4
Power and Energy for Polar Research
The second session of the workshop focused on a critical issue that cuts across virtually all aspects of Antarctic science: power and energy supplies for research instrumentation and operations. Several workshop participants highlighted the importance of new options for batteries, electronics, and other key elements of power systems that can withstand the Antarctic’s extreme cold conditions. At the same time, there is a long-standing interest to advance the use of renewable energy technologies that harness the Antarctic’s abundant wind and (seasonal) sunlight resources—and that could reduce the costly, difficult challenges of transporting liquid fuels to and within this remote part of the world.
In this session, workshop participants explored technology options both to increase the power supply for research instrumentation and activities and to increase the efficiency of research instrumentation and activities to minimize power requirements. Session speakers with polar field experience were asked to discuss technologies and strategies currently used to provide power in Antarctic research and the biggest problems and limitations of these systems. They were also asked to share thoughts on advances in energy technologies that could plausibly be pursued to better support the polar research enterprise. The session also included speakers who do not work in polar research, but who have helpful external perspectives on cutting-edge energy technologies that hold potential for possible application in polar science.
CURRENT CAPABILITIES, CHALLENGES, AND NEEDS FOR POLAR RESEARCH
Robyn Verrinder, University of Cape Town, discussed ice-tethered instruments (including sensors measuring temperature, pressure, humidity, and motion) being deployed in the sea ice of the Antarctic and the Southern Ocean. The instrument capabilities are constrained, as it is a small platform (~40 cm tall and 10 cm in diameter) that must be deployed directly from research vessels. The instrument must be able to operate autonomously for months at a time, in temperatures as low as −25ºC, and in extreme wind, wave, and storm conditions. Thus, careful design of the power budget is essential, Verrinder said. Data transmission technology is by far the largest power consumption component on the device. Data are stored and processed on board and transmitted primarily through the Iridium satellite network, which requires ~2.5 watts (compared to ~0.4 watts for regular operations).
The primary source of power for these devices is lithium thionyl chloride battery cells, which have excellent energy densities and very good low-temperature performance. However, they have poor peak current output capabilities, so they must compensate by using numerous cells in parallel. Lithium iron disulfide batteries have good performance at low temperatures and much better peak performance but do not have the same energy densities as lithium
thionyl chloride cells. Alkaline batteries have very poor low-temperature performance, and lead acid batteries using solar for recharging are not feasible due to deployment challenges and lack of sunlight.
Some active areas of technology development include improving power regulation management and control (e.g., improving the firmware design to optimize sampling, scheduling, and data processing), and considering a full systemwide design to improve all areas of power consumption. Data communication systems are another area that needs further advances, Verrinder said.
Craig Kulesa, University of Arizona, discussed mid-scale (100–1,000 watt) power strategies that have been used for deploying robotic telescopes for astronomy on the Antarctic plateau. The use of solar energy technologies is well established and continues to improve in terms of performance and cost, but the major downside is the lack of light in winter. There are challenges with implementing wind energy in polar regions, but Kulesa noted that it remains worth exploring despite the modifications required to operationalize commercial systems. (See Box 5 for more discussion on renewable energy.) For systems requiring more power, Kulesa has used small, single-cylinder diesel engines in the field, enclosed in insulated boxes, with some success. Diesel engines need maintenance, which is not always possible, so Kulesa’s team uses redundancy engines—burning through one engine that goes to another one, repeating through field campaigns. One new technology that may be beneficial is microturbines. These are lower maintenance and produce electricity as well as heat from the microturbine.
Kulesa emphasized the need to recognize that the environmental footprint for the experiment itself can be dwarfed by the logistics needed to get into the field and service the equipment. The longer that scientists can go without servicing instruments, the smaller the footprint. Choosing the cheapest option may sufficiently address the research questions, but can have logistical cost implications. Strategic investments upfront can save a lot on logistics later. Kulesa pointed to lessons learned from work done on small satellites, where a few watts and a few kilograms can make the difference of millions of dollars. Additionally, Kulesa suggested that teams improve the robustness of their systems before deployment, as it is better to make mistakes in the lab rather than in the field. The more an instrument is tested before deployment, the more likely it is to have a successful outcome. More open access to cold testing facilities would be a great value to the community, Kulesa said.
