Operation Characteristics Of Photovoltaic Self-driven Solar Air Heater

Self-driven solar air heaters use the electrical energy generated by photovoltaic panels to drive the fan operation of the system to achieve power self-sufficiency and have good application value.However,due to the periodicity and transient character of solar energy,this heater has limited operation time and large fluctuations in operation temperature.Therefore,this study proposes the idea of integrating a thermal energy storage unit in a selfdriven solar air heater in order to achieve self-sustained continuous heat output from the heater.In this paper,a photovoltaic self-driven solar air heater with thermal energy storage unit is constructed,the heat balance of the system is theoretically analyzed and the feasibility of its continuous 24-hour operation is verified.In addition,the operational performance of this novel heater is investigated under two power supply modes.The results show that the heater can automatically adjust the operating flow rate according to the solar irradiance when it is operated in photovoltaic-battery powered mode(the all-day flow rate is between 20.34 and 33.31m3/h),and its all-day thermal efficiency is 46.92%;the c heater’s all-day operating flow rate is stable in a small range when it is operated in battery-only powered mode(the all-day flow rate is between 20.58 and 21.41m3/h),and the all-day thermal efficiency is 34.63%,and this mode shows a better performance under lower solar irradiance.Additionally,the operating characteristics of the heater under a variety of experimental conditions are discussed,including heater with/without thermal energy storage unit,stable/unstable meteorology,facing due south/15° SSE/15° ESE,and winter conditions.The results show that:the introduction of the thermal energy storage unit can reduce the peak temperature of the heater outlet by more than 9 K and improve the photoelectric efficiency and performance ratio of the photovoltaic panels;the thermal performance of the heater is not sensitive to fluctuations in solar irradiation due to the existence of the thermal energy storage unit;the heater can utilize more solar energy by placing it properly to the west;the heater is difficult to maintain continuous operation throughout the day under unfavorable winter conditions(runs only about 11 hours),and the phase change material has not been melted,so it is recommended that the thermal energy storage container be redesigned for the winter system to reduce heat loss.Furthermore,in order to expand the range of research conditions,the numerical simulation study of the solar air heater with thermal energy storage unit is conducted using Fluent software,and the effects of amount of thermal storage,phase change melting point and leakage of phase change material on the heater performance are further discussed,and suggestions for the heater in the actual use process are made in response to the simulation results.The energy payback time of the system proposed in this paper is 42 months,and the research results can provide a new solution for solar thermal utilization systems such as agricultural drying.