Fixed and tracking PV system for Net Zero Energy Buildings: comparison between annual and monthly energy balance

The energy needs of a Net Zero Energy Building (NZEB) are fully met by renewable energy sources. These strongly depend on their characteristics and on meteorological-geographical factors, but also on different kinds of energy balance. The aim of this paper is to investigate the comparison between two different photovoltaic systems (fixed and tracking) and two kinds of energy balance (yearly and monthly), to evaluate which system better achieves the definition of NZEB for an existing residential building, so limiting exchanges with the national electricity grid. A dynamic energy simulation software (DesignBuilder) is used. The results show that the photovoltaic surface which attains the NZEB target on yearly basis not always achieves the same objective when the energy balance is performed on monthly basis. Furthermore, considering a monthly balance, the size of the photovoltaic system with biaxial solar tracking is 45% minor compared to the fixed photovoltaic system, thanks to a steadier energy production.