Obviously, market returns can be assumed to be 10% or higher depending on the span of years looked at and the indexed used.

Even at a market return of 10%, what assumptions do we make about

- increased savings from higher electricity costs over time and does that counteract the reduced generating capacity?

- Do we assume the extra $440 is invested each year?

- How do we assume savings on my income is taxed vs the extra income from investing the funds? Taxes seem to be avoided on the earnings in the solar panel scenario vs the invest the money scenario but tell me if you see that differently.

- Issues if the system is damaged by hail and needs to be repaired or something (likely $1,000 deductible for repairs and ding on homeowners insurance).

- Cost to remove them and repair roof once they are no longer useful (assuming after 20 years or so)?

I guess we could add more if I we thought about it long enough but yes, I agree it can be a complicated ROI equation. I think I went this way as it looked like a simple payback was about 6 or 7 years depending on what the price of electricity does and locking in utility rates (so to speak) was attractive on some level. I don't think it makes sense for a lot of people and some wouldn't agree that it made sense in my instance, but I think I would be saving about $440 to $500 a year for the first bit so I went ahead with it a while back. No regrets yet, but it has only been three years. If the panel degrade only by 20% in the first 20 years, I think I'll be in a good spot overall. If they degrade faster and are significantly less than 80% after 20 years, I might not come out as far ahead as I am hoping.