The efficiency of a coal-fired power station depends primarily on six factors: fuel quality, steam parameters, boiler and turbine efficiency, losses in the cooling system, the plant’s own consumption, and the actual operating mode of the unit. The highest values are achieved by modern ultra-supercritical hard coal units, and the lowest by older lignite-fired units. Data for units above 100 MWel show an approximate net efficiency of around 34% for old lignite-fired units and 36% for old hard coal-fired units. Of which approximately 38–39% net for the intermediate level, and approximately 43% net for modern lignite-fired units and 46% net for modern hard coal-fired units.
There is no single figure for the ‘efficiency of a coal-fired power station’. It is always necessary to determine whether the unit is old or new, what type of coal it uses, whether gross or net efficiency is being quoted, and whether it is operating at full load or at partial capacity. Two units with similar installed capacity may differ in efficiency by several, and sometimes even more than a dozen, percentage points.
Gross and net efficiency are not the same thing
This is the first point that clarifies the issue. The gross efficiency of a coal-fired power station indicates how much electricity the unit generates before deducting its own consumption. Net efficiency, on the other hand, indicates how much energy is actually left to feed into the grid after deducting the power consumed by pumps, fans, mills, flue gas treatment systems and other internal loads.
This is clearly illustrated by the example of the modern Dutch MPP3 power station. A study by CE Delft reports a gross electrical efficiency of around 48% and a net efficiency of around 46%. The difference of just 2 percentage points alone shows how much energy the unit consumes for its own needs. The same source also states a boiler efficiency of approximately 94.5% when burning hard coal. This clearly demonstrates that even a highly efficient boiler does not necessarily mean that the entire power station will be equally efficient.
Example: the efficiency of different types of blocks
| Vessel type | Approximate net efficiency |
|---|---|
| An old lignite-fired power station | approx. 34% |
| An old hard coal-fired power station | approx. 36% |
| Intermediate technical level block – brown | approx. 38% |
| Intermediate technical block – stone | approx. 39% |
| A modern lignite-fired power station | approx. 43% |
| A modern hard coal-fired power station | approx. 46% |
| Modern MPP3 – gross | approx. 48% |
| Modern MPP3 – net | approx. 46% |
The greatest lever: steam temperature and pressure
The greatest improvement in efficiency comes from enhancing the thermodynamic parameters of the steam cycle. The higher the temperature and pressure of the live steam, the greater the potential efficiency of the entire cycle. This is why older subcritical units are significantly less efficient than supercritical and ultra-supercritical units.
German sources report that, for modern reference units, a temperature of around 600°C enabled net efficiency of approximately 43% for lignite-fired units and around 46% for hard coal-fired units. At the same time, it was pointed out that further increases in efficiency require reaching levels of as high as around 700°C and approximately 350 bar. This, in turn, places very high demands on the materials used for the boiler, piping and fittings.
The Dutch documentation for Eemshaven describes this same logic explicitly: the temperature and pressure of the steam are set as high as corrosion and strength limitations allow. In practice, this means that the increase in efficiency is limited not only by thermodynamics, but primarily by the material capabilities of the boiler, piping and fittings.
The type of fuel makes a huge difference
A hard coal-fired power station generally has a better starting point than a lignite-fired one. The main reason is moisture. Lignite contains significantly more water and has a lower calorific value, so part of the energy generated is used not to produce useful steam, but to heat the fuel and evaporate the moisture.
A German study by ESYS indicates that the natural moisture content of lignite can be as high as around 60%, and that this can be reduced to around 12% after drying. This is one of the key factors in improving efficiency. The same report cites approximately 45% net as the best point for new lignite-fired units, and for further development options, as much as approximately 50% net.
This explains why a modern lignite-fired power station can be far superior to an old one, yet still tends to lose out to an equally modern hard coal-fired power station. The difference isn’t down solely to the boiler design. A large part of it lies in the fuel itself.
The boiler and turbine must operate as a system
The boiler itself cannot be viewed in isolation from the rest of the system. Even a very good combustion chamber and high boiler efficiency will not yield a satisfactory end result if the turbine, condenser and internal loads are poor.
For MPP3, a boiler efficiency of approximately 94.5% is stated, but the total net electrical efficiency is around 46%. This clearly illustrates how much energy is lost further down the power generation chain: in the turbine, generator, condensation process, auxiliary systems and flue gas treatment. The Eemshaven documentation identifies, among other things, large and efficient turbines, speed control where possible, and heat recovery and reuse as factors improving efficiency.
Cooling and the condenser consume huge amounts of energy
This is one of the most important practical considerations. In a conventional combined cycle power plant, a huge proportion of the energy is lost as waste heat, which is dissipated via the cooling system. Whilst this cannot be eliminated, the extent of these losses can be influenced by the design of the circuit, the condensation parameters and the cooling conditions.
This is very clearly evident in the energy balance of the modern Eemshaven power station. With an input of around 3,384 MW, the plant delivers approximately 1,560 MW net as electricity, around 1,550 MW goes to the cooling system, around 75 MW is consumed by the plant’s own operations, and around 135 MW accounts for other losses. This illustrates the scale: cooling and condensation are among the biggest sources of energy loss in the entire power station.
In practice, this means that efficiency is influenced not only by the unit itself, but also by local conditions. The temperature of the cooling water, the season, environmental constraints, the type of cooling tower and the pressure in the condenser all have a real impact on net efficiency. Dutch studies by TNO/ECN even indicated that cooling problems during very hot periods could reduce the efficiency of the units.
