The ability to effectively characterize Fresnel lenses over large areas is essential to verifying their system performance and efficiency for concentrating photovoltaics and solar thermal systems. Under high concentration, it becomes challenging to perform detailed spatial and spectral measurements under full sun conditions. We have developed a method to characterize large Fresnel lenses with unknown optical qualities for concentrating solar applications. Our Lens Characterization Unit (LCU) analyzes the resultant pattern of an incident laser beam which may be scanned across the lens. Using the LCU, we can evaluate the portion of refracted light that is concentrated on the receiver area at each incidence point.