[randyrand]

And advancements in fusion, fission, wind, etc that could make today's solar less worthwhile.

No one can predict how much the landscape can change in that time and I wonder if Googles 20-year savings model tries to account for predicted advancements -- and also importantly if their "savings" accounts for the time value of money -- the amount that could be had just by investing generally instead of investing in your own solar. Time to investigate....

Edit: Google "Assumes 2.2% annual increase in electricity prices." That's interesting. We should be talking present value terms so inflation is irrelevant. Are they assuming no tech advancements in the next 20 years? What would be driving up those costs other than inflation?