Current CSP plants typically include a condensing steam cycle power block which was preferably designed for a continuous operation and higher operating conditions and therefore, limits the overall plant cost effectiveness and deployment.
The drawbacks of this power block are as follows:
- no power generation during low insolation periods.
- expensive, large condenser (typically water cooled) due to the poor extracted steam properties (high specific volume, sub-atmospheric pressure).
- high installation and operation costs.
ASP has developed a new power block to eliminate these obstacles.
This power block includes a top Rankine cycle with a back pressure steam turbine and a bottoming Kalina cycle comprising another back pressure turbine and using ammonia-water mixture as a working fluid. The bottoming (moderate temperature) cycle allows power production during low insolation periods.
Because of the superior ammonia-water vapor properties, the condensing system requirements are much less demanding and the operation costs are lowered. Accordingly, air cooled condensers can be used with lower economical penalty.
Another advantage is that back pressure steam turbines have a less complex design than condensing steam turbines which make their costs lower. All of these improvements could make the combined cycle unit more cost effective.
This unit can be applicable in both parabolic trough and central receiver (solar tower) plants.
ASP Publication on New Power Block | 
 "Combined Rankine / Kalina Cycle for Trough")
 "Combined Cycle for Tower Plant")
