Receiver Tube Research Articles

A special type of tube receiver unit for solar thermal power generation towers

Generating power from solar thermal systems is an effective method for realizing grid-scale dispatchable power generation and replacing conventional energy. The central receiver plays a vital function in the entire power generation system. A special type of tubular receiver was proposed in this study. The proposed receiver was intensively investigated to decrease the tube wall temperature and improve the receiver efficiency and working life. In the proposed design, the panels consist of bayonet tubes instead of circular ones. The new bayonet tube consists of two concentric tubes with different diameters, which are connected by a bayonet end cap. The heat transfer performances of the traditional, inner bayonet, and outer bayonet tubes were compared by establishing a 3D model of the tube. When no boundary heat loss is incurred, the wall temperature of the traditional tube and the molten salt temperature of the outer bayonet tube are the highest among the three. The molten salt and tube wall temperatures of the inner bayonet are the lowest, which is the desired outcome. When the boundary heat loss is considered, the outer wall temperature of the inner bayonet tube is lower than that of the traditional straight one. When the flow rate is 4.4 kg/s, the thermal efficiencies of the straight and inner bayonet tubes are 91.5 % and 96.7%, respectively. When the heat flux is non-uniform, the tube wall temperature is uneven because of the cosine effect of the heating surface. The maximum temperature of the outer wall of the inner bayonet tube is lower than that of the straight one, which indicates that the proposed design is promising in the perspective of thermal efficiency. Further simulations were performed to investigate the influence of flow rate and heat flux variations.

Influence of CNT coating on the efficiency of solar parabolic trough collector using AL2O3 nanofluids - a multiple regression approach

The investigations deals with augmentation of the efficiency of the Solar Parabolic Trough Collector (SPTC) by using CNT coat on copper receiver tube with Al2O3 nano fluid as working fluid. Carbon nano tubes of 20–40 nm is coated over the copper receiver tubes with Al2O3 (40–50 nm) as working fluid with 0.5% (vol) concentration 0.05% The cyclic heat transfer and thermal performance enhancement of SPTC has been studied for the turbulent flow with Reynolds number ranging from 3416 to 8450. Notable improvement in collector efficiency was noticed in solar trough collector when employing Al2O3 nanofluid 0.05% volume concentration. The flow rate of nanofluid varied from 0.5 to 2.0 lpm with respect to ASHRAE 93, (2010) standards for determines the collector performance. Finally, it had been observed that the collector efficiency increased at 0.05% volume concentration will increase the collector potency of 3%.

Evaluation of Heat Flux Distribution Uniformity around the Receiver Tube of Parabolic Trough Collector based on Six Statistical and Geometrical Indices

In addition to the total amount of heat flux (HF), its distribution around the receiver tube has an outstanding effect on the outlet temperature (To) and thermal efficiency (ηth) of parabolic trough collectors (PTCs). According to former researches, whatever the heat flux around the receiver tube is more uniform, the collector efficiency increases. But no index has yet been provided for the evaluation of HF distribution. In this paper, the quality of HF distribution around the receiver tube of LS-3 PTC is investigated by definition of six statistical and geometrical indices, including S.D, A.E, Int, Avg, Ust, and Bst. To investigate these indices, first, the HF around the receiver tube should be varied by the change of focal length (f) and using Compound Parabolic Concentrator (CPC). Second, the above-mentioned indices are calculated based on the statistical formulations. Third, the receiver tubes affected by the miscellaneous HF distributions (as boundary conditions) are simulated using one validated numerical method. Finally, the correlations between the specified indices and To are investigated. According to the results, the index of Int indicates the number of sun rays hit on the receiver tube. Thus this index can represent optical efficiency (ηopt). Also, the inverse of both Ust and Bst parameters are introduced as the indices of uniform HF around the receiving tube. In other words, the statistical and circumferential uniformities of HF values are two effective parameters in the definition of the HF uniformity. Meanwhile, the regression expresses the effect of Ust is 84 times more than Bst on To and ηth. Also, the overall efficiency can increase up to 2.61% using the CPC-type reflector.

