Solar Process Heat Applications Research Articles

Impact of Temperature and Optical Error on the Combined Optical and Thermal Efficiency of Solar Tower Systems for Industrial Process Heat

Concentrating solar thermal (CST) power towers can provide high flux concentrations at commercial scale. As a result, CST towers exhibit potential for high-temperature solar industrial process heat (SIPH) applications. However, at higher operating temperatures, thermal radiation losses can be significant. This study explores the trade-off between thermal and optical losses for SIPH applications using a collection of three case studies at operating temperatures that range from 900-1,550 °C. We assume blackbody radiation to represent the thermal losses at the receiver and we use ray tracing to estimate the optical losses. The results show the impact of process temperature on the maximum attainable system efficiency, as well as the higher flux concentration requirements as the temperature increases.

An Integrated Light Pipe Receiver and Thermal Energy Storage

An integrated light pipe receiver and thermal energy storage (TES) architecture is proposed for solar process heat applications. Simulations demonstrate the benefits of increased heat transfer area to a low conductivity TES medium and reduced surface radiation losses. When compared against a baseline design with a hemispherical absorber, the integrated light pipe receiver enables up to a factor of three higher energy storage for distributed absorption relative to localized absorption at the top of the TES. For a lower thermal conductivity TES medium or baselining to a flat-top absorber, an increase in thermal energy storage up to a factor of five results.

Geopolymer Concrete Performance Study for High-Temperature Thermal Energy Storage (TES) Applications

Solar energy is an energy intermittent source that faces a substantial challenge for its power dispatchability. Hence, concentrating solar power (CSP) plants and solar process heat (SPH) applications employ thermal energy storage (TES) technologies as a link between power generation and optimal load distribution. Ordinary Portland cement (OPC)-based materials are widely used in sensible TES, but their use is limited to operation temperatures below 400 to 500 °C because of thermal degradation processes. This work proposes a geopolymer (GEO)-based concrete as a suitable alternative to OPC concrete for TES that withstands high running temperatures, higher than 500 °C. To this end, thermophysical properties of a geopolymer-based concrete sample were initially measured experimentally; later, energy storage capacity and thermal behavior of the GEO sample were modeled numerically. In fact, different thermal scenarios were modeled, revealing that GEO-based concrete can be a sound choice due to its thermal energy storage capacity, high thermal diffusivity and capability to work at high temperature regimes.

Solar process heat for sustainable production of concentrated peach puree

AbstractThe food industry is one of the most suitable sectors for solar process heat applications. Concentrating solar power (CSP) systems generate steam using mirrors or lenses to concentrate a large area of sunlight onto a receiver. In this study, how a CSP system connected hybrid to the boiler system can be utilized to produce more sustainable peach puree concentrate (PPC) have been examined. The amount of steam required for PPC production was calculated using the measurements rendered in a real fruit juice concentrate plant and the data obtained from them. A parabolic trough‐type CSP system of 1 MWthwas designed, which is placed in the area of the plant, and it was determined that the steam quantity obtained during the production period is able to meet how much of the current consumption. Also, it has been shown how much CO2eqemission reduction will be achieved by using CSP.Practical ApplicationsConcentrated fruit juice production is one of the thermal energy intense food processes. Therefore, utilization of renewable energy sources for process heat is very important. We designed a CSP system in this study with using production data from a real fruit juice factory. This CSP system is naturally applicable to both fruit juice and all food industry using steam at similar temperatures and pressures. Fossil fuels are one of the main responsible for global warming. For this reason, the use of solar thermal systems is promising to ensure sustainability in food production and reduce the environmental impacts of the product.

Improvement of Phase Change Materials (PCM) Used for Solar Process Heat Applications.

The high intermittency of solar energy is still a challenge yet to be overcome. The use of thermal storage has proven to be a good option, with phase change materials (PCM) as very promising candidates. Nevertheless, PCM compounds have typically poor thermal conductivity, reducing their attractiveness for commercial uses. This paper demonstrates the viability of increasing the PCM effective thermal conductivity to industrial required values (around 4 W/m·K) by using metal wool infiltrated into the resin under vacuum conditions. To achieve this result, the authors used an inert resin, decoupling the specific PCM material selection from the enhancement effect of the metal wools. To ensure proper behavior of the metal wool under standard industrial environments at a broad range of temperatures, a set of analyses were performed at high temperatures and an inert atmosphere, presenting a thorough analysis of the obtained results.

