Solar irradiances measured using SPN1 radiometers: uncertainties and clues for development

Abstract : The fast development of solar radiation and energy applications, such as photovoltaic and solar thermodynamic systems, has increased the need for solar radiation measure-ment and monitoring, for not only the global but also the diffuse and direct components. End users look for the best compromise between getting close to state-of-the-art mea-surements and keeping low capital, maintenance and operat-ing costs. Among the existing commercial options, SPN1 is a relatively low cost solar radiometer that estimates global and diffuse solar irradiances from seven thermopile sensors under a shading mask and without moving parts. This work presents a comprehensive study of SPN1 accu-racy and sources of uncertainty, drawing on laboratory ex-periments, numerical modelling and comparison studies be-tween measurements from this sensor and state-of-the art in-struments for six diverse sites. Several clues are provided for improving the SPN1 accuracy and agreement with state-of-the art measurements.