Renewable Energy: Can it Deliver?

The use of renewables is spreading rapidly. Over a quarter of global electricity is already generated from solar, wind, hydro and biomass energy. With costs falling significantly, renewables are booming, helping to avoid the major climate change risks associated with fossil fuel use in power stations, homes and vehicles. But can we get rid of all of these dirty energy sources – and nuclear power, as well – and deliver 100% of our energy from renewables? Or are renewable energy systems inherently unreliable and expensive, given the need to deal with their variability?