اثر استفاده از مواد تغییر فاز دهنده بر عملکرد یک سیستم فتوولتائیک خنک شونده
Abstract
1- Introduction
2- Experimental procedure
3- Results and discussion
4- Conclusion
References
Abstract
Nowadays, solar energy is harvested in two different ways including the extraction of thermal energy in solar collectors and electrical energy generation in photovoltaic panels. The Photovoltaic panels convert a small fraction of absorbed solar radiation into electrical energy and waste the rest in the form of thermal energy that results in increasing the panel temperature and decreasing the electrical efficiency. Photovoltaic thermal systems (PVT) equipped with phase-change materials (PCM) are capable of benefiting from the storage when phase change happens. In this manuscript, the effect of PCMs deployment on the performance of an air-cooled photovoltaic system is investigated, experimentally. As such, the effect of PCM is deliberated in a setup provided in which the PVT is equipped with a sheet of PCM. Herein, the first case considers a natural convection and the other three cases regard three different forced air convection. The experimental results indicate that using PCM sheets of six millimeters thick leads to reducing the panel temperature to 4.3, 3.4, 3.6 and 3.7 °C in average in a natural flow mode, forced high-velocity, medium and low velocity, respectively. Moreover, decreasing the temperature results in increasing the outlet power and electrical efficiency. Accordingly, it is concluded that using PCMs leads to a significant increase in natural and forced convection situations.
Introduction
The building precinct consumes more than 39% of the total consumed energies in the world and due to using conventional energy resources, it is responsible for a major part of environmental threats including pollution propagation and global warming [1]. To solve the problem, considerable attention has been given to the renewable energy resources. Solar energy harvesting by photovoltaic (PV) technology which can convert solar radiation into electric energy by photovoltaic effect is the most popular one [2]. One of the challenges in the utilization of PV technology is that all of the incident solar radiation to the PV cell surface do not convert to electricity. The maximum efficiency is in the range of 5–20%, and the rest is dissipated as heat raises the PV temperature [3]. Increasing PV cell temperature leads to further decrease in the PV efficiency which worsens the situation. Therefore, cooling technologies are essential to control the rise in temperature and to enhance the performance of the solar cells [4]. It is demonstrated that each 1 °C increase in temperature of a typical silicon-based PV panel leads to decrease in efficiency of around 0.5% [5]. Another study revealed that at 1000 Wm−2 solar radiation power, the produced electricity would be decreased from 240 W to 195 W when the surface temperature rises from 0 °C to 75 °C [6]. Moreover, it is reported that in the crystalline silicon panel the power of module will decrease approximately 0.4–0.65% per each 1 K increase of temperature, if the temperature rises 25 °C [7,8]. To address the issue, many types of research have been accomplished on the cooling of PV panels using PVTs [9]. Specifically, a simple way is to cool the panel by heat transfer fluids such as water or air [10,11]. In PVT systems, the objective is to extract the extra heat from the PV surface by using an operating fluid. The hot fluid can be used for endothermic processes in industrial or residential applications. The fluid can flow through the system in natural or forced circulation ways [12]. In Ref. [13], it is shown that the forced ventilation provides higher heat transfer than the natural flow circulation. However, it is necessary to use pumps (for water) or fans (for air) to generate forced convection. Natural or forced air circulation is a simple and low-cost way to remove heat from PV panels while water heat extraction is more expensive and causes pressure stresses and electrical problems for the PV cells due to its exposure to the water flow [12].