Thermodynamic Optimization of Electrical and Thermal Energy Production of PV Panels and Potential for Valorization of the PV Low-Grade Thermal Energy into Cold

In the present study, the evaluation of potential improvement of the overall efficiency of a common PV panel, valorizing the heat extracted by a heat exchanger that is integrated on its back side, either into work using an endoreversible Carnot engine or into cold by using an endoreversible tri-thermal machine consisting of a heat-driven refrigeration machine operating between three temperature sources and sink (such as a liquid/gas absorption machine), was carried out. A simplified thermodynamic analysis of the PV/thermal collector shows that there are two optimal operating temperatures and of the panels, which maximize either the thermal exergy or the overall exergy of the PV panel, respectively. The cold produced by the endoreversible tri-thermal machine during the operating conditions of the PV/thermal collector at is higher with a coefficient of performance (COP) of 0.24 thanks to the higher heat recovery potential. In the case of using the cold produced by a tri-thermal machine to actively cool of an additional PV panel in order to increase its electrical performances, the operating conditions at the optimal temperature provide a larger and more stable gain: the gain is about 12.2% compared with the conventional PV panel when the operating temperature of the second cooled panel varies from 15 to 35 °C.

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Calculation algorithm for operating parameters of steam-compressive chilling machine with adsorptive chillling unit

Computer modeling analysis control optimization ◽

10.32434/2521-6406-2020-8-2-3-9 ◽

2020 ◽

Vol 8 (2) ◽

pp. 3-9

Author(s):

E.A. Belyanovskaya ◽

◽

G.M. Pustovoy ◽

A.I. Sklyarenko ◽

M.P. Sukhyy ◽

...

Keyword(s):

Silica Gel ◽

Thermal Energy ◽

Sodium Acetate ◽

Operating Conditions ◽

Energy Utilization ◽

Coefficient Of Performance ◽

Adsorptive Capacity ◽

Operating Parameters ◽

Adsorption Refrigeration ◽

Refrigeration Unit

The work is focused on the development of an effective algorithm for calculating the operational characteristics of a steamcompressive chilling machine with an adsorptive chilling unit, which involves a cold box, an adsorber, an evaporator and a condenser, water being used as a refrigerant. An algorithm for calculating the operating parameters of the adsorptive chilling unit has been developed, which includes the determination of the cooling capacity of the steam compressor refrigeration unit, the heat load on the condenser, the power consumed by the compressor, the coefficient of performance of the steam compressor refrigeration unit, as well as the calculation of the mass of water, the mass of the adsorbent, the refrigerating capacity, the coefficient of performance of the adsorptive chilling unit and the coefficient of useful energy utilization of a steam compressive chilling machine with an adsorption chilling unit. The chilling capacity and the coefficient of performance of the adsorption chilling unit are estimated under the operating conditions of a typical steam compression chilling machine. The crucial factors affecting the efficiency of the adsorptive chilling unit are analyzed. It has been established that the chilling capacity, the coefficient of performance of the adsorption refrigeration module and the energy efficiency of the installation are determined by the thermal load on the condenser, and, therefore, by the mass of water that is desorbed and evaporated. The coefficient of performance of the adsorption chilling unit and the efficiency of the steam compressor chilling machine with the adsorptive chilling unit are estimated to be 0.878 and 4.64. The criteria for the selection of adsorbents for the adsorption module are analyzed. The temperature of regeneration is determined by the temperatures in the condenser, and the limit adsorption affects the mass of the adsorbent and the size of the adsorber. A comparison of the efficiency of adsorptive chi l l ing uni t based on silicoaluminophosphates and composite adsorbents «silica gel – sodium acetate» is carried out. The prospects of using composites «silica gel – СН3СООNa» are shown. The optimal composition of the composite was established, which corresponds to the minimal size of the adsorber, (80% sodium acetate and 20% silica gel). The prospects of using adsorptive conversion of thermal energy for utilization of low-potential thermal energy during the operation of steam compressive chilling machine are shown. Keywords: adsorptive conversion of heat energy, composite adsorbent, steam compressive chilling unit, adsorption, adsorptive capacity.

