Renewable energy sources such as solar, wind and hydropower are replenished naturally on human timescales. Their expansion can reduce dependence on fossil fuels and lower greenhouse-gas emissions, although environmental impacts and system constraints still need consideration. Solar and wind output can vary with weather, creating challenges for grid management. Storage, transmission, demand management and diversified generation can help address variability. The transition to renewable energy is therefore not simply a matter of installing more capacity; it requires changes in infrastructure, markets and system planning. Question: Demand management is relevant to: