--- title: "Hydro versus thermal: techno-economic and environmental" subject: "Power Plant Design" chapter: 1 key: "semester_8/power_plant_design:hydro-vs-thermal-techno-economic" source: https://www.bctengineer.com/q/semester_8/power_plant_design/hydro-vs-thermal-techno-economic site: BCT Engineering --- # Hydro versus thermal: techno-economic and environmental Power Plant Design · Chapter 1: Energy Sources and Electric Power Generation - Asked in: 2072 Magh, 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-thermal-techno-economic - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-1 ## Question Compare the operational characteristics of the hydroelectric power plant and thermal power plant considering factors such as techno-economic, environmental and so on. ## Short answer Hydro has 85-92% efficiency, fast start, excellent load following, zero fuel cost, low O&M, long life, but high capital and long construction. Thermal has 30-40% efficiency, slow start, firm output, high fuel and O&M cost, shorter life, and causes air and thermal pollution. Hydro is clean but capital intensive. ## Answer A **hydroelectric plant** converts the potential energy of stored or flowing water into electricity, while a **thermal plant** burns fuel to make steam that drives a turbine. #### Technical comparison | Aspect | Hydroelectric plant | Thermal plant | |---|---|---| | Energy source | Water; renewable | Coal, oil, gas; exhaustible | | Efficiency | 85–92% | 30–40% | | Starting time | Few minutes | Several hours | | Load following | Excellent; peak load | Poor; base load | | Operating range | Wide | Narrow (above about 40–50%) | | Reliability | Seasonal (RoR), firm with storage | Firm if fuel is available | | Location | Fixed by river and head; remote | Flexible, near load | | Transmission | Long lines | Short lines | | Auxiliaries | Few | Many (boiler, coal and ash handling, cooling) | | Life | 50–100 years | 25–30 years | #### Economic comparison | Aspect | Hydroelectric plant | Thermal plant | |---|---|---| | Capital cost | High (dam, tunnel, powerhouse) | Lower | | Construction time | Long (4–10 years) | Shorter (3–4 years) | | Fuel cost | Nil | High; most of running cost | | O&M cost | Low; few staff | High; many staff | | Cost per kWh over life | Low | High, rises with fuel price | | Risk | Geology, hydrology, sediment | Fuel price and supply | #### Environmental and social comparison | Aspect | Hydroelectric plant | Thermal plant | |---|---|---| | Air pollution | None in operation | CO₂, SO₂, NOx, particulates | | Waste | None | Fly ash, bottom ash | | Water impact | Changes river flow, fish migration, sediment | Thermal pollution of cooling water | | Land | Submergence by reservoir; resettlement | Land for plant, coal yard, ash pond | | Other benefits | Irrigation, flood control, drinking water, tourism | Employment in mining | | Climate | Small GHG (some methane from reservoirs) | Large GHG emission | #### Remarks Hydro has high initial cost but very low running cost, long life and clean operation; thermal is cheaper and quicker to build but expensive to run and polluting. For Nepal, with large hydro potential and no fossil fuel, hydro is the main option, with thermal only as standby. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Hydro compared with thermal has A. lower efficiency, slower start B. higher efficiency (85-92%) and faster start (minutes) C. same efficiency D. 30-40% efficiency Answer: B. Hydro is 85-92% and starts in minutes; thermal is 30-40% and needs hours. (Key point: Efficiency and starting) 2. Which economic statement is correct? A. Hydro has high capital cost but nil fuel cost and low O&M B. Hydro has nil capital cost C. Thermal has no fuel cost D. Hydro has shorter life Answer: A. Dam and tunnels cost much, but there is no fuel and the life is 50-100 years. (Key point: Economic trade-off) 3. Which is a hydro environmental or social issue? A. Fly ash disposal B. Submergence, resettlement and altered river flow C. SO2 emission D. Thermal pollution from coal yard Answer: B. Reservoir submergence and river ecology are hydro issues; ash and SO2 are thermal. (Key point: Environmental impact) 4. The main risk to hydro is A. Fuel price B. Geology, hydrology and sediment C. Ash disposal D. Coal supply Answer: B. Thermal's key risk is fuel price and supply. (Key point: Risks) 5. Why is thermal only standby in Nepal? A. Large hydro potential and no fossil fuel B. It is cheaper to run C. It is cleaner D. It has a longer life Answer: A. Nepal has abundant hydro and imports its fossil fuel. 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