In the past four decades, great efforts have been made worldwide to collect accurate ground-based measurements of solar radiation. This comes in light of the growing interest in climate change, of which solar radiation is a critical factor. At the same time, solar-radiation-based energy is one of the most promising energy alternatives to fossil fuels. This present thesis is primarily based on irradiance data collected at different orientations. The measurements were conducted over severalyears in Hannover, Germany, through the use of silicon solar sensors and thermopile pyranometers to investigate the following research questions: (1) How accurate are the transposition models that estimate the global and diffuse solar irradiance on tilted planes; (2) is there an alternative concept for increasing self-consumption via use another orientation of photovoltaic (PV) systems than the south direction; and (3) how accurate are the silicon-based irradiance sensors, and what is the deviation to thermopile sensors?