3 to 4 years? I use 500kw avg per month and pay about $65/month avg. So if payback were to begin in 4 years, I would have to find a system that cost $3500.
Irrelevent, and a misconception. What you use is not the point.
Think of yourself as a power plant.
If you can install a system that "generates", (forget what YOU consume), $100 a month worth of power. It costs you $10,000 to install.
After 8 years, you are "making" $100 a month pure profit.
If that $10,000 system generates $200 worth of power a month, after 4 years, you profit $200 a month for the life of the system.
The utility would pay you for the difference.
This would also apply to Deps arguement.
It does not matter what his A/C draws. What matters is return from investment.
A person with the best solar supply and the highest rates would benfit the most.