Solar Power for added Income?

[Ray B.]

I live in Portland Maine, I have been thinking on placing solar panels on some of my rental's land. The idea is to supplement (or cash flow) my own electric bill at a different home I live in. The home is too tree covered for solar. 

Does anyone have any experience "Selling" power back to the utilities company?
Why is every inch of unused farm land not covered in solar? Seems like the ultimate "Passive Income"
What problems have people encountered? Especially using solar on land they do not occupy.

Thanks!