| With the development of economic and the improvement of our life, the consumption of the energy gets much enormous. However, the storage of fossil fuel is limited, which cannot meet the life demand in a long period, and the use of fossil fuel leads to severe environment issues. Thus it gets more and more important to actively change the energy structure and vigorously develop clean energy technologies. Solar energy as one of the renewable energy, which distributes widely and has no harm to environment, can play a key role in this process.The hybrid photovoltaic/thermal (PV/T) technology integrates the mature solar thermal collector technology and photovoltaic power generation, which can absorb the waste heat to produce hot water and/or air and reduce the temperature of solar cells to improve the electric efficiency. PV/T has a promising future for it promotes solar production per unit of area and favors to integrate with buildings. The photovoltaic cell and the photovoltaic part of the PV/T can generate hot spot and decrease the output and damage the cells for the shading of leaves, buildings and/or the collector edge. Then this paper investigates the worst case of hot spot and the influence of the PV/T on the hot spot. Besides, due to the lifetime mismatch of photovoltaic cells and the absorber for the hot spot and/or stagnation, the paper designs and constructs a detachable tube-sheet PV/T and a detachable parallel flow aluminum flat tube PV/T, and researches the performance experimentally and simulatively.The main researches are shown as follows:(1) A theoretical model on the hot spot of PV is proposed and the influence of inhomogeneous illumination and incomplete shading of solar cells is investigated respectively to find the maximum power dissipation and the worst heating power. The result demonstrates that the maximum power dissipation of shaded cell always happens at short-circuit condition in both situations and is affected by the number of solar cells which are paralleling with a bypass diode. The hot spot can cause permanent damage, so it is needed to simulate and analyze when a PV module is designed.(2) Based on the energy balance equations, simulation are performed about hot spot in five situations-normal PV module, tube-sheet PV/T and parallel flow aluminum flat tube PV/T with an air gap and without an air gap. The affect of different ambient temperature, water temperature and heating power on the cell temperature is researched. The results demonstrate that PV/T is much efficient to reduce the temperature of the shaded cell where hot spot happens and the parallel flow aluminum flat tube PV/T is the best. But the tube-sheet PV/T with an air gap is not good, which has small safety margin.(3) Experiment and simulation are performed for the designed and constructed detachable PV/T on the instantaneous efficiency. The simulated results of tube-sheet PV/T are validated with experimental data. It shows that the instantaneous efficiency of tube-sheet PV/T is 43.6%, and the total PV/T efficiency is 57%. However the contact resistance between the absorber plate and PV module are too large to improve the thermal efficiency. The instantaneous efficiency of parallel flow aluminum flat tube PV/T is 43%, and the total PV/T efficiency is 55.5%. It is especially needed to modify the design to improve thermal efficiency. |
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