Solar Collector Field Research Articles

Techno-economic assessment of a pilot-scale plant for solar desalination based on existing plate and frame MD technology

This work presents the results of the techno-economic analysis of a proposed 100m3day−1 desalination plant based on existing plate and frame MD technology coupled with a static solar collector field as main heat supply. The experimental results of one commercial and two pre-commercial MD modules characterized previously under real operational conditions were used. Three different cost-effective solar technologies (evacuated tube collectors (ETCs), flat plate collectors (FPCs) and compound parabolic collectors (CPCs)) were considered for the analysis and the results were compared to a fossil source. For the dimensioning of the solar field, meteorological data from Almeria (South-Spain) where the experimental campaign took place were selected. A thorough economical assessment was performed to calculate the cost of water (WPC) for the different considered scenarios. The best results obtained show a WPC in the range of 10–11.30€m−3 for the combination of the most efficient MD module and solar collector. The fossil-driven option showed a similar (i.e. 7.19€m−3) yet lower WPC. Although the MD technology here analyzed is in an early stage of development, the results obtained suggest solar MD can be already competitive with PV-RO and PV-ER according to reported data for similar capacities (~100m3day−1).

Simple calculation tool for central solar heating plants with seasonal storage

Central Solar Heating Plants with Seasonal Storage (CSHPSS) are able to produce thermal energy from solar radiation during all the year providing a significant part of the residential sector demands for Space Heating (SH) and Domestic Hot Water (DHW), using district heating systems. The yearly dynamic simulation is a complex process requiring local detailed climatic and demand data in order to properly design/sizing the plant components to reach the desired solar fraction. In this paper is proposed a simple method for the calculation of CSHPSS using demand data and easy to find available public climatic data. The proposed method is a useful tool to evaluate the CSHPSS system at early project stage as well as to perform parametric analysis in order to establish optimization and design criteria. The method is completely described and applied for a specific location in Spain to size the main components of the system which are the solar collector field area and the volume of the seasonal storage. It is also applied to perform a comparative analysis of CSHPSS located in different climatic areas of Spain. The obtained results reveal that the location of the plant and the different demands corresponding to different climatic areas affect very significantly the sizing and design criteria of CSHPSS.

Solar repowering of PCC-retrofitted power plants; solar thermal plant dynamic modelling and control strategies

Solar repowering of high pressure side feed water preheaters of post combustion carbon capture (PCC) retrofitted power plants offers a promising capability to offset the power plant output penalty due to capture plant reboiler duty. In this work, a model based approach is used to investigate the technical, operational and control aspects of the solar thermal installation of the super structure (power plant+PCC+solar thermal plant). The base case is a 660MWe PCC-retrofitted power plant operating at 100% capacity and 90% capture rate in Australia. This is repowered by a solar thermal plant consisting of (a) a parabolic trough solar collector field with 806,520m2 aperture area, (b) a thermal storage system with 8 full load hours of thermal storage and (c) an auxiliary gas heating unit, ensuring the solar thermal plant provides the high pressure side feed water preheating duty at all times without requirement to withdraw any steam from the power plant turbine circuit. A total of 230MWth is provided from the solar thermal plant installation, being 100% supply for high pressure and intermediate feed water preheaters duty plus a surplus of 30% for maintaining the deaerator operation. A key feature here is trying to eliminate the frequent changes to the steam flow rate in the turbine circuit for solar feed water preheating and thus promoting ease of retrofit of repowering technology to PCC-retrofitted power plants. Details of the component sizing and modelling of solar thermal installation are provided and control and operating schemes are identified and analysed. A comprehensive dynamic model in TRNSYS dynamic modelling software is developed and used to analyse the solar thermal plant dynamic responses to external disturbances including climatic changes (Typical Meteorological data for Sydney is used). The analysis limitations and capabilities are highlighted. The model performance for month December is assessed showing its full capability to track the changes from power plant duty requirement and meteorological data within the time lapse of 0.01s.

