To me, the correct way to do this is to compute the (implied) rate of returns of solar investment over the lifetime of the panels :
(x-x^25)/(1-x)=20/3.2 ⇒ x ~ 0.85
x = 1/(1+r) ⇒ x ~ 0.17
So yes, a 17% rate of returns is insanely good (if the two assumptions, “25 years lifetime” and “3.2k/year”, stands) and will beat pretty much every other investment.
(which should makes you suspicious about the assumptions)
To me, the correct way to do this is to compute the (implied) rate of returns of solar investment over the lifetime of the panels :
(x-x^25)/(1-x)=20/3.2 ⇒ x ~ 0.85
x = 1/(1+r) ⇒ x ~ 0.17
So yes, a 17% rate of returns is insanely good (if the two assumptions, “25 years lifetime” and “3.2k/year”, stands) and will beat pretty much every other investment.
(which should makes you suspicious about the assumptions)