Though, the returns are (edit: "not great") if the figures above INCLUDE net metering revenues.
Heatpump = Negative IRR until y8
Solar = Negative IRR until y16
Heatpump + Solar = 0 NPV through y25 | 8% discount rateIt also doesn't include the negative externalities because of tragedy of commons. Sadly, these kind of flawed 'financial' calculations are widespread.
What is inspiring from the OPs comment is that this is doable in harsh Canadian winters with negligible solar and it breaks even. Most of the world is living in significantly more sunshine, so it should work out a lot better financially for >99% of the population.
A modern furnace works via a heat exchanger, where the combustion produced pollutants never mix with the indoor air being pushed through. All pollutants are expelled outside via a property functioning chimney. This is one reason why you should have the furnace (and chimney function) inspected annually. Aging heat exchangers will show hotspots before there is a possibility of air being mixed, giving plenty of time to plan for a replacement. Of course there is a possibility of failure, which is why you should have a carbon monoxide detector.
For externalities or immediate health benefits, heatpumps are pretty defensible. However, solar isn't a saint. Rare earth/mineral mining is hazardous plus only a fraction of solar panels are getting recycled properly.
> this is doable in harsh Canadian winters with negligible solar and it breaks even
It's doable alright. OP got subsidies (See comment re: risk free loan and grants). Talk about externalities, this is definitely wealth transfer.
The wealth transfer you are alluding to, it is from the poor (everyone) to the rich (fossil fuel billionaires), isn't it?
If you believe the externalities of solar are a problem, what do you propose to do instead? Should we subsidize some other alternative? Redirect resources from oil to nuclear? Other?
Solar cells are made of silicon, not rare earths.
For solar, you need to mine ONCE for 25 - 50 years. Fossil fuels are burnt every second continuously. Perhaps you can do the math if its not obvious?
You're right about the 8 year negative IRR for the heatpump, although I'm being very conservative about propane costs, it's likely much shorter. I was pretty conservative about the solar savings too, I generally go for the worst case in these estimates.
Your overall NPV calculation seems a bit off. It's ~21 years to zero NPV at 8% discount rate, spending $80 up front to save $8/year. Factoring in the 10 year interest free government solar loan makes it more like 14 years. My working:
=nper(8%, -8, 80)
20.9
=nper(8%, -8, pv(8%, 10, -4)+40)
14.3
Correct. It's 21y. I missed $500 from a reading error and was assuming $7.5k/y (not $8k/y).
edit: I see your mention of the grant, too. Combined, that's cutting the NPV=0 point in half from 21y to ~12y. Good job.