Yep, but it was a comparison aimed to the real world and costs, not abstract efficiency. Given that you need for both 5-10 square meters of surface exposed to

Yep, but it was a comparison aimed to the real world and costs, not abstract efficiency. Given that you need for both 5-10 square meters of surface exposed to the sun and assuming (and it is not necessarily given) that solutions "A" and "B" have the same "current" (maintenance, spares, consumables) costs, I don't care if solution "A" is more efficient than solution "B", I only care if solution "A" costs less than "B". If it does, then it should cost much less, as solution "B" might have a tangible advantage (once you have purified enough water the solar energy can be used for other uses). Now, be nice, check the actual Solar Spring Gmbh site /the spin-off of the Fraunhofer Institute for Solar Energy Systems mentioned in the wikipedia article ), and see how - strangely enough - they build/sell both "A" and "B" solutions: https://solarspring.de/en/products-and-services/#pg-356-2 https://solarspring.de/en/products-and-services/#pg-356-2 https://solarspring.de/en/solar-purification/ https://solarspring.de/en/solar-purification/ In any case high efficiency - usually - means more sophistication, added components, and what not, so rarely exists a solution that is more efficient AND costs less.