Womble is right - heat recovery systems rely on controlled ingress of ventialtion air - older houses tend to not be "airtight" enough for them to work well. Heat pumps are clever too, but relatively expensive, require electricity as their "fuel" and won't work with any old radiator system.
I'm sure you have though about this a lot, and its great to hear what you are putting into action, but it never hurts to review whether you are putting your hard earned cash ito the right places.
One widely accepted philiospohy on cost-effective energy strategy is be lean, clean then green. In other words, reduce your energy consumption first, then be more clever with the energy you are using (e.g. using heat recovery - which is moving energy from one place to another) and then look at renewable energy generation.
I would focus on these "lean" items if not already done:
- Loft insulation
- Draught sealing (windows, doors, joints)
- lagging pipework and hot water tank
- If feasible but probably not: cavity or internal wall insulation, double or secondary internal glazing
Then, can the LPG boiler be replaced with a wood-chip or log fired unit, if you have a reliable fuel source? If you already have the "wet" system i.e. radiators in place, this could be a good bet.
Are the solar panels "PV" (i.e electricity generating) or the hot water type? You may find that the hot water type give you a better return against burning LPG than the PV ones will against electricity. A few sums should give you the answer.
The water-wheel sounds interesting... if you were a tinkerer, you could consider a DIY water heating system using for example an old car alternator, a 12V heating element and a thermostat. I take no resposibility for the results! The problem with a full-blown "micro hydro" system is the expense of generating 240V, 50hz electricity to feed your house in sync with the grid.
Let us know how you get on.
Olly
