= Solution
Hydropower can convert a renewable water flux efficiently, has low operating fuel requirements, and reservoir schemes can provide rapid dispatch, <inertia> and storage. Long plant lifetimes can make capital expenditure worthwhile, while <pumped storage> shifts <energy> rather than producing a new primary resource.
Limitations include finite favorable sites, seasonal drought, sedimentation, <habitat fragmentation>, blocked fish migration, displaced populations and major civil-engineering/failure risks. Reservoir evaporation and methane emissions can matter, especially in warm flooded landscapes, so life-cycle emissions are not uniformly zero. Run-of-river plants avoid some reservoir impacts but offer less controllable output. A project assessment must compare useful annual <energy> and firm capacity, ecological and social costs, and the counterfactual electricity system.
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