PVT Systems Research Articles

Minimization of Residential Energy Costs for PV-SWH and PV-T Systems

Abstract Photovoltaic (PV) systems transfer solar energy into electric form. PV-T is a hybrid system that converts solar radiation into electrical and thermal energy. For residential users with limited solar panel area, there are two options to achieve economic use of solar energy. One is to install both PV and solar water heater (SWH) systems, called PV-SWH, another one is to apply the PV-T system. In this work, a residential household energy cost model is built up that includes electric vehicle (EV), energy storage system (ESS), and the back-up electricity system in PV-SWH or hybrid PV-T. The model is used to explore operation strategies to minimize user’s energy cost. The case study results suggest that the hybrid PV-T system provides more benefits for the end user from long-term perspective. Compared with typical operation without optimization, the cost saving with the proposed strategy is evident.

Numerical and outdoor real time experimental investigation of performance of PCM based PVT system

Photovoltaic power generation is a suitable option to counter depleting and environmentally hazardous fossil fuels. However, increased cell temperature of the photovoltaic module reduces the electrical performance. Therefore, for enhancing the electrical performance as well as to obtain the useful thermal, a combined photovoltaic thermal system is suitable technology. Furthermore, the addition of phase change materials into photovoltaic thermal systems adds more dual benefits in terms of cooling of PV cell as well as heat storage. Hence, there are still issues to transfer heat from the system efficiently, which cause lower performance of PVT and PVT-PCM systems. In this paper, the aluminium material of thermal collector is used by introducing a novel design to enhance heat transfer performance, which is assembled in PVT and PVT-PCM systems. Experimental validation is carried out for the 3D FEM-based numerical analysis with COMSOL Multiphysics® at 200 W/m2 to 1000 W/m2 varying irradiation levels while keeping mass flow rate fixed at 0.5LPM and inlet water temperature at 32 °C. The experiment is carried out at outdoor free weather conditions with passive cooling of the module by an overhead water tank scheme. A good agreement in numerical and experimental results is achieved through experimental validation. Cell temperature reduction of 12.6 °C and 10.3 °C is achieved from the PV module in case of the PVT-PCM system. The highest value of the electrical efficiency achieved is 13.72 13.56% for PV and 13.85 and 13.74% for PVT numerically and experimentally respectively. Similarly, for PVT-PCM, electrical efficiency is achieved as 13.98 and 13.87% numerically and experimentally respectively. In the case of the PVT system, electrical performance is improved as 6.2 and 4.8% and for PVT-PCM, it is improved as 7.2 and 7.6% for numerically and experimentally respectively.

Comparative investigation of performances for HIT-PV and PVT systems

Crystalline silicon heterojunction solar cells are a promising candidate for high efficiency solar cells, and the heterojunction photovoltaic (HIT-PV) module is strongly dependent on the temperature. In this study, we design three heterojunction photovoltaic modules to improve the performance by preventing from over-heating, with, glass, Tedlar/Polyethylene terephthalate/Tedlar (TPT) and aluminum substrates, respectively. The efficiencies of those HIT-PV modules are investigated under four different outdoor climates. The aluminum-module shows the best thermal dissipation; while the glass-module/TPT-module have the better electrical efficiency and electrical energy, since there is the high reflectivity layer on the surface of the glass (and TPT) substrates rather than the aluminum substrate. In order to increase the output power of HIT-PV modules, we design a heterojunction photovoltaic thermal (HIT-PVT) system based on HIT solar cells and aluminum thermal collector. The measured results of HIT-PVT system show that the coolant circulation increase the output power, and the HIT-PVT module can provide the domestic hot water supply (up to 51.2 °C) under outdoor conditions. In addition, the cost of HIT-PVT systems are much lower than those of the conventional photovoltaic systems, and the investment payback time can be less than 3 years.

