--- title: "Combined cycle gas turbine versus hydro" subject: "Power Plant Design" chapter: 1 key: "semester_8/power_plant_design:ccgt-vs-hydro" source: https://www.bctengineer.com/q/semester_8/power_plant_design/ccgt-vs-hydro site: BCT Engineering --- # Combined cycle gas turbine versus hydro Power Plant Design · Chapter 1: Energy Sources and Electric Power Generation - Asked in: 2079 Shrawan, 6 marks - Video: [Gas Turbines and Combined Cycle Power Plants Explained (Combustion Turbines)](https://www.youtube.com/watch?v=N-V_uGeCFNg) — saVRee - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/power_plant_design/ccgt-vs-hydro - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-1 ## Question Compare Combined Cycle Gas Turbine power plant with hydro power project considering various possible aspects. ## Short answer CCGT uses fossil fuel, efficiency 50-60%, low capital, short 2-3 years construction, firm all year, but high fuel cost and emissions. Hydro uses renewable water, efficiency 85-92%, nil fuel cost, long construction, long life, excellent load following, but high capital and environmental impacts. For Nepal hydro is preferred. ## Answer A **combined cycle gas turbine (CCGT)** plant uses a gas turbine and recovers its exhaust heat to drive a steam turbine. A **hydropower plant** uses the potential energy of water through a water turbine. #### Comparison | Aspect | CCGT plant | Hydropower plant | |---|---|---| | Energy source | Natural gas / oil (fossil) | Water (renewable) | | Efficiency | About 50–60% | About 85–92% | | Fuel cost | High, price volatile | Nil | | Capital cost per kW | Low to moderate | High (civil works) | | Construction time | Short, 2–3 years | Long, 4–10 years | | Location | Near gas pipeline or load centre | Fixed by river and head; often remote | | Transmission | Short lines | Long lines often needed | | Starting time | 10–30 min (GT), hours for full CC | A few minutes | | Load following | Good | Excellent; best for peaking and frequency control | | Reliability | Firm all year if fuel is supplied | Seasonal (run-of-river); firm if storage | | Life | About 25–30 years | 50+ years | | Maintenance | Hot-gas path parts, HRSG; skilled staff | Simple; sediment erosion of runners | | Emissions | CO₂, NOx (less than coal) | Nearly zero in operation | | Environmental/social | Air pollution, cooling water | Submergence, resettlement, river ecology | | Ambient effect | Output falls with temperature and altitude | Not affected | | Suitability for Nepal | No domestic gas; imported fuel costly | Large potential; main source | #### Remarks CCGT is cheap and quick to build but depends on imported fuel; hydro has high initial cost but very low running cost and long life. For Nepal, hydro is clearly preferred, while CCGT suits countries with gas supply as flexible mid-merit plants. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which efficiency pair is right? A. CCGT 85-92%, hydro 50-60% B. CCGT 50-60%, hydro 85-92% C. Both 50-60% D. Both 85-92% Answer: B. Hydro water-to-wire efficiency is much higher. (Key point: Efficiency comparison) 2. Compared with hydro, CCGT has A. higher capital cost and longer construction B. lower capital cost and shorter construction but high fuel cost C. no fuel cost D. longer life Answer: B. CCGT builds in 2-3 years at lower cost per kW but pays for fuel. (Key point: Cost and construction time) 3. Which output is affected by air temperature and altitude? A. Hydro B. CCGT C. Both equally D. Neither Answer: B. CCGT output falls with temperature and altitude; hydro is unaffected. (Key point: Ambient effect) 4. Why is hydro preferred in Nepal? A. Nepal has large domestic gas B. Large hydro potential and no domestic gas, so CCGT would use costly imported fuel C. CCGT has no emissions D. Hydro starts slower Answer: B. Hydro is abundant; CCGT depends on imported fuel. (Key point: Suitability for Nepal) ## Related in Power Plant Design - [Operational characteristics of combined cycle plant](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Accgt-operational-characteristics) — Power Plant Design, chapter 1 - [Geothermal versus conventional thermal plant](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Ageothermal-vs-thermal) — Power Plant Design, chapter 1 - [Thermal versus nuclear power plant](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Athermal-vs-nuclear) — Power Plant Design, chapter 1, asked 2× - [Tidal versus wind power plant](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Atidal-vs-wind) — Power Plant Design, chapter 1 - [Hydro versus thermal: techno-economic and environmental](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Ahydro-vs-thermal-techno-economic) — Power Plant Design, chapter 1 - [Solar versus hydro operational characteristics](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Asolar-vs-hydro-economics) — Power Plant Design, chapter 1, asked 5× ## Related in other subjects - [Reheat gas turbine power plant](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Agt-reheat-plant) — Power Plant Equipment, chapter 6 - [Open cycle gas turbine with intercooling](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Agt-intercooling-sketch) — Power Plant Equipment, chapter 6 - [Working of combined gas-steam plant](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Acombined-gas-steam-working) — Power Plant Equipment, chapter 8 - [Open cycle gas turbine on heavy oil](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Agt-heavy-oil-capacity) — Power Plant Equipment, chapter 6