Appendix A: Design and test
summary
This appendix gives a brief description of how the SPN1 design works and a summary
of the results of the test program. More detailed versions of these are available from
Delta-T.
Introduction
Measurement of Direct and Diffuse components of solar radiation has many
applications - in modelling the interaction of light with crop canopies, studying the
energy balance of structures, or as a meteorological indicator. Instruments that make
these measurements have generally been expensive and require considerable
attention.
One common approach has been to have two sensors, one measuring radiation from
the whole sky, the other measuring the whole sky apart from the sun. The shading is
generally done using a shade ring, adjusted to match the track of the sun across the
sky for that day, or using an occluding disk held on a robot arm. Both of these
approaches require accurate alignment to the Earth's axis, and regular adjustment.
Another well established approach is the Campbell-Stokes recorder, which uses a
glass sphere to focus the Direct solar beam onto a recording chart causing a burn,
which indicates Direct beam strength.
Design objectives
The aim of the SPN1 design was to measure the Direct and Diffuse components of
incident solar radiation, and provide a measure of sunshine hours, in a sensor that
used no moving parts, and required no specific polar alignment or routine adjustment.
The outputs should be compatible with electronic data loggers, and work at any
latitude.
How the design evolved
The prime requirement for this design was to create a system of radiation sensors
and a shading pattern such that wherever the sun is in the sky:
•
at least one sensor was always exposed to the full solar beam
•
at least one was always completely shaded
•
all sensors receive equal amounts of Diffuse light from the rest of the sky
hemisphere.
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Appendix A: Design and test summary
SPN1 User Manual v1.0