Simulation Study of the Thermal Performance of MSF Desalination Unit Operating by Solar Vacuum Tube Collectors

The Center for Solar Energy Research and Studies (CSERS) has good experience in operating and evaluating the thermal performance of small scale 5 m3/day Multi-Stage Flushing (MSF) desalination plant connected to solar pond according to the local weather conditions of Tajoura area. However, a new project has been suggested to run the desalination plant with vacuum tubes solar thermal collectors utilizing available technology and experience.In this study, an attempt was made to make the best use of readily available components to operate the MSF desalination unit with field of solar thermal collectors. Several configuration of collectors and tank arrangements were designed and examined through the use of simulation software, TRNSYS. The study has shown that the layout-3 (two 500 liter storage tanks each of them connected to 9x5 vacuum tube collectors) gives the best performance with an annual solar fraction over 77% at a load temperature of 70 °C with a flow rate of 2500 lit/hr, and over 68% at load temperature of 80 °C for working condition of 8 hours daily. The study has also shown that running the desalination plant for 24 hours a day reduces the solar fraction of the solar collector field to 25%

Molten Salt as a Heat Transfer Fluid in a Linear Fresnel Collector – Commercial Application Backed by Demonstration

Abstract Motivated by the need of thermal storage, Novatec decided in 2012 to put the major product development focus on the development of the direct molten salt technology, applying molten salt directly as a heat transfer fluid (HTF)in Fresnel collector solar fields. After an intense engineering phase, Novatec started the experimental testing of molten salt specific issues in 2013. Several small-scale demonstrators with a cumulated pipe length in the order of 1 to 30 m have been built to gain first experience with salt-specific challenges such as Joule heating and salt freezing and re-melting. End of 2013, a demonstrator consisting of all piping and process components that will be used in future direct molten salt plants has been built, including over 550 m of solar receiver and connection piping. This paper presents the major challenges of future large-scale direct molten salt plants from today's perspective and how they were addressed experimentally including the testing results. To conclude: So far, all previously expected challenges related to the use of molten salts in Novatecs solar collector pipes have been experimentally tested. As a result, no point of concern for the use of molten salt as HTF was found. Even if freezing occurs, which likely can be avoided by night circulation or draining, measures have been proven to safely re-thaw the salt again. The testing was performed with HITEC® salt mixture.

Simulation of a Solar Collector Array Consisting of two Types of Solar Collectors, with and Without Convection Barrier

Abstract The installed area of solar collectors in solar heating fields is rapidly increasing in Denmark. In this scenario even relatively small performance improvements may lead to a large increase in the overall energy production. Both collectors with and without polymer foil, functioning as convection barrier, can be found on the Danish market. Depending on the temperature level at which the two types of collectors operate, one can perform better than the other. This project aimed to study the behavior of a 14 solar collector row made of these two different kinds of collectors, in order to optimize the composition of the row. Actual solar collectors available on the Danish market (models HT-SA and HT-A 35-10 manufactured byARCON Solar A/S) were used for this analysis. To perform the study, a simulation model in TRNSYS was developed based onthe Danish solar collector field in Braedstrup. A parametric analysis was carried out by modifying the composition of the row, in order to find both the energy and economy optimum.

Monitoring Results of a Solar Process Heat System Installed at a Textile Company in Southern Germany

A solar process heat system was realized within the project “Soltex” (Solar process heat for a medium-sized textile industry company) and equipped with a detailed monitoring system. The solar process heat system is installed at the premise of a textile company located in the south of Germany providing hot water for different production processes. The solar collector field consists of parabolic trough collectors having a nominal collector power of 70 kWth and is installed with an east-west axis orientation on the roof of the building. The present paper will give a general overview of the system and the installed measurement equipment followed by a presentation of the operation results for the period of September 2013 to August 2014.

Dynamic Simulation and Exergo-Economic Optimization of a Hybrid Solar–Geothermal Cogeneration Plant

This paper presents a dynamic simulation model and a parametric analysis of a solar-geothermal hybrid cogeneration plant based on an Organic Rankine Cycle (ORC) powered by a medium-enthalpy geothermal resource and a Parabolic Trough Collector solar field. The fluid temperature supplying heat to the ORC varies continuously as a function of the solar irradiation, affecting both the electrical and thermal energies produced by the system. Thus, a dynamic simulation was performed. The ORC model, developed in Engineering Equation Solver, is based on zero-dimensional energy and mass balances and includes specific algorithms to evaluate the off-design system performance. The overall simulation model of the solar-geothermal cogenerative plant was implemented in the TRNSYS environment. Here, the ORC model is imported, whereas the models of the other components of the system are developed on the basis of literature data. Results are analyzed on different time bases presenting energetic, economic and exergetic performance data. Finally, a rigorous optimization has been performed to determine the set of system design/control parameters minimizing simple payback period and exergy destruction rate. The system is profitable when a significant amount of the heat produced is consumed. The highest irreversibilities are due to the solar field and to the heat exchangers.

