The purpose of this research was to investigate energy harvesting in the marine environment for the purpose of supplementing the energy budgets of remote sensor systems such as wildlife tags or autonomous underwater vehicles. The goal was to analyze potential ambient energy sources and assess their viability for marine sensor systems, and then to build, test, and deploy a marine power harvesting prototype.

The research effort resulted in a number of key outcomes. Initial efforts involved characterization of various ambient marine energy sources. A sub-surface solar power assessment model was developed to determine how geographic location, depth, temperature, water turbidity, and weather combine to affect the performance of submerged photovoltaic (PV) cells. This model was published and publicly released. Concurrent with the model development, a subsurface power harvesting measurement tag was designed, built, tested, and integrated with a commercial marine wildlife tag. This custom PV assessment module (CPAM) was designed to measure the current-voltage relationship in the marine environment, allowing characterization of the potential instantaneous power and long-term energy production of a silicon PV module. These devices were mounted to Northern elephant seals during their spring migration, where they transect a portion of the Pacific Ocean and make regular dives to depths of complete darkness. This diving behavior enabled measurement of PV cell performance in a variety of light conditions across a wide geographic area. The deployment of the CPAMs was completed in the spring of 2018 and included approximately 10 weeks of data for each of the three deployed tags. The resulting dataset provided solar cell performance measurements in a geographic region from Santa Cruz, CA to the Aleutian Islands of Alaska for depths from the water surface to 22 m (72 ft), beyond which too little power was available to be measured by the CPAM devices. Prior to this deployment, very limited measurements of PV harvesting performance in the oceans was available, since prior efforts only recorded data at a small number of discrete locations at a single time of day. Based on this dataset, a complex data analytics effort generated insights that will greatly assist development of next-generation devices and systems for long-term deployments in the sub-marine environment.

In addition to this deployed PV cell characterization effort, laboratory experiments were also conducted to characterize cell performance while controlling for light level, spectral filtering, and temperature. Using known light filtering characteristics of oceanic water, a tunable solar simulator was used along with a temperature controller to characterize the current-voltage relationship and power output of a silicon solar cell. A dataset was generated and archived online that allows users to extract the current-voltage relationship of a cell for any of the standard oceanic water types, any depth, any surface irradiance, and any temperature. This dataset complements and extends the deployment data collected in 2018, enabling detailed prediction of solar power in conditions beyond the water types, temperatures, and light conditions experienced by the elephant seals.

To broaden the impact of this research, outreach to the local and regional public through high school STEM programs and community events was proposed to highlight the research and impacts on engineering design and scientific discovery. Throughout the duration of this project the research team participated in the annual Flagstaff Festival of Science and Flagstaff STEM Nights. The team also developed and taught a program in energy transduction for the Upward Bound Program at Northern Arizona University, contributing to the education and college preparation of high school students who will be first-generation college graduates and/or are from disadvantaged backgrounds.

Last Modified: 01/04/2022
Modified by: Michael W Shafer