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Energy Analysis of a Novel Ejector-Compressor Cooling Cycle Driven by Electricity and Heat (Waste Heat or Solar Energy)

Sustainability ◽

10.3390/su12198178 ◽

2020 ◽

Vol 12 (19) ◽

pp. 8178

Author(s):

Fahid Riaz ◽

Kah Hoe Tan ◽

Muhammad Farooq ◽

Muhammad Imran ◽

Poh Seng Lee

Keyword(s):

Low Temperature ◽

Thermal Energy ◽

Waste Heat ◽

Solar Thermal ◽

Coefficient Of Performance ◽

Condensation Temperature ◽

Low Grade ◽

Solar Thermal Energy ◽

Temperature Heat ◽

Vapour Compression

Low-grade heat is abundantly available as solar thermal energy and as industrial waste heat. Non concentrating solar collectors can provide heat with temperatures 75–100 °C. In this paper, a new system is proposed and analyzed which enhances the electrical coefficient of performance (COP) of vapour compression cycle (VCC) by incorporating low-temperature heat-driven ejectors. This novel system, ejector enhanced vapour compression refrigeration cycle (EEVCRC), significantly increases the electrical COP of the system while utilizing abundantly available low-temperature solar or waste heat (below 100 °C). This system uses two ejectors in an innovative way such that the higher-pressure ejector is used at the downstream of the electrically driven compressor to help reduce the delivery pressure for the electrical compressor. The lower pressure ejector is used to reduce the quality of wet vapour at the entrance of the evaporator. This system has been modelled in Engineering Equation Solver (EES) and its performance is theoretically compared with conventional VCC, enhanced ejector refrigeration system (EERS), and ejection-compression system (ECS). The proposed EEVCRC gives better electrical COP as compared to all the three systems. The parametric study has been conducted and it is found that the COP of the proposed system increases exponentially at lower condensation temperature and higher evaporator temperature. At 50 °C condenser temperature, the electrical COP of EEVCRC is 50% higher than conventional VCC while at 35 °C, the electrical COP of EEVCRC is 90% higher than conventional VCC. For the higher temperature heat source, and hence the higher generator temperatures, the electrical COP of EEVCRC increases linearly while there is no increase in the electrical COP for ECS. The better global COP indicates that a small solar collector will be needed if this system is driven by solar thermal energy. It is found that by using the second ejector at the upstream of the electrical compressor, the electrical COP is increased by 49.2% as compared to a single ejector system.

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Recovery and Utilization of Low-Grade Waste Heat in the Oil-Refining Industry Using Heat Engines and Heat Pumps: An International Technoeconomic Comparison

Energies ◽

10.3390/en13102560 ◽

2020 ◽

Vol 13 (10) ◽

pp. 2560 ◽

Cited By ~ 1

Author(s):

Nikunj Gangar ◽

Sandro Macchietto ◽

Christos N. Markides

Keyword(s):

Heat Source ◽

Thermal Energy ◽

Heat Pumps ◽

Coefficient Of Performance ◽

Oil Refining ◽

Low Grade ◽

Energy Prices ◽

Steam Generation ◽

Electricity Prices ◽

Oil Refineries

We assess the technoeconomic feasibility of onsite electricity and steam generation from recovered low-grade thermal energy in oil refineries using organic Rankine cycle (ORC) engines and mechanical vapour compression (MVC) heat pumps in various countries. The efficiencies of 34 ORC and 20 MVC current commercial systems are regressed against modified theoretical models. The resulting theoretical relations predict the thermal efficiency of commercial ORC engines within 4–5% and the coefficient of performance (COP) of commercial MVC heat pumps within 10–15%, on average. Using these models, the economic viability of ORC engines and MVC heat pumps is then assessed for 19 refinery streams as a function of heat source and sink temperatures, and the available stream thermal energy, for gas and electricity prices in selected countries. Results show that: (i) conversion to electrical power with ORC engines is, in general, economically feasible for heat-source temperatures >70 °C, however with high sensitivity to energy prices; and (ii) steam generation in MVC heat pumps, even more sensitive to energy prices, is in some cases not economical under any conditions—it is only viable with high gas/low electricity prices, for large heat sources (>2 MW) and higher temperatures (>140 °C). In countries and conditions with positive economics, payback periods down to two years are found for both technologies.

