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 which 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 night. Tracking accuracy is enhanced using a simple optical feedback technique which adjusts error offset variables while monitoring the edges of a focused solar image with just four photodiodes. Control electronics are modular, and our software is written in Python, running as a webserver 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°.