wrote:
Ian Stirling wrote:

... you would admittedly need a very large additional thermal mass -
a ton or two of water probably, to keep the heating on overnight,
with a 10-20C drop.

A decently designed solar space heating system would not be using water
in the first place. Picking hydronic for space heating is pretty much a
design death blow.

Secondly, an entirely different method would be used to maintain temp
after dark. There is a comfort zone, not just one fixed temp at which
people are cosy. Heat to as high in that zone as solar power provides,
and you have n hours after sundown of sufficient warmth. N depends on
design details.

Watching you wave your hands about solar heating is like watching
a 2-year-old draw a 300' tree with a 1" diameter trunk or hearing
an earthy-crunchy person say he can heat his house by running
rainwater from his roof through his microhydro plant :-)

Numbers give a sense of perspective in this energy newsgroup.

Nick