Do you think all Grid tied Solar PV systems sell back to the grid?

Yes. The system is designed so that what you sell all year equalizes your needs and when you are out -- at work, school, shopping -- you supply your neighbors and are credited. At nioght you use the grid, and if the system is designed correctly, you equal out by years end. Payback to own your own power is typically 8-12 years on a system warranted for 25 years. It's really a now brainer that people owning their own power source is a good investment. People who don't believe seem like Oil sheep and misinformed ;-)