# Steam turbines and thermal power plants: Engineering methods

From giant coal units to small waste-heat engines

Source page: https://www.materialinsights.org/energy/e_steam_turbines/methods/

What this tab covers The engineering methods that can do this conversion, compared on efficiency, scale, economics, limitations and reliability.

All these methods are heat engines; they differ in the fuel, the working fluid and the temperature of the heat they can use.

#### Comparison

| Method | Efficiency | Scale | Economics | Limitations | Reliability |
|---|---|---|---|---|---|
| **Coal power plant (subcritical to ultra-supercritical)**^[1](https://www.eia.gov/electricity/annual/html/epa_08_01.html)^[2](https://www.powermag.com/chinas-pingshan-phase-ii-sets-new-bar-as-worlds-most-efficient-coal-power-plant)^[3](https://www.lazard.com/media/uounhon4/lazards-lcoeplus-june-2025.pdf)^[5](https://www.enerdata.net/publications/daily-energy-news/harbin-electric-wins-bids-two-2-gw-coal-fired-power-projects-china.html)^[16](https://www.eia.gov/analysis/studies/powerplants/capitalcost/pdf/capital_cost_AEO2025.pdf)^[20](https://www.power-eng.com/business/policy-and-regulation/nerc-conventional-generation-outages-rose-as-reliability-risks-become-more-systemwide/) | about 32% average US fleet (calculated, HHV); 49.37% best (LHV) | a few hundred MW to 1,350 MW per unit (Pingshan II); EIA's reference plant is 650 MW | USD 71-173/MWh new build (US) | Highest CO2 per MWh; slow to start; large water use. | Weighted forced outage rate of North American coal units rose from 11.2% in 2024 to 14.1% in 2025; Pingshan II tested below 20% of rated load; plants run 40 years or more. |
| **Oil-fired plant**^[1](https://www.eia.gov/electricity/annual/html/epa_08_01.html) | about 31% average for US petroleum plants (calculated from 10,969 Btu/kWh) | tens to hundreds of MW | Fuel costs much more per unit of heat than coal or gas. | Expensive fuel and high emissions. | Proven, but mostly run as peaking or emergency supply. |
| **Rankine cycle in nuclear, biomass and waste plants**^[1](https://www.eia.gov/electricity/annual/html/epa_08_01.html)^[10](https://arabellesolutions.com/our-technology/generators-for-nuclear-power-plants/gigatop-generators) | about 33% for US nuclear (calculated from 10,443 Btu/kWh) | a few MW (biomass) to the largest reactors, whose generators reach 2,250 MVA | Dominated by the heat source's capital cost. | Lower steam temperature limits efficiency. | Turbine-generator sets run for decades; the GIGATOP generator design has more than 50 years of service history. |
| **Organic Rankine and Kalina cycles**^[6](https://re.public.polimi.it/retrieve/629bcfbb-9b26-41cb-883b-c5ddbf134764/The%20organic%20Rankine%20cycle%20power%20systems%20market%20Recent%20developments.pdf)^[7](https://task33.ieabioenergy.com/wp-content/uploads/sites/33/2022/07/06Bini-Turboden.pdf)^[21](https://www.power-eng.com/operations-maintenance/kalina-cycle-enjoying-commercial-success/) | about 16-20% net for biomass ORC | about 1 kW to 35 MW; geothermal units average about 13 MW, but half are below 4.5 MW; Kalina example: Husavik, 2 MW | About 4.1 GW installed in more than 2,700 plants by 2020 (the paper's abstract says 4.5 GW); a 375 kW unit's equipment cost is about 70% turbine-generator, 30% heat exchangers. | Low efficiency from low-temperature heat; some fluids are flammable or greenhouse gases. | Over 98% availability at a reference biomass plant; runs down to 10% load. |
| **Stirling, hot-air and thermoacoustic engines**^[8](https://newsreleases.sandia.gov/releases/2008/solargrid.html)^[9](https://sites.science.oregonstate.edu/~hetheriw/energy/topics/doc/thermo/heat_eng/Stirling_engine/thermoacoustic-Stirling.heat.engine.detailed.study.j.acous.soc.2000.pdf) | 31.25% sunlight-to-grid record; 30% heat-to-acoustic | under 1 kW (laboratory thermoacoustic) to 26.75 kW net from the record Stirling dish | Not commercially competitive for grid power. | Bulky heat exchangers and high cost per kW. | Sealed hydrogen or helium must not leak; few long-run field data. |

Efficiency rises with the temperature of the heat: coal and oil steam at about 600 C give 31-49%, nuclear steam about 33%, organic cycles running on low-grade heat about 20% at best. Scale follows the same pattern, from gigawatt coal and nuclear units down to kilowatt ORC and Stirling machines. Coal steam plants are mature and reliable but carry high capital costs and the most CO2, so their economics depend on running many hours. ORC is the practical way to make power from low-grade heat; Stirling and thermoacoustic engines remain niche despite good laboratory efficiency.

