PV Temperature Research Articles

Model predictive control of air-based building integrated PV/T systems for optimal HVAC integration

High performance of HVAC connected Building Integrated Photovoltaic/Thermal (BIPV/T) systems relies on appropriate control. However, optimal control is often overlooked, resulting in systems that operate inefficiently. This paper investigates how model predictive control (MPC) can improve the operation of open loop air-based BIPV/T systems connected to multiple thermal applications.The BIPV/T system at the first institutional net-zero energy building in Canada, the Varennes library, is used as an archetype. The BIPV/T covers 16% of the south-facing roof and operates under a simple rule-based control strategy. The developed control and design strategies consider variations of this system, to achieve higher thermal utilization efficiency.A control-oriented BIPV/T model is developed and calibrated using monitored data. The BIPV/T airflow is regulated through MPC for simultaneous heat supply to an Energy Recovery Ventilator and air-to-water heat pump. The BIPV/T air flow is efficiently controlled, considering the connected thermal applications, environmental conditions, and PV temperature. Model-based control for BIPV/T systems can increase the amount of useful heat and reduce PV overheating. The MPC controller for the examined system reduced the building energy consumption compared to the business-as-usual operation by 40% and together with increased BIPV/T area can supply excess heat to adjacent buildings.

Development and economic evaluation of a CPVT system with PHP cooling; An experimental study

In this paper, the experimental investigation of the performance of a concentrated hybrid photovoltaic thermal solar system is sought. Accordingly, there is a parabolic trough concentrator receiver that consists of three components: a triangular duct, photovoltaic cells covering the duct, and a three-turn PHP. The PHP cools down the photovoltaic cells efficiently and regenerates waste heat. The duct is filled with a heat transfer fluid surrounding the PHP’s evaporator. The condensation section of the PHP is located outside the solar concentrator. Using a one-axis polar mechanism, the concentrator tracks the sun from east to west. The system experiment setup was fabricated and tested outdoors in Tehran’s climate. Different heat transfer fluids, including Glycerine, Ethylene Glycol, and Calcium Chloride water mixture, were tested. Given the enhancement of PHP performance, a variety of working fluids were tested, including graphene oxide nanofluid/water, acetone, and pure water. The experiments showed that graphene oxide nanofluid/water mixture provided the highest thermal performance. With the use of graphene oxide nanofluid/water (as a working fluid) and glycerine (as heat transfer fluid), experiment results showed a decrease of 7.84 °C in PV temperature and a consequent increase of 21.85% in electrical efficiency in best condition. Furthermore, the provided cooling system recycles a maximum of is 190.4 kJ of thermal energy equivalent 52.5% thermal efficiency, increasing overall efficiency by 74.35%. Lastly, the IRR of 65.41%, PBT of 1.04 years, and LCOE of 1.84 $/kWh demonstrate appropriate financial profitability.

Multiobjective Optimization and Machine Learning Algorithms for Forecasting the 3E Performance of a Concentrated Photovoltaic-Thermoelectric System