Receiver tube heat transfer analysis of a CCP collector designed based on branched fractals geometry

For the development of systems related to renewable energy and specifically for thermo-solar energy, it is essential to study and analyze the different thermal phenomena of heat transfer, in search of the best conditions that allow strengthening the designs. Phenomena such as radiation, convection, and conduction are highly studied, from the field of materials to the field of infrastructure, finding day to day optimal solutions that guarantee a great use of the solar resource available on the earth's surface. This study presented the results of heat transfer analysis on a receiver pipe in a CCP; designed using the theory of branched fractal geometry to improve the heat transfer associated with concentrating solar capture systems. A fractal structure as a branch or arboreal fractal type network, influenced thermal and electrical parameters, as electrical resistance, thermal resistance, and convective heat transfer, so increasing the level branch heat transfer can be enhancement along of the pipe. The use of renewable energies in agriculture benefits the industrial processes that require a continuous power system, due to climatic conditions and geographical location is not a guarantee in food production fields, which reason solar capture systems contribute to food dehydration processes, water heating, refrigeration, and energy production. Keywords: heat transfer, fractal geometry, solar collector, fractality, fractal dimension, parabolic cylindrical concentrator, DOI: 10.25165/j.ijabe.20201305.4733 Citation: Palacios A, Amaya D, Ramos O. Receiver tube heat transfer analysis of a CCP collector designed based on branched fractals geometry. Int J Agric & Biol Eng, 2020; 13(5): 56–62.

Thermal performance analysis of a low volume fraction Al2O3 and deionized water nanofluid on solar parabolic trough collector

The present work analyzes the performance of unshielded receiver tube integrated solar parabolic trough collector where Al2O3/deionized (DI) water nanofluid of low concentrations was used as heat transfer fluid (HTF) element. Nanofluid is synthesized at various volume fractions starting from 0.2 to 1.0% with surfactant-free condition, by ultrasonic technique. Several researchers investigated the performance of higher nanofluid concentrations (1.0–5.0%) with and without surfactants on parabolic trough solar collector. The outdoor experiments are conducted for two HTF flow rates of 0.010 kg s−1 and 0.015 kg s−1. When the nanofluid is subjected as HTF, the DI water acted as a base fluid. While DI water is allowed to flow through the absorber, it performs both as HTF and heat storage fluid. The synthesized nanofluid at various volume fractions is allowed to flow through the receiver for the purpose of analyzing the thermal performance and compare the results with DI water. The collector efficiency increases with the mass flow rate as well as the concentration of nanofluid. For 0.015 kg s−1, the maximum efficiency was calculated as 59.13% (hourly) and 58.68% (average).

Thermal-hydraulic and thermodynamic performance of parabolic trough solar receiver partially filled with gradient metal foam

With the aim to improve overall thermal-hydraulic and thermodynamic performance of parabolic trough solar receiver (PTR), a new configuration with partial insertion of gradient metal foam (GMF) is proposed. The effects of GMF with pore density gradient or porosity gradient on turbulent forced convection heat transfer, flow resistance, entropy generation rate and exergetic efficiency of PTR tube are numerically analyzed. The distribution of non-uniform heat flux on receiver tube wall is calculated by Monte Carlo Ray-Trace Method, and the local thermal non-equilibrium model is used, which considers the temperature difference between metal skeleton and fluid. The numerical method is validated by experimental data. The results show that GMF enhances the heat transfer of PTR tube, with Nusselt number being increased by 43.7%–812.6%; brings the increase of flow resistance, with friction factor being 4.2 to 16.7 times of empty tube; improves the overall thermal-hydraulic performance with performance evaluation criteria ranging from 1.5–3.6. The GMF causes maximum reduction of total entropy generation rate and maximum enhancement of exergetic efficiency to be 92.6% and 24.4%, respectively. The PTR tube partially filled with GMF can obtain higher thermal-hydraulic and thermodynamic performance than that with uniform metal foam.

Hybridization of rotary absorber tube and magnetic field inducer with nanofluid for performance enhancement of parabolic trough solar collector

A considerable amount of energy is lost in the parabolic trough solar collectors due to the poor capability of working fluid in full absorption of the concentrated solar irradiation across the receiver tube. A new hybrid method is recommended here to cover up such deficiency by simultaneously using a rotary absorber tube and magnetic field inducer with nanofluid. Results showed that the combination effects of the receiver rotation and the magnetic field improve the convection mechanism in the absorber and increase both energetic and exergetic performance of the collector. The study reveals that there is an optimal rotational speed in the each magnetic field intensity for different hydrothermal and thermodynamic parameters. That is, in comparison with the case with no magnetic field and rotational tube employment, the total heat loss in the collector can be saved by 37.4% when a magnetic field of 1000 G and a rotary tube with speed of 0.4 rad/s are employed simultaneously. In this comparison, a maximum improvement of 101% and 24% in the performance evaluation criteria (PEC) and exergy efficiency of the system is achieved by employing the proposed hybrid method, respectively. Results also revealed that there is an optimal rotational speed in the each magnetic field intensity, in which employing a magnetic field at this rotational speed does not increase pressure drop for the sake of improving energetic and exergetic efficiencies of the solar collector.

