Hi tech stuff is all very nice but have you checked on the price of a
suntracker lately? These types of system often don't pay you back for
maybe 20 years or so.

There's a lot that can be done with simple materials. You might
achieve a collector efficiency of only 60% compared to maybe 80% of a
vacuum tube collector or a suntracker but if it costs 1/10th the price
then it could be worth it.

This is a good link:

http://www.ece.vill.edu/~nick/

The solar closet is a simple and cheap 'heat battery' to buffer the
avialable solar energy so it last overnight and maybe even over
several overcast days.

Having said all this, I've done some checking and active solar space
heating is considered not to be viable in the UK since it is usually
overcast in winter time... ah well.

Nick.