Experimental Investigation On Natural Convection Heat Loss Characteristics Of Photovoltaic Panel

Photovoltaic cell is one of the important components to realize photoelectric conversion. Heat loss from PV panel has a significant impact on its electrical efficiency. Therefore, research on the heat loss characteristics plays an important role in forecasting and improving the performance of PV system. Based on this, Electrical heating was employed to realize the linear heat flux boundary condition. an experimental investigation also has been carried out to analyze the effect of heat flux gradient parameter k, the total input heat flux qw and tilt angle ? on the heat loss characteristics of PV panel, such as temperature distribution, local convective heat transfer coefficient hl, average convection heat loss Nusselt number Nuc and average radiation heat loss Nusselt number Nur. In addition, empirical correlations of Nuc and Nur according to experimental results were obtained. Main findings are as follows:Under the condition of uniform heat flux boundary condition, i.e., k=0, when the panel is inclined at an angle of 90°, hl decreases firstly and then comes to a steady tendency from the bottom to the top of the panel. With a decrease of ?, local convective heat transfer intensity near the top of the panel is gradually increased due to the separation of thermal boundary layer. Therefore, when ?=0°, local convective heat transfer intensity decreases firstly and then rises up along the flow direction. Besides, a symmetrical distribution of hl could be also found. When under the condition of linear heat flux boundary condition, i.e., k>0, because a change of heat flux destroys the thermal boundary layer, a fluctuation variation of hl is seen from the bottom to the top of the panel when ?=90°. However, as ?=0°, thermal boundary layer is not the dominant factor influencing convection heat transfer, so there is not much difference of hl variation existed between the conditions of k=0 and k>0.The average convection heat loss Nusselt number of the panel is influenced by the coupling effect of three parameters, i.e., k, ? and qw. When k>0, heat flux gradient promotes the local convective heat transfer while the decrease of qw weakens the heat transfer intensity. With varying ?, Nuc has a first decrease and then rises again. And the critical ? corresponding to the minimum Nuc decreases with the increase of k. Thus, the variation of Nuc is relatively complex. As for the average radiation Nusselt number, Nur is always increased with the increase of qw due to the major influence factor of the total heat flux. While in relation to other parameters, not much effect is discovered.