Thermal Collector System Research Articles

Predictive modelling for solar thermal energy systems: A comparison of support vector regression, random forest, extra trees and regression trees

Predictive analytics play an important role in the management of decentralised energy systems. Prediction models of uncontrolled variables (e.g., renewable energy sources generation, building energy consumption) are required to optimally manage electrical and thermal grids, making informed decisions and for fault detection and diagnosis. The paper presents a comprehensive study to compare tree-based ensemble machine learning models (random forest – RF and extra trees – ET), decision trees (DT) and support vector regression (SVR) to predict the useful hourly energy from a solar thermal collector system. The developed models were compared based on their generalisation ability (stability), accuracy and computational cost. It was found that RF and ET have comparable predictive power and are equally applicable for predicting useful solar thermal energy (USTE), with root mean square error (RMSE) values of 6.86 and 7.12 on the testing dataset, respectively. Amongst the studied algorithms, DT is the most computationally efficient method as it requires significantly less training time. However, it is less accurate (RMSE = 8.76) than RF and ET. The training time of SVR was 1287.80 ms, which was approximately three times higher than the ET training time.

Towards achieving net-zero energy communities: Investigation of design strategies and seasonal solar collection and storage net-zero

This paper explores a solar mixed-use community and its potential towards achieving net-zero energy status. This mixed-use community combines residential and commercial/institutional buildings. Energy performance of this neighbourhood is estimated in terms of energy consumption and generation potential by means of building integrated PV systems. A solar thermal collector system combined with a borehole thermal energy storage (BTES) is designed to investigate the impact on the overall performance of the neighbourhood. The design of solar thermal collectors and the sizing of short-term thermal energy storage is based on the analysis of the thermal loads for heating and domestic hot water in each district of the community.The results of the performance of the thermal collectors and BTES align with existing communities, which employ similar technologies. The results indicate that implementing energy efficiency measures together with PV systems, allows the neighbourhood to generate around 70% of its total energy consumption. The implementation of thermal collectors and seasonal storage, in this high-energy performance neighbourhood, leads to a net positive energy status.

Modeling and optimization of a solar system based on concentrating photovoltaic/thermal collector

Concentrated photovoltaic thermal (CPV/T) solar collector systems are designed to provide simultaneously thermal and electrical energies. This paper analyzes a numerical model of a photovoltaic thermal collector in order to evaluate its performances from energy and economic viewpoints. Therefore, a two dimensional numerical model has been developed and applied in this study. This electrical/thermal model is based on the energy balance of the CPV/T receiver in order to calculate the net thermal and electrical output energy. A comparison between the numerical results and those obtained by experimental studies is presented in order to prove the viability of our developed model. The results show that the output power predicted by the numerical model has a good agreement with the experimental data with low mean percentage errors. Indeed, the effects of several parameters on the performance of the system were examined and discussed in details. The simulation process has allowed evaluating the power generation of the CPV/T system and performing a comprehensive economic analysis study under Chambery and Tunisia conditions. The CPV/T system has proven its viability and feasibility especially in regions with high solar radiation.

Architectural Integration of Photovoltaic and Solar Thermal Collector Systems into Buildings for new Urban Planning

ABSTRACTThe existing buildings are responsible for use of large amount of energy for lighting, heating, cooling and use of various energy run equipments mostly powered by electricity grid from fossil energy. Today’s intention should be to replace this fossil fuel by solar energy which is free and available in abundance.At the moment, solar technologies in the form of photovoltaics PVs and solar thermal collectors STC are available in competitive prices. However, their use has not been to the expectation specially in building sector. The main reason for these technologies not being popular in building integration is the lack of good architectural quality rendered not meeting desired design considerations. Innovative approaches have to be explored in terms of design and implementation in order to match the modern technological components to the scale, proportion, material, colour scheme and balance of buildings. So, the objective of this study is to pave possible ways of integrating these technologies into buildings, both on existing and new constructions to add emphasis on the overall architectural expression in addition to producing energy. PVs and solar thermal collectors STC can deliberately be used as architectural design elements in a distinctive way. The development towards passive house, zero energy and zero emission buildings will cause a more frequent use of building integrated solar energy systems as a source of renewable energy. Many solar systems do exist on the market, and with better and better energy performance. It looks like PV integration have brought about some improvements in the architectural quality of building integration, but the solar thermal collectors STC lacks on this part to some extent. While the technical development and energy performance improvements are always in progress, the actual use of these systems in buildings is not increasing as it could and should do. Integrating these PV and solar thermal collectors STC systems into buildings is not only for clean energy but also to use them as multifunctional elements where they replace the conventional building elements. With this, the economical viability of integration is met and most importantly, they become architectural components. So the possible ways of architectural integration of PV and STC systems have been explored and analysed in this study with special focus made on the aesthetic part of integration. So the urban planners should tack into consideration the concept called nearly Zero Energy Buildings (ZEB). By the end of 2020, all EU member states need to ensure that all newly constructed buildings consume ‘nearly zero’ energy and that their energy needs are produced locally as much as possible and with renewable sources. Planning for such ZEBs in cities is therefore a difficult task since urban planners often do not have the technical knowledge to quantify the contribution of solar energy in their urban plans. This study also shows an exploration of geometrical forms of urban blocks and the potential of solar energy to the local production of energy. The following photos are practical examples of PVs and STC application systems for this study.

