In my experience, almost none ( yes none) of these domestic "green" energy initiatives make any sense financially. Almost everyone of them has to be subsidised. The fact is that hydrocarbons are cheaper then bottled water.
I and some of my friends, looked at solar hot water heating, wind power, PV generation, Nothing has less then a 10 year payback, lots has over a 20 years payback ( arguably greater then the life of the equipment). Thats not even taking into account the net future value of money etc.
Even if you look at adding insulation to existing homes, the payback doesn't make sense, just buy more oil.
Unless these technologies fall dramatically in price, they will be consigned to the dustbin of history.
( PS I was amazed at one commentator , suggesting that to heat a 100sqm house in france ( yes an uninsulated one was costing €4000 a year - what I smell is BS)
Here in Ireland, we have some of the highest oil prices in Europe , Heating oil is now around €0.72 /litre. An average family home here ( typically rural as most towns have Naturel gas, which is much much cheaper) ,is around 160-200 sqm, and would rarely consume in excess of €2000-2500 to heat. my house is 100sqm and is built to insulation standards of 1995, its costs under €1000 to heat. Heating season in Ireland would typically be End of September to May.
Thats make your original payback calculation way longer, approaching 20 years. a 20 year ROI is ridiculous
Very very few of these "green" initiatives make sense, Oil is cheaper then bottled water or milk, until that changes really dramatically the situation will remain