Hybrid techniques to enhance solar thermal: the way forward

Solar is one of the pillars for clean and environment friendly energy. The drawback of the solar is the interruption during the night and cloudy and rainy weather. This paper presents the author’s experience on enhancing the solar thermal systems by integration techniques with either other energy resources or thermal energy storages (TES). The present works includes the hybrid solar drying through integration with thermal backup unit. The experimental results on hybrid drying showed enhancement of 64.1% for Empty Fruit Bunch, and 61.1% for chili pepper, compared with open solar mode drying. Secondly, solar water heating was proved to be sufficient to supply hot water during the day and night time by integration with TES. The experimented system was able to maintain the water hot up to the next morning. On large scale and industrial application, experimental results on modified inclined solar chimney had shown enhancement via integration with wasted flue gas. By this technique, the system was developed to operate 24 hours a day. The efficiency was enhanced by 100% in case of hybrid operation compared with solar mode operation. The research results are demonstrating that the integration techniques can contribute effectively in enhancing the performance of the thermal solar systems.The author acknowledges Universiti Teknologi PETRONAS for providing the financial, technical and logistic support to execute the solar hybrid program. The program is sponsored under many internal research funds, e.g. STIRF no. 24/07.08, STIRF no. 44/08.09, URIF 19/2012 and URIF 22/2013. Ministry of Higher Education of Malaysia is acknowledged for providing the research fund of the solar hybrid drying program under PRGS scheme

Using a side-branched volume to tune the acoustic field in a looped-tube travelling-wave thermoacoustic engine with a RC load

Travelling-wave thermoacoustic engine utilises a compact acoustic network to obtain a right time-phasing between the acoustic velocity and pressure oscillations within the regenerator to force gas parcels to experience a Stirling-like thermodynamic cycle. As such, thermal energy can be converted to mechanical work (i.e., high-intensity pressure waves). It is therefore crucial to control the time-phasing carefully to improve the performance of thermoacoustic engines. Various ways have been proposed and demonstrated for adjusting time-phasing, including both passive and active methods. The aim of this study is to introduce a new passive phase tuning method (i.e., a side-branched acoustic volume) to tune the time-phasing within a looped-tube travelling wave thermoacoustic engine. The proposed concept has been investigated both numerically and experimentally in this research. An experimental rig was simulated and designed using DeltaEC software (Design Environment for Low-amplitude ThermoAcoustic Energy Conversion). It was then constructed according to the obtained theoretical model. The result of this study showed a qualitative agreement between experimental measurement and numerical simulations, demonstrating that the proposed technique can effectively adjust the phase angle between the acoustic velocity and pressure oscillations within the loop-tube thermoacoustic engines, and improve its performance

Numerical investigation of a looped-tube travelling-wave thermoacoustic engine with a bypass pipe

A new configuration (“a looped-tube with a bypass pipe”) was recently proposed for low temperature travelling wave thermoacoustic engines and a prototype using atmospheric air as the working gas achieved an onset temperature difference as low as 65 °C. However, no further research has been reported about this new configuration to reveal its advantages and disadvantages. This paper aims to analyse this type of engine through a comprehensive numerical research. An engine of this type having dimensions similar to the reported prototype was firstly modelled. The calculated results were then qualitatively compared with the reported experimental data, showing a good agreement. The working principle of the engine was demonstrated and analysed. The research results show that an engine with such a bypass configuration essentially operates on the same thermodynamic principle as other travelling wave thermoacoustic engines, differing only in the design of the acoustic resonator. Both extremely short regenerators and a near-travelling wave resonator minimise the engine’s acoustic losses, and thus significantly reduce its onset temperature difference. However, such short regenerators likely cause severe heat conduction losses, especially if the engine is applied to heat sources with higher temperatures. Furthermore, the acoustic power flowing back to the engine core is relatively low, while a large stream of acoustic power has to propagate within its resonator to maintain an acoustic resonance, potentially leading to low power density. The model was then applied to design an engine with a much longer regenerator and higher mean pressure to increase its power density. A thermoacoustic cooler was also added to the engine to utilise its acoustic power, allowing the evaluation of thermal efficiency. The pros and cons of the engine configuration are then discussed

Numerical investigation of a looped-tube traveling-wave thermoacoustic generator with a bypass pipe