Following on Kulesa’s remarks, Caitlin Callaghan, Cold Regions Research and Engineering Laboratory (CRREL), discussed how CRREL supports cold region instrument testing. She helped develop the Cold Regions Energy Research, Development, Testing, and Evaluation (RDTE) program, which addresses many of the challenges that other speakers highlighted. A goal of CRREL is to identify appropriate technologies and minimize disruptions that may happen in cold climates. For any given technology, CRREL assesses its capabilities and optimal applications (e.g., long-duration or slow-supply needs versus short-duration or fast-response needs). In addition to assessing individual parts, it considers systems as a whole, including practical deployability issues (e.g., on vehicles or at a forward operating site, minimizing what soldiers have to carry).
Callaghan noted a few specific projects the RDTE program is working on. One major focus is on batteries. They have projects to evaluate commercially available battery technologies (e.g., how to mitigate performance degradation) and work with partners to develop innovative solutions for new battery chemistries that can work in extremely cold climates. They have several cold chamber facilities used for this testing (at both their Hanover, Hew Hampshire, facility and field deployment sites in Alaska).
For power generation, one technology of interest that is already being used in some places is stationary fuel cells, which are good for minimizing noise and mission footprint, maximizing fuel efficiency, and minimizing maintenance needs. For more information on CRREL’s testing sites, see Zoe Courville’s remarks in Chapter 7.
Another relevant project that Callaghan noted is the Energy Atlas for Department of Defense Lands in Alaska,1 which allows one to layer in different
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types of resources and site information for a big-picture view of what is available. This tool could potentially be expanded to other areas of the globe, she said.
Robert Clauer, Virginia Tech, discussed his experience with low-power autonomous instruments on the East Antarctic plateau. Clauer and his team’s instruments use solar panels and lead acid-absorbed glass mat (AGM) batteries for power storage during the winter period when there is limited sunlight. (See Box 6 for more discussion on batteries and energy storage.) When the battery voltage drops below a certain threshold, the systems hibernate and wait for sunlight, when the solar panels can produce power again. When that happens, heaters warm the batteries and the system wakes up and resumes operation. The solar panels and lead acid batteries have performed consistently well since their first deployment in 2008. The data are obtained by a two-way radio communication system.
Clauer noted that one helpful practice he and his team employ is to have engineers join initial installation testing, as they can help make system revisions that simplify the installation. For example, instead of using nuts and bolts, they switched to using pins to join the tower sections (so that the installation can be performed with gloves on) and using a harness system with clips (adapted from the auto industry) that enable batteries to be hooked up in parallel and only in one direction (so it cannot be done wrong). To test the system, Clauer and his team talked to a person back in their home laboratory (via Iridium phone) who was seeing the data in real time and could advise on what field installation details to alter. Additionally, he noted that it is important to duplicate the system in the laboratory for diagnosis and testing.
Matthew Lazzara, University of Wisconsin–Madison, discussed the power and energy challenges of the Antarctic Automatic Weather Station program. This system has been evolving for many decades. Historically, the system used radioisotope thermal electric generators for power, but those generators were removed by the 1990s due to environmental concerns. Current systems use lead acid and gel cell batteries and solar panels. As other speakers noted, the lack of light in the winter can be a challenge. Lazzara and his team rely on solar charging of the batteries throughout the summer and then slowly discharge the batteries in the winter to continue operations. They tried limited wind installations, but the equipment did not hold up well. These systems generally only need one watt or less of power at any given time, although as more sensors are added there is a greater need for power.
