Costs of wind, solar, and batteries have fallen rapidly and are projected to continue falling due to innovation and economies of scale. Moderate amounts of wind and solar energy, which are variable energy sources, can be integrated into the electrical grid without additional infrastructure such as grid energy storage and demand-response measures. These sources generated 8.5% of worldwide electricity in 2019, a share that has grown rapidly. A sustainable energy system is likely to see is shift towards more use of electricity in sectors such as transport, energy conservation and the use hydrogen produced by renewable electricity or with carbon capture and storage.