Using a sunrays trap in direct-absorption solar collector (DASC) to enhance the thermal efficiency of collector

In this work, a new model of direct absorption solar collector (DASC) is presented, in which for the first time one sunrays trap is applied to capture as much solar energy as possible and consequently to enhance the efficiency of the collector. Also, the second innovation of the presented model is the sequential reflections of sunrays in the receiver tube which leads to the augmentation of sunrays path length and subsequently the reduction of the nanoparticles agglomeration based on Beer-Lambert law. The reduction of nanoparticles agglomeration can decrease the cost and higher operational stability. To achieve the higher efficiency and stability, as well as the reduced cost, the new-presented sunrays trap is comprised with an evacuated envelope surrounding the receiver tube as well as a compound parabolic concentrator (CPC) which swallows the sunrays. The walls of the receiver tube and envelope are reflective and insulated respectively which attenuate the heat losses from receiver tube in which Plasmonic nanofluid is applied to collect solar energy. The COMSOL software is applied to trace sunrays optically and then to simulate the internal space of receiver tube numerically. Using the validated simulation method, the effects of variables on collector efficiency are analyzed. These variables include the width of the CPC exit (w2), the outer diameter of receiver tube (do), absorption coefficient (α), the place of focus point, and inlet temperature (Ti). Finally, it was concluded that using presented collector not only results about 4% more efficiency than the conventional DASC, but also can significantly reduce the agglomeration of nanoparticles in the base fluid. These positive results can be achieved vesus Ti = 310 K, α.P=3.46, and do = 7 cm.

Theoretical design, material study and material selection for compact linear Fresnel reflector concentrating system

A comparative study is made between two different Compact Linear Fresnel reflector concentrating (CLFRC) systems with tubular absorber. The CLFRC systems with constant width reflectors and varying width reflectors are taken for study. The systems are analyzed with design parameters and Material study. By varying various design parameters like width of the reflector plates, shift between the plates, the height of the receiver tube from the reflector plane and diameter of the receiver tube, by using the geometrical equations calculations are done using MATLAB and the optimum values are taken for the design. The solar flux is considered to be a constant of 0.6 kW/m2. Concentrated ratio and concentrated flux are determined for each case to select the best system. Results show that the CLFRC system with constant width plates has better performance with concentration power, C.P = 3.15 kW and concentration ratio, C.R = 103.3 are better than those with varying width plates, while considering optimum design parameters of height from reflector plane, width of the plates and diameter of the receiver tube as 1.5 m, 0.03 m and 0.015 m respectively. The best system is selected through theoretical study and software analysis the system is modified with different reflectors (Glass mirror, Acrylic sheet, Chromium coated sheet, Polished Aluminum sheet) glass mirror is found to be the best reflector based on it reflectivity (ρ = 0.98) and the absorber is coated with different coating materials (Black Copper-Cu, Black Chrome- Ni-Cu/Steel, Black Nickel- Steel/Ni coated steel, Ni-Nox- Al) the best coating material is found to be Black Chrome- Ni-Cu/Steel absorber through theoretical and CFD analysis.

WITHDRAWN: Estimating allowable energy flux density for the supercritical carbon dioxide solar receiver: A service life approach

Abstract The allowable energy flux density on a solar receiver is strongly correlated with the receiver’s service life and, ultimately, the feasibility of the surrounding concentrated solar power plant. Understanding this link may enable high temperature solar receivers which are viable for driving the advanced supercritical CO2 cycle. In this study, by using a receiver’s service life approach based on the simulation of temperature, stress and creep-fatigue damage, the allowable energy flux density of a supercritical CO2 coiled tube receiver is estimated. Our analysis reveals that when solar radiation lands on the coiled tube with an absorbance of 1.0 and 0.6, the allowable flux densities are 138.8 and 172.5 kW/m2, respectively; while when directly exposed to a uniform flux distribution, the allowable energy flux density is 163.80 kW/m2. It is found that since structure failure occurs at the “weakest” region of a receiver (i.e. where the local damage exceeds the total allowable accumulated damage), decreasing the inlet temperature or increasing the flow rate can help to mitigate regions exposed to high temperature and stress, resulting in the higher allowable energy density for receivers. This study is significant because it provides design guidelines for the safe operation of emerging, high temperature, supercritical CO2 solar receivers.