Previous theoretical research efforts which were validated by experimental findings demonstrated the thermo-economic benefits of the hybrid concentrated photovoltaic-thermoelectric (CPV-TE) system over the stand-alone CPV. However, the operating conditions and TE material properties for maximum CPV-TE performance may differ from those required in a standalone thermoelectric module (TEM). For instance, a high-performing TEM requires TE materials with high Seebeck coefficients and electrical conductivities, and at the same time, low thermal conductivities ( k ). Although it is difficult to attain these ideal conditions without complex material engineering, the low k implies a high thermal resistance and temperature difference across the TEM which raises the PV backplate’s temperature in a hybrid CPV-TE operation. The increased PV temperature may reduce the overall system’s thermodynamic performance. To understand this phenomenon, a study is needed to guide researchers in choosing the best TE material for an optimal operation of a CPV-TE system. However, no prior research effort has been made to this effect. One method of finding the optimum TE material property is to parametrically vary one or more transport parameters until an optimum point is determined. However, this method is time-consuming and inefficient since a global optimum may not be found, especially when large incremental step sizes are used. This study provides a better way to solve this problem by using a multiobjective optimization genetic algorithm (MOGA) which is fast and reliable and ensures that the global optimum is obtained. After the optimization has been conducted, the best performing conditions for maximum CPV-TE energy, exergy, and environmental (3E) performance are selected using the technique for order performance by similarity to ideal solution (TOPSIS) decision algorithm. Finally, the optimization workflow is deployed for 7000 test cases generated from 10 features using the optimal machine learning (ML) algorithm. The result of the optimization chosen by the TOPSIS decision-making method generated an output power, exergy efficiency, and CO2 saving of 44.6 W, 18.3%, and 0.17 g/day, respectively. Furthermore, among other ML algorithms, the Gaussian process regression was the most accurate in learning the CPV-TE performance dataset, although it required more computational effort than some algorithms like the linear regression model.

Power and Thermal Analysis of A Pcm-Cooled Photovoltaic Thermal System With A 1-D Mathematical Model for Different Environmental and Boundary Conditions: A Case Study

Reducing the PV panel temperature significantly increases the PV panel efficiency. The most important parameters affecting the temperature of the PV panel are; environmental temperature, wind speed, sunbathing time, and irradiation. Although there are many methods for PV panel cooling, one of the most common methods is to cool the panel by placing PCM material on the PV panel's bottom surface. In this study, PV/PCM integration under different boundary conditions was investigated with a 1-D mathematical model. In the study, environmental conditions were determined using real meteorological data, and the results were shared for four seasons. The mathematical model was performed for the conventional PV model, the PV/PCM integrated model, and the integrated PV/PCM which the base is kept at a constant temperature. As a constant temperature value, 10, 15, and 20 oC were chosen. The results were analyzed in terms of PV temperature, PCM melting rate, electricity production, energy absorbed by PCM, and thermal and electrical efficiency. If the annual performances are examined, the maximum electricity production is 263000 kW for the case where the PV/PCM base is kept constant at 10 degrees, and this value is 1200 kW higher than the traditional PV panel. The maximum absorbed energy by PCM was obtained as 26990 kW for the PV/PCM integration.

Insight into the investigation of Fe3O4/SiO2 nanoparticles suspended aqueous nanofluids in hybrid photovoltaic/thermal system

This experimental study aims to evaluate the energetic performance of a photovoltaic-thermal system with a serpentine tube collector. A photovoltaic-thermal unit with a serpentine tube collector is used to compare the unit's performance metrics to those of a PV panel without cooling. The considered heat transfer fluid is the hybrid nanofluid prepared using water and Fe3O4/SiO2 nanoparticles. Using irradiance data from an average day in Aligarh, India, the experiment is conducted in indoor environment in a solar simulator under regulated operating circumstances. Effects of mono and hybrid nanofluids are examined at 3% wt. concentration for varying flow rates (20, 30, 40 LPM). The experimentation analysis showed that the maximum drop in PV temperature at 20 LPM is 25 °C, 24 °C, and then 16 °C for Fe3O4/water, SiO2/water, and Fe3O4/SiO2 nanofluids-based PVT systems, respectively with a highest possible increase in electrical efficiency of 12.6 percent, 18.46 percent, and 24.34 percent, respectively, when compared to traditional PV systems. At a flow rate of 40 LPM, the best performance is obtained using a hybrid PVT method coupled with an aqueous Fe3O4/SiO2 nanofluid. Additionally, it is discovered that hybrid nano-fluid-based PVT systems exhibit 10.5% and 5% greater thermal efficiency than Fe3O4-Water and SiO2-Water PVT systems, respectively. The overall highest efficiency of 67% is achieved for hybrid nanofluid at a flow rate of 40LPM. The hybrid Fe3O4/SiO2 nanofluid is capable of serving as an acceptable cooling fluid for the PV/T collector, as evidenced by the PV/T system's notable improvement in thermal and electrical efficiency and prominent cooling impact. Keywords : Solar energy, Hybrid nano-fluid, Heat transfer, Electrical Power, Thermal Efficiency, PVT system. • The role of hybrid nanofluids for the performance of PVT systems was studied. • Hybrid nature of nanofluid make it more stable than mono-nanofluid. • Electrical and thermal efficiency were analysed at fixed concentration and varying flowrate. • Comparison of Fe 3 O 4 /SiO 2 nanofluid is carried out with individual mono-nanofluid.