A Hybrid Electric and Thermal Solar Receiver

Summary Solar energy offers a promising renewable energy source; however, it is expensive to store electricity from photovoltaics (PV), the most widely deployed solar electricity technology. Solar thermal energy technologies can be paired with inexpensive thermal storage, but are more expensive overall. We have developed a solar receiver that combines PV and solar thermal systems to efficiently convert solar radiation to electricity (to be used immediately) and thermal energy (to be stored and converted to electricity on demand). This paper describes the Hybrid Electric And Thermal Solar (HEATS) receiver and models its performance. An idealized model predicts high solar-to-electricity efficiency (35.2%) with high dispatchability (44.2% of electricity from thermal energy) at an operating temperature of 775 K. Modeling using measured performance values for HEATS subcomponents predicts 26.8% efficiency and 81% dispatchability with silicon PV and 28.5% efficiency and 76% dispatchability with gallium arsenide PV, both operating at 700 K.

A comparative entropy based analysis of Cu and Fe3O4/methanol Powell-Eyring nanofluid in solar thermal collectors subjected to thermal radiation, variable thermal conductivity and impact of different nanoparticles shape

Abstract The efficiency of any nanofluid based thermal solar system depend on the thermophysical properties of the operating fluids, type and shape of nanoparticles, nanoparticles volumetric concentration in the base fluid and the geometry/length of the system in which fluid is flowing. The recent research in the field of thermal solar energy has been focused to increase the efficiency of solar thermal collector systems. In the present research a simplified mathematical model is studied for inclusion in the thermal solar systems with the aim to improve the overall efficiency of the system. The flow of Powell-Eyring nanofluid is induced by non-uniform stretching of porous horizontal surface with fluid occupying a space over the surface. The thermal conductivity of the nanofluid is to vary as a linear function of temperature and the thermal radiation is to travel a short distance in the optically thick nanofluid. Numerical scheme of Keller box is implemented on the system of nonlinear ordinary differential equations, which are resultant after application of similarity transformation to governing nonlinear partial differential equations. The impact of non dimensional physical parameters appearing in the system have been observed on velocity and temperature profiles along with the entropy of the system. The velocity gradient (skin friction coefficient) and the strength of convective heat exchange (Nusselt number) are also investigated.

Performance analysis of a multi-pass solar thermal collector system under transient state assisted by porous media

An enhanced forced convective multi-pass solar air heating collector (MPSAHC) system aided with granite pebble bed has been investigated in this present article. The air heating collector system was tested in the outdoor solar research site of Universiti Teknologi PETRONAS, Malaysia (4.385693° N and 100.979203° E). Transport pipe for movement of heated air around the system was eliminated in the design of the MPSAHC facility to minimise the thermal losses, pressure drop and the pumping cost of the hot air in the control volume. The daily ambient temperature and relative humidity range recorded during the repeated tests are 21.09–36.64 °C and 48.04–87.9%, respectively. The collector unit achieved a peak temperature of 80.29 °C while the optimum system air mass flow rate of 0.016 kgs−1 was applied. Despite high relative humidity of the environment, the stream of ambient air was heated to 48.53 °C, 57.75 °C and 71.19 °C at different positions in the MPSAHC which correspond to single pass, double pass and multi-pass effects, respectively. The porous matrix exhibited slow energy discharge at night time with air temperature difference of 14.27 °C at 18:00 h to 4.54 °C at 24:00 h over environmental air temperature. MPSAHC system delivered specific energy demand (SED) of 11.51 kWh kg−1 while the maximum thermal collector and daily average transient collector efficiencies of 72.59% and 36.38% were achieved, respectively. A good agreement has been established between reported studies and the present investigation. Although continuity of system operation at night was achieved using porous matrix but improvement is still needed to optimise the system performance.