Peak shaving strategy through a solar combined cooling and power system in remote hot climate areas

An effective combination of district cooling with electric power production in an integrated solar combined cycle is presented and evaluated. A remote area in hot climate is assumed as location to highlight the importance of peak shaving strategy in an isolated or weakly interconnected power system. Two solutions for handling peak power demand are taken into account in the present investigation. On the one hand, the integration of a Concentrated Solar Power system (CSP) with a combined cycle power plant is considered to match peak power demand on the grid. On the other hand, the adoption of a district cooling system where cooling energy is produced by absorption chillers is proposed, instead of mechanical refrigeration, to reduce and flatten the load profile.The case study refers to a combined cycle (CC) based on a 46MW Siemens SGT-800 gas turbine. The CC plant is integrated with a parabolic trough collectors (PTC) solar field and double-effect steam driven absorption chillers feeding a district cooling network. The solar combined cooling and power (SCCP) system is designed to operate in “island mode” to match both electrical and cooling demand on an hourly basis, on a typical winter and summer day. A modeling procedure is applied to accurately simulate the plant operation, including off-design behavior of all plant components. During the day the solar source has the highest priority, whilst the gas turbine (GT) is operated at part-load to follow the load profile.Electric efficiency and fuel savings for the SCCP plant are computed and compared against the ones resulting from a conventional pure fossil system based on analogous combined cycle and compression refrigeration units. Results show that a SCCP system can significantly reduce fossil fuel consumption in both summer and winter peak hours, while providing higher overall efficiency through the whole day, both in summer and winter.

Exergy analysis of DSG parabolic trough collectors for the optimal integration with a combined cycle

A comprehensive energy and exergy analysis was conducted for various components of a direct steam generation (DSG) parabolic trough solar collector field under nominal operating conditions to assess performance of the components and to optimally integrate them with a thermal system. The solar field was modelled mathematically to compute thermal loss and consequently the thermodynamic efficiencies. To minimise inefficiencies in the solar field and to integrate it optimally with a reference combined cycle, the solar field was coupled to the bottoming cycle of the power plant. The solar energy was exploited in this conceptual integrated solar combined cycle (ISCC) to preheat the condensate water and to evaporate the water from economiser up to the prescribed quality of 0.8 in a once–through DSG system. This ISCC was further investigated for optimal design variables including inlet temperature of the water to the solar field and bleed pressure of the steam to deaerator.

Design and simulation of a prototype of a small-scale solar CHP system based on evacuated flat-plate solar collectors and Organic Rankine Cycle

This paper presents a dynamic simulation model of a novel prototype of a 6kWe solar power plant. The system is based on the coupling of innovative solar thermal collectors with a small Organic Rankine Cycle (ORC), simultaneously producing electric energy and low temperature heat. The novelty of the proposed system lies in the solar collector field, which is based on stationary evacuated flat-plate solar thermal collectors capable to achieve the operating temperatures typical of the concentrating solar thermal collectors. The solar field consists of about 73.5m2 of flat-plate evacuated solar collectors, heating a diathermic oil up to a maximum temperature of 230°C. A diathermic oil storage tank is employed in order to mitigate the fluctuations due to the variability of solar energy availability. The hot diathermic oil exiting from the tank passes through an auxiliary gas-fired burner which provides eventual additional thermal energy. The inlet temperature of the diathermic oil entering the ORC system varies as a function of the availability of solar energy, also determining an oscillating response of the ORC. The ORC was simulated in Engineering Equation Solver (EES), using zero-dimensional energy and mass balances. The ORC model was subsequently implemented in a more general TRNSYS model, including all the remaining components of the system. The model was used to evaluate the energy and economic performance of the solar CHP system under analysis, in different climatic conditions. The results show that the efficiency of the ORC does not significantly vary during the year, remaining always close to 10%. On the other hand, the efficiency of the solar collectors is very high in summer (>50%) and significantly lower during the coldest winter days (down to 20%). Pay-back periods are extremely attractive in case of feed-in tariffs (about 5years), whereas the profitability of the system is scarce when no public funding is available. A sensitivity analysis was also performed, in order to determine the combination of system/design parameters able to maximize the thermo-economic performance of the system. It was found that the system may be economically feasible for the majority of locations in the Mediterranean area (pay-back periods around 10years), whereas the profitability is unsatisfactory for Central-Europe sites.

Energetic experimental evaluation of the active systems of the RDB building 70 of the SSP-ARFRISOL

Within the finished Singular Strategic Project about Bioclimatic Architecture and Solar Cooling (SSP-ARFRISOL), five buildings were built or restored – Research and Development Buildings – using bioclimatic architectural designs and solar based HVAC and DHW systems. This article is about the overall operation of the HVAC and DHW system installed in the building number 70 of CIEMAT in Madrid. It consists of a solar collector field, linked with absorption machines to obtain cold water, “Solar Cooling”, as well as the support of conventional means. The system and its operation are described, and then an eleven-month period of operation, under real use conditions, is analyzed from an energetic point of view.The methodology described in this article allows detecting energy sinks and abnormal operations, where the critical points are, and eases to make corrections. We also include an example of optimization using this methodology applied to this system and, after the changes were made in the configuration and the operation, a further energy analysis for the next four months.

