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A note on the annual variability of solar radiation at Hobart Airport, Tasmania

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Nunez, M (1979) A note on the annual variability of solar radiation at Hobart Airport, Tasmania. Papers and Proceedings of the Royal Society of Tasmania, 113. pp. 1-3. ISSN 0080-4703

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Abstract

The annual variability of solar radiation at Hobart airport is calculated.
The implication of this variability for the solar energy potential of Tasmania is
discussed.
There is at present an increasing awareness of the potential for the use of
solar energy in domestic and industrial application. An important facet in any
practical use of solar energy is the day to day variability of the incoming solar
radiation. This factor has largely been ignored in geographical assessments of solar
radiation as they mostly deal with climatological monthly averages (Hounam 1963;
Paltridge and Proctor 1976).
To illustrate the magnitude of the variability, ten years of daily solar radiation
data (1968-1977) collected over Hobart airport were used in this analysis. The data
was obtained from the Australian Bureau of Heteorology which maintains a network of
solar energy monitoring stations throughout Australia. The data was collected by a
pyranometer. At any one instant of time the instrument produces a millivolt signal
proportional to all direct and diffuse solar energy incident on a unit horizontal
surface per unit time (Robinson 1966). Integrating the signal over a day yields the
daily flux which is commonly expressed in units of Mega-Joules per metre2 per day
(MJm- 2day- 1).
Cloudless conditions were investigated first since solar radiation under these
conditions would represent a convenient upper boundary to the energy received at the
surface. Inspection of these days gave a smooth curve for the daily distribution of
solar radiation over the year (fig. 1). All data were then analyzed by grouping
together daily totals of solar radiation for each day of the year with its counterparts.
The mean and standard deviation were then calculated for each group and are shown in
figure 1. A ten day running mean through both data sets shows a maximum standard
deviation in early January which exceeds 6 MJm- 2day-l or 28% of the incoming solar
radiation. This value decreases with solar elevation reaching a minimum of 1.6 MJm-2
day-l in late June which represents approximately 35% of the incoming radiation.
The daily variability is dominantly a function of cloud cover, and to a lesser
extent will depend on atmospheric water vapour and dust content (Davies et al. 1975).
Therefore it is possible to represent the cloudless solar radiation as a smooth curve
which is usually within 5% of the observed daily values. On the other hand solar
radiation depletion by clouds can be extremely variable since it depends on such cloud
properties as type, amount, thickness, liquid water and water vapour content, etc.

Item Type: Article
Keywords: Royal Society of Tasmania, RST, Van Diemens Land, natural history, science, ecology, taxonomy, botany, zoology, geology, geography, papers & proceedings, Australia, UTAS Library
Journal or Publication Title: Papers and Proceedings of the Royal Society of Tasmania
Page Range: pp. 1-3
ISSN: 0080-4703
Collections: Royal Society Collection > Papers & Proceedings of the Royal Society of Tasmania
Additional Information:

Copyright Royal Society of Tasmania

Date Deposited: 28 May 2012 02:18
Last Modified: 18 Nov 2014 04:36
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