Optimized design of a Linear Fresnel reflector for solar process heat applications

Abstract Heat demands in industrial processes represent a high rate of the thermal energy consumption that could be directly delivered by a concentrated solar thermal technology. Linear Fresnel reflectors are a promising example of this kind of technology. This paper presents an innovative and optically optimized design of linear Fresnel collector for solar process heat applications. An in-house ray trace code was employed to evaluate different geometrical options of the solar collector over conventional concepts, aiming to maximize its optical performance and tackle the inherent weakness of this concentrating solar technology when it is compared to other type of concentrators. Geometrical modifications accomplished in the optimization process include the tilt of the concentrator and receiver, the receiver displacement and the concentrator rotation along with the optimization of other relevant parameters. As a result, a significant upgrade of the monthly power on the receiver was achieved, with an average enhancement ranging from 2% to 61%, compared to a standard linear Fresnel collector without the proposed modifications. This result provides a more homogenous thermal power profile delivered along the year, which is an important requirement to place the technology in the spotlight.

Latent thermal energy storage for solar process heat applications at medium-high temperatures – A review

Solar thermal energy has the potential to cover the heat demands of industrial processes. However, there may be a time mismatch between energy supplied by the solar field and the process demand. In this case, a thermal energy storage (TES) allows the use of heat at hours without solar irradiation available. Thermal energy storage for solar hot water or heating systems using low temperatures have been optimized since many decades and are in a mature stage. Developments at high temperatures (above 200 °C) for CSP applications have also been deeply studied. However, until this present paper, limited attention has been paid to TES for solar thermal industrial applications at medium-high temperatures (120–400 °C), where there is a potentially huge demand. When talking about TES several aspects have to be discussed: the heat demand that TES is going to be designed to supply, the material where the energy will be stored and the performance of the TES system which includes not only the material but also tanks, piping and connections.In this review, food, brewery and chemical industries were identified as the industries with higher potential in which TES and solar energy could be integrated. Heat integration methodologies have been reviewed to optimize the use of the solar energy in the industrial processes.Regarding the material, latent heat storage or phase change materials (PCM) were selected for this study because they are a very promising type of storage to be integrated in thermal industrial processes, although the state of the art of latent heat thermal energy storage (LHTES) systems is still far from broad commercialization. Until now, no reviews of latent heat storage for industrial applications at medium-high temperatures (120–400 °C) have been published. Therefore, literature related to PCM and latent heat storage (LHS) systems to be used in industrial thermal processes is here reviewed in order to have a general overview of the available technologies for their integration together with solar thermal energy in industrial processes at both experimental and numerical level. More than 100 potential PCMs for heat storage applications in the range of temperatures 120–400 °C have been found. Inorganic eutectic compositions are the group with more potentially available PCM for these applications, with values of heat of fusion between 74 and 535 kJ/kg.Finally, the works related to the performance of the system from the experimental and modelling point of view were presented. The review of experimental TES systems which include PCM in the studied range of temperatures 120–400 °C showed that most of the experimental set-ups were developed for direct steam generation for CSP applications. Regarding numerical modelling, the type of configuration more simulated is the shell and tube configuration.

Stability of sugar alcohols as PCM for thermal energy storage

Sugar alcohols as phase change materials (PCM) are very promising due to their high storage capacity, safety and economic reasons. Their phase change temperatures make them suitable for medium temperature storage, which is needed for solar process heat or waste heat recovery applications. To guarantee a long PCM working lifetime they should be tested under a repeated number of freezing/melting cycles to check whether the thermophysical properties remain constant or not. The cycling stability of d-mannitol, myo-inositol and galactitol has been studied with DSC and the chemical stability with FT-IR. Myo-inositol shows a good cycling stability under the chosen measuring parameters. The cycling and chemical stability of d-mannitol up to 20 cycles can be achieved by controlling some parameters. The variable affecting it the most is the amount of oxygen in contact with it. Hence, in the storage unit this could be prevented with an inert or vacuum atmosphere.

