The main goal of the Competitive Solar Power Towers (CAPTure) project is to significantly reduce costs of concentrated solar power (CSP), in order to pave the way for its deserved competitiveness on the power market.
In order to increase plant efficiencies and reduce levelized cost of electricity (LCOE), the project will develop all relevant components that allow implementing an innovative plant configuration.
Figure 1: The CAPTure plant configuration is based on a multi-tower decoupled advanced solar combined cycle approach
This plant configuration is based on a multi-tower decoupled advanced solar combined cycle approach that not only increases cycle efficiencies but also avoids frequent transients and inefficient partial loads, thus maximizing overall efficiency, reliability as well as dispatchability, all of which are important factors directly related to cost competitiveness on the power market.
The innovative solar receiver will be an open volumetric receiver allowing operating temperatures beyond 1000 °C, providing the absorbed solar heat to the pressurized air circuit of the Brayton cycle via a network of fixed bed regenerative heat exchangers working in alternating modes (non-pressurized heating period, pressurized cooling period).
Figure 2: Alternative power plant layout: Solar powered combined cycle scheme with open volumetric air receiver and high-temperature TES upstream the gas turbine – The low-temperature TES enables regenerative use of return air heat.
Figure 2 shows a scheme of an alternative plant layout that is also analysed in WP1. In contrast to Figure 1, here the thermal energy storage system is placed upstream the gas turbine, allowing dispatchable operation of the combined cycle. This alternative solar powered combined cycle plant applies the same open volumetric air receiver technology, a high-temperature thermocline air/ceramic TES and the CAPTure regenerative system coupling the high-temperature atmospheric air stream with the pressurized air loop of the topping Brayton cycle. It must be emphasized that the temperature level of the “cold” return air stream leaving the air/air heat exchange system, is a function of compressor outlet temperature (i.e. compressor pressure ratio and ambient temperature) and the exit temperature of the first turbine stage, in the case of reheat. The resulting air-return temperature level is too high for efficient blower operation and the recirculation to the high-temperature TES or the receiver is thus not feasible. A low-temperature air/rock thermocline TES is thus proposed in order to reuse the return air heat in regenerative manner. In order to keep air transport parasitic power consumption acceptable, the operating temperature of the blower should be kept at ambient temperature level.
The global objective of this project is to increase concentrated solar power plant efficiencies and reduce levelised cost of electricity (LCOE) by developing the key components of an innovative plant configuration. This plant configuration is based on a multi-tower decoupled advanced solar combined cycle approach (see Figure 1 and Figure 2) that not only increases cycle efficiencies but also avoids frequent transients and inefficient partial loads, maximizing overall efficiency, reliability as well as dispatchability.
More specifically, CAPTure will focus on the following activities
- The development of an innovative, highly efficient open volumetric solar receiver:
• As of November 2016, first receiver prototypes are being tested at the PSA in the south of Spain
- A network of highly efficient fixed-bed regenerative heat exchangers working in alternating modes – atmospheric heating and pressurized cooling
• During the first half of 2017, the design of the system will be optimized and during the second half it will be manufactured and assembled
- A high efficiency two-stage, intercooled Brayton gasturbine cycle.
• Progress as of February 2017 includes a full thermodynamic model of a two-stage intercooled Brayton cycle. This model uses a hybrid of known performance for the low pressure and power turbine stages together with models developed for the high pressure and intercooler parts.
- Validation-scale prototypes for the key elements as well as a complete solar-receiver, regenerator and turbine unit will be developed and tested.
- Development of small-area downsized heliostats that will enable improved solar flux control at the solar receiver through automatic heliostat field calibration.
• An accurate cost effective small size heliostat has been developed based on low cost “off the shelf” available motors and low cost cable transmission.
- The complete theoretical assessment and optimisation of the modular multi-tower decoupled solar combined cycle concept (DSCC) for easing capital investments.
The solar receiver prototypes tests started in November 2016. The chosen test facility is the ‘’Plataforma Solar de Almería’’, a well-known solar test area in southern Spain, where all required infrastructure for the validation of the concept, such as an experimental tower and heliostat field are already available.: