Protecting Your Pyranometer Investment: Isolation, Grounding, and Protection for Modern Pyranometers

Pyranometers are an Integral Part of any modern, large scale solar system. Previously, pyranometers were generally straight-forward devices, which output a small value of mV in relation to the sun. These instruments, still the mainstay of solar resource measurement, have grown Modbus(R) RS-485 interfaces, as well as other types of outputs, including 0-5V, 4-20mA, and others, native on the instrument.

The importance of this topic is based on the problems long-cable runs have on Digital communications signals now common in Pyranometers. Whereas the old mV output instruments were relatively immune to noise and surges common during lightning events, the new devices are now so robust. This paper looks at failure modes of various pyranometers in real-world applications, and discusses means to control and prevent these problems through the use of surge protection devices, voltage isolation, and proper cable and grounding routing.

This topic is relevant to anyone who has ever been in a position of performing O&M work in the maintenance and swapping of pyranometers for calibration, or replacing damaged instruments after a lightning or electrical switching event. The immediate application is to suggest ways to prevent damage to your installed base of Pyranometers and related telemetry and monitoring equipment. The target audience is in new system designers, looking to implement RS-485 based systems for pyranometers, as well as people who have suffered other Serial communications related issues resulting from system damage from noise, lightning, or ground loops in system communications designs.