (overcast, moderately graded, with azimuthal uniformity) (9.7%). The most predominant cloudless sky is V.5 (cloudless, polluted, with a broad solar corona), with a frequency of occurrence of 7.6%.