  The finiteness of fossil fuels implies that future electric power systems may
predominantly source energy from fuel-free renewable resources like wind and
solar. Evidently, these power systems without fuel will be environmentally
benign, sustainable, and subject to milder failure scenarios. Many of these
advantages were projected decades ago with the definition of the soft energy
path, which describes a future where all energy is provided by numerous small,
simple, and diverse renewable sources. Here we provide a thorough investigation
of power systems without fuel from technical and economic standpoints. The
paper is organized by timescale and covers issues like the irrelevance of unit
commitment in networks without large, fuel-based generators, the dubiousness of
nodal pricing without fuel costs, and the need for new system-level models and
control methods for semiconductor-based energy-conversion interfaces.
