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Solar electricity generation system (SEGS) which employs cascade steam-organic Rankine cycle (SORC) and steam screw expander (SE) is promising due to the high efficiency at moderate heat source temperature. This paper puts a special emphasis on heat storage and thermo-economic evaluation. Preferable operating temperature of the system is first clarified on the basis of SE characteristics. The temperature-dependent permissible stress of steam accumulator is modelled and the capital cost is investigated. Comparison between the direct steam generation (DSG) SEGS and an indirect one using thermal oil is made at a power capacity of 1 MW and storage of 6.5 h. The results indicate the DSG system has both thermodynamic and economic superiorities. The hot side temperature (THTH) of SORC generally does not exceed 250 °C to achieve an optimum solar thermal power efficiency. Given radiation of 750 W/m2, the maximum efficiency (ηT,mηT,m) is 14.3% with a corresponding THTH around 240 °C. The material cost of pressure vessels is 2.55 million RMB. For the indirect system, the optimal THTH is about 230 °C and ηT,mηT,m approximates to 13.2% and the estimated oil cost is 7.92 million RMB. It is recommended to adopt steam accumulators in the SE-driven SEGS.

An innovative solar thermal power generation system using cascade steam-organic Rankine cycle (SORC) and two-stage accumulators has recently been proposed. This system offers a significantly higher heat storage capacity than conventional direct steam generation (DSG) solar power plants. The steam condensation temperature (

Existing commercial parabolic trough power plants use thermal oil as a heat transfer fluid, with working temperatures in the region of 400 °C. In order to achieve more efficient generating systems, a second generation of parabolic troughs that operate at temperatures higher than 400 °C is being developed. One possibility Abengoa Solar is assessing is the use of direct steam generation (DSG) inside parabolic troughs in order to achieve higher temperatures; in a first stage heating up to 450 °C and in a second stage heating up to 550 °C. For the future market potential of parabolic trough power plants with DSG, it is beneficial to integrate thermal energy storage (TES) systems. Different TES options based on the most known technologies, steam accumulators, molten salts (MS), and phase change materials (PCM), are presented and compared in this paper. This comparison shows as main conclusion of the study that a combined system based on PCM-MS has a clear advantage in the ratio with 6 or more equivalent hours of storage, while with lower than 6 h, steam accumulators are considered the best option. The work partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER)). Prof. Luisa F. Cabeza would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123). This project has received funding from the European Commission Seventh Framework Programme (FP/2007-2013) under Grant agreement N°PIRSES-GA-2013-610692 (INNOSTORAGE) and from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 657466 (INPATH-TES).

Five different tillage systems were researched in a Cambisol of a loam texture in the long-term experiment: conventional ploughing at 22–24 cm (CT), shallow ploughing at 16–18 cm (ShT), harrowing at 8–10 cm (MT1), harrowing at 14–16 cm (MT2), and no tilling (NT). The aim of this study was to determine how different tillage and inter-cropping influence the accumulation and distribution of SOC (soil organic carbon) and its compounds in different soil layers. SOC content changed depending on the soil tillage system and inter-crops used. Stratification ratios (SR) of SOC in the surface soil (0–10 cm) to that in the 10–20 cm (SR1) and 20–30 cm (SR2) were calculated. In our research, SR for SOC varied in the range from 0.97 to 1.35 for SR1 and from 1.02 to 1.99 for SR2. The main conclusion was that inter-crops increased the SOC accumulation in the 0–10 cm layer of all investigated treatments. It was concluded that different soil tillage systems and inter-crops influenced processes of soil carbon changes and affected OM humification in the soil. The formation of humified carbon compounds should be considered not only as a preservation and improvement of the soil productivity, but also as an environmental assessment of their impact on the soil sustainability and reduction in carbon dioxide emissions into the atmosphere. Our results suggest that sustainable tillage and inter-cropping management may contribute to climate mitigation regarding SOC accumulation in soil.

© 2018 Elsevier Ltd Steam accumulators are the only commercial solution for heat storage of direct steam generation (DSG) solar thermal power plants. Current accumulators have low storage capacity as the turbine suffers from inefficient off-design operation during heat discharge, thereby restricting the development of DSG technology. This work presents a novel approach to solving this problem by using two-stage accumulators and steam-organic Rankine cycles (RC-ORC). The system involves unique two-step heat discharge. Heat is initially released via water vaporization in a high temperature accumulator (HTA) to drive the RC-ORC, leading to an HTA temperature drop of approximately 30 °C. Water at a reduced temperature then flows from the HTA to a low temperature accumulator through a heat exchanger and the heat is used only to drive the ORC. Water temperature further drops by 130–190 °C. The fundamentals of the system are illustrated. A comparison with the conventional DSG system is conducted at a nominal power of 10 MW with an accumulator volume of 2500 m3. Thermodynamic performance of the system is investigated. The equivalent payback period (EPP) regarding the use of the second step heat discharge is estimated. Results indicate that the second step heat discharge can increase the storage capacity by 460%, with an EPP of less than 5 years in most cases. Overall, the proposed solution improves the cost-effectiveness of the DSG system.