Overview of Bifluid-based Photovoltaic Thermal (PVT) Systems

<p>This review presents various research and development, as well as design and performances of bifluid-based PVT systems. Moreover, the development of PVT system is a very promising area of research. PVT systems using in various applications, such as solar drying, solar cooling, water heating, desalination, and pool heating. With the recognition of the potentials and contributions of PV system, considerable research has been conducted to attain the most advancement which may produce reliable and sustainable PVT system. The cooling system’s design refers to the absorber design which mostly focuses on water and air-based PVT systems. An air-based system has been developed through different absorber configurations, air flow modes and single- or double-pass design. Bifluid-based PVT system is used to remove heat accumulated in a PV panel and reuses the waste heat (hot air and water) in an appropriate way. PV, thermal and PVT efficiencies of bifluid PVT systems were 6.6%-18.6%, 31%–90% and 60%-83%, respectively. </p>

Energy and exergy analysis of the PVT system: Effect of nanofluid flow rate

Solar energy is one of the promising resources to fulfil the energy demands to some level in place of fossil fuels to avoid environmental pollution. The efficiency of solar technology, e.g. photovoltaic panels, thermal systems or a combination of both technologies as photovoltaic thermal is a concern to increase at an optimum level. A three-dimensional numerical analysis of PVT systems using water and MWCNT-water nanofluid has been completed with FEM based software COMSOL Multiphysics®. A numerical investigation has been validated by the indoor experimental research at different mass flow rates of 30 to 120 L/h while keeping solar irradiation fixed at 1000 W/m2, inlet fluid and ambient temperature at 32 and 25 °C, respectively. Percent improvement of electrical efficiency of PV with nanofluid cooling at flow rate 120 L/h is obtained about 10.72 and 12.25% of numerical and experimental cases respectively. Optimization of the nanofluid for weight concentration is achieved at 0.75% MWCNT-water. Solar cell temperature reduces about 0.72 °C experimentally and 0.77 °C numerically per 10 L/h flow rate increment. Approximately 7.74 and 6.89 W thermal energy is enhanced per 10 L/h flow rate increment in numerical and experimental studies respectively. Percentage increment of thermal efficiency is found as 5.62% numerically and 5.13% experimentally for PVT system operated by water/MWCNT nanofluid with compared to water.

Characterization of PVT systems equipped with nanofluids-based collector from entropy generation

In this study, a PVT system equipped with a nanofluid-based collector is investigated from entropy generation viewpoint. The purpose of this study is characterizing a PVT system in order to enhance its performance. For this purpose, the effects of adding nanoparticles on entropy generation are investigated using a 2D-transient numerical model validated with experimental measurements. The experiments were performed for various nanofluids (Al2O3/water, TiO2 /water and ZnO /water by 0.2wt%, and SiO2 /water by 1wt% and 3wt%) on a PV system equipped with a serpentine collector tube to increase its efficiency. A good agreement is observed between model calculations and those of the measurements. The effect of various metallic and metalloid nanofluid mass fractions on thermal (locally) and frictional fluid entropy generations, and the total entropy generation of the PVT system are investigated. The effects of various nanofluids on thermo-physical properties, coolant fluid heat transfer, and energy and exergy efficiencies are also examined. The results show that adding nanoparticles improves the thermal exergy efficiency of the system. ZnO /water had the highest and SiO2 /water had the lowest thermal exergy efficiency. In addition, it is observed that by increasing the mass fraction of metallic-water nanofluids (Al2O3, TiO2 and ZnO /water) in the range considered in this study, less entropy is generated due to the improvement made in the nanofluid thermo-physical properties. For Al2O3 /water nanofluid, the best performance in terms of thermal and total entropy generation is obtained. The ZnO /water nanofluid is also found to generate the least frictional entropy generation. However for metalloid nanofluid considered in this study (SiO2/water nanofluid) is found to have the most entropy generation which is not favorable.

Explore the performance limit of a solar PV – thermochemical power generation system

Performance limit of a solar hybrid power generation system integrating efficient photovoltaic (PV) cells and methanol thermal (T) decomposition is explored from a thermodynamic perspective within the capability of state-of-the-art technologies. This type of PVT system features potentially high “net solar-to-electric efficiency” in general, primarily resulting from a key difference in the design of the thermal part compared with conventional PVT systems, i.e. replacing heat engines by a thermochemical power generation module for thermal energy utilization. Key design parameters of the system, including PV cell type, emissivity, solar concentration ratio and solar concentrator type, are individually studied. A system combining all such optimized aspects is projected to achieve net solar-to-electric efficiencies up to 51.5%, after taking all major (e.g. optical, radiative) losses into consideration. This study reveals important insights and enriches understanding on design principles of efficient PVT systems aimed at comprehensive and effective utilization of solar energy.

