A review of solar hybrid photovoltaic-thermal (PV-T) collectors and systems

In this paper, we provide a comprehensive overview of the state-of-the-art in hybrid PV-T collectors and the wider systems within which they can be implemented, and assess the worldwide energy and carbon mitigation potential of these systems. We cover both experimental and computational studies, identify opportunities for performance enhancement, pathways for collector innovation, and implications of their wider deployment at the solar-generation system level. First, we classify and review the main types of PV-T collectors, including air-based, liquid-based, dual air–water, heat-pipe, building integrated and concentrated PV-T collectors. This is followed by a presentation of performance enhancement opportunities and pathways for collector innovation. Here, we address state-of-the-art design modifications, next-generation PV cell technologies, selective coatings, spectral splitting and nanofluids. Beyond this, we address wider PV-T systems and their applications, comprising a thorough review of solar combined heat and power (S–CHP), solar cooling, solar combined cooling, heat and power (S–CCHP), solar desalination, solar drying and solar for hydrogen production systems. This includes a specific review of potential performance and cost improvements and opportunities at the solar-generation system level in thermal energy storage, control and demand-side management. Subsequently, a set of the most promising PV-T systems is assessed to analyse their carbon mitigation potential and how this technology might fit within pathways for global decarbonization. It is estimated that the REmap baseline emission curve can be reduced by more than 16% in 2030 if the uptake of solar PV-T technologies can be promoted. Finally, the review turns to a critical examination of key challenges for the adoption of PV-T technology and recommendations

Dynamic simulation tool for a performance evaluation and sensitivity study of a parabolic trough collector system with concrete thermal energy storage

Plant developers of parabolic trough collector (PTC) systems for industrial steam generation face various challenges. Some of the main challenges are availability of land, buildings in the vicinity of the plant that cast shadows on the collectors as well as land restrictions. The typical north-south collector axis alignment in many cases may not be possible due to limits of available ground. These were challenges that were faced in the planning phase for installing a PTC plant on the premises of the KEAN Soft Drinks Ltd factory in Limassol, Cyprus. As these issues cannot be avoided they must be accounted for by the plant developer, especially when a performance guarantee is given. This work presents, amongst other things, factors that should be analysed in order to predict the energy yield in the planning phase as best as possible by using a simulation model. In the sensitivity study presented in this paper, several effects on the energy yield were investigated theoretically. These effects include: Tracking inaccuracy, non-parallel collector row axis orientations as well as north-south vs. east-west collector alignment. A dynamic simulation model developed by the Solar-Institut Jülich (SIJ) [1] was further developed and used for the analysis. The simulation model features a deviation between the measured and simulated oil temperature at the collector outlet of only 1.5 K (rms). The findings are presented in this paper and give an insight into the effectiveness of mid-sized PTC systems for the industry sector

Operational experience and behaviour of a parabolic trough collector system with concrete thermal energy storage for process steam generation in Cyprus

As part of the transnational research project EDITOR, a parabolic trough collector system (PTC) with concrete thermal energy storage (C-TES) was installed and commissioned in Limassol, Cyprus. The system is located on the premises of the beverage manufacturer KEAN Soft Drinks Ltd. and its function is to supply process steam for the factory’s pasteurisation process [1]. Depending on the factory’s seasonally varying capacity for beverage production, the solar system delivers between 5 and 25 % of the total steam demand. In combination with the C-TES, the solar plant can supply process steam on demand before sunrise or after sunset. Furthermore, the C-TES compensates the PTC during the day in fluctuating weather conditions. The parabolic trough collector as well as the control and oil handling unit is designed and manufactured by Protarget AG, Germany. The C-TES is designed and produced by CADE Soluciones de Ingeniería, S.L., Spain. In the focus of this paper is the description of the operational experience with the PTC, C-TES and boiler during the commissioning and operation phase. Additionally, innovative optimisation measures are presented

