Page 31 - Applied Photovoltaics

Typical meteorological year (TMY) data
Insolation data is sometimes available in the form of a ‘typical meteorological year’
(TMY) data set (Hall, 1978; Perez, 2001; Lorenzo, 2003). This is a full year of data
combined from individual months, each of which has been selected from an historical
record as being ‘typical’. Several selection methods exist and smoothing may be
applied to reduce discontinuities that could arise from concatenating months of data
from different years (Perez, 2001). Lorenzo (2003) argues at length that although a
TMY data set may consist of hourly values, its use in modelling does not necessarily
produce results more accurate than those of a set of 12 monthly values.

Satellite cloud cover data
Every hour, satellite cloud cover data are updated at the Australian Bureau of
Meteorology (2004). The digitised data corresponding to photographs such as that in
Fig. 1.13 are also available and have a resolution of 2.5 km. Such data can be fed
directly into a computer for processing and analysis to facilitate very accurate
estimates of percentages of cloudy and sunny weather (Beyer et al., 1992). Satellite
data, accumulated over many years, can then be used in conjunction with Eqn. (1.19)
below, and the equations of Appendix B, to estimate insolation levels.

Figure 1.13. Infrared satellite cloud cover photograph, 16 August 2006 (Used with
permission of the Bureau of Meteorology , "MTSAT-1R : Satellite image originally
processed by the Bureau of Meteorology from the geostationary satellite MTSAT-
1R operated by the Japan Meteorological Agency.")

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