Storage in Solar Process Heat Applications

The subject of this paper is the integration of solar energy into industrial heat supply systems – focusing on the use of solar tanks. Within the framework of the project “Solar Process Heat Standards” funded by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) load profiles of electroplating processes were measured, a typical load profile was described and simulations were done regarding the dimensioning of the solar tank volume. Depending on the load profile and process temperature, either a large tank volume or a tank-less system leads to the highest solar yields.Furthermore, a new concept of hydraulic tank integration is presented. It facilitates the quick supply of high solar temperatures which are often demanded for solar process heat applications. State of the art tank integration makes the solar system thermally inert, while simulations and measurements have already proven a considerable advantage of the new alternative.Moreover four solar process heat applications are analyzed; three belong to the electroplating industry while the fourth uses solar energy for heating water in the food industry (193 – 570 m2). Especially two of the four solar process heat plants presented severe operating errors and a high optimizing potential. One solar plant was improved in order to facilitate the new storage concept. This modification ensures the possibility of shifting between the conventional storage integration and the innovative approach for a comparative evaluation.

Levelized Cost of Heat for Linear Fresnel Concentrated Solar Systems

In this paper, a deep investigation upon levelized cost of heat (LCOH) produced by small-scale solar linear concentrating Fresnel collectors (CSLFC) is proposed. Solar industrial process heat applications have temperature requirements from about 60°C to 260°C. CSLFCs can effectively integrate conventional fossil fuel thermal systems. The study is addressed to assess technology cost projection needed to achieve competitive LCOH. So, on the basis of a framework specifically developed for these economic assessments, the best investment scenarios, in terms of industrial application, geographical location and technical design solutions, where to effectively apply the technology of CSLFC, are highlighted.The analysis has been focused on specific cost of several existing CSLFCs associated with declared performances at different operating temperatures. Two main classes of CSLFC with different total efficiency (optical and thermal) corresponding to various design solutions and specific cost were selected. The expected performances in the whole application temperature range have been evaluated through Glayx Tech proprietary simulation code, including optical and thermal unsteady analysis.A huge database coming from full CSLFC simulation varying latitude, yearly DNI, operating fluid, outlet temperature, thermal storage options, has been collected. CLSFC design and performance requirements are the key-choice to achieve competitive LCOH: the use of high efficiency – high cost components is not always rewarding in terms of final LCOH and must be attentively decided basing on site, irradiation, heat quality and LCOH target. In this perspective, CLSFCs are the most promising for industrial small scale heat applications since they show the greatest potential to reduce manufacturing costs.

Potential Assessment in Mexico for Solar Process Heat Applications in Food and Textile Industries

Industrial sector of Mexico is the second energy consumer, approximately 28% of the national consumption, according to the National Balance of Energy. A potential study carried out within the micro and small food and textile industries has established that they are using 68% of the total energy consumption as thermal energy, most supplied by liquefied gas and followed by natural gas and diesel. The processes use water, low and medium pressure steam mainly at temperatures from 60 to 180°C. In this context, solar concentrators, especially parabolic troughs, could give an important portion of the required thermal energy. The introduction in the country of a strategy change in the use of the energy is a formidable challenge. Beginning in the country with the erection of small parabolic trough plants in such industries could allow a technical and economic advancement of the technology and the benefits could be presented almost immediately. The methodology for the potential assessment for solar process heat applications in food and textile industries was based on statistical information from the National Balance of Energy, the National Directory of Economic Units and together with questionnaires, phone calls, workshops and in some cases personal interviews. According to such considerations, three scenarios were established and will be described within this paper in terms of the potential of the parabolic trough technology applied in the appropriated industries.