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Improving Performance of Refrigerant Cooled Steam Power Plant by Using Cooling Thermal Storage

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.3078385 ◽

2009 ◽

Vol 131 (5) ◽

Cited By ~ 4

Author(s):

A. S. Hegazy

Keyword(s):

Operating Conditions ◽

Coefficient Of Performance ◽

Combined System ◽

Steam Power ◽

Storage Container ◽

Peak Loads ◽

Excess Power ◽

Steam Plant ◽

Refrigeration Machine ◽

Plant Power

It is proposed in the current paper to combine the steam plant with two refrigeration cycles and a cooling storage container. Throughout the time of a day, the steam plant is made to work at full power, where the excess power generated over the electric power demand is used to drive the compressors of the refrigeration cycles. The stored cooling is used for dissipating the heat absorbed by the cooling refrigerant in the steam condenser during the period of peak-loads, while the two refrigeration machines are stopped. In this way, the energy used for driving the refrigeration machine is saved so that the whole power generated by the steam plant is exported to the grid. Energy analyses of the proposed combined system has led to inferring that the net power of the steam plant during the period of exclusive direct cooling of the steam condenser (only the first refrigeration machine is running) is about 70–86% of the whole power generated by the steam plant when the coefficient of performance of the first refrigeration cycle lies in the range of 4–10. Also, it has been found that relatively small coefficients of performance of the first and second cycles, less than 6 and 1.5, respectively, result in low net power of the steam plant over the period of charging the cooling storage container (both refrigeration machines run in unison). In this case, the net plant power amounts to less than 26% of the total generated plant power when the time of storing the cooling is lower than double the time of the peak-loads. This necessitates increasing the storing time to assure reasonable available power to be exported to the grid. Economical analyses of the proposed system have showed that both the capital cost and energy charges are less for the proposed system than that of the steam plant without cooling storage for practically possible operating conditions.

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Overview of the hybrid solar system

Analecta Technica Szegedinensia ◽

10.14232/analecta.2020.1.100-108 ◽

2020 ◽

Vol 14 (1) ◽

pp. 100-108

Author(s):

Mohammed Alktranee ◽

Péter Bencs

Keyword(s):

Hybrid Systems ◽

Thermal Energy ◽

Rural Areas ◽

Electric Energy ◽

Operating Conditions ◽

Solar Thermal ◽

Geothermal System ◽

Pv Panel ◽

Separate System ◽

Continuous Power

This paper investigates the uses of solar energy systems in various applications to define the most appropriate system that has highly efficient and reliable. Most of the urban even rural areas that suffer from lack of continuous power supplies it prefer to depend on hybrid systems like solar/wind systems, solar/geothermal system and solar/diesel-battery systems. Investigation indicates that hybrid systems could meet the required loads in different proportions depending on the operating conditions and components of the hybrid system compare with the separate system but has complexity regarding their components of the system with the high initial cost Moreover, Utilize hybrid solar/thermal system is more sufficient than had systems that mentioned as a result of the improvements at his parts to increase the overall efficiency by use PCM, nanofluid or a mix of PCM - nanofluid as cooling the PV panel to keep the efficiency of the solar cells and increase thermal energy. Thus, hybrid solar/thermal systems had proven effective to meet the required loads of electric energy and good capacity to provide thermal energy simultaneously without toxic emissions with a negligible complexity of its components.

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Thermal Energy Storage Through Melting of a Commercial Phase Change Material in an Annulus with Radially Divergent Longitudinal Fins

International Journal of Thermofluid Science and Technology ◽

10.36963/ijtst.20070102 ◽

2020 ◽

Vol 7 (1) ◽

Author(s):

Tonny Tabassum Mainul Hasan ◽

Latifa Begum

Keyword(s):

