Bummer Questions: - How much does it cost? - Does it require special expertise to install? I'd hope/assume the sphere can be filled with water on-site - How oft

Bummer Questions: - How much does it cost? - Does it require special expertise to install? I'd hope/assume the sphere can be filled with water on-site - How often will it need to be inspected/repaired? Will that require a specialist? - How often will it need to be cleaned? This wouldn't seem to make much sense for individual installations (unless you're wealthy and want something to show off on your roof), but I wonder if the economics would work out in medium-sized arrays, to fill the gap between small residential/commercial installations and huge solar collector operations. Still though, is a 35% efficiency increase enough to justify this particular design? Is it that much better than other concentration methods?