Photovoltaic/Thermal (PV/T) systems: Status and future prospects

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Abstract

In the last four decades, greater attention has been paid to PV/T systems due to their advantages compared with PV or solar thermal systems alone. This paper aims to study various aspects of PV/T systems through the existing literature in order to highlight key points as future work in this field as well as illustrate different techniques used for such systems. In addition, PV/T systems are reviewed in terms of thermal and electrical side views. Furthermore, the analysis of solar thermal systems, various system applications such as air, water, air/water, phase change material PCM and Nanofluid systems are summarized. In light of most attempts to improve the PV/T system, more focus has been paid to the thermal rather than the electrical side. Furthermore, comparisons between PV/T systems in terms of performance parameters and efficiencies are presented. A critical review of many findings of previously conducted research is also discussed. It is found that the PV/T air heater system is promising for future preheating air applications. Moreover, it is suggested that the use of nanoparticles and water as base fluid improves the overall system efficiency. Furthermore, the PV side views require more attention in technical and cost terms. However, more research is essential to reduce the cost and, improve the effectiveness and technical design of such systems.

Introduction

The global demand for energy has increased due to the growth in population and improved economic situation in most parts of the world. While energy demand is growing, its primary sources, namely fossil fuels, are beginning to be exhausted due to over-consumption. The man activities resulting from energy consumption and the pollution caused have led to rapidly changing weather conditions, such as global warming, the melting of ice at the north and south poles, and damage to the ozone layer [1]. Environmental pollution and global warming problems can be reduced in the future by using renewable energies such as solar energy, specifically solar energy based on photovoltaic (PV) technology. PV is used to convert solar energy (light) to electrical DC energy. The smallest unit is called a solar cell and these are connected in series and parallel to produce a PV module. PV modules are also connected in series and parallel to produce PV arrays. Indeed, PV power plants shares have increased around the world, and many countries are now planning to increase the proportion of alternative energies in electricity generation. For example, the EU has decided to develop a plan to increase the share of renewables in energy production to a minimum of 30% by 2030, with this proportion rising to 100% in 2050 [2]. For countries still lagging behind in the establishment of power plants that operate using renewable energies, for example, Gulf Cooperation Council (GCC) countries, all the states in the region preparedness plans for the construction and production of energy from renewable sources. This development comes from the increased understanding and awareness of the decision-makers in these countries about the importance of changing the GCC power profile [3]. Modern statistics showed a very significant increase in the use of PV between 2004 and 2014, as the electrical energy produced by PV increased from 3.7 to 7 GW between 2004 and 2007. In contrast, this figure grew from 7 to 40 GW between 2008 and 2011. During one decade (2004–2014), the share of PV increased from 3.7 to 177 GW [4].

PV has attracted great interest from researchers, manufacturers, and decision-makers as a source of clean power generation due to its economic and environmental benefits [5]. There is great potential for the usage of PV plants with high efficiency in several areas around the world due to the high intensity of solar radiation in these regions. Ref. [6] indicates that building a station in the Sahara can supply the Mediterranean area, North Africa, and Europe with electricity. So, the whole expectations suggested increasing the demand for PV to compensate the shortfall in power supply nowadays, especially in remote and distant areas. Therefore, the use of solar energy will reduce fossil fuel consumption. PV is more attractive, thanks to its many promising advantages, such as the lack of serious maintenance and low operating costs, long life, and a reduction of CO2 emissions, resulting in a clean environment for future generations.

The electrical power generation capacity of a power station run on PV will vary depending on several factors, such as the site of the PV plant, meteorological variables, the solar energy technology itself, and the power station capacity. PV technology still faces many significant challenges, such as its sporadic productivity and the uncertainty in the solar PV is the most obvious. Fluctuations in output are mainly due to changes in the solar radiation intensity received by the solar panels [7], [8]. PV plants integration in the existing electricity grid has increased the technical issues, and the most important is the stability of equipped power, directly or indirectly. This issue arises because of the continuous changes in the solar radiation intensity and temperature with time, which disrupts the reliability of the network. Some of the fluctuations in the productivity of PV can be due to seasonal or environmental reasons. Large differences in weather conditions increase the uncertainty of the energy generation systems of PV. Therefore, the energy storage systems of PV are necessary to avert fluctuations in electrical power production [9], [10].

