In this paper, a clear day is defined as one generating a thermal load, and its daily level of solar energy, HgIT, is higher than the daily threshold energy imposed by the process, Hmin. In Madrid, for the air-conditioning of indoor spaces, Hmin varies from about 24 MJ m−2 day−1 in June to about 18 MJ m−2 day−1 in September. Using the representative input data of a clear day in Madrid and applying the Hottel-Willier, Duffie, Beckman and Klein model, taking into account the heat capacity effects and the variable regime, a theoretical simulation of a lithium bromide absorption cooling system was performed to obtain a daily collector efficiency of about 22%, a daily COP of the cooling machine of about 55% and a daily efficiency of the solar energy-cooling conversion of about 12%.