Prototype of a novel hybrid concentrator photovoltaic/thermal and solar thermoelectric generator system for outdoor study

In this study, a novel prototype of a hybrid concentrator photovoltaic/thermal and solar thermoelectric generator system has been designed and constructed for combined heat and power production. In the developed hybrid system, both the solar cells and thermoelectric modules that share a common heat transfer medium are exposed to concentrated irradiance via a compound parabolic concentrator and a parabolic trough concentrator, respectively. To assess the performance of the hybrid system, a prototype of the hybrid system was built and tested under outdoor operating conditions, and the findings were compared with those of a transient numerical simulation conducted using ANSYS Fluent. The average PV temperature obtained during the test period at a flow rate of 3.8 L/min is 318.19 K which is ∼5.6% lesser compared with a conventional hybrid CPVT-TEG system. The outdoor trials show maximum electrical efficiency of 4.86% and thermal efficiency of 40% when the solar irradiance is greater than or equal to 1000 W/m2. The overall efficiency of the developed prototype is 3 times higher compared to a standalone PV system. The hybrid system helps to reduce carbon emission by 0.5 kg/h, with an associated environmental cost of 0.025 €/h.

A Thermal Model to Estimate PV Electrical Power and Temperature Profile along Panel Thickness

The production of electricity from photovoltaic panels has experienced significant developments. To manage the energy flows introduced into the electricity grid, it is necessary to estimate the productivity of PV panels under the climatic conditions. In this study, a photovoltaic panel is modelled from thermal and electrical points of view to evaluate electrical performance and identify the temperature distribution in the layers. The analysis performed is time dependent and the problem is solved using the finite difference technique. A methodology is introduced to estimate the cloudiness of the sky, which affects radiative heat exchange. The calculation method is validated using experimental data recorded in a laboratory of the University of Calabria. Temperature and electrical power are predicted with RMSE of 1.5–2.0 °C and NRMSE of 1.2–2.1%, respectively. The evaluation of the temperature profile inside the panel is essential to understand how heat is dissipated. The results show that the top surface (glass) is almost always colder than the back of the panel, despite being exposed to radiation. In addition, the upper surface dissipates more heat power than the lower one. Cooling systems, such as spray cooling, work better if they are installed on the back of the panel.

Experimental study on photovoltaic panels integrated with metal matrix sheets and bio-based phase change materials

In this research, a new bio-based phase change material (PCM) composed of oleic acid and beeswax is synthesized to absorb excess heat from the PV panel. Metal matrix sheets (MMS) inserted inside the PCM container to augment heat diffusion and improve the thermal and electrical efficiency of the PV panel. The influence of number of MMS (N = 1,2,3,4 and 5) and weight of the PCM (W = 1.6-4 kg) on the temperature, output power and electrical efficiency of the PV panel are analyzed. The results represent that using the bio-based PCM reduces the PV panel temperature from 58.92 °C to 51.45°C, when MMS is not applied. It has been observed that using MMS provide lower PV temperature than using PCM alone and improve the electrical efficiency (η). Further, it is identified that N = 5 has the highest electrical efficiency, but the difference between N = 4 and N = 5 is not very remarkable. Increase in the weight of the bio-based PCM from 1.6 kg to 4 kg results in a significant improvement in the PV performance. The values of N = 5 and W = 4 kg are found to achieve a maximum electrical efficiency of 11.73% and output power of 7.04 W in the PV/bio-based PCM system.

