An interesting alternative or complement to Moore's Law … Computing power: A deeper law than Moore's?:
a new analysis, by Jonathan Koomey of Stanford University and his colleagues, [sic] seems to have uncovered a deeper law relating to the energy-efficiency of computers, dating back to the era of vacuum tubes. The researchers found that the electrical efficiency of computing has doubled every 1.6 years since the mid-1940s. “That means that for a fixed amount of computational power, the need for battery capacity will fall by half every 1.6 years,” observes Dr Koomey.