| Solar energy is a kind of clean renewable energy, the present utilization ways of solar energy are mainly solar-thermal and photovoltaic. The solar photovoltaic-thermal (PV/T) system is a kind of hybrid system as a combination of solar-thermal and photovoltaic, the principles of PV/T system is to integrate a pipe into a PV module for working fluid flowing to output electrical energy and heat energy simultaneously. In this paper, chapter one introduces the new energy technologies on the background of the worldwide energy crisis, and summarizes the history and latest developments of PV/T systems; chapter two and three conducts simulation analyzes on the dynamic performances of PV/T systems adopting different working fluids respectively; chapter four designs a series of PV/T systems with different pipe configurations and conducts comparative analyzes of their dynamic performances. The analysis results in this paper are listed as follows:1. The PV/T system adopting water as working fluidThe dynamic perofrmances of a PV/T system using water as working fluid have been investigated. Via the energy-balance model, the analytical expressions of performance indicators, including outlet temperature of working fluid, solar cell temperature, photovoltaic efficiency, overall electrical and thermal power are derived, and the hourly varition of performance indicators are presented under given climate condition. Besides, the influences of configuration parameters, including series-wound number of PV modules, inlet temperature and mass flow rate of working fluid on the dynamic perofrmances of PV/T system are analyzed. Some conclusions are drawn as follows:Under the given conditions, with the increasing of solar radiation intensity, the operating temperature of PV module rises and the photovoltaic efficiency decreases consequently, however the overall photovoltaic and thermal power still rise; When other conditions keep unchanged, with the increasing of series-wound number of PV modules, the operating temperature of PV module rises and the photovoltaic efficiency decreases consequently, however the overall photovoltaic and thermal power still rise; When other conditions keep unchanged, with the increasing of inlet temperature of working fluid, the operating temperature of PV module rises and the photovoltaic efficiency decreases consequently, besides the overall photovoltaic and thermal power decrease; When other conditions keep unchanged, with the increasing of mass flow rate of working fluid, the operating temperature of PV module decreases and the photovoltaic efficiency rises consequently, besides the overall photovoltaic and thermal power rise; In addition, the influences of inlet temperature or mass flow rate of working fluid on the overall photovoltaic and thermal power of the PV/T system are much smaller than that of series-wound number of PV modules.2. The PV/T system adopting refrigerant R410A as working fluidThe dynamic perofrmances of a PV/T heat collector using refrigerant R410A as working fluid have been investigated. Via energy-balance model, the analytical expressions of performance indicators, including backplance temperature, solar cell temperature, photovoltaic efficiency, overall electrical and thermal power are derived, and the hourly varition of performance indicators are presented under given climate condition. Besides, the influences of vaporizing temperature on the dynamic perofrmances of PV/T system are analyzed. Some conclusions are drawn as follows:Under the given evaporating temperature, with the increasing of solar radiation intensity, the operating temperature of PV module rises and the photovoltaic efficiency decreases consequently, however the overall photovoltaic and thermal power still rise; When other conditions keep unchanged, with the increasing of evaporating temperature, the operating temperature of PV module rises and the photovoltaic efficiency decreases consequently, besides the overall photovoltaic and thermal power decrease; In addition, the operating temperature is only slightly higher than the evaporating temperature, which indicates that a lower evaporating temperature will cool the PV module effectively, besides the operating temperature or photovoltaic efficiency of PV module is less influenced by changing solar radiation intensity and ambient temperature, which indicates that the performances of PV/T system will be more stable and reliable.3. The PV/T systems with different pipe configurationsThe dynamic performances of serveral PV/T solar systems with different pipe configurations have been investigated. Via energy-balance models, the analytical expressions of performance indicators, including the solar cell temperature, photovoltaic efficiency, overall electrical power and efficiency, as well as overall thermal power and efficiency are derived, and the hourly varition of performance indicators are presented under given climate condition. Besides, the influencs of different pipe configurations on the dynamic perofrmances of PV/T system are analyzed. Some conclusions are drawn as follows:Under the given evaporating temperature, with the increasing of solar radiation intensity, the operating temperature of PV module rises, the photovoltaic efficiency and the overall electrical efficiency decrease consequently, however the overall photovoltaic and thermal power still rise, besides the overall thermal efficiency remains stable; In the respect of electrical performances of PV/T systems with different pipe configurations, when the working fluid flows under the PV module, the heat extraction will be enhanced, the operating temperature of PV module decreases, the photovoltaic efficiency and the overall electrical efficiency rise, and the overall electrical power rises consequently. When the working fluid flows over the PV module, the heat extraction will be weakened, the operating temperature of PV module rises, the photovoltaic efficiency and the overall electrical efficiency decreases, and the overall electrical power decreases consequently. When working fluid simultaneously flows under and over the PV module, if the upper and under pipes are connected, the heat extraction will be enhanced, and if the upper and under pipes are independent, the heat extraction will be weakened; In the respect of thermal performances of PV/T systems with different pipe configurations, the overall thermal power is higher when working fluid flows over the PV module than under the PV module; The influences of pipe configurations on the electrical and thermal performances of PV/T systems are different. Generally the electrical performances are improved at the cost of the degradation of thermal performances and vice versa; In addition, it is verified numerically that the radiative heat transfer can be neglected to simplify calculations in simulation analyzes of dynamic performances of PV/T systems. |
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