Transient performance assessment of a hybrid PV-TEG system integrated with PCM under non-uniform radiation conditions: A numerical investigation

The utilization of PCM in PV-TEG system could lead positive effect. However, the system's performance may vary with the insertion position of the PCM, especially in transient and non-uniform conditions. Hence, to narrow the knowledge gap of this issue, a detailed 3D transient model is established in this study using finite element solution. The temperature-dependent properties of thermoelectric materials and the natural convective flow of the melting PCM is regarded to reduce the deviation from the reality. The influence of the PCM height and insertion position of the PCM in PV-TEG system is analyzed. Furthermore, a comparative analysis is also performed to compare the performance of the considered layouts under the uniform and non-uniform radiation conditions. The obtained results show that the increment of the PCM height leads to higher comprehensive performance in PV-TEG-PCM system, the maximum conversion efficiency difference could reach up to 1%. In addition, the PV-PCM-TEG system possesses a higher overall performance in comparison with the PV-TEG-PCM system, and the maximum PV temperature reduction of 19.22 K is observed. Moreover, an increased power of 0.23 W and 0.33 W in PV-TEG-PCM and PV-PCM-TEG systems is obtained compared with the non-uniform illumination conditions.

Combining photovoltaic double-glazing curtain wall cooling and supply air reheating of an air-conditioning system: Energy-saving potential investigation

To address the problems of PV facade overheating and air-conditioning cold-heat offset, this study proposed a novel PV double-glazing ventilated curtain wall system (PV-DVF) that combined PV cooling and dew-point air reheating. A case study was conducted based on an office building with a south-facing PV-DVF in Hefei, compared to one with a conventional PV double-glazing insulated curtain wall system (PV-DIF). This study mainly includes mathematical modeling and validation, performance prediction, and parametric analysis. During a typical summer week, the results reveal that the PV-DVF system achieved (1) a 4.64 °C drop in PV temperature and a 3.4 W (1.07 %) increase in power output, with 7.10 % electrical efficiency; (2) a 2083.22 W reduction in cooling energy consumption; (3) a 4431.81 W reduction in reheat energy; and (4) total electricity savings of 27.92 kWh/day. In the summer, the total electricity savings reached 1566.33 kWh, with an energy-saving ratio of 27.51 %. Furthermore, parametric study results show that properly increasing channel thickness and PV coverage ratio achieves better energy-efficient performance.

Experimental Evaluation of the Thermoelectrical Performance of Photovoltaic-Thermal Systems with a Water-Cooled Heat Sink

A design for a photovoltaic-thermal (PVT) assembly with a water-cooled heat sink was planned, constructed, and experimentally evaluated in the climatic conditions of the southern region of Iraq during the summertime. The water-cooled heat sink was applied to thermally manage the PV cells, in order to boost the electrical output of the PVT system. A set of temperature sensors was installed to monitor the water intake, exit, and cell temperatures. The climatic parameters including the wind velocity, atmospheric pressure, and solar irradiation were also monitored on a daily basis. The effects of solar irradiation on the average PV temperature, electrical power, and overall electrical-thermal efficiency were investigated. The findings indicate that the PV temperature would increase from 65 to 73 °C, when the solar irradiation increases from 500 to 960 W/m2, with and without cooling, respectively. Meanwhile, the output power increased from 35 to 55 W when the solar irradiation increased from 500 to 960 W/m2 during the daytime. The impact of varying the mass flow rate of cooling water in the range of 4 to 16 L/min was also examined, and it was found that the cell temperature declines as the water flow increases in intensity throughout the daytime. The maximum cell temperature recorded for PV modules without cooling was in the middle of the day. The lowest cell temperature was also recorded in the middle of the day for a PVT solar system with 16 L/min of cooling water.

