Integration of green roof and solar photovoltaic systems

Green roof and solar photovoltaic (PV) systems are two technologies that could contribute to sustainable building development and reduction of greenhouse gas emissions. When they are combined together on the building roof, it can enhance their functions and effectiveness by cooling and shading effects. This paper explains the major findings of a research to study the benefits of integrating green roof and solar PV systems. The important factors affecting the interactions between the two systems are assessed. The thermal and energy effects are analysed by theoretical models, experiments and field studies. A hypothetical case study to retrofit the roof of an existing building in Hong Kong with such integration is carried out to evaluate the practical design issues. The experimental results showed a positive influence for this integration: green roof surface and soil temperatures are reduced from the shading and higher power output of PV panel is achieved from the cooling. The findings of year-round building energy simulation using EnergyPlus for a low rise commercial building indicated that the energy consumption for air conditioning of the integrated system is slightly lower than the stand-alone system and the PV system on integrated approach generates 8.3% more electricity than the stand-a-lone option. The extent of the benefits depends on the system design and how to determine the optimum arrangement for a particular building site.