--- title: "Thermal, geothermal and PV plants compared" subject: "Power Plant Design" chapter: 1 key: "semester_8/power_plant_design:thermal-geothermal-pv" source: https://www.bctengineer.com/q/semester_8/power_plant_design/thermal-geothermal-pv site: BCT Engineering --- # Thermal, geothermal and PV plants compared Power Plant Design · Chapter 1: Energy Sources and Electric Power Generation - Asked in: 2071 Magh, 10 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/thermal-geothermal-pv - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-1 ## Question Compare the operational characteristics of thermal, geothermal and PV plant on the basis of reliability, grid connection, efficiency, operating range and maintainability. ## Short answer Thermal is firm, synchronous, 30–40% efficient, moderately flexible, but polluting with high fuel cost. Geothermal is steady base load with 80–90% capacity factor and only 10–20% efficiency, site-limited with corrosion issues. PV is intermittent, inverter-based, 15–20% capacity factor, low cost, simple maintenance, and clean. ## Answer **Thermal power plants** burn fossil fuel to raise steam; **geothermal plants** take steam or hot water from the earth's heat; **PV plants** convert sunlight directly into DC electricity using semiconductor cells. #### Working in brief ```text Thermal: Fuel -> Boiler -> Steam -> Turbine -> Gen Geotherm: Well -> Separator/HX -> Turbine -> Gen (brine reinjected) PV: Sun -> PV array -> Inverter -> Grid ``` #### Comparison | Basis | Thermal | Geothermal | Solar PV | |---|---|---|---| | Reliability | Firm and dispatchable if fuel is available; availability about 70–85% | Very steady; capacity factor about 80–90%; resource declines if brine is not reinjected | Only in sunshine; capacity factor about 15–20%; needs storage/backup | | Grid connection | Large synchronous units near load; provide inertia and reactive power | Synchronous units of 5–100 MW at remote geothermal fields; long lines may be needed | Inverter based; no inertia; harmonics, voltage rise and reverse flow; can connect at distribution level | | Efficiency | About 30–40% | About 10–20% | About 15–22% (module), system lower | | Operating range | Minimum stable load about 40–50%; slow start (hours); moderate ramp | Base load; little load-following ability | Output from zero to peak by irradiance; MPPT; not dispatchable | | Maintainability | Complex; boiler, coal and ash handling, cooling system; many skilled staff | Corrosion and scaling by dissolved minerals; well workovers | Very low; module cleaning, inverter replacement every 10–15 years; no moving parts | | Fuel cost | High | Nil | Nil | | Capital cost | Moderate | High (exploration and drilling risk) | Low and falling | | Construction time | 3–4 years | 3–6 years | Months | | Location | Flexible | Only at geothermal fields | Wherever there is sunshine and land/roof | | Environment | CO₂, SO₂, NOx, ash | Low; H₂S, minerals, land subsidence | Clean in operation; land use and panel disposal | | Life | 25–30 years | 30–50 years | About 25 years | #### Remarks - **Thermal**: most flexible in location and output, but high fuel cost and pollution. - **Geothermal**: ideal clean, firm base load where the resource exists; but inflexible (little load following) and site-limited. - **PV**: cheapest and simplest to build and maintain, but intermittent; best combined with hydro or storage. For Nepal, thermal is limited to diesel standby, geothermal is only at low-temperature hot springs (direct use), and PV is growing as a complement to run-of-river hydro. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is geothermal reliability described as very steady yet at risk over time? A. Capacity factor about 90%, but the resource may decline if brine is not reinjected B. It depends on sunshine C. Capacity factor is about 15-20% D. It needs imported fuel Answer: A. Geothermal gives about 90% capacity factor but the reservoir declines without reinjection. (Key point: Geothermal reliability) 2. What describes the thermal plant operating range? A. Can run from zero load instantly B. Base load only with no ramping C. Minimum stable load about 40-50%, slow start in hours D. Output follows irradiance Answer: C. Thermal plants have a minimum stable load about 40-50% and take hours to start. (Key point: Thermal operating range) 3. Why is PV maintenance very low? A. It has boilers needing little care B. It has no moving parts; only cleaning and inverter replacement every 10-15 years C. It has gearboxes that are sealed D. Wells need no workover Answer: B. PV has no moving parts, needing only module cleaning and periodic inverter replacement. (Key point: PV maintenance) 4. Which statement on location is correct? A. Geothermal can be built anywhere B. Thermal only at geothermal fields C. PV only near rivers D. Geothermal only at geothermal fields; thermal is flexible Answer: D. Geothermal is site-limited to geothermal fields while thermal location is flexible. (Key point: Location flexibility) ## Close variants set in other exams - [Thermal, geothermal and nuclear plants compared](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Athermal-geothermal-nuclear) — Power Plant Design, chapter 1, asked 7× - [Thermal, wind and PV plants compared](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Athermal-wind-pv) — Power Plant Design, chapter 1, asked 7× - [Thermal versus hydro operational characteristics](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Athermal-vs-hydro-operational) — Power Plant Design, chapter 1, asked 8× - [Thermal, hydro and solar PV plants compared](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Athermal-hydro-solar-pv) — Power Plant Design, chapter 1, asked 8× ## Related in Power Plant Design - [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× - [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 - [Solar PV versus hydro and their combination](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Asolar-pv-hydro-combination) — Power Plant Design, chapter 1 - [Hydropower versus solar PV in Nepal](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Ahydro-vs-solar-pv-nepal) — Power Plant Design, chapter 1 - [Grid-tied solar PV versus hydropower](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Agrid-tied-pv-vs-hydro) — Power Plant Design, chapter 1 - [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