Last weekend I decided to change the oil and tune up my classic car, a 1972 Datsun 1200. (My wife has other names for it.) It sports a “four on the floor” and a simple four-cylinder engine that doesn’t even need fancy smog controls.

Automobiles were once high-maintenance luxuries that only the wealthy could afford. Renewable energy, such as that from photovoltaic sources, also is a luxury among whose sole redeeming qualities are its uninterruptable nature—at least during the daytime.