Thermal characterization of a photovoltaic panel under controlled conditions

To avoid large variability in environmental factors, the thermal and electrical behavior of a 310 W PV panel exposed to a 6 kW halogen light source was studied in a 48 m3 climatic room. The physical quantities measured were panel temperature (front and back), radiation illuminating the panel, ambient temperature, air speed, panel current and panel voltage. Under these conditions, it was possible to estimate the thermal constant of the panel at 9 minutes. The effect of forced convection on the panel temperature was quantified using a fan. The results obtained confirm that the panel temperature decreases exponentially with air speed. The part of the incident radiation that is converted into electricity and therefore does not contribute to the heating of the panel was quantified. The results show that the front panel temperature decreases by about 3°C and the rear panel temperature by about 3.7°C when the system produces electricity. The Maximum Power Point from I–V and P–V characteristics was studied for different PV temperatures to confirm the linear decay of the electrical efficiency with increasing cell temperature.

Effect of solar energy concentrating and phase change cooling on energy and exergy performance improvement of photovoltaic/thermal systems

The application of compound parabolic concentrator (CPC) in photovoltaic/thermal (PV/T) system increases the thermal and electrical energy gain, and the phase change material (PCM) helps cool down the operating temperature of cells. In this study, an open-air experiment is constructed to compare the overall performance of conventional flat photovoltaic (FPV), concentrating photovoltaic/thermal (PV/T-CPC) and concentrating photovoltaic/thermal phase change (PV/T-CPCM) system. The maximum PV backplane temperature is 69.9 °C in PV/T-CPC, 59.2 °C in PV/T-CPCM and 36.7 °C in FPV system respectively, and the PV temperature distribution non-uniformity in PV/T-CPC is 1.5 times higher than that in PV/T-CPCM system, showing the application of concentrator enhances the useful thermal energy and meanwhile the PCM effectively improves the local overheating and temperature distribution non-uniformity problem. The average thermal energy and efficiency of PV/T-CPCM are over 2462.0 kJ and 9.0% higher than those of PV/T-CPC system respectively. Besides, the electrical power/total exergy of PV/T-CPCM system are over 1.3/4 and 1.6/2 times of FPV and PV/T-CPC system respectively. Results present that the PV/T-CPCM system owns superior thermal, electrical and exergy performance among the three systems, and the application of CPC and PCM has great advantages in improving the overall performance of the PV/T unit.

Energy, exergy, and economic assessment of thermal regulation of PV panel using hybrid heat pipe-phase change material cooling system

There has been a theoretical investigation for energy, exergy, and economic evaluation of thermal regulation of PV panels via an innovative hybrid cooling system of flat heat pipes (HPs) coupled with phase change material (PCM). PV panel dissipates its heat through the HP evaporator while the HP condenser is cooled by PCM. The cooling system performance is investigated for different PCM quantities and types (RT42, RT35HC, and SP31) for summer and (RT21, RT18HC, and SP15-gel) for winter conditions in Egypt. A thorough study and analysis have been conducted for the impact of the cooling system on PV panel's temperature, electric efficiency, output power, PCM energy storage, and system efficiency. The results show that compared with conventional PV, the best PCM type for PV performance in summer is SP31 of 3 cm thickness, which achieves a maximum PV temperature reduction of 20.6 °C with a maximum improvement in PV electric efficiency of 11.5%. SP15-gel of thickness 2.5 cm is the best PCM for winter conditions, achieving 14.1 °C temperature reduction with 7.2% enhancement in PV electric efficiency. The exergy efficiency of the PV panel is higher than in PCM, where it rises as the phase change temperature of the PCM increases. PV maximum average daily exergy efficiency is 13.4% for SP15-gel, compared with 12.71% for conventional PV in winter, while SP31 achieved 12.25%, 1% higher than reference PV in summer. PCM's maximum average daily exergy efficiency is 0.69% and 0.7% for RT42 and RT21 in summer and winter, respectively. The minimum payback period for conventional PV is about 18.01 years, while it is approximately 13.39 years for PV with HP and PCM. The studied cooling system at different PCMs proves its capability to enhance the PV performance with higher energy and exergy efficiencies and lower cost and store the excess heat inside the PCM.

