There's a huge amount of space available - it's called a roof, and many people have them.
The PV panels on my roof are, to a certain extent, self-cleaning. They're designed that way, and it works quite well as long as they're mounted properly. Panels should be mounted at an angle roughly corresponding to your latitude (I'm at ~26 deg south), and rainfall is enough to keep them clean. I get up on the roof to inspect them every couple of months, and I clean them once a year or so. All it takes is a long-handled broom, and a bucket of water.
And speaking of efficiency, why do many people ignore the fact that you only receive about 40% of the energy in the coal when you turn on an appliance?