Manufacture of Malt and Beer with Low Temperature Solar Process Heat

The manufacture of malt and beer requires large amounts of electrical and thermal energy which is nowadays mainly based on fossil fuels. In State of the Art breweries 7.5–11.5 kWhel [1] and 16.7–33.3 kWhth [1,2] per hl of beer are needed (reference: final energy demand) and the annual output of medium to large sized breweries may easily exceed one million hl. The entire process heat demand of the thermally driven processes in breweries and malting plants can be met with heat at a temperature of between 25 and 105°C on process level [3,4]. This enables the integration of solar thermal energy supplied by conventional, non- concentrating solar thermal collector technologies such as flat-plate or evacuated tube collectors. In fact, providing thermal energy by means of solar thermal systems is mostly energy efficient if the energy from the sun is converted into heat and supplied to the process at minimum required temperature level (referred to as solar integration on process level). With this regard and in the framework of a European Union-funded demonstration project, three large-scale solar thermal systems (each with an installed thermal peak capacity ≥ 1 MWth) are being realized. The focus of the project is to demonstrate the integration of large scale solar thermal systems on process level for different applications (mashing, pasteurization of beer, drying of green malt) at process temperatures below 80°C. This script mainly focuses on technical solutions for the hydraulic integration of large solar process heat applications equipped with flat plate collectors for a direct heat supply to thermally driven processes in the brewing industry.

Performance investigation on a novel single-pass evacuated tube with a symmetrical compound parabolic concentrator

Development of the cost-effective single-pass evacuated tubular collector (SPETC) for the solar processes heat is a particular topic of active research. A novel SPETC with a symmetrical compound parabolic concentrator (CPC) has been introduced, experimentally investigated and theoretically analyzed in this paper. The novel SPETC is mainly composed of a double-glass evacuated tube deposited the selective absorbing coating, as well as six expansion joints. Correspondingly, the symmetrical CPC has been designed and fabricated using the high-reflectivity 3M mirror films pasted over the stainless steel substrate. In addition, detailed numerical models for thermal behaviors of the SPETC with the CPC reflector, based on the three-dimensional CFD method, have been developed and validated with experimental data. The objective of this paper is to report the test results of the novel SPETC with the CPC, evaluate optical and thermal performances including the heat flux distribution on the absorber surface, heat losses, as well as thermal efficiencies, thereby providing useful data for practical solar process heat application. Experimental results indicate that a daily thermal efficiency of 48% can be reached at a difference of 59.6K between inlet and ambient temperatures under a volume flow rate of 0.0077m3s−1. Corresponding numerical prediction shows that the operational volume flow rate between 0.007 and 0.01m3s−1 is suggested to the SPETC using the HTF (air) under the geometry and operational conditions in this paper. These results suggested that the novel SPETC is feasible for industrial process heat and solar cooling system combined with the adsorption chiller or the desiccant wheel.

Comparative study on two novel intermediate temperature CPC solar collectors with the U-shape evacuated tubular absorber

Two truncated compound parabolic concentrating (CPC) solar collectors, which combine the external CPC and the U-shape evacuated tube together, have been developed and tested in this paper. The CPC solar collectors are edge-ray and gap-lossless collectors with different concentration ratios of 3.06 (3×) and 6.03 (6×) and half-acceptance angles of 10° and 3°, respectively. A theoretical model of the CPC collector has been created and the detailed numerical simulation for optical, thermal and heat transfer fluid (HTF) behaviors of the CPC collector is carried out. In addition, the theoretical model has been validated using experimental results obtained by the testing system. The main objective of this paper is to report test results of the 3× and the 6× CPC solar collectors with the U-shape evacuated tube, and to evaluate thermal performance which includes the overall heat loss as well as thermal efficiency, thereby providing useful data for practical solar process heat applications at the intermediate temperature within 80°C and 250°C, such as industrial process heat and solar cooling. Experimental results indicate that the tilt angle of the 3× CPC collector is unnecessary to be adjusted in 1day, however, it should be adjusted during the year. Correspondingly, the 6× CPC collector does need to be adjusted five times in 1day due to its small half-acceptance angle. Under given test conditions, the daily thermal efficiencies of the 3× and the 6× CPC collectors can reach 40% and 46% at the collecting temperature of 200°C, respectively. These verify that these kinds of CPC solar collectors are feasible for a wide range of intermediate temperature applications.

