Article,
Statistical investigation of the optimal averaging time for solar irradiance on horizontal and vertical surfaces in the UK.
Solar Energy, 68 (2): 179--187 (2000)
Abstract
As output from photovoltaic (PV) panels is closely related to sunlight
levels, monitoring solar irradiance levels is crucial for system
design and predictive purposes. With advances in PV technology, urban
sites at northerly locations, where both horizontal and vertical
solar irradiance make significant contributions, are becoming increasingly
important. The aim of this paper is to compare solar irradiance for
horizontal and vertical orientations and to assess the relative effectiveness
of differing averages, from 10 min to 1 h, for use in short-term
prediction of solar irradiance levels for a UK site. Vertical and
horizontal solar irradiance observations were collected from a monitoring
station on the roof of a five-storey building at an urban site in
Newcastle-upon-Tyne, UK (latitude 558N). 10-min data was collected
for 13- or 15-day periods in two summers (1994, 1995) and two winters
(1993, 1994). Although mean levels for horizontal and vertical irradiance
were different, as expected, general patterns were very similar indicating
the possibility of predicting vertical irradiance from horizontal
at the same location. 10-min, 20-min, 30-min and 1-h averaging times
were compared utilising autocorrelation coefficients and ARIMA models
to assess the information lost when using longer averaging intervals.
For consideration of short-term changes, 10-min averages were most
informative whilst hourly averages were substantially poorer.