Numerical investigation on the factors influencing the temperature distribution of photovoltaic/thermal (PVT) evaporator/condenser for heat pump systems

Due to a high solar energy utilizing efficiency, Direct-expansion Solar-Assisted Heat Pump (DX SAHP) system has been a research hotspot for many years, especially for the system using PV/T module as the evaporator. The heat transfer throughout the PVT evaporator is an important factor for either electrical or thermal performance. We have developed and analyzed numerically the temperature distribution of a multi-source PVT heat exchanger of serpentine shape to fit a function as evaporator/condenser for Direct-expansion Photovoltaic/Thermal-Heat Pump (DX PVTHP) system. The suitability of the developed model was based on the calculated results of the efficiency factor and simulated results of temperatures of heat exchanger and working fluid as well the working fluid pressure drop. During the numerical simulations, we have considered different temperature influencing factors such as the refrigerant and refrigerant flow rate, spacing between the adjacent tubes of the heat exchanger, backside convection and radiation effect and finned heat exchanger. Simulated results showed that the serpentine PVT heat exchanger with fins and small space between tubes (62.5 mm) at 0.02 kg/s flow rate could achieve better results in terms of uniform temperature distribution, smaller fluid pressure drop (0.078 bar) and the highest efficiency factor (0.9873) which make it recommended as the best option for suitable evaporator/condenser. The average PV temperature reached by cooled and uncooled PVT evaporator at 0.02 kg/s flow rate was 47.81 °C and 71.11 °C, respectively. It was 40.99 °C and 37.07 °C at the flow rate of 0.035 kg/s and 0.05 kg/s, respectively, and 44.44 °C for PVT evaporator with smaller space between tubes at 0.02 kg/s. The average PV temperature reached by the PVT evaporator with fins was 40.734 °C at the flow rate of 0.02 kg/s while it was 53.956 °C when the unit is insulated.

Efficiency and sustainability assessment of evaporative cooling of photovoltaics

The cooling of PV has been shown to increase electricity production. Among passive techniques, evaporative cooling has one of the greatest potentials. In this work, the efficiency and sustainability of this technique have been investigated for various climatic conditions. In-situ experiments were conducted to develop parametric models for PV cell temperatures and back surface convective heat transfer coefficient. Experiments have revealed an up to 20.1 °C lower peak PV temperature and up to 9.6% increased electric power. Year-round analysis was made for eight cities to determine the required roof size to capture precipitation and the volume of rainwater storage for sustainable evaporative cooling. The study shows that sustainable PV evaporative cooling is possible in cities with temperate and continental climates, where 1–3 m2 of roof area and 50–150 l of rainwater storage are needed for 1 m2 of PV. The annual electricity production can increase by 5.9–9.4 kWh/m2a, which is a 3.6–4.6% increase. In the semi-arid climate of Lampedusa, a roof above 4 m2 and a storage of up to 500 l per m2 of PV are required. In the desert climate of Almeria and Athens, sustainable evaporative cooling is not feasible.

A numerical evaluation of the bifacial concentrated PV-STEG system cooled by mini-channel heat sink

The operating temperature of the novel bifacial concentrated photovoltaic-solar thermoelectric generator (PV-STEG) system is a decisive factor in determining the working performance. In this study, a mini-channel heat sink with superior heat transfer characteristics is selected to preserve the lower operating temperature of the PV cell and create sufficient temperature differences for the STEG unit. To settle the related problems, a three-dimensional numerical model is developed. Moreover, the conventional PV system is used as a reference configuration for comparative evaluation. The impact of adopting various flow channel shapes, input solar irradiance, Reynolds number, and inlet temperature is thoroughly explored. The obtained results suggested that the square mini-channel heat sink is more suitable. Furthermore, to maximize the power yield of the system, stronger solar irradiance, higher Reynolds number, and lower inlet temperature is recommended. Besides, the influence of employing diverse nanofluids is also analyzed. The outcomes indicated that the average PV temperature and power output could be significantly reduced/improved by utilizing nanofluids. Specifically, the total efficiency rose by 14.59% compared to the PV alone and PV-STEG systems using single-walled carbon nanotube (SWCNT) nanofluid. Besides, an enhancement of 23.21% in exergy efficiency was obtained compared to the sole PV system.

