The result, according to the figures of the organization selling the equipment, would be to reduce the annual utility bill to $0.00. In other words, I'd spend $16,500 to save $780 annually, so it would take about the life of the equipment to break even.
But actually, I'd be costing myself money. The next "Alternative" block figures the return of taking that $16,500, investing it, and using the proceeds to pay the utility bill. At 5% return, I'd be doing better on my utility bill than with the solar power. At 3% return (3.22% is the last reported yield on 20-year Treasury bills), I'd be paying less than $25 a month for power. Plus, at the end of the 20 years, I'd still have my $16,500.