Direct Steam Generation Solar Power Research Articles

Assessing parabolic trough collectors and linear Fresnel reflectors direct steam generation solar power plants in Northwest México

Concentrating solar power (CSP) systems offer promising solutions for harnessing solar energy. Parabolic trough collectors (PTC) are prevalent in CSP, but direct steam generation (DSG) in solar fields is an innovative alternative that eliminates the need for thermal oils. This study compares EuroTrough PTC and optimized linear Fresnel reflector (LFR) geometries for DSG for Mexican operating conditions. Two 10 MW Rankine cycles with two and three steam extractions are considered. The study evaluates 16 solar field configurations capable of delivering 400 °C superheated steam at 100 bar. Assessment parameters include effective concentration area, nominal loop inlet pressure, energy and exergy efficiency, and hypothetical thermal storage size. The findings strongly favor PTC solar fields with 14 loops, exhibiting superior performance. However, three-loop LFR configurations are suggested where pressure reduction prevails. Three-loop LFR arrays minimize land utilization for spatially constrained installations, while larger five-loop configurations optimize efficiency. Employing 14 PTC loops prioritizes thermal energy storage. In contrast, 8 PTC loops maximize storage capacity. The study underscores the advantages of Fresnel reflectors over parabolic troughs in specific scenarios, presenting avenues for future exploration. This analysis lays the groundwork for assessing these technologies in the distinctive context of Mexican operations, offering valuable insights into sustainable energy applications.

Modelling and performance evaluation of a direct steam generation solar power system coupled with steam accumulator to meet electricity demands for a hospital under typical climate conditions in Libya

This study aims to build a dynamic model of a direct steam generation (DSG) solar power system coupled with a steam accumulator to meet electricity demands for a hospital under transient environmental conditions in Libya. The main components of the system are DSG parabolic trough collectors, a steam accumulator, a turbine, a condenser and a circulation pump. The system is modelled via using Simulink\\Simscape software blocks with integrated MATLAB functions to run a dynamic simulation. As the simulation tool reflects the transient operation of the components, advanced control strategies were applied to the model. Using the proportional integral controller (PI controller), safe operation of the system is secured by pump flow rate control, safe turbine operation is provided by pressure control and power output is matched with the demand by using a throttle valve control. 1584 m2 solar collector area and 160 m3 total volume of pressurized steam tank are used in the simulation considering the electricity demand of the hospital and solar radiation in the location. The produced work output was controlled to match the demand profile of the hospital, which needs 200 kW in the peak period and 50 kW at the night. The designed system shows a maximum thermal efficiency of 23.5% for the operation condition.

Energy and Exergy (2E) Analysis of an Optimized Solar Field of Linear Fresnel Reflectors for a Conceptual Direct Steam Generation Power Plant

Direct steam generation is a promising alternative to conventional heat transfer fluids for solar thermal power plants using linear concentrators because water and steam do not have thermal and chemical stability problems. The novelty of this study, an energy and exergy (2E) analysis, was that it was performed on several configurations of a conceptual direct steam generation solar power plant with optimized Fresnel reflectors in Agua Prieta, Mexico coupled with a regenerative steam Rankine power cycle to quantify their efficiency and establish a reference for future implementation of this technology in concentrated solar power plants in Mexico. The thermal model was assumed to be a 1D steady-state flow and validated against results in the literature. It was then applied directly to a case study to determine the size of the solar field. The design point was the lowest solar irradiance day, and evaluating the solar multiple with the highest solar irradiance, taking care not to oversize the solar field, as suggested for solar plants without energy storage. Comparing the performance of the optimized Fresnel field against the FRESDEMO field of Plataforma Solar de Almería, a considerable decrease in the length of the loop has been demonstrated with a low reduction in thermal efficiency.

