Simulation studies for the mitigation of summer urban heat island by rooftop solar photovoltaic deployment in Nanjing area

The installation of rooftop solar photovoltaic is expected to relieve the energy crisis and urban thermal damage caused by urbanization to some extent. The non-hydrostatic version of the Weather Research and Forecasting (WRF) model coupled with the single layer urban canopy model (UCM) is utilized to simulate the mitigating effect of rooftop solar photovoltaic with various power efficiencies under sunny and breezy weather condition from 27 July to 5 August 2010. The results indicate that:(1) the installation of rooftop solar photovoltaic can reduce the amount of energy needed to import into the city since it can generate energy for local use. This leads to cooling in the urban area since the energy generated by the solar panels can be used locally, which would otherwise heat the urban surface and radiate energy into the atmosphere. The cooling effect becomes more significant with increasing solar panel efficiency, and the daytime cooling effect is stronger than that in the nighttime. The maximum 2 m air temperature can be decreased by 0.4-1.3 and 0.2-0.5℃ in the daytime and nighttime, respectively; (2) the installation of rooftop solar photovoltaic can reduce the planetary boundary layer (PBL) temperature, and the cooling effect is significant below 400 and 200 m in the daytime and nighttime, respectively. The maximum decrease in the PBL temperature during the daytime occurs around noon, and the decreases can be up to 0.1-0.8 and 0.1-0.5℃ in the daytime and nighttime, respectively; (3) the power generation capacity is 18.1×10⁹ kW·h within 9 d with the power generation efficiency of 40%.