PVT collector technologies in solar thermal systems: A systematic assessment of electrical and thermal yields with the novel characteristic temperature approach

Abstract Photovoltaic-thermal PVT collectors generate solar electricity and heat in a single component. The annual electrical and thermal yields depend in particular on the efficiency of the PVT collector technology, climate, and the type of solar thermal system. This paper provides a systematic comparison of the performance of unglazed, glazed, and PVT collectors with low-emissivity coatings. The yields of these PVT technologies are assessed in four types of solar thermal systems including domestic hot water systems and combi systems in single and multi-family homes at four European locations. For this purpose, an empirical PVT performance model is presented, validated and implemented into TRNSYS. Analyzing the simulation results, the assessed PVT collector technologies reach either high electrical or high thermal yields. This compromise originates from the technological trade-off between a good optical efficiency versus a high level of insulation. Thermally optimized glazed PVT collectors with low-emissivity coatings achieve the highest overall yields and the best energetic utilization of the collector area. These collectors achieve up to three times the electrical output compared to a side-by-side installation of flat plate collectors and PV modules with equal thermal output. The variations between the investigated systems can be attributed to the governing operating temperatures of the PVT collector which are found to be of central relevance. A novel approach puts these temperatures into the focus and introduces the characteristic temperature Tchar as new indicator with a strong correlation to both electrical and thermal yields. This approach can be used to assess electrical and thermal yields of PVT systems and select a suitable collector technology for a given application.

Effect of tilt angle and connection mode of PVT modules on the energy efficiency of a hot water system for high-rise residential buildings

The tilt angle and connection mode of PVT modules are critical factors influencing the energy efficiency of PVT systems. To evaluate their effect, we built a PVT hot water system which is naturally driven by gravity and the PVT modules are installed on vertical facades of high-rise residential buildings. We develop a dynamic model for the simulation of the PVT hot water system. The simulation results are in good agreement with indoor experimental data. Compared with parallel connection, electric power for series connection decreases by 2.0%, thermal energy increases by 11.4% and total energy increases by 5.4%. The connection mode has more obvious influences on thermal energy than electrical power. Considering only total energy, PVT modules with a tilt angle of 20° can produce maximum energy benefits. However, the projection lengths of PVT modules should also be considered when selecting the optimum tilt angle. The optimum tilt angle is chosen as 40° when both total energy and projection length are considered. These findings are good references for the installation of PVT modules on vertical facades of high-rise residential buildings.

동적 시뮬레이션을 이용한 태양광열 시스템의 성능특성 분석

Purpose: A photovoltaic/thermal system is a solar collector combining photovoltaic module with a solar thermal collector, which produces electricity and heat at the same time. PVT system removes heat from PV module through air or liquid that would help to raise the efficiency of the PV systems performance. Many innovative systems and products have been put forward and their quality evaluated by academics and professionals. However, even though various of PVT system were developed and several systems were applied to practical use, there have been few researches for the performance analysis using the dynamic simulation. Method: In this study, the review of recent research and development trend for PVT systems were conducted. Furthermore, in order to develop the optimum design method, the performance analysis for PVT system was conducted by a dynamic simulation. Result: In the results, it was found that the performance of PVT system significantly depends on the ambient temperature and solar radiation. Moreover, in the weather condition of Seoul, average efficiency of electricity and heat in heating season were 13.79 and 41.85%, and they in cooling season were 14.39% and 26.18%, respectively.

Design and Dynamic Simulation of a Combined System Integration Concentrating Photovoltaic/Thermal Solar Collectors and Organic Rankine Cycle

