1,720,997 research outputs found
Hybridization of CSP plants with biogas boilers: A techno-economic assessment
No full textThis study aims at investigating the performance and the economic benefits coming from the integration of CSP power plants with anaerobic digestion processes. To demonstrate the capabilities of hybrid CSP-biogas power generation systems, the CSP section of the Ottana solar facility (Italy) is considered as case study. A simulation model for the performance analysis of the overall hybrid power plant has been developed on Matlab environment. The effects of the variation of the anaerobic digester volume and biogas storage capacity on the main performance indexes of the hybrid power plant have been evaluated. Finally, a preliminary economic analysis has been carried out to assess the economic benefits led by the hybridization and the optimal configuration able to minimize the energy production cost. The obtained results demonstrate the benefits in terms of improvement of plant capacity factor and plant efficiency arising from a proper sizing of the biogas section. In fact, an oversizing of the biogas section results in an important increase of the solar field energy curtailment due to the limited TES capacity with a consequent degradation of the plant performance. Consequently, the optimal configuration, even from an economic point of view, is achieved by sizing the biogas section to guarantee the continuous operation of the ORC unit at its minimum load
Robust optimization for the preliminary design of solar organic Rankine cycle (ORC) systems
No full textOrganic Rankine cycle (ORC) powered by solar energy is a viable and effective option for a high efficiency conversion of solar thermal energy into electricity at a distributed scale but recurring fluctuations of the thermal energy often force solar-based ORC systems to operate at part-load conditions. With the aim of including the effects of the expected variations of the heat source and heat sink characteristics, even during the design phase, a novel optimization approach for the preliminary design of ORC systems integrated with concentrating solar collectors is presented and analysed. In particular, the minimization of the expected levelized cost of energy (LCOE) of the ORC unit is chosen as an objective function, while the generation of various scenarios is proposed to face the expected fluctuations on the heat source mass flow rate and temperature and cooling inlet temperature. In this way, the expected off-design performances are involved during the design step, giving robustness to the optimal design solution. The proposed methodology is tested by referring to the solar ORC system configuration of the Ottana solar facility. Firstly, the effect of a robust optimization on the preliminary ORC design is investigated by considering an increased number of scenarios for each of the three most significant ORC input variables (heat source mass flow rate and temperature and ambient temperature). Subsequently, the proposed methodology was applied to an ORC design case by considering a concurrent variation of the three variables and three different working fluids. The results of this study demonstrate that a multi-scenario approach drives towards an ORC configuration with lower performance under design conditions, but less sensitive to the variation of the main inputs. Less expensive solutions are therefore achieved by the proposed methodology, but the annual energy production obtained is comparable with those achieved by adopting a single scenario approach, with a consequent reduction of the LCOE
Optimal design of a hybrid CSP-PV plant for achieving the full dispatchability of solar energy power plants
No full textWith the aim of providing fully dispatchable power using only solar energy, this paper focuses on a hybrid power generation system based on Concentrating Solar Power (CSP) and Photovoltaic (PV) plants. In particular, the CSP section is based on linear Fresnel collectors using thermal oil as heat transfer fluid, a two-tank direct TES system and an Organic Rankine Cycle (ORC) power plant. In the PV section, the PV array is coupled with a battery bank for electrochemical storage. The study evaluates the optimal design parameters (solar field area, TES capacity and ORC nominal power for the CSP section, nominal power of the PV array and battery capacity for the PV section) that minimize the energy production cost of the hybrid CSP-PV plant while the plant is constrained to follow a power output curve characterized by a constant power level. Moreover, to assess the influence of meteorological conditions, the study considers two different locations: Ottana (Italy) and Ouarzazate (Morocco). The results demonstrate that hybridization of PV and CSP technologies becomes highly cost-effective if a constant power output is required for daily time periods longer than about 16 h, when the distinguishing feature of CSP plants of decoupling power generation from sunlight is effectively exploited, independently of the location under study. On the contrary, for production periods shorter than 8 h, the use of a PV system coupled with a proper battery bank is the most cost-effective solution for both locations evaluated. Solar energy availability and unmet load fraction remarkably influence the hybrid plant design, especially for load duration periods in the range between 8 and 16 h/day. As expected, due to the lower amount of available solar energy, the hybrid solar plant located in Ottana needs larger sizes of both CSP solar field and PV arrays than the same plant located in Ouarzazate resulting in higher energy production costs
