An Investigation into the Energy Performance Gap between the Predicted and Measured Output of Photovoltaic Systems Using Dynamic Simulation Modelling Software – A Case Study

The use of solar energy can help reduce the CO2 emission and dependency on fossil fuels, and using Solar Photovoltaic (PV) systems to generate electricity is a popular route to validate the building energy performance in the UK. To help achieve the targets set out in the Climate Change Act, Part L of the Building Regulations 2013 stated that a building must achieve the approved minimum energy performance requirements. EDSL Tas, a dynamic modelling software, is often used by building consultant companies whose designers use the facility to simulate PV systems and integrate the energy output results into the overall energy performance of a building. There is, however, a clear performance gap between the measured and predicted energy output when using dynamic modelling software. Therefore, this paper is to use a comparative study to address this issue by using EDSL Tas software to predict PV system’s energy output and comprehensively analyse a case study at Poole Methodist Church. There are many causes for the potential deviation of results, although the most influential in relation to energy performance is the use of weather data, future climate change, adverse weather conditions and environmental factors affecting the PV array. The results indicate an 8.6% higher measured energy output from the installed PV system although the performance gap has little detrimental effect in regards to achieving Building Regulation compliance, but could lead to the unreasonable design of the PV system and inappropriate use of capital investment. Further simulation using projected future weather data from several different climate change scenarios was undertaken. 2020, 2050 and 2080 with low, medium and high emission scenarios indicated that the PV array would increase energy output by up to 5% by 2080 compared with using current weather data, indicating a rise in PV energy output in relation to increased CO₂ emissions. This is due to a projected reduction in cloud cover and increased downward shortwave radiation.