We had our questions answered, and decided to go ahead with the deal.
I doubt that I can build a 12 panel solar collector, the inverter, the tie-ins and electrical panel upgrades, the batteries, the mounting structure, and wiring for $3200, which is 10% electrical capacity above our highest usage to offset the inevitable loss of efficiency by aging equipment. It will pay for our $1100 yearly electric bill and an additional return of $350 as a yearly rebate together, which adds to $1450 yearly return for 20 years (in today's' dollars). The payback is an estimated 45% declining to 40% every year over 20 years.
I also do not have to tie up land, nor maintain the collector, nor worry about vandalism, nor accidental damage. Edit add: An additional government rebate dropped my cost from $4800 to $3200. This swung the offer to be so convincingly enticing.