Energy Storage ◽

Phase Change ◽

Phase Change Material ◽

Thermal Energy ◽

Thermal Energy Storage ◽

Storage System ◽

Operating Conditions ◽

Melting Time ◽

Bottom Part ◽

Change Material

This study reports on the unsteady two-dimensional numerical investigations of melting of a paraffin wax (phase change material, PCM) which melts over a temperature range of 8.7oC. The PCM is placed inside a circular concentric horizontal-finned annulus for the storage of thermal energy. The inner tube is fitted with three radially diverging longitudinal fins strategically placed near the bottom part of the annulus to accelerate the melting process there. The developed CFD code used in Tabassum et al., 2018 is extended to incorporate the presence of fins. The numerical results show that the average Nusselt number over the inner tube surface, the total melt fraction, the total stored energy all increased at every time instant in the finned annulus compared to the annulus without fins. This is due to the fact that in the finned annulus, the fins at the lower part of the annulus promotes buoyancy-driven convection as opposed to the slow conduction melting that prevails at the bottom part of the plain annulus. Fins with two different heights have been considered. It is found that by extending the height of the fin to 50% of the annular gap about 33.05% more energy could be stored compared to the bare annulus at the melting time of 82.37 min for the identical operating conditions. The effects of fins with different heights on the temperature and streamfunction distributions are found to be different. The present study can provide some useful guidelines for achieving a better thermal energy storage system.

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Heat Pump Bridge Analysis Using the Modified Energy Transfer Diagram

Energies ◽

10.3390/en14010137 ◽

2020 ◽

Vol 14 (1) ◽

pp. 137

Author(s):

Florian Schlosser ◽

Heinrich Wiebe ◽

Timothy G. Walmsley ◽

Martin J. Atkins ◽

Michael R. W. Walmsley ◽

...

Keyword(s):

Energy Transfer ◽

Heat Pump ◽

Heat Recovery ◽

Heat Pumps ◽

Coefficient Of Performance ◽

Combined Application ◽

Recovery Potential ◽

Composite Curve ◽

And Performance ◽

The Individual

Heat pumps are the key technology to decarbonise thermal processes by upgrading industrial surplus heat using renewable electricity. Existing insight-based integration methods refer to the idealised Grand Composite Curve requiring the full exploitation of heat recovery potential but leave the question of how to deal with technical or economic limitations unanswered. In this work, a novel Heat Pump Bridge Analysis (HPBA) is introduced for practically targeting technical and economic heat pump potential by applying Coefficient of Performance curves into the Modified Energy Transfer Diagram (METD). Removing cross-Pinch violations and operating heat exchangers at minimum approach temperatures by combined application of Bridge Analysis increases the heat recovery rate and reduce the temperature lift to be pumped at the same time. The insight-based METD allows the individual matching of heat surpluses and deficits of individual streams with the capabilities and performance of different market-available heat pump concepts. For an illustrative example, the presented modifications based on HPBA increase the economically viable share of the technical heat pump potential from 61% to 79%.

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Different Techniques to Mitigate Partial Shading in Photovoltaic Panels

Energies ◽

10.3390/en14133863 ◽

2021 ◽

Vol 14 (13) ◽

pp. 3863

Author(s):

Tiago Alves ◽

João Paulo N. Torres ◽

Ricardo A. Marques Lameirinhas ◽

Carlos A. F. Fernandes

Keyword(s):

Cell Model ◽

Research Work ◽

Experimental Tests ◽

Operating Conditions ◽

Pv System ◽

Partial Shading ◽

System Architectures ◽

Pv Systems ◽

Advantages And Disadvantages ◽

Pv Panel

The effect of partial shading in photovoltaic (PV) panels is one of the biggest problems regarding power losses in PV systems. When the irradiance pattern throughout a PV panel is inequal, some cells with the possibility of higher power production will produce less and start to deteriorate. The objective of this research work is to present, test and discuss different techniques to help mitigate partial shading in PV panels, observing and commenting the advantages and disadvantages for different PV technologies under different operating conditions. The motivation is to contribute with research, simulation, and experimental work. Several state-of-the-artsolutions to the problem will be presented: different topologies in the interconnection of the panels; different PV system architectures, and also introducing new solution hypotheses, such as different cell interconnections topologies. Alongside, benefits and limitations will be discussed. To obtain actual results, the simulation work was conducted by creating MATLAB/Simulink models for each different technique tested, all centered around the 1M5P PV cell model. The several techniques tested will also take into account different patterns and sizes of partial shading, different PV panel technologies, different values of source irradiation, and different PV array sizes. The results will be discussed and validated by experimental tests.

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