Many studies [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30] have shown that the performance of PV systems is linked to the geographical contrast, both at the city or remote areas levels. Differences in geographic location have a direct impact on the intensity of solar radiation in addition to changes in wind speed, humidity, dust, and air pollution deposits on the PV panel. Each of these variables cause low productivity and performance fluctuation in PV [11], [12], [13].

Refs. [14], [15] studied the impact of climate conditions on PV performance. Ref. [14] found that PV is heavily influenced by exposure to intense sunlight and high temperatures over a long period. Ref. [15] clarified the insignificant wind impact on the system temperature during the period tested. The increase in air temperatures caused a significant voltage drop and an insignificant increase in current value leading to a significant reduction in power. Refs. [[16], [17]] studied the effect of solar radiation on the performance of PV in Oman. The study showed that despite the adverse effects of rising temperatures in the area studied, the high intensity of solar radiation in the region for a long time during the day, especially during the peak period of use, makes this technology promising and economically efficient.

Ref. [18] investigated the effect of relative humidity on the productivity of PV panels. Relative humidity affects PV panels alongside other weather variables. The study showed the great effect on the performance of the PV panel as the voltage, current, and power dropped with increasing relative humidity. The researchers concluded that PV panels have a medium efficiency in a high relative humidity atmosphere.

The conversion efficiency of solar radiation in PV panel into electricity, ranging from 12% to 18% currently, and up to 80% of solar radiation either reflected or turn into heat [19]. As mentioned earlier, increasing the temperature of the PV panel reduces the performance. Every increase of 10 °C caused a decrease in PV panel efficiency of 5% [20].

Several researchers [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31] have suggested the removal of this heat using cooling fluids such as air and water to pull the heat from the PV panel and used it in other applications. In this case, the PV panel is called a hybrid PV/T solar collector. In addition to increasing the electricity produced from the PV panel, this hybrid PV/T solar collector system can heat air or water or both at the same time. Photovoltaic efficiency depends mainly on the solar radiation and temperature as the performance if PV/T includes the electrical and thermal efficiencies of the PV panel. Thermal efficiency usually includes the useful thermal profit ratio while the electrical efficiency shows the percentage of the advantages taken by the system from the solar radiation to produce electricity during a specified period.

Ref. [29] indicated that the use of building integrated PV thermal (BIPVT) is much more efficient than the building integrated PV (BIPV) system. The efficiency of the energy produced by the BIPVT system is 17–20% higher than similar standards in the BIPV system. Ref. [30] took advantage of the heat extracted from a BIPVT solar heating system to increase the efficiency of a solar distiller production.

This paper aims to review the most significant developments in the PV/T research area. The study will focus on the type of fluid used and its effect on the thermal and electrical efficiency of the system. In this study, and in order to uniquely for many high valued publications in this field, ultra-modern studies related to PV/T systems will be reviewed in terms of changes in the energy production and the system's electrical, thermal, and total efficiency. PV/T has the potential to be the future of PV technology and dispense with fossil fuels as an energy source.

This paper contains the following sections and subsections. PV/T principle and performance; thermal studies for PV/T systems, which is divided into: air, water, water and air cooled PV/T systems, using PCM and heat pipes with PV/T systems; electrical studies for PV/T systems; critical review and conclusions.

Section snippets

PV/T principles and performance

In general, PV modules are used in different system configurations: standalone, grid connected, hybrid and tracking systems. Usually, a PV system contains a PV module/array, charge controller and maximum power point tracking MPPT, battery (optional), and inverter, as shown in Fig. 1.