Thermal Analysis of Naturally Ventilated BIPV systems

The aim of this study is to investigate the thermal behaviour of naturally ventilated BIPV systems. This study focuses on the systems with natural ventilation because it is believed that there is a good potential to improve their performance with design configurations, in order to provide sufficient ventilation to circulate the air and avoid the use of a fan with extra cost, noise and maintenance requirements. The ultimate goal is to estimate the convective heat transfer coefficients in all sections of a BIPV system. An extensive experimental analysis is carried out in outdoor environmental conditions and in indoor controlled conditions with the use of a solar simulator. It was pointed out that the air exits the duct at around 10ºC hotter than it enters and for this reason the PV’s temperature increases from the bottom to the top. Regarding the inclination angles tested, it is observed that the system develops higher temperature when is inclined at 30º and less when is placed vertically (90º). Subsequently, an analysis of the natural convection is carried out using fundamental convection equations and as a result, two correlations for the estimation of the convective heat transfer coefficients (CHTC) are extracted for the first time. These can be applied to estimate the CHTC in the air gap between the PV panels and the outer skin of the building, in double skin BIPV systems, for windy and no windy conditions. Afterwards, a 3D computational fluid dynamic (CFD) model was built in COMSOL Multiphysics and it is validated with the experimental results. The general conclusion is that the experimental results were in a good agreement with the simulation results. Additionally, based on the measured temperature distribution of the system from the experimental procedures, energy and exergy analyses are carried out and the correlations for the estimation of the energy and exergy efficiencies are presented for the first time for a naturally ventilated BIPV system. The energy efficiency of the system is estimated to be up to 26.5‐33.5% while the exergy efficiency is estimated to be between 13‐16%. Finally, the gained knowledge is applied to a real BIPV demonstration system. A building simulation model is carried out to predict the temperature of the PV panels and the energy production of the system for one year. A good agreement is observed between the calculated and measured data.Complete

A BIPV demonstration building: On-site system monitoring and simulation based investigation for annual energy production prediction

New technology saw tooth (PV) modules developed under the BFIRST project for building integration are installed in a residential building in Mons, Belgium. The new modules are named roofing shingles (RS) PV panels and they can replace the normal roof tiles to produce electrical energy. The RS modules they are installed on the south part of the building’s roof with an inclination angle of 40⁰. The installation comprises of 57 RS modules of 32 monocrystalline Silicon cells each, and the total installed power of the system is 7.01 kWp. This study presents a simulation model setup to predict the energy production of the system before the installation and compare the predicted results with real on-site monitoring data. It is concluded that the results from the simulation agree with the monitoring results measured on site regarding the energy production of the system. Simulations showed that an air gap of 0.1 m is adequate to maintain low PV temperature and the monitoring results agree with this finding

Target for 100% Renewable Energy Systems Use in Cyprus for Electricity Production

Cyprus covers 93% of the energy demand using fossil fuels which are fully covered from imports. This does not only stand as a barrier to the various European Directives and measures which apply for all EU members, but it is also a drawback for the economy of Cyprus. Around 1000 tons of heavy fuel oil is required every year by the Electricity Authority of Cyprus to cover the energy demand. The household electricity prices including taxes paid in Cyprus are the 7th highest in Europe. From 2009, renewable energy systems have started to be used, but due to the price of the systems they were limited. However, price was not the main problem of the systems to explain why they didn’t expand more. Many other parameters are still affecting the use of RES in Cyprus; the public acceptance, the education of people, the environmental consciousness, but the most important is the motivation and ease of the applications and licensing from the government parties. Here in this study, an overview of the current energy situation is discussed and suggestions to increase the use of RES are mentioned as well. These include the use of electricity production RES for the domestic needs and measures for the improvement of energy efficiency of the building sector in general, which is the second biggest energy consumer in Cyprus after the commercial sector

Double skin facades (DSF) and building integrated photovoltaics (BIPV): A review of configurations and heat transfer characteristics

This article presents the state of the knowledge on the thermal analysis of double skin facades with integrated photovoltaic (PV) panels called the Building Integrated Photovoltaics (BIPV) in terms of the published studies carried out on these systems. The idea of integration of the PV panels by replacing building elements, increase the prospects of the renewable energy systems. Taking also into account the need to use more renewable energy systems in buildings, the investigation of the BIPV systems to improve their performance is of a great importance. The literature studies are separated into experimental and theoretical for naturally ventilated systems and mechanically ventilated with external means e.g. fan use. It is concluded that most researchers studied the systems with mechanical ventilation rather than the systems with natural ventilation because the latter are more complex in terms of the air flow behaviour in the air duct. Additionally, various researchers proposed Nu number correlations and convective heat transfer correlation under several assumptions and conditions every time, for different range or Ra number which are presented and compared in this paper

Thermal testing of new photovoltaic (PV) modules for building integration, encapsulated with glass fibre reinforced composite materials and comparison with conventional Photovoltaic

