Solar tracker with optical feedback and continuous rotation
Abstract. Solar trackers are often used by spectrometers to measure
atmospheric trace gas concentrations using direct sun spectroscopy. The
ideal solar tracker should be sufficiently accurate, highly reliable, and
with a longevity that exceeds the lifetime of the spectrometer that it
serves. It should also be affordable, easy to use, and not too complex should
maintenance be required. In this paper we present a design that fulfils
these requirements using some simple innovations. Our altitude–azimuth
design features a custom coaxial power transformer, enabling continuous
360 ∘ azimuth rotation. This increases reliability and avoids the
need to reverse the tracker each day. In polar regions, measurements can
continue uninterrupted through the summer polar day. Tracking accuracy is
enhanced using a simple optical feedback technique that adjusts error
offset variables while monitoring the edges of a focused solar image with
four photodiodes. Control electronics are modular, and our software is
written in Python, running as a web server on a recycled laptop with a Linux
operating system. Over a period of 11 years we have assembled four such
trackers. These are in use at Lauder (45 ∘  S), New Zealand, and
Arrival Heights (78 ∘  S), Antarctica, achieving a history of good
reliability even in polar conditions. Tracker accuracy is analysed regularly
and can routinely produce a pointing accuracy of 0.02 ∘ .