It'll take about 25 years to pay back.
Brad, yes....there-in lies the rub. Even doing one's darnedest to be PC with energy fails to deliver in the way it really 'should do'.
One of the early uses for 'active' solar [In Australia] was with Hot Water sevices....only issue was that at BEST they took 10 years to cover costs....and being boilers they were REQUIRED to be replaced every....wait for it..... 10 years.
Kinda self-defeating.
Australia has the dubious 'honour' of having the largest median house size on the planet - and the logical solution to limiting/reducing energy use is to 'try to' convince users that houses can be quite survivable when smaller. An average house can easily be reduced by 30% in size and still accommodate people 'adequately'....and the reduction in 'envelope' benefits all at all levels of energy use from manufacture to construction to on-going sustainability.
Legislation brings in all sorts of requirements these days for 'Energy Ratings' on dwellings..... and it's probably of note that the first, true 'environmentally competent' Public Building was/is the Melbourne City Council offices here in Oz.
Where practical it's often just simplest to 'think small'....