Advantages and disadvantages of hydropower

Hydropower uses the potential energy of falling water to turn turbines. Compared with thermal, nuclear and other sources it has the following merits and demerits.

Advantages

• Renewable and clean: Water is replenished by the hydrological cycle; there is no fuel, no ash, and very low greenhouse gas emission.
• Low running cost: No fuel cost; operation and maintenance are low, so unit cost falls over time.
• Long life: Dams and civil works last 50-100 years; machines last 30-50 years.
• Quick start and flexibility: A hydro unit can be started and loaded in minutes, so it suits peak load and frequency control. Thermal plants need hours.
• High efficiency: Overall efficiency is 85-90%, much higher than the 30-40% of thermal plants.
• Multipurpose: Reservoirs give flood control, irrigation, water supply, navigation, fisheries and tourism.
• Economy: Uses local resources, saves foreign exchange on imported fuel, and creates local jobs.
• Export potential: Surplus energy can be sold, as Nepal can sell to India.

Disadvantages

• High capital cost and long gestation: Dams, tunnels and roads need heavy investment and 5-10 years to build.
• Site specific: The plant must be built where water and head exist, often remote, so long transmission lines are needed.
• Dependence on hydrology: Output falls in dry years and in the low-flow season (Nepal: winter).
• Environmental and social effects: Submergence of land and forests, displacement of people, loss of fish migration, change in downstream flow and sediment.
• Sedimentation: Reservoirs lose capacity and turbines wear in Himalayan rivers.
• Geological risk: Earthquake, landslide, GLOF and dam failure cause large loss.