Stefano Giuliano

Analysis of Solar-Thermal Power Plants With Thermal Energy Storage and Solar-Hybrid Operation Strategy

Selected solar-hybrid power plants for operation in base-load as well as midload were analyzed regarding supply security (dispatchable power due to hybridization with fossil fuel) and low CO2 emissions (due to integration of thermal energy storage). The power plants were modeled with different sizes of solar fields and different storage capacities and analyzed on an annual basis. The results were compared to each other and to a conventional fossil-fired combined cycle in terms of technical, economical, and ecological figures. The results of this study show that in comparison to a conventional fossil-fired combined cycle, the potential to reduce the CO2 emissions is high for solar-thermal power plants operated in base-load, especially with large solar fields and high storage capacities. However, for dispatchable power generation and supply security it is obvious that in any case a certain amount of additional fossil fuel is required. No analyzed solarhybrid power plant shows at the same time advantages in terms of low CO2 emissions and low levelized electricity cost (LEC). While power plants with solar-hybrid combined cycle (SHCCVR , Particle-Tower) show interesting LEC, the power plants with steam turbine (Salt-Tower, Parabolic Trough, CO2-Tower) have low CO2 emissions.

Design and Operational Aspects of Gas and Steam Turbines for the Novel Solar Hybrid Combined Cycle SHCC

Solar hybrid power plants are characterized by a combination of heat input both of high temperature solar heat and heat from combustion of gaseous or liquid fuel which enables to supply the electricity market according to its requirements and to utilize the limited and high grade natural resources economically. The SHCC® power plant concept integrates the high temperature solar heat into the gas turbine process and in addition — depending on the scheme of the process cycle — downstream into the steam cycle. The feed-in of solar heat into the gas turbine is carried out between compressor outlet and combustor inlet either by direct solar thermal heating of the pressurized air inside the receivers of the solar tower or by indirectly heating via interconnection of a heat transfer fluid. Thus, high shares of solar heat input referring to the total heat input of more than 60% in design point can be achieved. Besides low consumption of fossil fuels and high efficiency, the SHCC® concept is aimed for a permanent availability of the power plant capacity due to the possible substitution of solar heat by combustion heat during periods without sufficient solar irradiation. In consequence, no additional standby capacity is necessary. SHCC® can be conducted with today’s power plant and solar technology. One of the possible variants has already been demonstrated in the test field PSA in Spain using a small capacity gas turbine with location in the head of the solar tower for direct heating of the combustion air. However, the authors present and analyze also alternative concepts for power plants of higher capacity. Of course, the gas turbine needs a design which enables the external heating of the combustion air. Today only a few types of gas turbines are available for SHCC® demonstration. But these gas turbines were not designed for solar hybrid application at all. Thus, the autors present finally some reflections on gas turbine parameters and their consequences for SHCC® as basis for evaluation of potentials of SHCC® .Copyright

Assessment of mid-term growth assumptions and learning rates for comparative studies of CSP and hybrid PV-battery power plants

The main objective of this research is to present a solid foundation of capex projections for the major solar energy technologies until the year 2030 for further analyses. The experience curve approach has been chosen for this capex assessment, which requires a good understanding of the projected total global installed capacities of the major solar energy technologies and the respective learning rates. A literature survey has been conducted for CSP tower, CSP trough, PV and Li-ion battery. Based on the literature survey a base case has been defined for all technologies and low growth and high growth cases for further sensitivity analyses. All results are shown in detail in the paper and a comparison to the expectation of a potentially major investor in all of these technologies confirmed the derived capex projections in this paper.The main objective of this research is to present a solid foundation of capex projections for the major solar energy technologies until the year 2030 for further analyses. The experience curve approach has been chosen for this capex assessment, which requires a good understanding of the projected total global installed capacities of the major solar energy technologies and the respective learning rates. A literature survey has been conducted for CSP tower, CSP trough, PV and Li-ion battery. Based on the literature survey a base case has been defined for all technologies and low growth and high growth cases for further sensitivity analyses. All results are shown in detail in the paper and a comparison to the expectation of a potentially major investor in all of these technologies confirmed the derived capex projections in this paper.

Parameterization of High Solar Share Gas Turbine Systems

Existing solar thermal power plants are based on steam turbine cycles. While their process temperature is limited, solar gas turbine (GT) systems provide the opportunity to utilize solar heat at a much higher temperature. Therefore there is potential to improve the efficiency of future solar thermal power plants. Solar based heat input to substitute fuel requires specific GT features. Currently the portfolio of available GTs with these features is restricted. Only small capacity research plants are in service or in planning. Process layout and technology studies for high solar share GT systems have been carried out and have already been reported by the authors. While these investigations are based on a commercial 10MW class GT, this paper addresses the parameterization of high solar share GT systems and is not restricted to any type of commercial GT. Three configurations of solar hybrid GT cycles are analyzed. Besides recuperated and simple GT with bottoming Organic Rankine Cycle (ORC), a conventional combined cycle is considered. The study addresses the GT parameterization. Therefore parametric process models are used for simulation. Maximum electrical efficiency and associated optimum compressor pressure ratio πC are derived at design conditions. The pressure losses of the additional solar components of solar hybrid GTs have a different adversely effect on the investigated systems. Further aspects like high ambient temperature, availability of water and influence of compressor pressure level on component design are discussed as well. The present study is part of the R&D project Hybrid High Solar Share Gas Turbine Systems (HYGATE) which is funded by the German Ministry for the Environment, Nature and Nuclear Safety and the Ministry of Economics and Technology.