#### How each method works
**Coal power plant (subcritical to ultra-supercritical)**

Pulverised coal burns in a tall boiler lined with water tubes. Supercritical designs run above water's critical pressure, so water turns to steam without boiling, allowing hotter, more efficient steam.
**Oil-fired plant**

Same boiler and turbine cycle burning heavy fuel oil, or diesel engines and turbines burning distillates. Now mainly islands, the Middle East and backup.
**Rankine cycle in nuclear, biomass and waste plants**

The same water-steam loop with heat from a reactor, a biomass grate or a waste incinerator. Nuclear steam is cooler than coal steam, so efficiency is lower.
**Organic Rankine and Kalina cycles**

A refrigerant-like organic fluid or an ammonia-water mix replaces water so low- and medium-temperature heat can drive a compact turbine. Popular for geothermal and factory waste heat.
**Stirling, hot-air and thermoacoustic engines**

A sealed gas is heated and cooled from outside the engine; its expansion drives a piston or, in thermoacoustic engines, a standing sound wave with almost no moving parts.

#### Sources

1. [Electric Power Annual, Table 8.1: Average Operating Heat Rate for Selected Energy Sources, 2015 through 2025](https://www.eia.gov/electricity/annual/html/epa_08_01.html) US Energy Information Administration, 2026
2. [China's Pingshan Phase II Sets New Bar as World's Most Efficient Coal Power Plant](https://www.powermag.com/chinas-pingshan-phase-ii-sets-new-bar-as-worlds-most-efficient-coal-power-plant) POWER Magazine, 2023
3. [Lazard's Levelized Cost of Energy+ (LCOE+), June 2025](https://www.lazard.com/media/uounhon4/lazards-lcoeplus-june-2025.pdf) Lazard, 2025
4. [Harbin Electric wins bids for two 2 GW coal-fired power projects in China](https://www.enerdata.net/publications/daily-energy-news/harbin-electric-wins-bids-two-2-gw-coal-fired-power-projects-china.html) Enerdata, 2024
5. [The organic Rankine cycle power systems market: Recent developments and future perspectives (Wieland, Schifflechner, Dawo, Astolfi), Applied Thermal Engineering 224](https://re.public.polimi.it/retrieve/629bcfbb-9b26-41cb-883b-c5ddbf134764/The%20organic%20Rankine%20cycle%20power%20systems%20market%20Recent%20developments.pdf) Elsevier (author copy, Politecnico di Milano), 2023
6. [State of the art of ORC technology for biomass plants (R. Bini, Turboden)](https://task33.ieabioenergy.com/wp-content/uploads/sites/33/2022/07/06Bini-Turboden.pdf) IEA Bioenergy Task 33 workshop, 2010
7. [Sandia, Stirling Energy Systems set new world record for solar-to-grid conversion efficiency](https://newsreleases.sandia.gov/releases/2008/solargrid.html) Sandia National Laboratories, 2008
8. [A thermoacoustic-Stirling heat engine: Detailed study (Backhaus and Swift), J. Acoust. Soc. Am. 107(6)](https://sites.science.oregonstate.edu/~hetheriw/energy/topics/doc/thermo/heat_eng/Stirling_engine/thermoacoustic-Stirling.heat.engine.detailed.study.j.acous.soc.2000.pdf) Los Alamos National Laboratory / Acoustical Society of America, 2000
9. [GIGATOP generators](https://arabellesolutions.com/our-technology/generators-for-nuclear-power-plants/gigatop-generators) Arabelle Solutions, 2025
10. [Capital Cost and Performance Characteristics for Utility-Scale Electric Power Generating Technologies (AEO2025 capital cost study)](https://www.eia.gov/analysis/studies/powerplants/capitalcost/pdf/capital_cost_AEO2025.pdf) US Energy Information Administration, 2025
11. [NERC: Conventional generation outages rose as reliability risks become more systemwide (2026 State of Reliability)](https://www.power-eng.com/business/policy-and-regulation/nerc-conventional-generation-outages-rose-as-reliability-risks-become-more-systemwide/) Power Engineering, 2026
12. [Kalina cycle enjoying commercial success](https://www.power-eng.com/operations-maintenance/kalina-cycle-enjoying-commercial-success/) Power Engineering, 2002

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_steam_turbines/index.md)
- [Overview](https://www.materialinsights.org/energy/e_steam_turbines/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_steam_turbines/correlation/index.md)
- [Science and limits](https://www.materialinsights.org/energy/e_steam_turbines/science/index.md)
- [Value chain](https://www.materialinsights.org/energy/e_steam_turbines/valuechain/index.md)
- [Unit economics](https://www.materialinsights.org/energy/e_steam_turbines/economics/index.md)
- [Equipment and suppliers](https://www.materialinsights.org/energy/e_steam_turbines/equipment/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_steam_turbines/links/index.md)