Effect of regenerator on the direct steam generation solar power system characterized by prolonged thermal storage and stable power conversion

Abstract The direct steam generation (DSG) solar power system using two stage accumulators and cascade steam-organic Rankine cycle (RC-ORC) has remarkably enlarged storage capacity. It can facilitate stable power generation and address the challenges of conventional DSG systems. Regenerator is generally an issue worthy of discussion in organic Rankine cycle (ORC) systems. However, its influence on the newly proposed DSG system has not been investigated yet and is expected to be appreciable. Introducing a regenerator affects not only the ORC efficiency, RC-ORC efficiency, heat exchanger area, but also heat storage capacity, discharge duration, discharge efficiency, aperture area of collectors and the net profit ( Δ P ). Detailed performance comparison between the DSG systems without/with regenerator is carried out in this paper. The results indicate that at a given power output, aperture area is reduced by the regenerator especially for MM, R365mfc and pentane due to the increment in ORC, RC-ORC and discharge efficiencies, as well as the decrement in heat input. Discharge duration is shortened by 0.01–1.78 h depending on ORC fluids. R365mfc exhibits the maximum Δ P (4.19 ∼ 6.48 million USD), followed by MM and pentane. On the contrary, Δ P is negative for benzene (−5.61 ∼ -4.31 million USD).

A solar hybrid system integrating concentrating photovoltaic direct steam generation by chemical heat pump

A hybrid solar power generation system integrating a concentrating photovoltaic, direct steam generation solar collector with a chemical heat pump is proposed in this study. In the hybrid system, the chemical heat pump is used to chemically upgrade the dissipated heat of the concentrating photovoltaic. The upgraded heat, together with the heat from the direct steam generation solar collector, is applied to drive the high-parameter steam Rankine cycle for efficient power generation. The performance of the hybrid system was examined first, and it was found that the solar-to-electric efficiency of the hybrid system is more than 20% higher than that of the individual systems of concentrating photovoltaic and direct steam generation solar power generation systems. The influence of chemical heat pump on the performance of the hybrid system is analysed, and the efficiency of the hybrid system reaches the maximum (34.71%) when the exothermic temperature of the chemical heat pump equals 360 °C. The dissipated heat of the concentrating photovoltaic can be chemically stored in the chemical heat pump. This enables the hybrid system to generate electricity continuously. The performance of the hybrid system in a typical day is compared with the concentrating photovoltaic individual system. The result shows that, benefitting from better performance and energy storage, the average electricity output per aperture area of the hybrid system (192.36 Wm−2) is approximately 170% higher than that of individual system of concentrating photovoltaic (70.41 Wm−2). Integrating the dissipated heat of concentrating photovoltaic into a high efficiency cycle via the chemical heat pump, this work would provide a potential approach for utilizing solar energy efficiently.

Thermo-economic evaluation of an innovative direct steam generation solar power system using screw expanders in a tandem configuration

Tandem screw expander (SE) technology is a promising solution for large volume ratio situations. Tandem SE driven direct steam generation (DSG) system is first proposed for distributed solar thermal power generation. Steam accumulator is adopted for storage due to its moderate heat source temperature. Compared with the cascade steam-organic Rankine cycle (SORC) system, the novel tandem system has simpler structure, easier control strategy and lower technical requirements, less operating and maintenance fees, more stable power output and higher security. Thermodynamic analysis and economic evaluation of the novel system are conducted based on some parameters of a recently constructed tandem SE project. Steam Rankine cycle (SRC) efficiency of 18.49% is achieved by employing built-in volume ratio (rv,b) of 3 for the high-pressure SE (SE1) and rv,b of 7 for the low-pressure SE (SE2). The cost-effectiveness of the system is improved as the power capacity and heat storage time increase. Levelized electricity cost (LEC) of 0.118 $/kWh and payback period (PP) of 10.48 years are obtained for 1 MW tandem plant with 6.5 h heat storage. The cost of parabolic trough collectors accounts for nearly half of the total investment while the accumulators occupy less than 7%. The cost of SE2 is approximately seven times that of SE1 due to the larger design outlet volume flow rate and rotor diameter.

A novel approach to thermal storage of direct steam generation solar power systems through two-step heat discharge

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.

Development and application of a multi-domain dynamic model for direct steam generation solar power plant

Direct Steam Generation (DSG) concentrated solar plants are promising but complex power systems. This latter feature originates both from the variety of physical phenomena and the dynamic nature of the boundary conditions at play during plant operation. A representative yet computationally efficient numerical simulator is a valuable tool to assist engineers in the proper design, control and operation of such specific water-steam cycle. The present communication reports on the development of a multi-domain dynamic model representing a DSG plant. To do so, we followed a code-coupling approach and relied on the domain-decomposition paradigm. More specifically, we built three sub-models respectively in the thermal-hydraulic, the optical and the control-command domains and coupled them through an in-house co-simulation platform called PEGASE. We used the CATHARE system code to solve the thermal-hydraulic problem and the more generalist DYMOLA software to model the convective and radiative heat exchanges within the solar receiver. As an example, we then applicate the simulator to elaborate an efficient controller for the steam separator level.

