For the future market potential of parabolic trough power plants with direct steam generation (DSG), it is beneficial to integrate a thermal storage system. Heat storage media based on phase change materials offer heat transfer at constant temperatures needed for the evaporation process. Different options for a plant layout are presented and discussed. The interactions between the three subsystems—solar field, power block, and thermal storage—are analyzed, and boundary conditions arising from the thermal storage system are identified. Compared with a system without storage the number of operating points increases significantly since different combinations of storage charge and discharge operations go along with a varying power output of the solar field. It is shown that the large number of theoretical operating points can be reduced to a subset with practical relevance. Depending on the live steam parameters a reheat is necessary within the power block. Compared with parabolic trough fields with a single phase heat transfer medium such as oil, a special heat exchanger configuration is needed for a DSG plant. Different alternatives based on available technologies are presented and evaluated.

In recent years, linear Fresnel (LF) collector systems have been developed as a technical alternative to parabolic trough (PT) collector systems. While in the past, LF systems focused on low- and medium-temperature applications, today, LF systems are equipped with vacuum receivers and, therefore, can be operated with similar operating parameters as PT systems. Papers about the technical and economical comparison of specific PT and LF systems have already been published (Dersch et al., 2009, "Comparison of Linear Fresnel and Parabolic Trough Collecor Systems—System Analysis to Determine Break-Even Costs of Linear Fresnel Collectors," Proceedings of the 15th International SolarPACES Symposium, Berlin; Giostri et al. 2011, "Comparison of Two Linear Collectors in Solar Thermal Plants: Parabolic Trough vs. Fresnel," ASME 2011 5th International Conference on Energy Sustainability, Washington, DC; and Morin et al., 2012, "Comparison of Linear Fresnel and Parabolic Trough Collector Power Plants," Sol. Energy, 86(1), pp. 1–12). However, the present paper focuses on the systematic differences in optical and thermodynamic performance and the impact on the economic figures. In a first step the optical performance of typical PT and LF solar fields (SFs) has been examined, showing the differences during the course of the day and annually. Furthermore, the thermodynamic performance, depending on the operating temperature, has been compared. In a second step, the annual electricity yield of typical PT and LF plants has been examined. Solar Salt has been chosen as the heat transfer fluid. Both systems utilize the same power block (PB) and storage type. Solar field size, storage capacity, and PB electrical power are variable, while all examined configurations achieve the same annual electricity yield. As expected for molten salt systems, both systems are the most cost-effective with large storage capacities. The lower thermodynamic performance of the LF system requires a larger SF and lower specific SF costs in order to be competitive. Assuming specific PT field costs of 300 €/m² aperture, the break-even costs of the LF system with Solar Salt range between 202 and 235 €/m², depending on the site and storage capacity. In order to confirm the major statements, within a sensitivity analysis, it is shown that a variation of SF and storage costs does not have a significant impact on the relative break-even costs of the LF system.

This paper gives an overview on the SolarPACES guideline for Bankable STE Yield Assessment which was published in January 2017 by SolarPACES. After summarizing the history of the standardization activity behind this document, on overview on the content and its key elements is given. The paper ends by addressing the various players involved in STE yield assessment and how they can make benefit from applying this guideline in their day-to-day work. The document is available for free download from SolarPACES at http://www.solarpaces.org/yield-analysis-guideline.

In solar thermal power plants, at least the solar part undergoes a daily start-up process. Since duration and energy consumption of the start-up depend on irradiance and temperature boundary conditions, differences occur between the individual days and especially between the seasons. For a good representation in annual electricity yield calculations, the start-up process should be modeled on a daily basis. This paper presents a closed approach for the calculation of start-up and cool-down in solar thermal power plants especially designed for annual calculations. It is demonstrated by one example how the required parameters can be obtained and how the methodology is applied. A sensitivity analysis reveals the large impact of start-up consumption on the annual yield.

This study focuses on the techno-economic optimization of direct molten salt parabolic trough solar thermal power plants (STPPs) equipped with thermocline filler (TCF) thermal energy storage (TES). On one hand, this technology allows for cost reductions compared with state of the art two-tank (2T) TES. On the other hand, however, it leads to a performance decrease of the power block (PB) due to partial part load operation. To evaluate the dominating effect, annual simulations on a system level are performed for the TCF direct molten salt storage concept and, as a reference, for the two-tank direct molten salt storage concept. The levelized cost of electricity (LCOE) serves as a global measure to compare the two systems and to optimally size the TCF storage and the solar field (SF). The result of this study is that LCOE can theoretically be reduced by up to 8% by using a TCF instead of 2T storage system. The influence of temperature deviations from the nominal value at the end of charge or discharge, porosity and particle diameter of the TCF on LCOE, and system behavior is investigated in detail. This study further presents alternative operation strategies with improved system behavior and reveals determining factors for the integration of TCF storage into a system.