Estimating allowable energy flux density for the supercritical carbon dioxide solar receiver: A service life approach

The allowable energy flux density on a solar receiver is strongly correlated with the receiver’s service life and, ultimately, the feasibility of the surrounding concentrated solar power plant. Understanding this link may enable high temperature solar receivers which are viable for driving the advanced supercritical CO2 cycle. In this study, by using a receiver’s service life approach based on the simulation of temperature, stress and creep-fatigue damage, the allowable energy flux density of a supercritical CO2 coiled tube receiver is estimated. Our analysis reveals that when solar radiation lands on the coiled tube with an absorbance of 1.0 and 0.6, the allowable flux densities are 138.8 and 172.5 kW/m2, respectively; while when directly exposed to a uniform flux distribution, the allowable energy flux density is 163.80 kW/m2. It is found that since structure failure occurs at the “weakest” region of a receiver (i.e. where the local damage exceeds the total allowable accumulated damage), decreasing the inlet temperature or increasing the flow rate can help to mitigate regions exposed to high temperature and stress, resulting in the higher allowable energy density for receivers. This study is significant because it provides design guidelines for the safe operation of emerging, high temperature, supercritical CO2 solar receivers.

Experimental evaluation of a stationary parabolic trough solar collector: Influence of the concentrator and heat transfer fluid

In this article, a parabolic trough solar collector (PTC) was built and evaluated in different configurations. The prototype was built to minimize the cost and complexity of construction and operation since these are the main difficulties related to the dissemination of this type of system. PTC was designed to operate stationary and the thermosyphon regime was used to eliminate pumping dependence. The evacuated glass receiver tube was connected directly to the thermal storage system, to avoid using additional connections. PTC was evaluated under different configurations, incorporating a concentrator or not, and using different heat transfer fluids (HTF): water and thermal oil. Parameters such as optical efficiency, thermal performance, and general coefficient of thermal loss were calculated. Despite reducing the thermal efficiency of the system, the use of the concentrator contributed to an increase of approximately 97% in the total useful energy gain. With the use of the concentrator, the maximum instantaneous efficiencies were obtained when the angle of solar incidence was close to zero and gradually reduces as the angle moves away from this value. The maximum overall heat loss coefficient of the system was 1.50 W K−1 demonstrating that the isolation of the PTC was adequate. The proposed system proved to be economically viable, with an average level heating cost of 0.035 US$ kWh−1. The proposed PTC is a high potential alternative for several medium temperature agro-industrial applications, where high efficiency is not necessary and ease of operation is important.

Shaping High Efficiency, High Temperature Cavity Tubular Solar Central Receivers

High temperature solar receivers are developed in the context of the Gen3 solar thermal power plants, in order to power high efficiency heat-to-electricity cycles. Since particle technology collects and stores high temperature solar heat, CNRS (French National Center for Scientific Research) develops an original technology using fluidized particles as HTF (heat transfer fluid). The targeted particle temperature is around 750 °C, and the walls of the receiver tubes, reach high working temperatures, which impose the design of a cavity receiver to limit the radiative losses. Therefore, the objective of this work is to explore the cavity shape effect on the absorber performances. Geometrical parameters are defined to parametrize the design. The size and shape of the cavity, the aperture-to-absorber distance and its tilt angle. A thermal model of a 50 MW hemi-cylindrical tubular receiver, closed by refractory panels, is developed, which accounts for radiation and convection losses. Parameter ranges that reach a thermal efficiency of at least 85% are explored. This sensitivity analysis allows the definition of cavity shape and dimensions to reach the targeted efficiency. For an aperture-to-absorber distance of 9 m, the 85% efficiency is obtained for aperture areas equal or less than 20 m2 and 25 m2 for high, and low convection losses, respectively.