A novel concentrated solar power system using cascade steam-organic Rankine cycle and two-stage accumulators

A novel direct steam generation solar power system is proposed based on steam screw expander, cascade steam-organic Rankine cycle (SORC) and two-stage accumulators. The high temperature accumulator (HTA) enables smooth power conversion and stores thermal energy when solar radiation is available. The low temperature accumulator (LTA) is employed to elevate the storage capacity. One of the most remarkable features of the system is the heat discharge mode. First, heat is released via water vaporization in the HTA to drive the SORC. A maximum HTA temperature drop about 20 °C can be permitted. Then water at reduced temperature flows from the HTA to the LTA and heat is only used to drive the organic Rankine cycle (ORC). Nine organic fluids are adopted to analyze the system performance for seven regions worldwide. The results indicate that, compared with a conventional single-stage accumulator, the LTA can increase the storage capacity from 1.0 MWhe to 8.4 MWhe. The equivalent payback time in regard to the additional accumulator and collectors is estimated to be around 5 years in Phoenix and Lhasa. The LTA has great potential to improve the cost-effectiveness of the whole system.

Impacts of solar multiple on the performance of direct steam generation solar power tower plant with integrated thermal storage

Solar multiple (SM) and thermal storage capacity are two key design parameters for revealing the performance of direct steam generation (DSG) solar power tower plant. In the case of settled land area, SM and thermal storage capacity can be optimized to obtain the minimum levelized cost of electricity (LCOE) by adjusting the power generation output. Taking the dual-receiver DSG solar power tower plant with a given size of solar field equivalent electricity of 100 MWe in Sevilla as a reference case, the minimum LCOE is 21.77¢/kWhe with an SM of 1.7 and a thermal storage capacity of 3 h. Besides Sevilla, two other sites are also introduced to discuss the influence of annual DNI. When compared with the case of Sevilla, the minimum LCOE and optimal SM of the San Jose site change just slightly, while the minimum LCOE of the Bishop site decreases by 32.8% and the optimal SM is reduced to 1.3. The influence of the size of solar field equivalent electricity is studied as well. The minimum LCOE decreases with the size of solar field, while the optimal SM and thermal storage capacity still remain unchanged. In addition, the sensitivity of different investment in sub-system is investigated. In terms of optimal SM and thermal storage capacity, they can decrease with the cost of thermal storage system but increase with the cost of power generation unit.

Transient performance of direct steam generation solar power plants

Summary Parabolic trough power plants are currently the most commercial systems for electricity generation. In this study, a transient numerical simulation of a solar power plant was developed by using direct steam generation (DSG) technology. In this system, condensate water from a Rankine cycle is pumped directly to solar parabolic trough collectors. The pressurized water is heated and evaporated before being superheated inside the solar collectors and directed back to the steam turbines, where the Rankine cycle is a reheated-regenerative cycle. The plant performance with saturated steam production is compared with the performance of a superheated plant. A mathematical model of each system component is presented, with the solar power cycle modeled by the TRNSYS-17 simulation program. Annual transient performance, including plant power and efficiency, is presented for both plants. As expected, the power of the superheated plant outperforms the saturated plant by approximately 45%, whereas the efficiency decreases by approximately 10%. Furthermore, the power of such plants is considerably improved under the weather of Makkah, 22.4°N, and it is approximately 40 MW for both the spring and autumn seasons. The annual generated energy is approximately 8062 MWh. The levelized electricity cost (LEC) was estimated for both the DSG and the corresponding synthetic oil plants. The DSG plant has an approximately 3% higher LEC than a synthetic oil plant with heat storage and an approximately 11.2% lower LEC than an oil plant if the plant has no storage. Copyright © 2016 John Wiley & Sons, Ltd.

Modeling of Direct Steam Generation in Concentrating Solar Power Plants

A simulation procedure has been developed to predict the performance of a concentrating solar power plant with direct steam generation (DSG) technology. A detailed modelling of the DSG solar field was conceived for both parabolic troughs (PTC) and linear Fresnel collectors within an integrated Octave-TRNSYS® environment. Predictions from this model were compared with published operational data of the first pre-commercial 5 MW DSG solar power plant, designed within the INDITEP project. Attention was paid to the plant performance under two different operation modes, i.e. “fixed” or “sliding” steam turbine inlet pressure.

