--- title: "Hydropower versus solar PV in Nepal" subject: "Power Plant Design" chapter: 1 key: "semester_8/power_plant_design:hydro-vs-solar-pv-nepal" source: https://www.bctengineer.com/q/semester_8/power_plant_design/hydro-vs-solar-pv-nepal site: BCT Engineering --- # Hydropower versus solar PV in Nepal Power Plant Design · Chapter 1: Energy Sources and Electric Power Generation - Asked in: 2082 Shrawan, 8 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/power_plant_design/hydro-vs-solar-pv-nepal - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-1 ## Question Compare the electric power from hydropower with solar photovoltaic based power generation on the basis of reliability, grid-connection, efficiency, operating range and maintainability. Also consider the scenario in Nepalese context during comparison. ## Short answer Hydro is firm, dispatchable, grid-friendly with inertia and black-start, 85-92% efficient, but high sediment and long transmission. Solar PV is intermittent, inverter-based, 15-22% efficient, simple maintenance, quick install. In Nepal, dry-season solar complements monsoon-dependent run-of-river hydro; a hydro-solar mix with storage is most reliable. ## Answer **Hydropower** converts the potential energy of water into electricity using a turbine and synchronous generator. **Solar photovoltaic (PV)** converts sunlight directly into DC electricity in semiconductor cells, converted to AC by inverters. #### Comparison | Basis | Hydropower | Solar PV | |---|---|---| | Reliability | Firm for storage; run-of-river depends on seasonal flow but gives output day and night | Only in daytime; drops with clouds; capacity factor about 15–20%; needs storage or backup | | Grid connection | Synchronous generators; provide inertia, voltage and frequency control; can black-start | Through inverters; no natural inertia; harmonics and reverse power flow issues; needs grid-support functions | | Efficiency | About 85–92% (water to wire) | Module about 15–22%; system about 12–18% | | Operating range | Wide control 0–100% via governor; dispatchable | Output follows sunlight; not dispatchable; MPPT tracks maximum power | | Maintainability | Turbine erosion by sediment, civil works, skilled staff | Very low: module cleaning, inverter replacement (10–15 years) | | Construction time | Long, 4–8 years | Short, months | | Capital cost | High civil cost | Falling fast; modular | | Life | 50+ years | About 25 years | | Environmental impact | River ecology, land submergence | Land use; panel disposal | #### Nepalese context **Hydropower:** - Nepal's grid is almost fully hydro (over 3,000 MW installed). Most plants are **run-of-river**; only Kulekhani is a seasonal storage project. - Output is high in the monsoon (surplus, exported to India) and falls to about a third in the dry season (deficit, imports). - High sediment in Himalayan rivers causes turbine erosion and maintenance cost. - Long transmission lines from hills to load centres. **Solar PV:** - Good solar resource: about 4.5–5.5 kWh/m²/day, around 300 sunny days. - Solar output is highest in the dry season (clear skies), when hydro output is low, so it **complements** run-of-river hydro. - Widely used in remote areas (solar home systems, mini-grids, solar irrigation pumps) and in growing grid-tied plants in the Terai. - Limited by land cost, lack of storage and inverter-based grid issues; net metering for rooftop solar has been introduced. #### Conclusion Hydro gives cheap, controllable bulk power and grid stability; solar PV is quick to install and fills the dry-season and daytime gap. For Nepal, a **hydro–solar mix** with hydro reservoirs acting as storage is the most reliable approach. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is solar PV less reliable than hydro? A. Output only in daytime, drops with clouds, capacity factor about 15-20% B. Needs fuel C. Output is constant D. Capacity factor about 90% Answer: A. PV needs storage or backup, while hydro gives output day and night. (Key point: Reliability) 2. Which describes grid connection? A. PV uses synchronous generators and gives inertia B. Hydro gives inertia and can black-start; PV connects through inverters with no natural inertia C. Both give inertia D. Neither is grid connected Answer: B. Inverter-based PV has no inertia and can cause harmonics and voltage rise. (Key point: Grid connection) 3. Operating range: which statement is correct? A. PV is dispatchable 0-100% B. Hydro is dispatchable via the governor; PV follows sunlight and can only be curtailed C. Neither can be controlled D. Hydro follows sunlight Answer: B. PV is not dispatchable; MPPT only tracks the maximum power point. (Key point: Dispatchability) 4. Why do solar and hydro complement each other in Nepal? A. Solar output is highest in the dry season when river flow is low B. Both peak in monsoon C. Solar peaks at night D. Hydro peaks in the dry season Answer: A. Clear dry-season skies raise PV output when run-of-river hydro falls to about a third. (Key point: Nepal complementarity) 5. Which maintenance issue is typical for hydro in Nepal? A. Panel cleaning B. Turbine erosion by sediment in Himalayan rivers C. Inverter only D. No maintenance Answer: B. High sediment erodes turbines; PV maintenance is very low. 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