Experimental study of using system of flat heat pipe-phase change material inclusion heat sink for thermal regulation of simulated PV

ABSTRACT Flat heat pipe (HP)-phase change material (PCM) hybrid system used for thermal regulation of simulated PV is investigated experimentally. Three PCMs; Rubitherm RT-25 H (RT25), Rubitherm RT-35 H (RT35), and Rubitherm RT-44 H (RT44) coupled with the HP are tested for best cooling system. Impact of using one or two heat sinks compared with PCM only is studied. The results show that RT25 achieves lowest PV temperature, while RT44 achieves highest energy storage. Compared to RT25 and RT44, RT35 is considered the best for PV cooling and PCM energy storage. Including heat sinks reduces PV temperature and melting time and increases energy storage rate.

Performance improvement of a naturally ventilated building integrated photovoltaic system using twisted baffle inserts

Building integrated photovoltaic (BIPV) systems constitute a key concept for the realization of sustainable buildings. However, these systems have limited efficiency and durability due to their insufficient cooling capabilities. To overcome this drawback, it is necessary to maintain the operating temperature as low as possible. This study investigates the effectiveness of a passive low-cost strategy to improve the photovoltaic module (PV) performance of naturally ventilated BIPV systems by decreasing the module operating temperature. This strategy consists of inserting twisted baffles on the rear side of a PV module to enhance its cooling performance. A numerical investigation was performed using Computational Fluid Dynamics (CFD) simulations in order to explore the module surface temperature and its electrical efficiency. The effects of solar irradiance, the number and position of twisted baffles, and twist ratio have been investigated. The results revealed that the average temperature of the PV surface decreases with the increase of the number of twisted baffles (N), which leads to an improvement in the electrical efficiency. Indeed, the optimum performance enhancement is attributed to N = 15, and the corresponding PV temperature was decreased from 312.66 K to 310.15 K and from 348.42 K to 342.64 K for a solar irradiance variation from 200 to 1000 W.m-2, resulting in an improvement of 1.21–3.36% in electrical efficiency compared to the case without inserts. Concerning the effect of the twist ratio, it is shown that the optimum electrical efficiency improvement is reached for the lowest twist ratio, which is in the range of 1.7–6.1% for solar irradiance range from 200 to 1000 W.m-2.

Energy saving in buildings by using the exhaust air and phase change material for cooling of photovoltaic panels

Two air-type Photovoltaic Thermal (PVT) systems with and without Phase Change Material (PCM) were numerically investigated to evaluate the effect of using PCM as coolant on the air output temperature, amount of preheating temperature difference, the useful thermal and electrical power of the system as well as the participation of PVT/PCM system in supplying the typical required thermal load of the outside air (PEC). Based on the results, the PCM cooling decreases the PV temperature by 1.86–8.8 °C and 5.61–16.37 °C for 15 Jan and 15 Aug, respectively. In addition, the PCM causes to increase the PVT output air temperature rises by 2.96 °C even after sunset for 15 Jan. Moreover, the PVT system with surface area of 1.8 m2 produces 45.46–95.68 kWh useful thermal energy in the cold months. Besides, the monthly electricity generation rate of the system was obtained as 51.04–186.63 kWh. Moreover, the average PEC of the system was obtained as 66.86% for 12 months of the year. Also, PEC was obtained higher than 100 for two months of the year. Besides, the average monthly PEC increases with air mass flow rate to 0.5 kg/s due to increasing the electrical and thermal power of the system. However, for the higher air mass flow rates, the fan power escalates with increasing the air mass flow rate and diminishes the average PEC.