Performance of a 5 kW hot water driven diffusion absorption chiller

This paper presents experimental results of a 5kW Diffusion-Absorption Chiller (DAC). The chiller has been tested at varying inlet generator temperatures, inlet cooling water temperatures and inlet chilled water temperatures. The lowest driving temperature to keep the bubble pump running was about 90°C with 3.6kW cooling capacity and chilled water inlet temperature being set at 18°C. The maximum cooling capacity and COP reached for the DAC was about 4.52kW and 0.45, respectively. The prototype has demonstrated a good potential for air-conditioning applications, while not requiring electricity internally for its operation and allowing coupling with waste heat or solar thermal collector systems.

Performance assessment of an unglazed solar thermal collector for envelope retrofitting

Present trends on solar thermal systems for building integration define the need of integrated solar technologies for façades. Although other possibilities exist for solar thermal systems in new buildings, solutions for a suitable integration of solar thermal systems into building retrofitting actuations are needed.This paper presents a solar thermal collector system which hybridizes already existing ventilated façade cladding systems into a low temperature solar thermal collector. Numerical and experimental data is presented.

Experimental study of a concentrated PV/T system using linear Fresnel lens

Solar energy is an alternative source of fossil fuel. Photovoltaic/thermal (PV/T) solar systems emerged as an important research area as a result of the rising global concern on the utilization of energy resources such as oil and gas. PV/T solar systems utilize a photovoltaic system to generate electricity and a thermal collector system for hot water generation. In this study, an experimental investigation of a concentrated PV/T system was conducted in December 2015. This study evaluates the performance of pure thermal and integrated PV/T solar system under a concentrated linear Fresnel lens (5.85 Sun). The characteristic of PV module indicates that the 10.9% electrical efficiency of PV cells under normal condition decreases to 7.63% as a result of solar concentration. However, the output power of PV module increased by 28%. The total efficiency of pure thermal and PV/T systems under linear solar concentration reach 46.6% and 53% respectively. These values indicate good thermal and electrical performance under the metrological weather conditions of Shanghai, China.

CONCEPTUALIZACIÓN, DESARROLLO Y CARACTERIZACIÓN TÉRMICA DE UN COLECTOR SOLAR NO ACRISTALADO PARA INTEGRACIÓN EN FACHADA

In this work, an innovative solar thermal collector system is presented for facade integration. The developed modular unglazed solar collector system is designed for low temperature energy capture, and compatible with a heat pump based combined solar thermal system. The main advantage of this system is that the lack of a glazed surface allows for its integration into common facade systems without architectural implications. Modularity, color or textures are unaffected by the integration process. This work presents the development of the collector, together with its thermal modeling and experimental assessment. Keywords: Solar collector, Facade integration, Construction, Solar systems, Ventilated facade.

Potential for large-scale solar collector system to offset carbon-based heating in the Ontario greenhouse sector

ABSTRACTIn the Ontario greenhouse sector the misalignment of available solar radiation during the summer months and large heating demand during the winter months makes solar thermal collector systems an unviable option without some form of seasonal energy storage. Information obtained from Ontario greenhouse operators has shown that over 20% of annual natural gas usage occurs during the summer months for greenhouse pre-heating prior to sunrise. A transient model of the greenhouse microclimate and indoor conditioning systems is carried out using TRNSYS software and validated with actual natural gas usage data. A large-scale solar thermal collector system is then incorporated and found to reduce the annual heating energy demand by approximately 35%. The inclusion of the collector system correlates to a reduction of about 120 tonnes of CO2 equivalent emissions per acre of greenhouse per year. System payback period is discussed considering the benefits of a future Ontario carbon tax.

Experimental Analysis of Thermoelectric Heat Exchanger for Power Generation from Salinity Gradient Solar Pond Using Low-Grade Heat

Salinity gradient solar ponds act as an integrated thermal solar energy collector and storage system. The temperature difference between the upper convective zone and the lower convective zone of a salinity gradient solar pond can be in the range of 40-60°C. The temperature at the bottom of the pond can reach up to 90°C. Low-grade heat ( < 100°C) from solar ponds is currently converted into electricity by organic Rankine cycle engines. Thermoelectric generators can operate at very low temperature differences and can be a good candidate to replace organic Rankine cycle engines for power generation from salinity gradient solar ponds. The temperature difference in a solar pond can be used to power thermoelectric generators for electricity production. This paper presents an experimental investigation of a thermoelectric generators heat exchanger system designed to be powered by the hot water from the lower convective zone of a solar pond, and cold water from the upper convective zone of a solar pond. The results obtained have indicated significant prospects of such a system to generate power from low-grade heat for remote area power supply systems.

