You're not adjusting for inflation (cash + increases in electricity costs), ambitiously assuming an equivalent 10% return on other investments, or re-investing

You're not adjusting for inflation (cash + increases in electricity costs), ambitiously assuming an equivalent 10% return on other investments, or re-investing the amount saved per year in your calculations (that $1650 you save in the first year also compounds to ~$16.25k). Make those fixes and the numbers are much closer.