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A US research team has tested mini solar modules in marine data collection devices, using animal hosts for water column profile measurements. The results suggest that underwater photovoltaics can work effectively in these applications at depths of up to 22 meters.
A group of scientists in the United States has tested the use of special solar cells to monitor the behavior of seals during spring migration. They said this is the first long-term deployment of submerged solar cells in a realistic ocean environment.
“Our work presents the first longitudinal study of photovoltaic cell performance in the marine environment that spans location, time and depth,” researcher Collin A. Krawczyk told pv magazine . “We highlight novel methods of data collection in the marine environment, using animal hosts as vehicles for water column profile measurements. “Based on our power results and energy predictions, solar energy could feasibly provide all, or a significant portion, of the daily energy required by many marine wildlife telemetry modules.”
According to the researchers, the electricity needs of microelectronics applied to marine data loggers and other devices have decreased considerably in recent years, making photovoltaics a viable power supply option.
To test their method, the team attached special mini monocrystalline solar modules to four adult female northern elephant seals. These mammals provide an ideal sensor platform for subsurface water profiling, as they make an average of 2.9 dives per hour to depths of more than 400 meters and have migratory patterns that range from Southern California to the North Pacific.
The scientists connected the mini photovoltaic panel to a device that measured and recorded the current-voltage relationship, as well as a SPLASH10 tag that recorded the seals location, orientation, temperature and depth. Unique names were given to each device: Kilo, November, Oscar and Lima.
“Deployment of these devices began in late February 2018, and both Noviembre and Oscar returned to the initial deployment location in early May 2018. Kilo undertook a much longer deployment, returning in early June 2018,” the researchers point out. “During this extended deployment, Kilo filled his onboard memory. “The Lima results were corrupted by a device malfunction during deployment.”
After recovering the modules, the academics had to carry out exhaustive post-processing of them. They had to calibrate a time lag between the tags and the current-voltage devices and perform a curve fitting process for the latter. They also had to use a method that estimates the short circuit current of a flat panel based on their observed tilted results. That is, the module was mounted on the head of a diving animal, and its panel inclination angles were usually non-zero.
They discovered that the maximum power averages as a function of depth occur up to 22 meters deep.
“Beyond 22 meters, our data became dependent on our estimates of low irradiance curves, and the data here had very few medium/high irradiance curves,” they said. “At 5 meters deep, the results show a reduction of between 70% and 85% of the relative power at the surface, depending on the label. Although Kilo experienced a greater power reduction than November and Oscar, the power reduction for November and Oscar at 15 and 20 meters was approximately 84% and 90% reduction, respectively. At 15 meters, we observe a reduction in available power of between 85% and 95%, which increases to a reduction of between 90% and 98% at 20 meters.”
The researchers described their experiment in “ Trans-oceanic subsurface photovoltaic performance ,” recently published in Progress in Photovoltaics . They come from Northern Arizona University and the University of California at Santa Cruz. |