This study presents the design of a novel ultra-high efficient solar power system. The system is equipped with a concentrating PhotoVoltaic/Thermal (CPVT) solar collectors bottomed by an Organic Rankine Cycle (ORC). The basic idea is to use a high temperature CPVT device producing simultaneously electricity and hot diathermic oil. Then, this hot fluid is used to supply heat to the Organic Rankine Cycle producing additional electricity. The collector is based on a combination of a parabolic dish concentrating solar thermal collector and a high efficiency solar photovoltaic collector. Among the possible high-temperature PVT systems, this paper is focused on a system consisting in a dish concentrator and in a triple-junction PV layer. In particular, the prototype consists in a parabolic dish concentrator and a planar receiver. The system is equipped with a double axis tracking system. The bottom surface of the receiver is equipped with triple-junction silicon cells whereas the top surface is insulated. Similarly, the ORC subsystem is equipped with tube and shell heat exchangers, a pump and an expander. In order to analyze the performance of the CPVT collector and ORC cycle, detailed mathematical models were implemented. These models are based on zero-dimensional energy balances on the control volumes of the system. The simulation model allows one to calculate in detail the temperatures of the main components of the system and the main energy flows. Both CPVT and ORC models are integrated in a more complex dynamic simulation model, developed in TRNSYS environment. Here, additional components are included in the system: Pump, tank, controllers, valves, etc. The input parameters of the model include weather conditions (temperature, insolation, wind velocity, etc.) and the geometrical/material parameters of the systems. This novel system was compared with a more conventional one, consisting of a concentrating PV collector equipped with III-V cells. Results showed that such second system (only CPVT) is more profitable from an economical point of view, with a 20 years Net Present Value 15% higher than the novel system (CPVT+ORC). Conversely, the novel (ORC+CPVT) system produces 6% more electrical energy.

A UK-based assessment of hybrid PV and solar-thermal systems for domestic heating and power: System performance

The goal of this paper is to assess the suitability of hybrid PVT systems for the provision of electricity and hot water (space heating is not considered) in the UK domestic sector, with particular focus on a typical terraced house in London. A model is developed to estimate the performance of such a system. The model allows various design parameters of the PVT unit to be varied, so that their influence in the overall system performance can be studied. Two key parameters, specifically the covering factor of the solar collector with PV and the collector flow-rate, are considered. The emissions of the PVT system are compared with those incurred by a household that utilises a conventional energy provision arrangement. The results show that for the case of the UK (low solar irradiance and low ambient temperatures) a complete coverage of the solar collector with PV together with a low collector flow-rate are beneficial in allowing the system to achieve a high coverage of the total annual energy (heat and power) demand, while maximising the CO2 emissions savings. It is found that with a completely covered collector and a flow-rate of 20L/h, 51% of the total electricity demand and 36% of the total hot water demand over a year can be covered by a hybrid PVT system. The electricity demand coverage value is slightly higher than the PV-only system equivalent (49%). In addition, our emissions assessment indicates that a PVT system can save up to 16.0tonnes of CO2 over a lifetime of 20years, which is significantly (36%) higher than the 11.8tonnes of CO2 saved with a PV-only system. All investigated PVT configurations outperformed the PV-only system in terms of emissions. Therefore, it is concluded that hybrid PVT systems offer a notably improved proposition over PV-only systems.

Optimizing limited solar roof access by exergy analysis of solar thermal, photovoltaic, and hybrid photovoltaic thermal systems

An exergy analysis was performed to compare a conventional (1) two panel photovoltaic solar thermal hybrid (PVT x2) system, (2) side by side photovoltaic and thermal (PV+T) system, (3) two module photovoltaic (PV) system and (4) a two panel solar thermal (T x2) system with identical absorber areas to determine the superior technical solar energy systems for applications with a limited roof area. Three locations, Detroit, Denver and Phoenix, were simulated due to their differences in average monthly temperature and solar flux. The exergy analysis results show that PVT systems outperform the PV+T systems by 69% for all the locations, produce between 6.5% and 8.4% more exergy when matched against the purely PV systems and created 4 times as much exergy as the pure solar thermal system. The results clearly show that PVT systems, which are able to utilize all of the thermal and electrical energy generated, are superior in exergy performance to either PV+T or PV only systems. These results are discussed and future work is outlined to further geographically optimize PVT systems.

Opportunity to use PVT systems for water heating in industry

This paper presents a technical and economical assessment of the opportunity to use PVT systems for water heating in industry. For this purpose, a mathematical model is developed to evaluate the energy parameters and economic indicators according to three variables: solar irradiance, air temperature and water supply temperature. The critical reduced temperature parameter is defined corresponding to the zero difference between the output and input water temperature in the PVT system. The mathematical model developed is used to simulate the operation of such a system under different climatic locations in Romania. Numerical analysis revealed the influence of three variables on the energy parameters and economic indicators. The conclusion is that using a PVT system for water heating in industry is economically attractive, in the climatic conditions of Romania, and the payback period is lower than its lifetime.

