Advantages and limitations of hydropower

Hydro-electric power is electricity produced by using the potential energy of water falling through a head to drive turbines coupled to generators ($P = 9.81QH\eta$).

Advantages

1. Renewable source: water is renewed by the hydrological cycle and is not used up.
2. No fuel cost: running cost is very low; only operation and maintenance.
3. Clean: no smoke, ash or CO₂ during operation.
4. High efficiency: overall efficiency 80–90%, much higher than thermal plants (30–40%).
5. Quick start and load following: units can start and take load in a few minutes, so they are ideal for peak load and frequency control.
6. Long life: 50–100 years for civil works.
7. Reliable and simple: fewer moving parts, low breakdown rate.
8. Multipurpose benefits: storage projects also provide irrigation, flood control, water supply, fisheries and tourism.
9. No import dependence: for Nepal it uses local resources and saves foreign currency; surplus can be exported.

Limitations

1. High initial cost: dams, tunnels and access roads are costly.
2. Long construction period: usually 4–10 years.
3. Dependent on rainfall/flow: output falls in the dry season or drought years.
4. Site specific: plants are in remote hills, far from load centres, needing long transmission lines.
5. Environmental and social effects: submergence of land, displacement of people, effect on fish and the downstream river.
6. Sedimentation: reservoirs fill up and turbines are eroded, especially in Himalayan rivers.
7. Geological and seismic risk: landslides, weak rock and earthquakes can damage works.
8. Risk of dam failure and GLOF: large consequences downstream.