An experimental investigation on performance analysis of air type photovoltaic thermal collector system integrated with cooling fins design

Photovoltaic thermal (PV/T) system was introduced to meet the thermal and electrical energy. The heat removal by air or water prevents the deterioration of the PV cell efficiency due to the overheating of cells. In this study, an air type single pass PV/T collector system was proposed where a number of thin rectangular fins were introduced for heat dissipation. The collector’s performance was analyzed with a fin system that was integrated by a thin flat metallic sheet (TFMS). Then, the temperature parameters were measured and compared to several operating conditions and configurations. Analytical expression was derived from the energy balance equations for each component of the design. Average temperatures from the top/rear PV surfaces, the collector back wall surface and the collector inlet/outlet temperatures were experimentally recorded under different fin numbers (0–4), mass flow rates (0.02kg/s–0.14kg/s) and solar radiations (200W/m2–700W/m2). These readings were used in calculating the thermal and electrical efficiency of the proposed PV/T system. The maximum thermal efficiency and PV efficiency were obtained about 56.19% and 13.75% respectively for four fins at 0.14kg/s of mass flow rate and 700W/m2 of solar radiation. Besides, the root mean square percentages of deviation (e) and coefficient of correlation (r) were used to validate the result while also discussing the uncertainty values. This research will be helpful to design thermal collectors and provide valuable information regarding performance improvement methods in PV/T systems.

Mixed integer linear programming for the design of solar thermal energy systems with short-term storage

In this paper a mixed integer linear programming (MILP) model is developed to facilitate the design of a solar domestic hot water system. The MILP model does so by optimising the area of roof mounted flat plate solar thermal collectors and the volume of thermal energy storage that are required to minimise the annual capital and operational cost of the overall energy system. A new formulation of the MILP is presented in which the model is decomposed into two sub-modules that are iteratively solved. One module determines the optimal sizing of the solar thermal collectors and storage tank. The other module optimises the hourly energy production of the solar collectors based on the impact that the collector inlet stream temperature has on the collector efficiency. This iterative formulation is compared to both a conventional MILP formulation and a dynamic simulation model to determine if the iterative formulation results in a design tool that is able to accurately represent the dynamic behaviour of a solar domestic hot water system, while maintaining the computational tractability and scalability of the model. The novel iterative MILP formulation is applied to a case study of an apartment building in Rheinfelden, Switzerland. The results indicate that conventional MILP formulations overestimate the amount of energy that solar thermal collectors are able to produce, resulting in an oversizing of the required thermal storage tank. However, the iterative MILP model more accurately predicts the energy production of the solar collector, leading to the more realistic sizing of the component technologies. This result is important when evaluating the financial feasibility of solar thermal collector systems in comparison to other renewable generation technologies, as an overestimation of the generation potential of solar thermal collectors may result in an incorrect assessment of their investment attractiveness.

Effect of New Ellipse Design on the Performance Enhancement of PV/T Collector: CDF Approach

Photovoltaic and thermal collectors are combined via a photo­voltaic/thermal (PV/T) collector system to increase collector efficiency. The efficiency of photovoltaic collectors is known to decrease when ambient temperature increases and vice versa. PV/T collector systems function by absorbing the heat gained from the sun via photovoltaic panels and by converting this heat into electrical energy. Simulations CFD have been investigated to explore the impact of different mass flow rates against photovoltaic and thermal efficiencies of PVT collector using FVM. New ellipse design of collectors have been modeled and investigated to generate hot water and electricity. In this simulation, the absorber collectors were assumed to be attached underneath the photovoltaic (PV) module, and water is used as a heat transfer medium in absorber collectors. The results shown that new ellipse absorber collector generates a combined PV/T efficiency of 74.3% with electrical efficiency of 13.78%. The efficiency of the PV/T system should be improved further by developed the surfaces between the absorber and solar panel (PV module). However, different types of PV cells, such as amorphous silicon cells with black mat surface properties, should be used to improve the thermal absorption of PV/T systems. Highlights: (i) A three-dimension hybrid photovoltaic/thermal solar collector module was performed in CFD software; (ii) The results agree with those obtained through steady-state characterization; (iii) The simultaneous use of new ellipse design of absorber, which absorbs much more thermal energy compared to other normal designs, increase thermal and electrical efficiency significantly.