PV has received gradually more and been used in various applications. A large number of researchers have investigated PV design and how to improve efficiency and increase the applications that it can be used with.

Thermal studies for PV/T systems

Hybrid PV/T systems convert solar radiation into electrical and thermal energies at the same time. The basic form of this scheme consists of the open solar collector with a plate surface equipped with PV cells surface. The PV cells absorb sunlight and benefit from a part of this radiation by producing electricity, while the remaining portion is transferred to the cooling fluid (air or liquid) flowing through the collector. This hot fluid can be used at low or medium heat applications such as

Electrical studies of PV/T systems

In this section, the electrical side view of the PV/T is discussed and criticized in term of different parameters and key findings as shown in Table 6.

Tripanagnostopoulos et al. [114] investigated a PV/T water cooling system in Greece. The system was experimentally tested with and without glazing. The PV/T system's thermal conductivity was enhanced using aluminum reflectors. LCA, EPBT, and LCA were calculated. The authors claimed that the system EPBT is 0.8 years compared to 2.9 years for PV

Critical review

The research conducted for PV/T in the last four decades has been extensive. Research thus far has been successful in validating the importance of such studies in the effective adoption of PV/T as a reliable means of harnessing solar energy. However, the PV/T system is still under development and has many points and gaps that require intensive future studies. These points represent challenges to researchers and need to be overcome to establish effective PV/T design in term of technical and

Conclusions

The PV/T system converts solar energy into electricity and heat, respectively. In this review, a number of PV/T systems developed over the last four decades have been discussed and summarized with more emphasis on the electrical side view. The efficiencies (thermal and electrical) of the PV/T collector using different heat transfer fluids and designs, their advantages, limitations, applications, and scope for future research were discussed.

The thermal side views were classified into; air

References (146)

  • M.N. Abu Bakar et al.

    Design concept and mathematical model of a bi-fluid PV/thermal (PV/T) solar collector

    Renew Energy

    (2014)
  • H.A. Zondag et al.

    The thermal and electrical yield of a PV-thermal collector

    Sol Energy

    (2002)
  • A.A. Hegazy

    Comparative study of the performances of four PV/thermal solar air collectors

    Energy Convers Manag

    (2000)
  • S. Dubey et al.

    Thermal modeling of a combined system of PV thermal (PV/T) solar water heater

    Sol Energy

    (2008)
  • J.I. Rosell et al.

    Design and simulation of a low concentrating PV/thermal system

    Energy Convers Manag

    (2005)
  • L. Mei et al.

    Thermal modeling of a building with an integrated ventilated PV façade

    Energy Build

    (2003)
  • M. Sandberg et al.

    Buoyancy-induced air flow in PV facades: effect of geometry of the air gap and location of solar cell modules

    Build Environ

    (2002)
  • C.H. Cox et al.

    Design considerations for flat-plate-PV/thermal collectors

    Sol Energy

    (1985)
  • B. Agrawal et al.

    Life cycle cost assessment of building integrated PV thermal (BIPVT) systems

    Energy Build

    (2010)
  • G. Singh et al.

    fabrication, and performance evaluation of a hybrid PV thermal (PVT) double slope active solar still

    Desalination

    (2011)
  • F.P. Gasparin et al.

    Statistical analysis of I–V curve parameters from PV modules

    Sol Energy

    (2016)
  • V. Kapsalis et al.

    On the effect of roof added PVs on building's energy demand

    Energy Build

    (2015)
  • A.M. Al-Sabounchi et al.

    Design and performance evaluation of a PV grid-connected system in hot weather conditions

    Renew Energy

    (2013)
  • T.T. Chow et al.

    Computer modeling and experimental validation of a building-integrated PV and water heating system

    Appl Therm Eng

    (2008)
  • M.D. Bazilian et al.

    Cogeneration in the built environment

    Sol Energy

    (2001)
  • M. Hu et al.