Modeling and simulation of an isolated hybrid micro-grid with hydrogen production and storage
No full textThis work relates the study of system performance in operational conditions for an isolated micro-grid powered by a photovoltaic system and a wind turbine. The electricity produced and not used by the user will be accumulated in two different storage systems: a battery bank and a hydrogen storage system composed of two PEM electrolyzers, four pressurized tanks and a PEM fuel cell. One of the main problems to be solved in the development of isolated micro-grids is the management of the various devices and energy flows to optimize their functioning, in particular in relation to the load profile and power produced by renewable energy systems depending on weather conditions. For this reason, through the development and implementation of a specific simulation program, three different energy management systems were studied to evaluate the best strategy for effectively satisfying user requirements and optimizing overall system efficiency. (C) 2013 The Authors. Published by Elsevier Ltd
Impianti solari termodinamici operanti con collettori parabolici lineari e fluidi gassosi ad alta temperatura. Parte 1
No full textThis paper reports a performance assessment of advanced CSP power plants. The CSP system analyzed is based on parabolic troughs, CO2 heat
transfer fluid and thermocline thermal storage systems. The use of CO2 instead of the more conventional thermal oil as heat transfer fluid (550 °C
instead of 400 °C) can allow to increase the steam cycle conversion efficiency, whereas the use of thermocline storage systems allows to store and
recover the thermal energy at constant temperature. However, the increase of the CO2 temperature reduces the efficiency of the solar field whereas
the use of solid materials leads to some problems related to the utilization of the storage volume capacity. The performance of CSP systems have been
evaluated by means of specifically developed simulation models for the solar collector, solid storage system and the steam power plant. In particular,
the operating parameters of the steam cycle (steam pressure and temperature, steam extraction) have been optimized according to the different
temperature and composition of the heat transfer fluid. Moreover, the performance of the CSP system was evaluated with reference to different values
of solar module and storage capacity as a function of the solar radiation.
The results of the performance assessment show that the enhancement of the steam cycle efficiency overcomes the efficiency reduction of the solar field.
The analysis carried out with reference to the solar radiation of Cagliari demonstrate that the annual efficiency of the CSP power plant decreases with
increasing values of both solar module and thermal storage capacity. On the contrary, the annual net energy production from solar increases with
increasing values of these parameters. With reference to a solar module equal to 1.5 and a thermal storage capacity of 4-6 hours, the CSP efficiency
ranges from 18% to 19%. Moreover, the annual energy production of a 50 MW CSP plant is around 140-150 GWh/yr (that is 3.000 hour/yr)
Operating performance of a Joule-Brayton pumped thermal energy storage system integrated with a concentrated solar power plant
Full text linkThe expected performance of an innovative Pumped Thermal Energy Storage (PTES) system based on a closed-loop Brayton-Joule cycle and integrated with a Concentrated Solar Power (CSP) plant are analysed in this study. The integrated PTES–CSP plant includes five machines (two compressors and three turbines), a central receiver tower system, three water coolers and three Thermal Energy Storage (TES) tanks, while argon and granite pebbles are chosen as working fluid and storage media, respectively. A sizing of the main components of the integrated plant has been firstly carried out for the design of an integrated PTES-CSP plant with a nominal net power of 5 MW and a nominal storage capacity of 6 equivalent hours of operation. Specific mathematical models have been developed in MATLAB-Simulink to simulate the PTES and CSP subsystem in different operating conditions, and to evaluate the thermocline profile evolution within the three storage tanks during/charging and discharging processes. A control strategy has finally been developed to determine the operating modes of the plant based on the grid service request, the solar availability, and the TES levels. The performance of the system during a summer and a winter day have been analysed considering the integration of the PTES subsystem in the Italian energy market for arbitrage. Results have demonstrated the technical feasibility of the hybridization of a PTES system with a CSP plant and the ability of the integrated system to participate to energy arbitrage, although a lower exergy roundtrip efficiency (about 54 %) has been observed with respect to the sole PTES system (about 60 %)
Techno-economic assessment and grid impact of Thermally-Integrated Pumped Thermal Energy Storage (TI-PTES) systems coupled with photovoltaic plants for small-scale applications
Full text linkAssessment of a hybrid stand-alone power system with hydrogen production and storage
No full textIn stand-alone power generation systems the intermittence of solar and wind energy sources requires the use of energy storage devices able to follow the time-varying electrical load demand. Energy storage based on hydrogen technologies is one of the most interesting options.
