It seems like a completely silly concept – using Ziploc bags to concentrate solar on a tube to heat liquids. Can this really be efficient? What about storms, vandalism, and other physical/structural perils? And, plastics are not exactly the green product of the century.
However, there may be something to this. Most importantly, the cost of this technology could be very low, benefiting countries and societies that cannot afford the raw materials required for relatively complex solar thermal systems. People have been heating water with darkly colored vessels for millenia. Although science and technology has improved solar thermal heating quite a bit over the last several decades, there isn’t much magic to heating water with the sun. This could be simple and effective enough for some circumstances.
If you want to learn more, here is some more information:
http://www.research.fsu.edu/techtransfer/technologyopportunity/documents/energy/winger2.pdf