Think of it as “Easy Rider” meets “An Inconvenient Truth.” Or, maybe, the perfect Christmas gift for the environmentalist with everything. A solar motorcycle. Well, not solar, strictly speaking, but electric — with its battery charged by the solar panels on Rob Thayer’s Village Homes roof. Thayer, a UC Davis professor emeritus of landscape architecture, recently purchased the custom motorcycle for $7,000 from electricmotorsport.com, an Oakland company that’s one of a handful modifying or building electric motorcycles. His is a 2003 Spanish-built Derbi Grand Prix racer, its gas engine replaced with a battery and low racing handlebars replaced with...