Perhaps they've gotten their cost issues under control now, but this 2010 report from the Philly comptroller points out a whole bunch of problems: http://www.philadelphiacontroller.org/publications/other%20r...

The report shows all sorts of maintenance issues that weren't accounted for. It takes longer to empty the bags on these units, for example.

I helped write a proposal to buy some of these units (albeit for a university campus, not streetside in cities), and we didn't find any significant cost savings. The appeal is the PR/image boost of having solar panels on every trash can. It looks like you're doing something sustainable, even if the numbers don't add up.