Detailed analysis of the energy yield of systems with covered sheet-and-tube PVT collectors

Solar cells have a typical efficiency in the range of 5–20%, implying that 80% or more of the incident solar energy can be harvested in the form of heat and applied for low-temperature heating. In a PVT collector one tries to collect this heat. In this work, the electrical and thermal yield of solar domestic hot water systems with one-cover sheet-and-tube PVT collectors were considered. Objectives of the work were to understand the mechanisms determining these yields, to investigate measures to improve these yields and to investigate the yield consequences if various solar cell technologies are being used. The work was carried out using numerical simulations. A detailed quantitative understanding of all loss mechanisms was obtained, especially of those being inherent to the use of PVT collectors instead of PV modules and conventional thermal collectors. The annual electrical efficiencies of the PVT systems investigated were up to 14% (relative) lower compared to pure PV systems and the annual thermal efficiencies up to 19% (relative) lower compared to pure thermal collector systems. The loss of electrical efficiency is mainly caused by the relatively high fluid temperature. The loss of thermal efficiency is caused both by the high emissivity of the absorber and the withdrawal of electrical energy. However, both the loss of electrical and thermal efficiency can be reduced further by the application of anti-reflective coatings. The thermal efficiency can be improved by the application of a low-emissivity coating on the absorber, however at the cost of a reduced electrical efficiency.

The influence of pressure (0.1–160 MPa) on the isothermal compressibility and bulk viscosity of solutions of tetrahydrofuran in ethylene glycol at 298 K

The isothermal compressibility and bulk viscosity of solutions of tetrahydrofuran (THF) in ethylene glycol were measured on a unique Micro PVT Systems unit over the concentration and pressure ranges 0–20 mol % THF and 0.1–160 MPa, respectively, at 298 K. The results were interpreted from the point of view of structural changes in the ethylene glycol-THF system.

Dynamic phase transitions for ferromagnetic systems

This article presents a phenomenological dynamic phase transition theory for ferromagnetism, leading to a precise description of the dynamic transitions and to a physical prediction on the spontaneous magnetization. The analysis also suggests asymmetry of fluctuations in both the ferromagnetism and the PVT systems.

Dynamic phase transition theory in PVT systems

Department of Mathematics, Indiana University, Bloomington, IN 47405(Dated: February 4, 2008)The main objective of this article are two-fold. First, we introduce some general principles on phasetransition dynamics, including a new dynamic transition classi cation scheme, and a Ginzburg-Landau theory for modeling equilibrium phase transitions. Second, apply the general principlesand the recently developed dynamic transition theory to study dynamic phase transitions of PVTsystems. In particular, we establish a new time-dependent Ginzburg-Landau model, whose dynamictransition analysis is carried out. It is worth pointing out that the new dynamic transition theory,along with the dynamic classi cation scheme and new time-dependent Ginzburg Landau models forequilibrium phase transitions can be used in other phase transition problems, including e.g. theferromagnetism and superuidity, which will be reported elsewhere. In addition, the analysis forthe PVT system in this article leads to a few physical predications, which are otherwise unclearfrom the physical point of view.

PV thermal systems: PV panels supplying renewable electricity and heat

AbstractWith PV Thermal panels sunlight is converted into electricity and heat simultaneously. Per unit area the total efficiency of a PVT panel is higher than the sum of the efficiencies of separate PV panels and solar thermal collectors. During the last 20 years research into PVT techniques and concepts has been widespread, but rather scattered. This reflects the number of possible PVT concepts and the accompanying research and development problems, for which it is the general goal to optimise both electrical and thermal efficiency of a device simultaneously. The aspects that can be optimised are, amongst others, the spectral characteristics of the PV cell, its solar absorption and the internal heat transfer between cells and heat‐collecting system. Another important level of optimisation is for the PVT device geometry and the integration into a system. The electricity and heat demand and the temperature level of the heat determine the choice for a certain system set‐up. With an optimal design, PVT systems can supply buildings with 100% renewable electricity and heat in a more cost‐effective manner than separate PV and solar thermal systems and thus contribute to the long‐term international targets on implementation of renewable energy in the built environment. Copyright © 2004 John Wiley & Sons, Ltd.

A rigorous equation of state for magnetic systems

A rigorous equation of state for magnetic systems has been derived in analogy to PVT systems. As a practical application of this equation the Blume—Capel model for spin S = 1 has been considered in the molecular field approximation.