PV modules have a problem that the power generated decreases with the rise of the PV module temperature. In order to solve the problem, we recently developed a new PV cooling device utilizing siphonage. In the first report [1] of this series, we presented the experimental results on the PV mounted on an open rack and that the cooling system is effective in both the improvement of the PV efficiency and the reduction of fuel consumption by reusing hot water from the system. In this study, we conducted long-term monitoring tests on the open rack-mount PV system with a cooling panel behind the PV module and with an insulation board (made of foam polystyrene) behind the cooling panel, simulating the residential rooftop PV system. The data obtained in the experiment have been compared with those obtained for the previous system with the cooling panel but without the insulation board. The comparison shows that the increment in energy production after equipping the cooling panel is much more for the present system with the insulation board irrespective of the cooling start temperature, being the PV temperature when cooling water was started to flow. This result suggests that the installation of the cooling system is more useful for the residential rooftop PV system than the open rack-mount system.

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