In this paper, based on the recent development of looped-tube thermoacoustic engine with a bypass pipe, we propose and numerically demonstrate a travelling wave thermoacoustic electric generator using this configuration. It essentially employs a one wave-length travelling-wave acoustic resonator which has low acoustic losses. The engine branch consists of a compliance, a inertance tube, an engine core, and an alternator. An ultra-compliant alternator (i.e., a sub-woofer) is installed in the acoustic compliance section where the local acoustic impedance is relatively low but the cross sectional area is big. The numerical simulations demonstrate its working principle, and show that it can potentially achieve comparable performance as other types of travelling wave thermoacoustic electric generators

Investigation of travelling-wave thermoacoustic engines with different configurations

Thermoacoustic systems can either generate acoustic work (i.e., p-v work) from thermal energy, or consume acoustic work to transfer heat from low to high temperature sources. They are the so-called thermoacoustic prime movers or heat pumps, essentially acting as the acoustical equivalents of Stirling engines or coolers. If a travelling sound wave propagates through a regenerator with a positive temperature gradient along the direction of sound wave propagation, the gas parcels experience a Stirling-like thermodynamic cycle. As such, thermal energy can be converted to acoustic power. Similar to Stirling engines and thermo-fluidic oscillators, thermoacoustic engines can be externally heated with various heat sources and are capable of utilising low-grade thermal energy such as industrial waste heat and solar thermal energy. Both the simplicity, and even the absence of moving parts of thermoacoustic engines demonstrate that they have the potential for developing low-cost power generators therefore, they have attracted significant research effort for developing coolers or electric generators. The target design principle of a thermoacoustic engine is to maximise acoustic power production within the thermoacoustic core whilst minimising the acoustic losses in the resonator. One of the main issues with current thermoacoustic systems is low efficiency, which is largely attributed to acoustic losses in the resonator and the regenerator. There would be a significant impact on the thermoacoustic field if a suitable travelling wave resonator were developed with the least losses. Despite the different engine configurations for developing these engines, they all work on the same thermodynamic principle, i.e., the Stirling cycle. In this study, the first issue is resolved by employing a by-pass configuration, and the second is addressed by using a side-branched volume technique. The current study focuses on the investigation of looped-tube travelling-wave thermoacoustic engines with a by-pass pipe. The novelty of such a by-pass configuration is that the by-pass and feedback pipes actually create a pure travelling wave resonator. The engine unit extracts a small amount of acoustic work from the resonator, amplifies it and sends it back to it. As the pure travelling wave resonator has very low losses, it requires very little acoustic power to sustain an acoustic resonance. This idea is analogous to children playing on swings, where a small push could sustain the swinging for a long time. The present research demonstrates that travelling wave thermoacoustic engines with such a by-pass configuration can achieve comparable performances with other types of travelling wave thermoacoustic engines which have been intensively researched. According to the results, this type of engine essentially operates on the same thermodynamic principle as other travelling wave thermoacoustic engines, differing only in the design of the acoustic resonator. The looped-tube travelling-wave thermoacoustic engine with a by-pass pipe was then implemented in the design of an engine with a much longer regenerator and higher mean pressure to increase its power density. A thermoacoustic cooler was also coupled to the engine to utilise its acoustic power, allowing evaluation of thermal efficiency. A linear alternator has also been coupled to the tested engine to develop an electric generator. This research additionally addresses the effect of a side-branched Helmholtz resonator to tune the phase in looped- tube travelling wave thermoacoustic engine. This action is performed in order to obtain the correct time-phasing between the acoustic velocity and pressure oscillations within the regenerator, to force gas parcels to execute a Stirling-like thermodynamic cycle, so that thermal energy can be converted to mechanical work (i.e., high-intensity pressure waves). By changing its volume one can change the acoustic impedance at the opening of the Helmholtz resonator, and thus adjust the acoustic field within the loop-tubed engine. It can essentially shunt away part of the volumetric velocity at the low impedance region of the engine, so that the acoustic loss can be reduced within the engine. Both the simulations and the experimental results have demonstrated that the proposed side-branched volume can effectively adjust the acoustic field within the looped-tube engine and affect its performance. There is an optimal acoustic compliance corresponding to the best performance in terms of acoustic power output and energy efficiency when the heating power input is fixed

The transverse shear deformation behaviour of magneto-electro-elastic shell

Compared to the large number of possible magneto-electro-elastic shell theories, very few exact solutions determining the in-plane stresses, electric displacements and magnetic inductions are possible. While, solving the magneto-electro-elastic shell equations in terms of thermo-magneto-electro-elastic generalized field functions on arbitrary domains and for general conditions exactly are not always possible. In the present work, a linear version of magneto-electro-elastic shell with simply supported boundary conditions, solved exactly, provided that the lamination scheme is cross-ply or anti-symmetric angle-ply laminates. The exact solution that introduced herein can measure the in-plane stresses, electric displacements and magnetic inductions. It also allow for an accurate and usually elegant and conclusive investigation of the various sensations in a shell structure. However, it is important for micro-electro-mechanical shell applications to have an approach available that gives the transverse shear deformation Behaviourfor cases that cannot examine experimentally. An investigated examples were accompanied and noteworthy conclusions were drawn which highlight the issues of the implementation of the exact solution, implication of the effects of the material properties, lay-ups of the constituent layers, and shell parameters on the static Behaviour

