Fisheye lens design for sun tracking cameras and photovoltaic energy systems

Solar panels are gaining global popularity for electrical energy generation. However, efficiency of static solar panels can vary during the day. Solar panels can have increased energy output if they are actively oriented to capture the most amount of sunlight as the sun moves in the sky. In order to achieve this active orientation, sun’s angular position needs to be estimated. Sun’s position in the sky and zenith angle can be determined by automatic analysis of images captured by a whole sky camera. As the purpose of a whole sky, sun tracking camera is to accurately identify solar zenith angle, a special camera integrated with a fisheye lens with equidistant (f-theta) mapping can be designed. Due to the angular linearity of equidistant fisheye lenses, solar zenith angle can be directly calculated after the position of the sun in a whole sky image is detected with digital image processing algorithms. This paper presents the optical design of a compact, high-resolution equidistant fisheye lens with low deviation from the f-theta distortion profile. The lens can be integrated with a commercial image sensor array to form a low-cost whole sky camera for accurate sun tracking in solar energy generation systems.