LCOE reduction potential of parabolic trough and solar tower CSP technology until 2025

Concentrating Solar Power (CSP), with an installed capacity of 4.9 GW by 2015, is a young technology compared to other renewable power generation technologies. A limited number of plants and installed capacity in a small challenging market environment make reliable and transparent cost data for CSP difficult to obtain. The International Renewable Energy Agency (IRENA) and the DLR German Aerospace Center gathered and evaluated available cost data from various sources for this publication in order to yield transparent, reliable and up-to-date cost data for a set of reference parabolic trough and solar tower plants in the year 2015 [1]. Each component of the power plant is analyzed for future technical innovations and cost reduction potential based on current R&D activities, ongoing commercial developments and growth in market scale. The derived levelized cost of electricity (LCOE) for 2015 and 2025 are finally contrasted with published power purchase agreements (PPA) of the NOOR II+III power plants in Moroc...

16 – Central tower systems using the Brayton cycle

Solar-hybrid gas-turbine (SHGT) systems are a promising alternative to conventional solar thermal power plants, as gas turbine systems are cost effective and can reach higher efficiencies than steam cycles. Therefore, SHGT systems offer the potential for future reduction of solar electricity cost, while providing full dispatchability with the integrated hybrid option. Additional advantages are the reduced water consumption, the integrated hybrid option, fast system response, and simple plant control. Past developments in SHGT systems are summarized, and the actual status of the technology is discussed. The requirements for adaptation of commercial gas turbines and for the associated high-temperature receivers are outlined. Several configurations for the gas turbine cycle are described. Results of thermodynamic and techno-economic studies are discussed, supporting the economic potential of SHGT systems.

Modelling, Simulation and Assessment of Solar Thermal Power Plants: A First Step Towards Definition of Best Practice Approaches

With 620 MWel in operation [1] and more than 2.000 MWel under construction, concentrated solar power (CSP) experiences a renaissance mainly in Spain and the USA, but also in many other countries in the earth’s sunbelt. Due to their large capacity (50 MWel and more) and thus large investment, CSP projects are characterised by an extensive project development process. In several stages of this process, mathematical models of the system predicting its energy yield are required, among others to: • assess single CSP projects (e.g., feasibility or due diligence studies), • compare different CSP concepts (e.g., technology, site), • optimise a project (e.g., solar field size, storage capacity), • investigate the influence of component characteristics (e.g., receiver characteristics), • optimise the operation strategy (e.g., on-line surveillance) or to • assess system performance during commissioning. The models used for these different tasks differ in complexity and accuracy, e.g. the accuracy of a model used for project assessment during commissioning has to be higher than a model used for a pre-feasibility study. At the moment, numerous modelling approaches exist and every project developer uses his own system model and assessment methodology. This confusing situation hinders the acceptance of CSP technology by potential investors. This paper presents a methodology for structuring systems into sub-systems. This is the first step towards a standardized modelling approach for CSP systems. It is not the intention of the authors to present a final model and assessment methodology but to start a broader discussion on this important topic. In fact, it aims at initiating an international working group, devoted to the definition of guidelines for modelling, simulation and assessment of CSP systems, covering all CSP technologies such as solar towers, parabolic troughs, linear Fresnel collectors and solar dishes.Copyright

Atmospheric Extinction in Simulation Tools for Solar Tower Plants

Atmospheric extinction causes significant radiation losses between the heliostat field and the receiver in a solar tower plants. These losses vary with site and time. State of the art is that in ray-tracing and plant optimization tools, atmospheric extinction is included by choosing between few constant standard atmospheric conditions. Even though some tools allow the consideration of site and time dependent extinction data, such data sets are nearly never available. This paper summarizes and compares the most common model equations implemented in several ray-tracing tools. There are already several methods developed and published to measure extinction on-site. An overview of the existing methods is also given here. Ray-tracing simulations of one exemplary tower plant at the Plataforma Solar de Almeria (PSA) are presented to estimate the plant yield deviations between simulations using standard model equations instead of extinction time series. For PSA, the effect of atmospheric extinction accounts for losses between 1.6 and 7 %. This range is caused by considering overload dumping or not. Applying standard clear or hazy model equations instead of extinction time series lead to an underestimation of the annual plant yield at PSA. The discussion of the effect of extinction in Tower plants has to include overload dumping. Situations in which overload dumping occurs are mostly connected to high radiation levels and low atmospheric extinction. Therefore it can be recommended that project developers should consider site and time dependent extinction data especially on hazy sites. A reduced uncertainty of the plant yield prediction can significantly reduce costs due to smaller risk margins for financing and EPCs. The generation of extinction data for several locations in form of representative yearly time series or geographical maps should be further elaborated.

The first version of the SolarPACES guideline for bankable STE Yield assessment

The yield assessment guideline project has reached another milestone by the publication of the first version of the guideline (in 2016) as a SolarPACES report. It is the first document of its kind that systematically addresses the vital aspects of STE yield assessment and lists minimum requirements for high quality yield assessment. In the future, the guideline main document will be supported by a number of working documents which provide more details on modeling approaches.

Steps towards a CSP yield calculation guideline: A first draft for discussion in the SolarPACES working group guiSmo

This paper provides an overview on an important step towards a SolarPACES guideline for CSP yield calculation. With the increasing number of CSP installations, standardization becomes more and more important for further reduction of costs and increase in quality. Yield calculation is a key issue throughout all phases of project development and throughout most of the involved players. Due to the need for more complex process models for CSP compared to other renewables like PV or wind, the yield calculation procedure is more demanding. Uncertainties in the process are covered by additional but partially unnecessary risk surcharges since systematic approaches for avoiding expensive redundancies in risk buffers are not available. It is the main motivation of the mentioned CSP yield calculation guideline to overcome this situation by providing a detailed methodology for yield calculation. A first comprehensive draft version has been compiled and will be subject of discussion in the SolarPACES working group gui...