We report the direct observation of nanoscale photovoltaic current-voltage properties associated with directional steps of the electrostatic potential at 109 degrees domain walls in ferroelectric BiFeO3 thin films with highly ordered ferroelectric stripe domains. The unidirectional photovoltaic effect along the net-in-plane polarization direction is shown to exhibit anomalies at the micro- and nanoscale due to local differences in mesoscopic domain structure. Very high initial photovoltages for small electrode spacings are observed using a conductive AFM tip as one of the electrodes in photovoltaic I-V measurements.