Glasshouse-enclosed parabolic trough for direct steam generation for solar thermal-enhanced oil recovery (EOR) – energy performance assessment

ABSTRACT The present experimental work was carried out on a live plant at Sultanate of Oman for enhanced crude oil recovery by steam injection. The plant mainly consists of Glasshouse enclosed Parabolic Trough Collectors for direct steam generation at large scale. Energy performance aspects and losses occurred during the energy conversion were assessed in detailed for an evaporator loop of the plant. It was explored that the overall efficiency and losses of the installation are in the range of 46–56% and 44–54%. Energy received from the sun was in the range of 4800–6150 kW. Useful energy for steam generation varied between 2420 and 3210 kW. The maximum energy loss due to the glasshouse enclosure was about 460 kW. Similarly, radiation concentration and thermal losses were in the range of 1060–1480 kW and 480–520 kW, respectively. Both the quality and quantity of the steam generation increased significantly with increasing solar irradiation. As the energy losses occurring due to solar radiation concentration on to the receiver tubes were higher than all other kinds of losses, design parameters of trough need to be optimized in view of incidence angle, shadowing effects, and tracking errors. Detailed thermal efficiency and energy loss analysis could support to overcome the design challenges and find the opportunities for further optimization in design and development and eventually helps to reduce high capital cost for Glasshouse Enclosed Parabolic Trough installations.

Numerical Analysis of a Solar Tower Receiver Novel Design

Efficient operation of thermal solar power plants is strongly dependent on the central receiver design. In particular, as the receiver tube determines the temperature behavior inside the receiver, its geometry proves to be the main factor affecting the solar tower receiver performances. This paper investigates the effect of several 3D geometric concepts on both temperature evolution and velocity of the working fluid at the receiver, in order to obtain an enhanced design, with augmented efficiency. A novel receiver tube with helical fins is proposed, aiming an increased heat exchange surface and improved thermal conduction. Extensive numerical simulation is carried out in ANSYS CFX (CFD) to assess the performances of the proposed solar tower receiver design. An unstructured mesh, generated by a computation machine, and (k-ε) turbulence model are employed to this regard. The results show that the tubes with helical fins for solar tower receivers give a very important increase in the outlet temperature, which can reach up to 1050 K.

Convective heat transfer of molten salt-based nanofluid in a receiver tube with non-uniform heat flux

To tackle thermal challenges of solar receiver tubes due to the non-uniform radiation heat flux, the heat transfer performance of molten salt-based nanofluid was numerically investigated. Parameters influenced on the thermal performance of the receiver tube and molten salt with or without Al2O3 nanoparticles were investigated, including particle concentrations, inlet velocities, and heat flux profiles. The simulation results showed that all nanofluid performed better heat transfer performance than pure molten salt under both cosine and Gaussian-cosine heat flux boundaries. The 0.063% nanofluid maximally enhanced the heat transfer coefficient by 7.29% and Nusselt number by 6.90% under cosine heat flux boundary, and 7.25% and 6.85% under Gaussian-cosine heat flux boundary. The temperature distributions of the tube wall surfaces and the heat transfer fluid were highly non-uniform and related to heat flux boundaries. The maximum temperature of the outer and inner surfaces could be reduced by nanofluid and the highest drop was achieved by the 0.063% nanofluid, which will protect the solar receiver and prohibit the decomposition of molten salt. According to the analysis of parameters, the specific heat capacity contributed to most of the change in heat transfer performance when the mass fraction of nanoparticles was smaller than 0.125%, while the thermal conductivity became an influencing factor as the mass fraction grew. The Gnielinski correlation was found to guide for designing molten salt-based nanofluid solar receivers exposed to non-uniform radiation heat flux, after comparing with simulation results. This work could be useful as a reference to the application of molten salt-based nanofluid in the absorber tube.

