Your guess is wrong. A better term for what I calculated is the IRR of a series of cash flows. You're correct that stock is a liquid asset, I'm obviously aware that I can't liquidate the panels attached to my roof.

This whole thread got out of hand, I was just giving the anecdote that I saw a much better return on a heatpump than a solar installation. I don't care who believes or doesn't believe my calculations.

> Easy to verify though: what was your install cost and how much is it saving you on energy bills?

A rough estimate is given on my original comment in this thread.

I recently thought about running a BBQ gas line from my main 500 gallon propane tank, but with delivered propane close to $1/litre right now and a 20lb tank holding about 18 litres there's no saving over just using with the portable tanks. I prefer being able to move the barbecue around too, although I probably would run a line if I had an outdoor kitchen type setup.

I wish I'd never mentioned solar nor net metering now- I'm not on some crusade to promote either, I was just explaining the economics of my personal setup.

I don't have to imagine, I've actually installed it and I can see the impact on my bills. By most estimates it has a 12-15 year ROI that matches the stock market, and will continue to generate electricity for another 10-15 years after that. The 'math' is a function of many things: orientation, roof angle, occlusion, installation costs, electricity cost, latitude, grants/loans, net metering terms, etc. It's a huge assumption to say that what doesn't work in one location in Cleveland won't work for a property in Canada 2 degrees further north.

My local utility is well aware of that, applications for permits to net meter have to be made, and only a fraction (something like 15%) of properties in each area can net meter. Also the government is aware and there are no grants for net metering, only for battery systems.

I’m giving details about my personal system for one property in one location, not in any way making a statement about what works for anyone else.

A cheaper smaller system right sized for summer consumption with a battery would have my second best option, but for me never showed any potential payback due to the fixed costs of installation and the extra battery costs.

Further north where I am solar can only ever be a small component of total electricity generation due to the dark snowy cloudy winter months with close to zero solar generation for weeks on end.

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

The current Ontario solar grant is weird- it only applies to battery systems without net-metering. They also offered a 10-year interest free loan though so I took that, improves the ROI a little. I think battery systems do make more sense for people who are further sound and using more electricity at the time of year that they are generating it. The solar sales people estimated a 10-year ROI but they had to include a pretty high annual energy cost increase in their calculations (I think 8%/year), I estimated more like 15 years.

I didn't really consider replacement, by all reports the WaterFurnace pump should last 25-30 years and the propane furnace was probably 5 years old so would have lasted about the same. I would think that the WaterFurnace costs a little more to replace, maybe a winter's worth of propane.

Several people told me that ground source heat pumps were too expensive, but years later it still feels like the best investment I've ever made, the gentle heating and cooling is more comfortable too. Anyone with enough space who has to have fuel delivered (propane, oil, etc.) should seriously consider it.

Compared to say SoCal I generate 2/3 as much per year, much less evenly- a lot more in summer than winter, whereas further south there's less variation year round. Cooler temperatures improve solar panel efficiency too. There are online solar potential calculators if you want to compare for yourself.