Solar Power » Technologies

Energy Yield of Concentrated Solar Thermal (CST) Power Plants

Thermal Losses

In a CST power plant, most of the energy losses occur in the thermodynamic cycle that drives the turbine. The upper limit for efficiency of a thermodynamic process is given by the Carnot- efficiency:

Carnot Efficiency

Accordingly, the higher the input temperature and the bigger the difference in temperature between in and out, the higher the cycle's efficiency. With a high temperature of 560°C and a low temperature of 30°C (lake water cooling), which are typical values for a Rankine cycle, the theoretical maximum would be 64%. In practice, for plants operating with steam at subcritical pressures and steam temperatures of 560 °C, the Rankine cycle efficiency is around 43 %, but may be much lower..

Other Energy Losses in CST Systems

Energy Losses in CST SystemsOther significant losses stem from

  • the heat transfer fluid (~20%)
  • mirror reflection and concentration imperfections (~3%)
  • non-optimal tracking (~3%)
  • transfer fluid and heat exchanger (~20%),
  • mechanical losses in the turbine (~3%),
  • generator losses (~3%),
  • internal use of generated electricity for auxiliary equipment such as pumps (~6%) and
  • scheduled downtime (~2%)

In addition, there would be losses further downstream in transformers.

 

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