    Experimental study of the effect of inclination angle on the thermal performance of heat pipe PV/thermal (PV/T) systems with wickless heat pipe and wire-meshed heat pipe

    Appl Therm Eng

    (2016)
  • H. Saitoh et al.

    Field experiments and analyses on a hybrid solar collector

    Appl Therm Eng

    (2003)
  • J.K. Tonui et al.

    Performance improvement of PV/T solar collectors with natural air flow operation

    Sol Energy

    (2008)
  • F. Hussain et al.

    Design development and performance evaluation of photovoltaic/thermal (PV/T) air base solar collector

    Renew Sustain Energy Rev

    (2013)
  • G. Li et al.

    Numerical and experimental study on a PV/T system with static miniature solar concentrator

    Sol Energy

    (2015)
  • C. Good et al.

    Solar energy for net zero energy buildings – a comparison between solar thermal, PV and PV–thermal (PV/T) systems

    Sol Energy

    (2015)
  • J.J. Michael et al.

    Flat plate solar PV–thermal (PV/T) systems: a reference guide

    Renew Sustain Energy Rev

    (2015)
  • J.G. Ahn et al.

    A study on experimental performance of air-type PV/T collector with HRV

    Energy Procedia

    (2015)
  • X. Meng et al.

    A novel free-form Cassegrain concentrator for PV/T combining utilization

    Sol Energy

    (2016)
  • M. Farshchimonfared et al.

    Full optimization and sensitivity analysis of a PV–thermal (PV/T) air system linked to a typical residential building

    Sol Energy

    (2016)
  • V. Delisle et al.

    Cost-benefit analysis of integrating BIPV-T air systems into energy-efficient homes

    Sol Energy

    (2016)
  • E.D. Rounis et al.

    Multiple-inlet building integrated PV/thermal system modeling under varying wind and temperature conditions

    Sol Energy

    (2016)
  • J. Hu et al.

    Energy performance of ETFE cushion roof integrated PV/thermal system on hot and cold days

    Appl Energy

    (2016)
  • K. Connelly et al.

    Design and development of a reflective membrane for a novel Building Integrated Concentrating PV (BICPV) ‘Smart Window’ system

    Appl Energy

    (2016)
  • M. Hazami et al.

    Energetic and energetic performances analysis of a PV/T (PV thermal) solar system tested and simulated under to Tunisian (North Africa) climatic conditions

    Energy

    (2016)
  • A.M. Elbreki et al.

    The role of climatic-design-operational parameters on combined PV/T collector performance: a critical review

    Renew Sustain Energy Rev

    (2016)
  • V.V. Tyagi et al.

    Advancement in solar PV/thermal (PV/T) hybrid collector technology

    Renew Sustain Energy Rev

    (2012)
  • T.T. Chow

    Performance analysis of PV-thermal collector by explicit dynamic model

    Sol Energy

    (2003)
  • X. Zhang et al.

    Review of R&D progress and practical application of the solar PV/thermal (PV/T) technologies

    Renew Sustain Energy Rev

    (2012)
  • Y. Tripanagnostopoulos et al.

    Hybrid PV/thermal solar systems

    Sol Energy

    (2002)
  • A. Ibrahim et al.

    Efficiencies and improvement potential of building integrated PV thermal (BIPVT) system

    Energy Convers Manag

    (2014)
  • S.N. Jahromi et al.

    Exergy and economic evaluation of a commercially available PV/T collector for different climates in Iran

    Energy Procedia

    (2015)
  • M. Rosa-Clot et al.

    Experimental PV-thermal power plants based on TESPI panel

    Sol Energy

    (2016)
  • M.A. Al-Nimr et al.

    A novel hybrid PV-distillation system

    Sol Energy

    (2016)
  • A.R. Starke et al.

    Assessing the performance of hybrid CSP+PV plants in northern Chile

    Sol Energy

    (2016)
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