Just read about this in Make magazine: Interstellar Light Applications. They built this apparatus to collect and focus moonlight for therapy. There's all kinds of testimonials on the website.
"Situated in the Southern Arizona desert in a secure location 15 miles west of Tucson and 22 miles east of Kitt Peak National Observatory, the ILA collector is a parabolic, non-imaging optical collector composed of 84 mirrored collection panels. At 52 feet high, 60 feet across and weighing 25 tons, this breathtaking device is colossal, yet has the maneuvering capability and precision of a Swiss watch."