The below description of actions taken by a MA-based homeowner shows just how much you can do by being attentive to energy use in a home, before adding things like heat pumps and solar panels.
I have reviewed cursorily your well researched and detailed Green plan. I would only offer, from my less informed point of view, a slightly different perspective for you to consider. If it appeals, perhaps you could devise tables and guides to make it useful for those in similar situations to mine.
Your thrust, as I interpret it, is to “invest” in actions that reduce the use of fossil fuels by the most efficient means available, taking into account cost and payback.
My approach is two-pronged, namely 1) Conservation and 2)Investment in Efficiency.
For example, my house, built in 1957, 3169 sq. ft. living area, 2×4 walls, 2x 8 floor joists, and 2x 10 rafters has been insulated and weatherstripped thru a MassSave contractor, (walls were too narrow to add insulation). Windows are double pane, insulated. Blower door tests showed a reduction from 5k CFM to 3.5k.
Oil-fired hot water baseboard, which I put in in 2000, 12k LG mini-split, 3-ton Trane central air for the upstairs, connected to existing ductwork. Electrical panel is 100 amp.
Electricity usage, 3600kw/year. (Note that I pay about $0.43/kw, due to fixed delivery charges and add ons). Oil, about 400 gal/yr. Propane c.40gals/yr
To reduce carbon footprint, thus save money, we two occupants keep doors closed, in rooms we either don’t use, or wish to heat comfortably while occupied, supplementing with electric space heaters. We keep the heat “off” in the second floor heating zone, save for briefly bring temp up to 64 at bedtime. Hot water source is via propane stove heated kettle, save for necessary ablutions, or guest visits when we keep the 40-gallon hot water heater on. (Runs off the oil furnace)
Each year I look for ways to lower our electrical and fuel needs without impacting lifestyle. For example, I have always felt it unnecessary to run the 40-gallon hot water heater, off the furnace. I did winter/summer Hi-Lo setbacks on the furnace temp, and used the furnace on/off outside of heating season. Then, Last year I installed a twenty gallon electric hot water heater which serves nicely in place of the forty gallon one for about three seasons. It’s also installed closer to the bath/shower, thus avoiding a need to draw off any cold water. (We must do that with the large HW heater, but save the water in a bucket for plants.). This winter, I added another fuel saving step. I attached an on-off switch to the furnace powered hot water heater, thus powering it up the few times it’s needed each week. I figure this saves not only fuel, but the corresponding electricity necessary to run the burner.
With virtually no exceptions, we air dry the two loads of laundry each week, either clothesline or air dryers in basement and in front of wood burning fireplace insert .
I do expect to have to replace the 3-ton central air unit at some point, even though the replacement compressor is only ten years old. The coolant, I learned, was ordered “discontinued” by the US government, in 2010. How Trane was allowed to sell me a new unit in 2013, I will never know. Last year I had the unit serviced, and was charged $400 for one pound of coolant. Thus, I have decided to keep it going until it dies, unserviced, which could last another ten years, given that it only lost one pound in the first ten, and the services did not detect the source of a leak. Be that as it may, I’m prepared to spring for a mini split replacement, which will be far more efficient and cheaper to run than the central unit. (It will also save on fuel oil in the heating season).
Oh, and as an FYI, for emergencies I have two portable generators, 3500 and 4700 watts which hook into relays powering everything in the house.
Six sixty-gallon water barrels supply water for plantings, garden and lawn outside, car washing, etc.
One final point. Today’s footprint analysis could take into account auto use, as EVs are part of the equation, and one must consider “fueling” at home. At some point I expect battery storage will be advanced enough, so a small solar collector could supplement the mains for charging and supplementary utility, like lights, TVs, etc. in an emergency situation, or for charging an EV.