Marine wildlife telemetry systems are constrained in many of the same ways as their terrestrial and avian counterparts. Battery limitations, deployment duration, data sampling and communication energy requirements, and wide dispersion or migration routes conspire to reduce the fidelity of the data records. Terrestrial and avian wildlife telemetry modules can utilize solar power for some species to supply or supplement tag energy budgets. However, photovoltaic cells are absent from the majority of marine telemetry modules, both wildlife-mounted and robotic. In this paper, we present the development and deployment of custom photovoltaic assessment modules (CPAMs) designed to measure solar power in the marine environement. These devices collected current-voltage measurements on a monocrystalline silicon solar cell once per second over the course of four months. This work discusses the device functionality and design updates, calibration procedures, and the results of an oceanic deployment. During this deployment, CPAMs were mounted to four adult female northern elephant seals (Mirounga angustirostris) at the colony at Año Nuevo State Reserve (CA, USA) prior to their spring migration in the Pacific Ocean. Deployment results, including power production and energy results from the CPAM data record are presented. The elephant seals were at sea for between 76 and 107 days and provided measurements from a large geographic area between Santa Cruz, California and the Aleutian Islands of Alaska at depths up to 1287 m. We highlight how the recorded energy collection capacity of this cell compares to the daily energy usage of typical marine telemetry modules and show that even for animals that briefly surface, power harvesting electronics should be optimized for the surface environment.