This book covers the fundamental concepts of solar radiation and its path from sun to Earth, including topics such as terrestrial coordinates, solar motion and the different components of solar radiation, among others. Solar irradiance depends on a number of factors, including sunshine, temperature, geographical location, time of day and the nature of the clouds present. A great deal of research effort has gone into estimating solar irradiance at ground level, which is essential for sizing solar installations, forecasting solar radiation and assessing solar potential. It is also crucial to consider shading as a challenge when installing solar thermal systems for heating or photovoltaic systems for electricity generation, which requires accurate measurements of various irradiation parameters using appropriate instruments and equipment.