30% more efficient solar thermal power plants

© 2011 Courtesy of ASME

The efficiency of solar thermal power plants is improved by more than 30% thanks to the combination of two technologies.

EPFL’s Industrial Energy Systems Laboratory (LENI), under the leadership of EPFL professor Daniel Favrat, has demonstrated an efficiency improvement of 31% by combining two types of solar thermal power plants: parabolic trough and central tower systems. Based on a central tower plant with 15.2% efficiency and a trough plant of 12.9%, the study has shown an overall efficiency of 16.9% for a trough/tower combined plant of 80MWe. These results were awarded the EPFL Zanelli price for technology and sustainable development, and were presented to the World Engineers’ Convention (WEC) 2011 in Geneva.

As more and more solar thermal power plants are in operation, under construction and under planning in sunny regions such as South Spain, North Africa and California, effort is put both on development and on innovation to bring costs down and increase systems efficiency. Thanks to heat storage, solar thermal plants are able to operate nicht and day, which solves the issue of grid stability.

In order to demonstrate the interest of combining solar trough and solar tower plants, both systems have been integrated into each other for plants up to 100MWe. The lower temperature (400°C) of the parabolic trough collectors is used to evaporate the water that feeds a steam turbine. The high temperature (1000°C) at the tower receiver is used to operate a hot air turbine and to superheat the steam. Both the hot air turbine and the steam turbine are connected to the grid. Thus the combination itself, without improving the individual systems, allows a 31% improvement with respect to a 12.9% efficient trough plant and keeps an electricity cost of 8.8USct/kWhe.

Sources:

• J. López Moreno and G. Augsburger. Thermo-Economic Optimization of a Tower-Trough Combination Thermal Solar Power Plant. In Proceedings of the 4th World Engineers’ Convention, 2011.
• J. Spelling, D. Favrat, A. Martin and G. Augsburger. Thermoeconomic optimization of a combined-cycle solar tower power plant, in Energy, 2011.