Novel Solar Thermal Collector Systems in Polymer Design – Part 5: Fatigue Characterization of Engineering PA Grades for Pressurized Integrated Storage Collectors

A novel aging test method considering the superimposed mechanical and environmental (temperature and environmental medium) loads representative for pressurized integrated storage collectors (ICS) is described. Engineering polyamide (PA) grades with short glass fiber (GF) reinforcement, which are of high relevance for endcaps of steel-pipe ICS absorbers or all-polymeric absorber/storage-tanks, are characterized on a specimen level. Therefore, specific test devices and test arrangements for fracture mechanics specimens with or without weld-line are implemented on an electro-dynamic test machine. Fatigue crack growth kinetics data are obtained by conducting cyclic mechanical loads under various environmental testing conditions. The experimental results of two glass-fiber reinforced PA grades, using compact type specimens, performed at two different temperatures (23°C and 80°C) and in two environmental media (air and water), are compared in terms of crack growth kinetics. Moreover, the influence of welding on the crack growth kinetics for one PA grade is shown. For all specimens (unwelded and welded) the fatigue crack growth rates are enhanced in water compared to air. In welded specimens the fatigue crack growth resistance is significantly reduced compared to unwelded specimens.

Simulation of Very High Snow Loads on Solar Thermal Collectors

A new test device for the simulation and testing of very high mechanical loads on sloped roofs for a realistic rating of the snow load resistance of solar thermal collector systems was developed. Several sensors and cameras visualize the occurrence of snow load-induced damages during the test to identify structural weak points of a collector and its mounting system. In collaboration with the Swiss building insurances, a test and certification procedure was established aiming at a reduction of snow load cases.

TRANSIENT THERMAL PERFORMANCE PREDICTION METHOD FOR PARABOLIC TROUGH SOLAR COLLECTOR UNDER FLUCTUATING SOLAR RADIATION

As the effect of the global warming is becoming noticeable, the importance for environmental sustainability has been raised. Parabolic trough solar thermal collector system, which is one of the solutions to reduce the carbon dioxide emission, is a mature technology for electricity generation. Malaysia is a tropical country with long daytime, which makes suitable for solar thermal applications with parabolic trough solar thermal collectors. However, the high humidity causes the solar radiation to fluctuate. In order to simulate the solar thermal collectors’ performance at an early design stage of solar thermal power generation systems, fast still accurate transient thermal performance prediction methodis required. Although multiple transient thermal simulation methodologies exist, they are not suited especially at an early design stage where quick but reasonably accurate thermal performance prediction is needed because of their long calculation time. In this paper, a transient thermal prediction method is developed to predict exit temperature of parabolic trough collectors under fluctuating solar radiation. The method is governed by simple summation operations and requires much less calculating time than the existing numerical methods. If the radiation heat loss at the parabolic trough collector tube surface is small, the working fluid temperature rise may be approximated as proportional to the receiving heat flux. The fluctuating solar radiation is considered as a series of heat flux pulses applied for a short period of time. The time dependent solar collector exit temperature is approximated by superimposing the exit temperature rise caused by each heat flux pulse. To demonstrate the capabilities of the proposed methodology, the solar collector exit temperature for one-day operation is predicted. The predicted solar collector exit temperature captures the trend of a finite element analysis result well. Still, the largest temperature difference is 38.8K and accuracy is not satisfactory. Currently, the accuracy of the proposed method is being improved. At the same time, its capabilities are being expanded.

Lifetime modeling of polypropylene absorber materials for overheating protected hot water collectors

For the utilization of polymeric materials in high-demanding applications like solar thermal systems it is of utmost importance to define the performance requirements and to investigate the applicability of components for defined systems under service relevant conditions. This paper deals with the lifetime estimation of black-pigmented polypropylene (PP) absorber grades for overheating protected solar thermal collector systems for hot water preparation in five representative climate zones. Based on experimental aging data in hot air and heat carrier fluid at elevated temperatures (95°C, 115°C and 135°C) and climatic input data, as well as deduced loading conditions and absorber temperature distributions, the lifetime was calculated using a theoretical and an empirical extrapolation approach and assuming cumulating damages in service relevant temperature intervals. Depending on the PP grade, the extrapolation method and the location, endurance limits ranging from 8 to 50years were obtained. The PP grade with ß-spherulithic structures and less carbon black exhibited a superior performance (factor 2) compared to a well-established grade which is currently widely used for swimming pool absorbers.