Unsteady thermodynamic analysis for a solar driven dual storage absorption refrigeration cycle in Saudi Arabia

The impact of unsteady solar intensity and ambient conditions on operation and performance parameters of an aqua-ammonia absorption chiller of 5kW cooling power is explored. Unsteady analysis for five representative days in summer and winter in Dhahran, Saudi Arabia, is presented. The results give the variation of the absorption-chiller parameters every one hour. The absorption chiller comprises a dual (ammonia and ice) storage system to ensure cooling effect during nighttime. This storage system consists of an ice tank, one ammonia tank and two aqua-ammonia tanks. Capacity of these tanks and the required solar collector area are computed for 24-hour operation per day at a constant 5kW cooling power. The results show that, for the given cooling power and ambient conditions, the coefficient of performance is better in winter than in summer (0.57 as compared to 0.39) but the required solar collector field area is more in winter than in summer.

Analytical and Comparative Study of a Mini Solar-Powered Cogeneration Unit Based on Organic Rankine cycle for Low-Temperature Applications

In this paper, we analyze characteristics of a small Combined Heat and Power (CHP) system based mainly on Organic Rankine Cycle (ORC) and heating plant in actual series connection regarding the low-temperature heat carrier heated by purely solar flat collector field. Simultaneously and for specific power production, comparison of this layout with stand-alone ORC, and with the traditional ORC-CHP imposing gain of condenser heat for heating aims, in second step, has been conducted. For evaluation, energetic and design criteria have been determined opposite the heating effects and also temperatures of the heat source and sink. The simulations addressed interesting optimization ratios till 24 % for the power unit throughout this series CHP utility versus single power generation at the same conditions tested. Moreover, the high heat source temperatures and CHP ratios improve the performance of the overall series plant, while the high supply and return temperatures have negative effects. Finally, the ORC-CHP scheme handled here highlights distinctive exploitation aspects and more suitability in wide range of application in comparison to yielding the high-temperature condensation heat of ORC, especially at low ambient temperatures, high supply and heat source temperatures. So, it can be advised to be adopted instead of the two other strategies.

Study of Using Solar Thermal Power for the Margarine Melting Heat Process.

The heating process of melting margarine requires a vast amount of thermal energy due to its high melting point and the size of the reservoir it is contained in. Existing methods to heat margarine have a high hourly cost of production and use fossil fuels which have been shown to have a negative impact on the environment. Thus, we perform an analytical feasibility study of using solar thermal power as an alternative energy source for the margarine melting process. In this study, the efficiency and cost effectiveness of a parabolic trough collector (PTC) solar field are compared with that of a steam boiler. Different working fluids (water vapor and Therminol-VP1 heat transfer oil (HTO)) through the solar field are also investigated. The results reveal the total hourly cost ($/h) by the conventional configuration is much greater than the solar applications regardless of the type of working fluid. Moreover, the conventional configuration causes a negative impact to the environment by increasing the amount of CO2, CO, and NO2 by 117.4 kg/day, 184 kg/day, and 74.7 kg/day, respectively. Optimized period of melt and tank volume parameters at temperature differences not exceeding 25 °C are found to be 8-10 h and 100 m3, respectively. The solar PTC operated with water and steam as the working fluid is recommended as a vital alternative for the margarine melting heating process.

A practical hybrid predictive control algorithm for a low‐temperature thermosolar plant

SummaryThis work presents a control approach to deal with plants formed by several interconnected subprocesses and where the interconnection between subprocesses can change during the plant operation. The change from one operation mode to another, where each operation mode is defined by a discrete variable set, implies a change in the process behaviour that must be counteracted by the control system. In this work, a practical hybrid model predictive control is proposed to take the behaviour changes related to the hybrid nature of the process into account. The proposed control algorithm is based on the adaptation of several well‐known control strategies that have been successfully applied in the industrial field. A solar thermal system (composed of a solar thermal flat collector field, one or more accumulation tanks connected in series and a gas heater) is used to show the resulting control strategy through detailed simulations. Copyright © 2014 John Wiley & Sons, Ltd.