The aim of this study is to investigate the performance of stand-alone power generation systems where the excess of electrical energy produced by wind turbines and photovoltaic modules is used in PEM hydrogen generators. Gaseous hydrogen is stored in pressurized vessels and used in PEM fuel cell stacks to produce electrical energy when required by final users. Excess of electrical energy can also be stored in a battery bank.
In particular, this study was applied to the power generation and hydrogen storage facility being installed at the “Sardegna Ricerche Renewable Energy Cluster” near Cagliari in Sardinia. The expected performance of the stand-alone power generation system were evaluated through the commercial software HOMER, according to the available solar and wind resource data. Moreover, benefits coming from future implementations of the energy storage capacity were also assessed
Optimal energy management strategy for CSP-CPV integrated power plants with energy storage
No full textThis work focuses on the study of the most suitable energy management strategies for solar power plants based on the integration of a concentrating solar power (CSP) plant with thermal energy storage and a concentrating photovoltaic (CPV) power plant with electrochemical storage. Due to the presence of the energy storage system, these integrated CSP-CPV plants are able to produce electricity with scheduled profiles as well as to provide ancillary services at distribution level. The algorithm for the optimal plant management uses weather forecast data to schedule the optimum generation profile by maximizing the power production of the integrated plant, while different constraints due to equipment limits are satisfied. A comparative analysis is carried out by means of the implementation of a deterministic or a stochastic approach to take into account the uncertainties in weather forecast. A time horizon of 48 h is imposed in the optimization problem with an updating of the input data and results each 24 h. The integrated CSP-CPV power plant here analyzed refers to the solar pilot facility that is currently under construction in the industrial district of Ottana (Sardinia, Italy). The facility consists of a CSP plant based on linear Fresnel collectors using thermal oil as heat transfer fluid, a two-tank thermal energy storage system (capacity of about 15 MWh), a 600 kWe ORC power plant, a 400 kWe CPV power plant and an electrochemical storage system with a capacity of 430 kWh. The results of the study demonstrate that the use of a stochastic approach instead of a deterministic one allows to generate more robust solutions. In particular, with the proposed stochastic approach unexpected phenomena and the variation in the foreseen conditions only marginally affect the scheduling planning, which results in an improvement of about 3-5% in the yearly power production
Application of Concentrating Solar Technologies in the Dairy Sector for the Combined Production of Heat and Power
No full textThe use of concentrating solar technologies for supplying the heat and power demand of a typical dairy factory is investigated in this paper. A yearly-based performance analysis is carried out considering different values of solar field collecting area and thermal energy storage capacity with reference to a typical meteorological data set of a Sardinian location. Specific simulation models are developed for each section of the plant. Moreover, a novel energy management strategy is developed for the determination of the priority order between thermal and electrical demand. The results demonstrate that concentrating solar technologies could be a promising option if power and heat are both required. In particular, the presence of the energy storage section provides important flexibility features to the plant and by suitably setting the control variable, the energy management strategy allows to give priority to the heat or to the electrical demand of the dairy
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