The main causes of efficiency losses
| Area | Typical impact |
|---|---|
| Low temperature and vapour pressure | reduce cycle efficiency |
| Moist lignite | increases losses during drying and combustion |
| Losses in the capacitor and cooling system | absorb a very large amount of energy |
| The power station’s own consumption | reduces the net efficiency relative to the gross efficiency |
| Part-load operation | reduces actual performance |
| CCS installation | may reduce efficiency by several to over ten percentage points |
Operating at partial load reduces efficiency
This is very important from an operational perspective. A power station may have good design efficiency, but its actual performance may be poorer if it frequently operates outside its optimum range. Coal-fired units perform best close to full load. When they are reduced to partial load, efficiency drops.
The Dutch organisation TNO/ECN reported that, as market conditions changed and units operated more frequently at partial load, their efficiency declined. This applies not only to the load itself, but also to more frequent starts, shutdowns and power adjustments. In practice, the ‘catalogue’ efficiency may be significantly better than the efficiency achieved by a unit that has to respond to market fluctuations.
This is particularly significant today, as some conventional units are increasingly operating as flexible system support – a role directly linked to the stability requirements of the power system – rather than as a conventional base load. In this mode, the unit operates less frequently under conditions close to its design point, so its actual efficiency declines.
Internal consumption can also take up a lot
The difference between gross and net efficiency does not stem from a single component, but from the sum of internal power consumption. In practice, these include feedwater pumps, air and flue gas fans, coal mills, flue gas treatment systems, desulphurisation, denitrification, fuel transport and other auxiliary equipment.
Taking MPP3 as an example, the difference between 48% gross and 46% net efficiency shows that even in a modern power unit, the plant’s own infrastructure consumes a significant proportion of the energy. Therefore, two units with a similar ‘hot’ section may differ in net efficiency simply because one has a more energy-intensive auxiliary system.
CCS can significantly reduce efficiency
If CO₂ capture is added to a power station, efficiency drops. And not just marginally. A German study from TUM shows that for a 460 MWel hard coal-fired power plant with 90% CO2 capture, efficiency drops by approximately 11.6 percentage points for the conventional MEA process and by approximately 4.1 percentage points for the chilled ammonia process.
That is a great deal. From an engineering perspective, CCS improves environmental performance but worsens energy efficiency. That is precisely why the efficiency of a power unit with and without CO₂ capture cannot be assessed in the same way. The mere presence of a CCS system alters the unit’s entire energy balance.
Why does lignite usually perform less well?
The advantage of hard coal over lignite stems mainly from the characteristics of the fuel itself. The higher moisture content and lower calorific value of lignite mean that a greater proportion of the process energy is lost during the fuel preparation and combustion stages. Consequently, even with similar technology, lignite-fired units usually achieve lower net efficiency. However, modern fuel drying techniques and improved cycle parameters can partially mitigate this difference.
What really boosts fitness the most?
The greatest improvement in efficiency is achieved by combining high steam parameters, good-quality fuel and minimising losses in cooling and internal consumption. Operating practices are also significant, as a unit operating stably and close to its design point usually achieves better results than one that is frequently taken off load. The final efficiency is therefore determined by the balance of the entire system, rather than by a single component of the installation.
Summary
The efficiency of a coal-fired power station is determined by the quality of the fuel, the parameters of the steam cycle and operational losses. The final result is primarily determined by steam parameters, fuel properties, cooling, internal consumption and the unit’s operating mode. In practice, two units of similar capacity may have significantly different net efficiencies. They differ in terms of fuel, technology and operating conditions. In modern units, efficiency can reach around 46–48%, whilst older units tend to remain at around 34–36%. With the addition of CCS, efficiency may fall by a further few to over ten percentage points.
FAQ – Efficiency of a coal-fired power station
No. Electrical efficiency shows what proportion of the fuel’s energy is converted into electricity. Overall efficiency may be higher if some of the waste heat is additionally utilised, for example in combined heat and power generation.
Yes. Desulphurisation, denitrification and dust removal installations, as well as auxiliary systems, consume energy for their own needs. This reduces net efficiency, i.e. the amount of energy actually fed into the grid.
Yes. Older units usually operate at lower steam parameters, have less modern turbines and suffer greater losses in the thermal system. Additionally, wear and tear, fouling of heat exchange surfaces and a decline in equipment efficiency worsen the actual performance.
Not always, but large and modern units usually have an advantage over smaller and older ones. This is due to better operating parameters, more efficient turbines and the economies of scale of the entire system. However, installed capacity alone does not guarantee high efficiency.
Yes, although the extent of the reduction depends on the capture technology. A CCS installation consumes additional energy and increases the unit’s own load. For this reason, net efficiency after the implementation of CO2 capture is significantly lower than without it.
Sources:
Federal Environment Agency: https://www.umweltbundesamt.de/system/files/medien/1410/publikationen/171207_uba_hg_braunsteinkohle_bf.pdf
CE Delft: https://ce.nl/wp-content/uploads/2021/03/CE_Delft_3J22_CO2-reduction_at_a_modern_coal-fired_power_station_Def.pdf
ESYS: https://energiesysteme-zukunft.de/fileadmin/user_upload/Publikationen/PDFs/ESYS_Technologiesteckbrief_Konventionelle_Kraftwerke.pdf
Eemshaven documentation: https://repository.officiele-overheidspublicaties.nl/externebijlagen/exb-2021-19021/1/bijlage/exb-2021-19021.pdf
