Despite the increasing interest in photovoltaic (PV) cell powered small-cell base stations (SBSs), it has not been sufficiently studied yet how different PV cell angles can be utilized to achieve a good match between the energy arrival and consumption at the SBS. This is especially important in an urban environment where cellular network operators often struggle to apply optimal angles to the PV cells due to implementation constraints or shadowing effects of surrounding buildings. We develop an energy generation, storage and consumption model of a PV cell powered SBS, which includes the effects of PV cell orientations. A linear optimization problem is derived to optimize the energy performance of the SBS throughout the day. The effects of different PV cell orientations on the green energy utilization are evaluated assuming deployment in London in summer and winter. Our results show that west orientated PV cells (45° misalignment to the southern direction) are preferred in London during summer, whereas south orientated ones are preferred during winter. This reveals that the PV cell orientation needs to be optimized for not only the location and weather of the SBS deployment site but also the network traffic distribution in time (or energy consumption profile) of the deployment location.