Sensors for sun pointing
Authors: Fontani D., Francini F., Jafrancesco D., Mercatelli L., Sansoni P.
Autors Affiliation: CNR – Istituto Nazionale di Ottica Applicata, Largo E. Fermi 6, 50125 Firenze, Italy
Abstract: Sun tracking has been studied and experimented in our laboratory since 1997, developing mechanics, electronics and software to realise prototypes. Several possibilities for the sun pointing sensor have been examined. The paper proposes three promising solutions, comparing optical characteristics and performances. The first optical system, named pinhole sensor, is essentially a pinhole camera without lenses. The second proposed device, called slit sensor, includes a photodetector coupled to a slit. The third one, denominated wide angle sensor, is a commercial product composed of two inclined photodetectors. For all proposed solutions the paper describes optical system and working procedure. Furthermore, for pinhole sensor and slit sensor, the realisation of prototypes is discussed in details with mechanical drawings and electronic schemes.The sensors have been tested in laboratory under controlled and reproducible conditions. This laboratory experimentation includes a deep analysis of angular resolution and field of view of the sensors. For pinhole sensor and slit sensor the purpose of these tests is provide an optical characterisation of the devices. For the wide angle sensor the laboratory tests are aimed to compare the measured features to the nominal values belonging to the data sheet. Finally the sensors have been tested under operative conditions. The pinhole sensor is the most precise one and it performs sun tracking in two directions achieving a very high sensitivity. It is indicated for solar optical systems requiring high pointing precision, like collectors coupled to small optical fibres or tiny PV cells. The slit sensor reaches almost the same precision of the pinhole sensor but only in one direction. Hence it is usually applied to linear concentrators for solar light exploitation. The wide angle sensor is the cheapest and easier solution. It has lower precision than the previous sensors, but for most applications its sensitivity is sufficient to track the sun.
Conference title: World Renewable Energy Congress (WRECX)
Place: Glasgow (Gran Bretagna)
KeyWords: solar energy; solar collector; optical design