Study of solar irradiance for the European Solar Telescope

The collaboration between the European Solar Telescope (EST) and AEMET, through the Izaña Atmospheric Observatory, aims to improve the characterization of the radiative loads affecting the telescope’s optical components during operation. In the preliminary design phase of the EST, thermal analyses of the optical elements were performed using spectral solar irradiance data (280–4000 nm) obtained from atmospheric models such as the SMART model. However, in the current detailed design phase, it has become necessary to refine these estimates using experimental measurements and validated models that represent the irradiance conditions at high-altitude observatory sites in the Canary Islands.

In this context, AEMET operates specialized instrumentation at the Izaña Atmospheric Observatory capable of measuring spectral solar irradiance using spectroradiometers in the ranges 300–1100 nm and 900–2400 nm, as well as integrated radiation measurements. These datasets constitute a valuable scientific reference for characterizing both direct and diffuse solar radiation under atmospheric conditions representative of the region.

Access to these measurements will allow the EST team to analyze the spectral distribution of solar radiation and determine, as a function of wavelength, the fraction of incident energy that is absorbed or reflected by the different optical elements of the telescope. Furthermore, the availability of data for different solar elevations and for representative conditions of the summer and winter solstices will enable a more accurate definition of both extreme and operational thermal scenarios for the optical system. Overall, this collaboration will improve the reliability of the telescope’s thermal models and support the optimization of the design of its optical components.