Exergy and exergoeconomic analysis of sustainable direct steam generation solar power plants

Solar direct steam generation is considered as a promising technology for steam production in thermal power generation due to high temperature levels that can be achieved compared to other technologies that use indirect steam generation. This paper demonstrates exergy and exergoeconomic analysis of commercial-size direct steam generation parabolic trough solar thermal power plant. For steam power cycles, reheating might be necessary to avoid great wetness of steam which shortens the lifetime of the turbines. Therefore, two configurations have been considered in this study; the non-reheating configuration as well as reheating by steam–steam heat exchanger. For each component, exergy and exergy-costing balance equations have been formulated based on a proper definition of fuel–product–loss. Exergy results show that particular attention should be paid to solar field, condenser, low pressure turbine and high pressure turbine (in a descendant order) as they constitute the major sources of exergy destruction. Results from exergoeconomic analysis, however, show that the condenser should be the fourth component in the order of importance after the solar field and low/high pressure turbines. Increasing the temperature at the inlet of the low pressure turbine by 100K using steam–steam reheating is shown to result in 9.1% increase in the vapor fraction at the exit of turbine. This increase in steam quality, however, would be achieved by drop less than 1.5% in thermal and exergetic efficiencies, and about 2% increase in cost of electricity. Moreover, the effect of degree of reheating on exergetic exergoeconomic parameters has been investigated. The results revealed that there is a specific value of degree of reheating for which the exergetic efficiency would be on it’s lowest value. This point would be of importance during optimization procedure of reheating direct steam generation solar plants.

Analytical modeling of direct steam generation solar power plants

Analytical models for the physical processes governing direct steam generation line-focus solar thermal power plants are derived. Predictions compare favorably with the limited database available from published studies against which the accuracy of detailed model computations can meaningfully be assessed. That limited database should not be confused with extensive citations of system power delivery in the absence of comprehensive information. A physically transparent understanding is provided for heat transfer within the collectors, heat loss to ambient, fluid flow and steam cycle efficiency. With existing evacuated-tube parabolic-trough concentrators and steam turbines, net system conversion efficiencies can exceed 20% even for today’s small-scale (⩽100MW) power plants. A key limiting factor is that relatively low-power turbines inherently have poorer isentropic efficiencies than their high-power counterparts. Although a few strategies for improving system efficiency have previously been proposed, the analytical models presented here provide the ability to rapidly (a) quantify the performance advantages of these strategies and (b) project how assorted modifications should affect system behavior, in both cases, without the need for expansive simulations. Examples of these design options include (1) multiple fluid extractions in a regenerative turbine cycle, (2) higher isentropic efficiencies for larger turbines, and (3) raising cycle temperature.

Steam temperature stability in a direct steam generation solar power plant

Direct steam generation (DSG) is one alternative to the current oil-based parabolic trough solar thermal power plants. Within the German research project ITES, the dynamic behavior of a DSG collector field and the interactions with the conventional power block are assessed in detail. A transient solar field model developed by DLR is used to simulate the steam temperature behavior. Artificial irradiance disturbances as well as real irradiance data are used as input to the system. The resulting main steam temperature gradients are then analyzed by Siemens considering the standards for steam turbines. This paper presents the transient simulation results of the steam temperature as well as the corresponding results of the steam turbine analysis. It is found that the occurring temperature gradients are challenging for a safe turbine operation, if a conservative control system is used. Therefore, the use of an additional thermal inertia to stabilize the steam temperature is suggested. Its impact is also analyzed and discussed in this paper.

A Direct Steam Generation Solar Power Plant With Integrated Thermal Storage

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.

INDITEP: The first pre-commercial DSG solar power plant

This paper presents the conceptual design of the first solar power plant using Direct Steam Generation (DSG) in a parabolic-trough solar field. Experience and know-how in the DSG process acquired during the DISS project were applied in designing the solar field of this plant. The 5-MWe plant is composed of a DSG parabolic-trough solar field connected to a superheated steam Rankine power cycle. The solar field produces 410 °C/70-bar superheated steam. Detail engineering of this plant is currently underway within the framework of the INDITEP project, which is promoted by a German-Spanish consortium with the financial support of the European Commission (Contract No. ENK5-CT-2001-00540). The main design objective is to assure high operational flexibility and reliability. This is the reason why a robust superheated steam turbine has been selected, though the efficiency of its power block is modest.