I was looking at your pictures of the BGG and was wondering how the spiral showers worked

They have mains water which goes to each of the Tipis. Inside each Tipi, but outside the square shower cubicle in the middle of the Tipi, is a series of 5 or 6 cones which each have a coil of black pipe wound around them, each in series with the last. This enables them to adsorb heat from whichever direction the sun is during the day. The chap said there was a quarter of a mile of pipe, but I think that must be the whole system, not per Tipi. Sufficient hot water was produced for each Tipi to also supply the standalone shower cubicle next to it. I think there was also a backup up wood burner as well.
Mike