--- title: "Advantages and disadvantages of hydropower" subject: "Hydropower Engineering" chapter: 1 key: "semester_7/hydropower_engineering:hydropower-advantages-disadvantages" source: https://www.bctengineer.com/q/semester_7/hydropower_engineering/hydropower-advantages-disadvantages site: BCT Engineering --- # Advantages and disadvantages of hydropower Hydropower Engineering · Chapter 1: Introduction - Asked in: 2072 Kartik, 6 marks; 2071 Chaitra, 3+3 marks (asked 2 times) - Video: [Advantages and disadvantes of hydropower](https://www.youtube.com/watch?v=43ZCdBJwoDI) — Future Energy & Technology - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/hydropower_engineering/hydropower-advantages-disadvantages - Whole chapter: https://www.bctengineer.com/md/semester_7/hydropower_engineering/chapter-1 ## Question Discuss the advantages and disadvantages of hydropower projects compared to other sources of energy. ## Short answer Advantages: renewable, clean, low running cost, long life, quick start, high efficiency (85-90%), multipurpose, local resource and export potential. Disadvantages: high capital cost, site-specific, seasonal output, environmental/social impacts, sedimentation, geological and GLOF risks. ## Answer 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. | Point | Hydro | Thermal | |---|---|---| | Fuel | Free | Costly, imported | | Capital cost | High | Lower | | Running cost | Very low | High | | Pollution | Almost none | High | | Start-up | Minutes | Hours | | Site | Fixed by river | Flexible | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is hydropower suitable for peak load and frequency control compared with thermal plants? A. It has the same start-up time but higher efficiency B. It has a lower capital cost C. A hydro unit can be started and loaded in minutes, while thermal needs hours D. It does not depend on river flow Answer: C. Quick start and loading within minutes gives flexibility for peaks and frequency control. (Key point: Start-up flexibility) 2. What is the typical overall efficiency of hydropower compared with thermal plants? A. 60% against 60% B. 95-99% against 70% C. 85-90% against 30-40% D. 30-40% against 85-90% Answer: C. Hydro is about 85-90% efficient, far above the 30-40% of thermal plants. (Key point: Efficiency) 3. Why does hydropower output in Nepal fall in winter? A. Fuel is unavailable B. Turbines freeze at all sites C. Low river flow in the dry season D. Dams are closed for maintenance Answer: C. Output depends on hydrology, and flow is lowest in the winter dry season. (Key point: Hydrology dependence) 4. Which pair is a disadvantage of hydropower listed in the answer? A. Slow start-up and low efficiency B. High running cost and fuel import C. High capital cost with long gestation, and sedimentation D. Short life and heavy pollution Answer: C. Dams, tunnels and roads need heavy investment and 5-10 years; Himalayan sediment reduces reservoir capacity and wears turbines. (Key point: Disadvantages) ## Related in Hydropower Engineering - [Installed capacity, energy and daily peaking reservoir (2079)](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-capacity-plant-factor-18cumec-peaking-79) — Hydropower Engineering, chapter 3, asked 2× - [Installed capacity, energy and daily peaking reservoir (2072)](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-capacity-plant-factor-18cumec-peaking-72) — Hydropower Engineering, chapter 3, asked 2× - [Flow duration curve; firm and secondary energy](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Afdc-firm-secondary-energy-69) — Hydropower Engineering, chapter 3 - [Peaking RoR: max power and wet/dry energy ratio](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apeaking-ror-reservoir-250m-q25) — Hydropower Engineering, chapter 3 - [Full regulation: reservoir, capacity, annual energy](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Astorage-full-regulation-monthly-hydrograph) — Hydropower Engineering, chapter 3 - [RoR best installed capacity (NRs, 45 years)](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-best-capacity-nrs-10-percent) — Hydropower Engineering, chapter 3 ## Related in other subjects - [Risk sources in over-budget, delayed projects of Nepal](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Arisk-sources-nepal-delayed-projects) — Project Engineering, chapter 5 - [Sources of financing large projects](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Asources-of-project-finance-large-projects) — Project Engineering, chapter 6 - [Advantages of electrical energy over other forms](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Aadvantages-electrical-energy-other-forms) — Utilization of Electrical Energy, chapter 1, asked 2× - [Energy sources in Nepal and wind scope](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aenergy-sources-nepal-wind) — Power Plant Design, chapter 1, asked 2×