The copper coil heat exchanger was a little too wide for any of my containers, so I built a soft tank from 10′ of mylar coated bubble wrap and a garbage bag.. It’s well insulated and leak tight. I’m going float Styrofoam balls on the surface for added insulation. I got this idea from Tom Gocze almost 30 years ago. He still sells them at the link below. So far I the tank hasn’t exceeded 140F, so I haven’t really tested the high temp limits.

http://www.americansolartechnics.com/products/solar-packages-kits/softank-kits/

This is the first attempt at using the header and vertical stand pipe as a heat-pipe with a 10-tube collector. It seems to be functioning well, but there is a significant ΔT across the  steam pipe header. In full sunlight the dead end of the header runs at about 270F and the exhaust side runs steadily at 230F. The geyser pump exhaust runs at about 160F and is moderated by the tank temperature. The ΔT across the heat-exchanger is about 20F indicating a good pump rate from the geysering.

My next experiment will be to insert some kind of wicking agent into the header pipe to more effectively draw liquid to the dead end. My theory is that the dead end of the heat pipe is over heating because the liquid is evaporating before it reaches that end, thus the high ΔT across the header.