The tilt and azimuth angles of a photovoltaic (PV) array affect the amount of incident solar radiation exposed on the array. This paper develops a new mathematical model for calculating the optimum tilt angles and azimuth angles for building-integrated photovoltaic (BIPV) applications in Hong Kong on yearly, seasonal, and monthly bases. The influence of PV cladding orientation on the power output of PV modules is also investigated. The correlations between the optimum tilt angle and local weather conditions or local environmental conditions are investigated. The results give reasonable solutions for the optimum tilt angles for BIPV applications for both grid-connected and stand-alone systems.