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Energy Yield of Concentrated Solar Thermal (CST) Power Plants

When estimating the energy yield, we take into account the energy losses that occur along the system.

Energy Losses in CST Systems

Most of the 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 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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