This work investigates the problem of increasing the electrical energy generation efficiency of photovoltaic (PV) systems on electrical vehicles (EVs). The PV cell modules of an onboard PV system are mounted on the rooftop, hood, trunk, and door panels of an EV to fully make use of the vehicle surface areas. However, due to the non-uniform distribution and rapid change of solar irradiance, an onboard PV system suffers from significant efficiency degradation. To address this problem, this work borrows the dynamic PV array reconfiguration architecture in previous work with the accommodation of the rapidly changing solar irradiance in the onboard scenario. Most importantly, this work differs from previous work in that (i) we propose an event-driven PV array reconfiguration framework replacing the periodic reconfiguration framework in previous work to reduce the computation and energy overhead of the PV array reconfiguration; (ii) we provide a sensorless (and also event-driven) PV array reconfiguration framework, which further reduces the cost of a vehicular PV system, by proposing a solar irradiance estimation algorithm for obtaining the instantaneous solar irradiance level on each PV cell module. Experimental results demonstrate significant performance enhancement and energy overhead reduction.