Yes the figures are my approximate bills so include net metering revenues.
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:
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:
The solar system is fun to tinker with and should pay off 'eventually', it's not a no brainer of a decision like the heatpump though.