Energy Yield of Concentrated Solar Thermal (CST) Power Plants
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:
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
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.