Photovoltaic (PV) panels usage is increased dramatically the last years. The PV panels for building integration however are not so popular yet. This is because the Building Integrated Photovoltaic (BIPV) Systems play an important role on the design of the building. There are architects and designers who like the idea of PV panels integrated on the envelope of a building but there are also those who believe that the colour and shape of the panels eliminate their creativity. BFIRST (Building Integrated Fibre Reinforced Solar Technology) project developed a new solar cells’ encapsulation technology with glass fibre reinforced composite materials, and real size modules are manufactured. The idea behind this technology is to produce rigid photovoltaic panels with shapes that are not flat but they are also light-weight PV modules for building integration. The aim of this study is to compare a ‘BFIRST module’ with a conventional module from the market, in terms of temperature under different amounts of solar radiation and inclination angles. Thus, two experimental apparatuses are constructed to represent building integration, forming an air gap between the PV and a second skin. The purpose of the air gap is to cool the PV panels and avoid the decrease of their efficiency due to overheating. In this study, the ventilation of the air gap is natural without any mechanical means to drive the air. The tests are carried out in the Archimedes Solar Energy Laboratory (ASEL) at Cyprus University of Technology, Limassol, with the use of a large scale solar simulator. Although this is the first time the fibre reinforced encapsulation solar technology is tried, as the modules are produced only for research purposes, the tests show that this technology is very promising and worth to be developed. The maxi-mum temperature recorded was very close with the temperature of the conventional PV panel. The temperature of the BFIRST PV panel under 450 W/m2 constant solar radiation is 57.5ºC while the tem-perature of the conventional PV was 64ºC. For 800 W/m2 constant solar radiation the temperature of the BFIRST PV panel was 73.4ºC and 73.6ºC for the conventional PV panel. An additional test for the BFIRST PV under higher solar radiation is carried out to record highest PV temperature attainable, and the maximum temperature of the panel under 1000 W/m2 was 79ºC at the top side of the panel, which is satisfactor

Thermal Analysis of a Building Integrated Photovoltaic (BIPV) System

During the last few years photovoltaic (PV) panels are increasingly incorporated into the construction of buildings for generating electrical power (BIPV systems) or both electrical and thermal energy (BIPV/T systems). The integration creates heat in the gap between the PVs and the building’s skin, which if not removed to be used to cover part of the heating load of the building (winter) or to the atmosphere (summer), it decreases the efficiency of the PVs and increases the cooling loads of the buildings in summertime. This study aims to evaluate the thermal behaviour of a BIPV system in order to decide whether natural ventilation of the air behind the PV is adequate to cool it down and remove the excess heat. The examination of the effect of the air gap of a BIPV system as well as the slope of the system or the amount of solar radiation are very important parameters as they can lead to better understanding of the conditions that allow the higher efficiency of the PV panels and accordingly higher efficiency of the BIPV system. The investigation of the above parameters is done experimentally in a laboratory with a large scale solar simulator (SS) and a representative apparatus of a BIPV system, able to change the air gap of the duct and the slope in order to simulate roof or façade installation. The experimental results are compared with 3D modelling simulation results obtained using COMSOL Multiphysics software

Part I: Thermal analysis of naturally ventilated BIPV system: Experimental investigation and convective heat transfer coefficients estimation

The purpose of this two-part study is to present the experimental analysis carried out on a naturally ventilated Building Integrated Photovoltaic (BIPV) system and the new correlations developed for the estimation of the convective heat transfer coefficients (CHTC) in the air gap, and use the developed correlations to construct a simulation model which is validated with the experimental data. In BIPV systems the air gap is responsible to cool the PVs and remove excess heat to avoid building overheating. The ventilation of the air gap can be natural or mechanical. However, naturally ventilated systems are less studied although they have important advantages over the mechanically ventilated ones, such as the avoidance of extra energy of the fans, maintenance and noise. The present Part I of this study presents an experimental based thermal analysis of a naturally ventilated vertical BIPV system. A series of experiments on a custom made BIPV system were carried in real outdoor conditions as well as indoors with the use of a large scale solar simulator to measure the thermal characteristics of the system and its thermal behaviour. Indoor experiments were performed to avoid external disturbances from wind that may occur outside. The results show that an open-ended air gap of 0.1 m can create adequate air flow on naturally ventilated systems and can ensure low PV temperatures to avoid PV efficiency decrease. The experimental data are then used to estimate the convective heat transfer coefficients to fit the real conditions of the BIPV systems. Then two correlations are proposed for the estimation of the Nusselt number that fits best the thermal characteristics of a naturally ventilated BIPV system