In a net zero energy (NZE) facility the roof is an important source for energy savings and production. A project can utilize passive solar design, reflective roof surfaces, a green roof, skylights, and/or renewable energy generation. In a NZE design, the roof must contribute either significant energy savings or energy generation. In particular, two uses of the roof space are directly tied to energy; skylights to reduce lighting energy and photo-voltaics (PV) to produce renewable energy. However, when it comes to implementing these technologies in energy efficient or NZE projects, competition for roof space occurs.

This paper highlights the importance of proper calculations in choosing technology for best utilization of roof space in a NZE building and presents the main factors. First, this paper introduces the common energy efficiency technologies competing for roof space and their potential to contribute to NZE and conflict with one another. Next, the NZE path is chosen and a metric for NZE evaluation is introduced. Finally, sample scenarios for PV generation and skylight savings are analyzed and PV’s impact is favored. The findings demonstrate that PV produces more net energy than skylights save.