DRYING OF EMPTY FRUIT BUNCHES AS WASTED BIOMASS BY HYBRID SOLAR–THERMAL DRYING TECHNIQUE

Solar drying of EFB is highly feasible and economic, but the solar drying process is interrupted during cloudy or rainy days and also at night. In the present paper, a combined solar, as the main heat input, and biomass burner, as an auxiliary source of thermal energy, has been investigated experimentally to dry EFB. An experimental model consisting of a solar dryer integrated with a thermal backup unit was designed and fabricated. A series of experimental measurements were carried out in four different drying modes, namely, open sun, mixed direct and indirect solar, thermal backup, and hybrid. The results from the four modes used to dry 2.5 kg of EFB were summarized and compared. The results indicated that the solar drying mode required around 52 to 80 hours to dry the EFB, while the open sun drying mode required 100 hours. Usage of the thermal backup as heat source reduced the drying time to 48–56 hours. With the hybrid mode, the drying time was considerably reduced to 24–32 hours. The results demonstrate that the combined solar and thermal backup effectively enhanced the drying performance. The application of a solar dryer with a biomass burner is practical for massive production of solid fuels from EFB

Analysis of Solar Photovoltaic Panel Integrated with Ground Heat Exchanger for Thermal Management

In spite of high solar radiation being an advantage for the performance of solar photovoltaic (PV) panels, the caused high surface temperature of the panel surface reduces their efficiency, as well as lifetime span due to cyclic thermal stresses. PV panels are deteriorating due to two setbacks from a harsh climate: shallow temperatures during the night leading to condensation and overheating during the day leading to reduced efficiency. The present paper discusses and resolves the two setbacks in the PV performance by cooling the panel during the day and heating the panel during the night using water circulation in a ground embedded heat exchanger. Experimental and numerical methods were used to carry out the investigation on the influence of the proposed technique on the PV performance. Following the experiments, a computational model has been developed to simulate the experimental set-up. Two PV modules have been tested simultaneously in outdoor environment; one is bare and the second is integrated with ground heat exchanger. Results revealed that the integrated heat exchanger has managed to reduce the PV surface temperature by around 8oC during the daytime and rise the PV surface temperature by around 3oC more than the due temperature, at which condensation takes place during the night time. The developed technique has proved to be highly efficient as a PV thermal control method.The authors acknowledge PETRONAS – Malaysia for the financial support of the research under research grant YUTP-FRG, CS: 015LC0-206. Also, Universiti Teknologi PETRONAS (UTP), Malaysia is acknowledged for the logistic and technical support to carry out the research in the solar site of the solar thermal advanced research centre [STARC]

Review and Comparative Analysis of Renewable Energy Policies in the European Union, Russia and the United States

The activity of the world community in the field of climate and environmental conservation is increasing every year. The Paris Agreement, signed in 2015 by the majority of governments, and the additional goals set on COP26 in 2021 set the objectives of maximum reduction of greenhouse gas emissions into the atmosphere and the transition to renewable energy sources (RES). Consequently, the energy sector, as the largest sector of the world economy and the largest environmental polluter, is undergoing the greatest change. The development and implementation of an effective policy in the field of RES, which is part of the energy development strategy, is one of the factors of renewable energy market’s rapid development and stimulating the transition to clean energy. However, despite the measures taken by the world community to reduce the environmental impact of the energy sector and the development of renewable energy, the volume of greenhouse gas emissions continues to show an upward trend: from 2000 to 2021, the volume of CO2 emissions produced by the power sector increased by 74.7%. This trend might be associated with a low level of elaboration of the current renewable energy policy, with barriers to the development of the renewable energy market or with the specifics of the energy sector. The purpose of this study is to review and analyze renewable energy policies in the European Union, Russia, and the United States in order to identify specific approaches to the development of renewable energy, key tools, and barriers. The current state of the energy sectors of the considered countries was analyzed, their features were identified, and a review as well as a comparative analysis of their renewable energy policies were conducted.The research funding from the Ministry of Science and Higher Education of the Russian Federation (Ural Federal University Program of Development within the Priority-2030 Program) is gratefully acknowledged