شبیه سازی سیستم یک خطی با متمرکز بر سیستم فتوولتائیک همراه با سیستم خنک کننده فعال

Recent interest in concentrating photovoltaics (CPV) have led to research and development of multiple CPV systems throughout the world. Much of the focus has been on 3D high concentration systems without cell cooling. This research makes use of a system simulation to model a medium 2D solar concentration energy system with an active cooling system. The simulation encompasses the modeling of a GaInP/GaAs/Ge triple-junction solar cell, the fluid and heat transfer properties of the cooling system, and the storage tank. The simulation was coded in Engineering Equation Solver and was used to simulate the linear concentrating photovoltaic system (LCPV) under Phoenix, AZ, solar and climactic conditions for a full year. The output data from this simulation was used to evaluate the LCPV system from an economic and environmental perspective, showing that over one year a 6.2 kWp LCPV system would save a residential user $1623 in electricity and water heating, as well as displace 10.35 tons of CO2.

Because of their high electricity conversion efficiencies, multijunction cells have seen a significant increase in research interest and research funding over the last ten years. PV cell manufacturing techniques have improved in recent years, assisting in higher material purity and less material defects. As these techniques improve, so too do the efficiencies of the multijunction cells. Of the different solar cell technologies, the multijunction concentrator cells have demonstrated the greatest increases in efficiency, reaching a record breaking 41.1% [1]. Because of their high efficiency, multijunction cells have one of the largest potentials for decreased solar energy production costs now and in the future. In order to be cost effective, these systems must have a concentration system, and therefore must also have a solar tracking system. Further efficiency gains can be accomplished by including a cooling system to reduce the cell temperature. As solar cells increase in temperature, the cell efficiency decreases. This decrease can have adverse effects on the cell efficiency and therefore power output at medium and high concentration levels. This research focuses on the young and growing field of concentrating PV systems, specifically that of linear concentrating systems that use high efficiency multijunction cells. The linear concentrating photovoltaic system (LCPV) system that was simulated combines a linear Fresnel lens, high efficiency GaInP/GaAs/Ge cells, and a fluid cooling channel. A conceptual drawing of this system can be seen in Fig. 1, where the solar radiation is focused onto the multijunction cells and the heat is removed using an active cooling system. The cooling system is used to cool the cells so that higher cell efficiencies can be maintained, and the excess heat that is withdrawn from the module is then stored and used as a heat source. Fig. 2 gives a heat flow example of how this heat would be extracted and stored in a system designed for residential use. When the LCPV system receives solar radiation, the pump turns on, constantly circulating the fluid from the storage tank. The fluid in the tank heats up, and can be used for heating purposes. The hot fluid produced by the LCPV system can thereby partially or fully displace the energy consumption associated with hot water generation in a residential home, for instance. A three-dimensional drawing of the LCPV system as it would look in service with a tracking system is shown in Fig. 3. This drawing represents a 6.2 kWp system under standard test conditions of 1000 W/m2 solar radiation and 25 °C ambient temperature. The drawing does not include the entering and exiting fluid piping or any balance of system components, but it can be seen from the drawing that there are five separate 5 m long modules that are secured to a steel rack. The LCPV is mounted on a two axis tracking system, capable of tracking the sun within one degree on both axes, that moves via an electric motor and is stabilized by a concrete base. Taking a closer look at the end of an LCPV module more clearly reveals that there is a flow channel at the bottom of the module that runs the length of the module, as show in Fig. 3. During operation, this flow channel would be filled with a flowing fluid that comes from the storage tank and would enter through the top via a connected flow tube. The fluid would flow down the channel, absorbing heat as it goes, and would exit out of the bottom of the channel through another flow tube that would bring the fluid back to the storage tank. The top surface of the LCPV module is the Fresnel lens that concentrates the solar radiation by a factor of 80 times. The housing would be made of aluminum and the tracking system components would be largely made from galvanized steel. The system as shown in Fig. 1 through Fig. 4 represents the system as it is simulated using the LCPV model.

The LCPV system simulation has aided in broadening the energy and environmental knowledge in the field of concentrating photovoltaic simulation. A simulation was created for a linear concentrating photovoltaic (LCPV) system that uses an active fluid cooling channel. The simulation was comprised of many electrical circuits, heat transfer, and fluid flow equations, as well as thermodynamic functions, to calculate the output parameters of the LCPV system under any given solar and climatic conditions. Many input parameters in the simulation can be altered to simulate a specific system and therefore the LCPV simulation is a very flexible model. The LCPV simulation was used to successfully model a 6.2 kWp LCPV system under Phoenix, AZ, solar and climactic conditions. Using this information and the solar/climactic data for Phoenix in 2005, a complete yearlong simulation of the LCPV system was conducted. This simulation led to some promising conclusions for the LCPV system. It was found that the LCPV system produced 5089 kWh of thermal energy and 14,215 kWh of electricity, with a multijunction cell efficiency average of 34.75%. This led to a significant reduction in purchasing electricity and natural gas throughout the year, totaling $1623 and $202, respectively. These values would lead to a dollar savings of $48,720 over the course of 30 years, or the expected lifetime of the LCPV system. Additionally, the GWP offsets would equate to 9.14 tons of electricity-produced CO2 and 1.21 tons of natural gas-displaced CO2. Over 30 years, this totals 310 tons of CO2 that would be no longer emitted into the atmosphere from a single home. If we assume that just 10% of the approximately 110 million households in the U.S. were able to reduce their CO2 by 310 tons over 30 years, that would equate to a GWP reduction of 3.41 million tons of CO2.