In additon to my last post regarding loft conversions and CH etc we have
a large area of south facing roof. Admitedly we will be adding a number
of Velux style windows to this but I am considering some solar water
heating as well whilst we have the option.

Are there any guidelines as to how long it takes for these systems to
pay for themselves in saved heating costs?

I've seen stats on web pages selling the systems but you get the feeling
that they are trying to sell the equipment so are going to give "best
possible" scenarios.

If I'm having a new boiler and converting the loft what steps (cheap
ones) can I take to make it easier to add solar water heating at a later
date. Is it just a case of running extra pipes from the proposed
location of the panels on the roof to the space where the boiler will be
or would a different boiler/HW tank make sense too?

Chris