Experimental analysis of parabolic trough collector system with multiple receiver geometries and reflective materials

Solar parabolic trough collector systems provide an attractive solution especially for solar thermal power generation. The performance of these systems significantly depends on receiver geometries. Therefore, in the current study, an experimental analysis has been performed using three different receiver geometries along-with two reflective materials. These receiver geometries include: simple tube (reference geometry A), receiver tube with straight absorber plate (geometry B), and receiver tube with curved absorber plate (geometry C), whereas, the reflective materials include: aluminum and stainless steel. The experimentation was performed under subtropical climate conditions of Taxila, Pakistan. From experimentation, it was identified that peak heat gain obtained from receiver geometries C and B were 71%, and 30% higher as compared to the reference geometry A, respectively. The, thermal efficiency of the system with geometry A was 20%, geometry B was 28%, and geometry C was 34%. Furthermore, two reflective materials i.e. aluminum and Stainless steel were used on geometry C which yielded best results for further parabolic trough collector performance analysis. It was observed that peak thermal efficiencies were 34.8% and 31% with aluminum and stainless steel as reflector materials. The results indicated that aluminum reflector was approximately 12% efficient as compared to stainless steel reflector. The results will help to cultivate the advantages of innovative receiver geometries and alternative reflective materials.

Parametric study on thermodynamic performance of a novel PV panel and thermal hybrid solar system

The current study presents a novel hybrid solar multi-segment photovoltaic panel/thermal (PVPT) system. The design principle of the PVPT system is introduced. The arranged optical filters are employed as the concentrator for the solar receiver tube in this PVPT system. A new optical filter design is conducted. The optical behaviour evaluation of the PVPT system is launched and the results demonstrate that with the receiver height increased, an optimal receiver height exists, leading to the highest energy flux on the thermal receiver. Under a typical fixed parameter condition, the total output power of the PVPT system is 2078.3 W. The thermodynamic performance evaluation results of the PVPT system demonstrate that with the solar irradiance increased, the total output power and overall energy efficiency of the PVPT system both increase. The increase of PV cell temperature can result in the decreases of the output power and energy efficiency of the PVPT system. As the operating temperature of the solar receiver tube increases, the output power of the PVPT system has the peak value. An optimal receiver tube temperature exists, leading to the maximum output power.

Thermohydraulic Behavior of the Liquid–Vapor Flow in the Receiver Tube of a Solar Parabolic Trough Collector

Abstract Liquid–vapor flows are present in many industrial applications. In particular, in the solar field, these flows are encountered in the new generations of solar parabolic trough collectors with direct steam generation (PTCs-DSG). In this technical brief, we compare the two-phase convective transfer and the pressure drop models in the PTC-DSG. The results show that the heat exchange coefficients estimated by Chen–Cooper, Shah, Gungor–Winterton, and Kandlikar models have same trend with difference between them. However, the models of Liu–Winterton and Steiner–Taborek seem inappropriate due to the decrease in the exchange coefficient for moderate and high steam qualities. In addition, a comparison of the models describing pressure drops with experimental data of literature was carried out. The results show that the pressure decreases as the steam quality increases and the differences between these models remain small. Friedel's model is the closest to the experiment for high inlet pressures and flow rates, while Chisholm's model gives the best prediction of the pressure drop for low inlet conditions. Effect analysis of inlet conditions shows that the increase in inlet water mass flow and decrease in pressure favor convective heat transfer. The variation of heat flux on tube wall does not affect the convective boiling heat coefficient evaluated by the Chen–Copper model, whereas it influences the calculating coefficient by Gungor–Winterton model for high heat flux and particularly for low steam qualities. Pressure drops are higher at high flow rates and low pressures.

High Temperature Solar Linear Receiver Enclosed in a Reflecting Elliptic Cavity

Abstract A linear receiver able to achieve temperatures up to 800 °C is presented. The high-temperature resistance is achieved by avoiding critical aspects (vacuum, glass-metal joints, surface films) that limit the temperature in usual receivers; the thermal insulation is obtained by enclosing the receiver tube in an elliptic reflecting cavity. The tube is placed near a focus of the cavity, and the primary collector concentrates the radiation on the other focus, where the cavity has a small opening: the ellipse reflects the radiation toward the tube and largely contains the reflected radiation and thermal emission, thus acting both as a secondary reflector and as a cavity receiver. Optical and thermal simulations show that temperatures up to 800 °C can be achieved, with optical efficiency above 70% and thermal efficiency in the range 45–85% for temperatures in the range 500–800 °C; the local overall efficiency ranges from about 40% to 66%, depending on the receiver tube emissivity and fluid temperature. In this way, the field of applicability of the linear collector technology can be significantly extended to include a vast amount of processes such as thermochemical cycles for hydrogen production, and solar fuel production processes, which require temperatures above 700 °C.