Science Daily reports on a study from the University of Delaware and Delaware Technical Community College suggests that wind and solar could power the grid 99.9% of the time if combined with a certain amount of energy storage and fossil fuel backups for the rare occasion that clean energy alone was not enough.
Using computer modeling, the researchers explored 28 billion combinations of renewables and storage mechanisms, each tested with four years of weather and energy demand data. The results were encouraging, and because the study focused not just on matching supply with demand, but rather achieving the most cost effective solutions, it revealed some rather useful findings. For one, that it is cheaper to over-build generation capacity to a point where there is excess supply on sunny or windy days, and still an adequate direct supply when demand is high but wind or sun are in short supply.
During the hours when there was not enough renewable electricity to meet power needs, the model drew from storage and, on the rare hours with neither renewable electricity or stored power, then fossil fuel. When there was more renewable energy generated than needed, the model would first fill storage, use the remaining to replace natural gas for heating homes and businesses and only after those, let the excess go to waste.
The study used cost estimates for renewables in 2030, that showed wind and solar at roughly half the installation price they are today, with maintenance costs remaining roughly constant. Add energy conservation and sustainable resource use and what have you?!