Diploma thesis includes description of physical principles for cloud detection, development, of the cloud sensor and analysis of its measurements. Cloud sensor works on a principle of measuring infrared electromagnetic irradiance of the sky. For this purpose it applies Seebeck thermoelectric effect. Cloud sensor consists of four major components, namely the IR sensor, relative humidity sensor, Wi-Fi module and microcontroller. Microcontroller is responsible for communications with all components as well as data analysis and transmission to the Internet via Wi-Fi module. Power is supplied by Li-Ion batteries which are charged with the solar panels, thus it is a fully autonomous, self-sufficient and wireless device. Analysis of obtained cloud sensor measurements reveals linear dependence of measured IR irradiance in relation to absolute humidity in the vicinity of the sensor. These findings were then used at defining clear sky parameter, which determines in all seasons of the year whether sky is clear, cloudy or if it is raining. Results were verified with the pyranometers’ measurements as well as the pictures from all-sky cameras.