Abstract
Two main groups of solar irradiance models can be identified in the literature: the “horizontal diffuse irradiance models”, whose goal is to process the global horizontal irradiance to calculate the beam and the diffuse components, and the “irradiance models for tilted surfaces”, which are used to determine the solar radiation incident on generic surfaces starting from the horizontal measured data, if beam and diffuse components are available, or from the results of a model of the first group. According to the state-of-the-art, there is no pair of “horizontal diffuse irradiance model” and “irradiance model for tilted surfaces” which can give the same level of accuracy worldwide, since they were developed starting from solar irradiance data of specific meteorological stations, with typical weather and sky cover conditions. In addition, this becomes particularly critical for locations in mountain regions, characterized by many natural obstacles altering the view of the sky, its radiance distributions, as well as the ground reflections in a very dynamic and localized way, with an impact on the solar diffuse and beam radiation available.
In this research, the performance of 22 “horizontal diffuse irradiance models” and 12 “irradiance models for tilted surfaces” were discussed, using as benchmark the global solar irradiance data collected for both horizontal and vertical surfaces in a multi-year solar monitoring campaign performed in Bolzano, a city in the Italian Alps. After identifying the most and the least accurate models, they were adopted to simulate the energy needs for space heating and cooling for a dataset of 48 simplified building configurations, in order to discuss the impact of the calculated incident solar irradiance on the simulated building energy performance.