Lazzara noted a few key challenges and limitations of the current systems. There are transportation and deployment constraints because power systems are heavy and expensive to ship to Antarctica. Batteries are thermally stable, but snow accumulation can often make retrieval of batteries difficult. There is also a growing demand to run more sensors, which means there is a need for more power and new data communication systems. Lazzara’s team uses the Argos community system, which has a low power draw, but limited data transmission capacity. They are exploring Iridium to increase transmission capability, but some of those capabilities are harder to run at the temperatures found on the Antarctic plateau. In looking for lighter, less expensive power systems, Lazzara said that lithium-ion rechargeable batteries are appealing, but they can be a real challenge to operate in colder temperatures, and they raise concerns about transporting hazardous materials (i.e., flight restrictions).
ENERGY TECHNOLOGY ADVANCES WITH POTENTIAL FOR GREATER POLAR SCIENCE APPLICATION
As someone who does not work directly in polar science, Eric Wachman, University of Maryland, offered his perspective on recent developments in power generation and storage technologies more generally. Because liquids become viscous and freeze at low temperatures, he suggested that solid-state or gas fuel is better suited for polar regions. This includes batteries where a phase change in typical liquid electrolytes will make their resistance too high at low temperatures, whereas solid-state batteries do not undergo a phase change, thus avoiding a drastic increase in resistance. Similarly, low temperatures increase the viscosity of lubricants and fuels used for internal combustion engine generators, resulting in excessive maintenance requirements, so there is a growing interest in fuel cells. A typical proton exchange membrane fuel cell (PEMFC) has a water-hydrated membrane, which can freeze and cause a catastrophic system failure, meaning PEMFC would require foolproof thermal insulation.
In contrast, solid oxide fuel cells (SOFCs) are solid and therefore do not freeze. Typically, they operate at higher temperatures, but there is ongoing work to bring operating temperatures down. SOFCs are fuel flexible and are efficient and scalable over a wide range of sizes (from hundreds of watts to hundreds of kilowatts). SOFCs can also be used in combined heat and power
operations—heat generated can be directed to help with heating batteries to enable charging. They can also operate in electrolysis mode, which means they can generate power by consuming fuel-like hydrogen (H2) but also run in reverse and generate H2 and store it. It is thus both a power generation and a storage technology.
Yi Chao, Seatrec, discussed some ocean robotic platform and sensor technologies he helped develop at the National Aeronautics and Space Administration and the California Institute of Technology (some of which are now patented) and is now commercializing. According to Chao, the biggest challenge in using ocean robotic platform and sensor technologies in remote areas is the expense and difficulty of retrieving instruments and changing or recharging batteries. Disposable platforms (i.e., platforms not retrieved for repowering) present environmental concerns and the loss of valuable instruments. Chao’s work aims to find more sustainable and scalable solutions to power these systems by harvesting ocean thermal energy associated with temperature differentials between warm surface waters and cold water at depths. This temperature difference can be 10oC or more in the upper 1,000 m throughout much of the world’s oceans.
To do this, Chao uses an energy harvesting technology based on a phase change from solid to liquid. When an ocean-profiler instrument moves up and down the water column, material that is solid at the cold water depths will melt as it rises to the warm surface waters. This phase change generates a hydraulic pressure that can be harnessed to spin a motor and generate electricity (see Figure 10). This energy can charge batteries and be stored. This thermal energy harvesting technology is scalable—every kilogram of phase change material can produce on the order of 1,000 joules of energy.
Seatrec is currently looking at how to apply this solid-to-liquid concept to a liquid-to-gas phase change process. In laboratory research and development studies, it can generate tens of watts once the temperature difference exceeds 12ºC. This approach could potentially be applied in other contexts as well. For example, in the Arctic winter, there can be large temperature differences between the cold air and relatively warm water below the ice. Seatrec is currently partnering with Woods Hole Oceanographic Institution on a project (funded by the Office of Naval Research) to harvest this air-sea temperature difference in the Arctic to generate continuous power on the order of 50 watts. The hope is that this approach can power the sensors on the ice as well as underwater equipment and provide a sustainable long-endurance source of power.
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