Productivity analysis of two spiral-wound membrane distillation prototypes coupled with solar energy

The use of solar energy to feed the MD desalination process is being evaluated at Plataforma Solar de Almería, the largest European facility for solar energy research, located in SE Spain. A test bed for the evaluation of membrane distillation modules is under operation coupled to a field of static solar collectors. Different commercial modules and real-scale prototypes are tested in continuous operation and coupled with a solar thermal source, in order to obtain data in conditions closer to real applications than the tests performed at laboratory scale. This particular study shows an evaluation of two different modules using spiral-wound membranes, one with a liquid-gap configuration (built by Solar Spring) and the other with an air-gap configuration (built by Aquastill). An assessment of the influence of the operational parameters in the performance was done within the allowed ranges of operation of each prototype, with special attention to the temperatures and the feed flow rate. Also, the influence of the salinity was investigated using feed water with salts at different values of conductivity. The characterization of the systems is done based on the quality of the distillate, as well as the measured values of distillate production and thermal performance, choosing the specific distillate flux obtained and the gain output ratio (GOR) as performance indicators. The main results of the analysis are summarized and compared, discussing the particular operational experiences in each case.

SOLMED: solar energy and polymers for seawater desalination

Combining thermal solar energy and polymer materials allows seawater desalination while fossil fuels are saved and use of chemicals against fouling and corrosion is reduced. SOLar Multi-Effect Desalination (SOLMED) meets recommendations of the US National Research Council and Middle East Desalination Research Center of Oman regarding the future of water desalination. Water cost reduction and development of technologies with low environmental impact are the main guidelines of SOLMED. Thermal efficiency is at the heart of SOLMED. Process is based on low-temperature multi-effect distillation (LT-MED) powered by a thermal solar collector field, or better, by heat recovery at the outlet of a solar power plant. Heat transfer surfaces are made of thin wall polymer tubes to ensure a high thermal duty in spite of low thermal conductivity of polymers. Targeted capacities lie within 500–1,000 m3/d. The objective is to develop a LT-MED prototype made of polymers and to operate the system plugged to a solar heat source. To reach these objectives, SOLMED gathers a consortium of six partners, merging experts of thermal systems and components, experts in polymers and transformation, and engineering partners in the field of solar energy and processes. Social aspects are also taken into account through acceptability, sustainability, design, management of innovation, market, and life cycle assessment. SOLMED is a three years project funded by the French National Research Agency. The first step is to build a 10 m3/d prototype to bring a proof of concept. The prototype will be operated with a 100 kW peak solar heat source. Developments are related to the modeling of the process itself and its integration in a solar system including heat storage, thin-wall tubes fabrication, optimization of tubes fixing, investigations related to heat transfer, and hydraulic. Regarding polymer materials, the challenge is to combine high thermal rate with long lifetime. Commercial step has to consider new optimization approach, taking into consideration the whole process, including heat source.

A Novel Combined Low Temperature Cycle for Electricity and Fresh Water Production

This work is an extension and modification of the novel thermal cycle reported in the study “Techno-Economic Evaluation of a Novel Thermal Cycle for Electricity Generation and Fresh Water Production From Solar Ponds.” For low temperature power generation, such as the case of solar ponds or a field of solar flat plate collectors (60–90 °C), it is a common practice to use an organic Rankine cycle. The novel cycle uses water vapor as a working medium under pressure values lower than atmospheric. This is achieved by a turbovapor generating unit, a conventional low-pressure steam turbine, and a condenser working in an open cycle. Such a plant has a low thermal efficiency which approaches 12%, because of the small temperature range between evaporator and condenser (80–30 °C). The ratio of fresh water to electric power is also fixed for a certain temperature range (e.g., 14 tons/MW h for temperatures of 80 °C evaporator and 30 °C condenser). To increase the thermal utilization of the available heat flux and to achieve a variable fresh water production, a conventional multistage flash evaporation plant (MSF plant) is incorporated between the evaporator and condenser. The thermodynamic analysis of the plant shows that the thermal utilization of the available energy may reach 90%, while the amount of fresh water could be raised from 14 tons/MW h to 300 tons/MW h, for the same temperature range. This system has the advantage of being self-sufficient, yielding a net electric power after having supplied its own needs of pumping power.

Two degree-of-freedom design for a send-on-delta sampling PI control strategy

A complete event-based two-degree-of-freedom PI controller is presented. The architecture of the control system is based on two decoupled PI controllers, one for the set-point following and one for the load disturbance rejection task. The distinctive feature of the proposed approach is that the two controllers have the same parameters and the reference tracking performance is improved by suitably modifying the reference signal applied to the set-point following controller. Examples of the technique are given. In particular, the control strategy has been applied to a distributed solar collector field.