Demonstration of Three Large Scale Solar Process Heat Applications with Different Solar Thermal Collector Technologies

The recently started European FP7 Project InSun aims to demonstrate the reliability and efficiency of three different collector technologies suitable for industrial process heat supply in different climatic regions. The technologies demonstrated reach from improved flat-plate collectors for supply temperatures of up to 95°C in moderate northern Europe climate to tracked concentrating collectors (linear Fresnel collectors and parabolic trough collectors) for supply temperatures between 160 and 250°C in hot and dry Mediterranean climate in Italy and Spain. The main problem for a fast market development if this young and innovative technology is that a reliable performance of the production process has still a much higher priority for the industrial companies than energy savings reached. In consequence often only proven and standardized solutions are considered with payback times not longer than 3 to 5 years. Apart from the cost issue which changes with changing energy prices and the industrialization of the production process of the collectors, the reliability of the technology needs to be demonstrated. Here, intelligent control strategies for the integration in different industrial processes and methods for automated performance observations are required. These topics are given a high priority within the InSun project team with ZAFH-NET as coordinating research partner, EURAC as scientific research partner and Soltigua, Solid and Solera as industrial partners. This paper reports on the preliminary design of the three installations in terms of system layout, foreseen operating conditions and the industrial processes involved.

Latent Heat Storage Systems for Solar Thermal Power Plants and Process Heat Applications

Solar thermal systems using absorber evaporating steam directly require isothermal energy storage. The application of latent heat storage systems is an option to fulfill this demand. This concept has been demonstrated mainly for low temperature heating and refrigeration applications, the experience for the power level and temperature range characteristic of solar process heat and solar thermal power plants is limited. Cost effective implementation of the latent heat storage concept demands low cost phase change materials (PCMs). These PCMs usually show low thermal conductivity limiting the power density during the charging/discharging process. This paper describes various approaches, which have been investigated to overcome these limitations. Based on fundamental PCM-research and laboratory-scale experiments, the sandwich concept has been identified to show the highest potential. The sandwich concept has been demonstrated successfully for three different storage units ranging from 2 kW to 100 kW at melting temperatures of 145°C and 225°C.

Optimization of parabolic trough solar collector system

Process heat produced by solar collectors can contribute significantly in the conservation of conventional energy resources, reducing CO2 emission, and delaying global warming. One of the major problems associated with solar process heat application is fluctuation in system temperature during unsteady state radiation conditions which may cause significant thermal and operation problems. In this paper a transient simulation model is developed for analysing the performance of industrial water heating systems using parabolic trough solar collectors. The results showed that to prevent dramatic change and instability in process heat during transient radiation periods thermal storage tank size should not be lower than 14.5 l m−2 of collector area. Small periods of radiation instability lower than 30 min do not have significant effect on system operation. During these periods when water flow rate of collector loop is doubled the time required to restore system normal operating condition increased by a ratio of 1.5. Copyright © 2005 John Wiley & Sons, Ltd.

04/01426 The potential of solar industrial process heat applications: Kalogirou, S. Applied Energy, 2004, 76, (4), 337–361

04/01426 The potential of solar industrial process heat applications: Kalogirou, S. Applied Energy, 2004, 76, (4), 337–361

The potential of solar industrial process heat applications

The temperature requirements of solar industrial process heat applications range from 60 °C to 260 °C. The characteristics of medium to medium-high temperature solar collectors are given and an overview of efficiency and cost of existing technologies is presented. Five collector types have been considered in this study varying from the simple stationary flat-plate to movable parabolic trough ones. Based on TRNSYS simulations, an estimation of the system efficiency of solar process heat plants operating in the Mediterranean climate are given for the different collector technologies. The annual energy gains of such systems are from 550 to 1100 kWh/m 2 a. The resulting energy costs obtained for solar heat are from 0.015 to 0.028 C£/kWh depending on the collector type applied. The viabilities of the systems depend on their initial cost and the fuel price. None of these costs however is stable but change continuously depending on international market trends and oil production rates. The costs will turn out to be more favourable when the solar collectors become cheaper and subsidisation of fuel is removed. Therefore the optimisation procedure suggested in this paper should be followed in order to select the most appropriate system in each case.

Thermal Energy Storage Development for Solar Electrical Power and Process Heat Applications

Development of thermal energy storage technologies for solar thermal systems has been conducted since the mid-1970s. This paper presents an overview of past and present experimental activities for electrical power and process heat applications both within and outside the United States. The factors affecting the selection of a storage technology for these applications, as well as the nature of those applications, are discussed. Future research needs are also described.