By Brett Baker

Formed through the recent merger of IRIS and UNAVCO, EarthScope Consortium assists the research community in procuring, deploying, and maintaining scientific instruments used in geophysics and other Earth sciences, as well as related data archiving and distribution services.

As the operator of the U.S. National Science Foundation’s GAGE and SAGE Facilities for geoscience, EarthScope often works in harsh environments, ranging from the polar regions to scorching deserts to deep drilled holes and more. Most applications are off the grid, requiring the use of battery-powered devices. Harsh environments such as these present challenges for batteries, perhaps none more extreme than the polar regions, the solutions for which provide valuable insight applicable to other remote deployments.

 

 

Wireless Challenge in Polar Climate

Among the most desolate regions on Earth, the Antarctic has temperatures that can reach -90° C during winter. Despite being so inhospitable, this frozen continent attracts researchers from around the globe who seek to unlock the secrets of Earth’s structure and formation, including plate tectonics, earthquakes, volcanoes, glacial ice movement, and more. Many polar projects require highly specialized batteries that are capable of performing reliably in extreme cold. These batteries power wireless devices.

EarthScope and Tadiran Batteries have collaborated to develop the TLP-93101E battery pack, which is assembled by EVS Supply and designed to withstand the extreme environment at the poles.

The TLP-93101E battery pack incorporates 50 Tadiran TL-4930 D-size bobbin-type LiSOCl₂ cells along with five HLC-1550A hybrid layer capacitors (HLCs) that deliver the high pulses required for wireless communications. Based on average current draw requirements, each pack is designed to last one to two years while delivering 190 Ah of energy at 18.57 V with up to 15-A pulses. This pack is inherently safe and environmentally friendly. It is also ruggedly constructed using Schottky diodes, positive temperature coefficient (PTC-200) thermistors (thermally resettable fuses), 18-gauge wire, a weather pack shroud-style (WPS) connector, PVC jacketing, and shrink enclosure.

While most battery chemistries perform poorly in extreme cold, bobbin-type LiSOCl₂ chemistry stands apart, remaining stable down to -55° C, modifiable to withstand -100° C.

Another key feature is miniaturization. Compared to an equivalent pack using cold-rated lithium iron phosphate (LiFePO₄) batteries, TLP-93101E packs fit within a 93 percent smaller footprint (13.62-by-2.59-by-6 in. versus 28-by-14-by-7.4 in.), with an 85 percent weight reduction (11 versus 70 lb.).

This difference becomes even greater when compared to lead-acid batteries. By reducing size and weight, shipping costs from New Zealand to Antarctica are significantly reduced while also meeting UN and International Air Transport Association guidelines for transporting hazardous goods.

In addition, the small footprint of the TLP-93101E permits greater numbers of battery packs to fit into the cargo holds of small planes and helicopter slings used to transport this equipment to remote sites.

 

 

The Value of Lower Self-Discharge

Self-discharge results from internal chemical reactions that occur even when there is no connection between the electrodes or to any external circuit. As a result, many low-power devices lose more energy annually due to self-discharge than is exhausted while operating the device, resulting in premature battery failure.

Bobbin-type LiSOCl₂ cells have a unique ability to limit self-discharge by harnessing the passivation effect. Passivation involves a thin film of lithium chloride (LiCl) that forms on the surface of the anode to separate it from the electrode, thereby reducing the chemical reactions that cause self-discharge. When a continuous current load is applied to the cell, the passivation layer causes initial high resistance and a drop in voltage until the discharge reaction begins to dissipate the passivation layer, which is a continually repeating process.

By effectively harnessing the passivation effect, the self-discharge rate of certain cells can be reduced to just 0.7 percent per year, thereby permitting wireless devices to operate for up to 40 years without having to replace the battery.

 

 

Field Examples

A common example of this type of battery pack being deployed in Antarctica involves a seismometer installed in the ground, with power supplies and data recording equipment enclosed in above-ground cases. Reliance on lead-acid batteries during dark winter months would necessitate overbuilding the power supply, which would further exacerbate the size/weight issue.

TLP-93101E battery packs are being deployed to power seismometers that surround Mt. Erebus, an active volcano located approximately 20 mi. from the McMurdo Station, the U.S. Antarctic research facility operated by the National Science Foundation. This wireless network provides real-time data and aids in the study of the volcano’s dynamics. While this particular application is located within reasonable proximity of the McMurdo Station, which is rare for Antarctic deployments, industrial-grade LiSOCl₂ battery packs are still required in order to withstand high altitude and katabatic winds.

Another prime example involves a network of seismometers that monitor the Thwaites Glacier. These instruments detect seismic signals produced by cracking or lurching movement of the ice along the bottom. They also provide data used to map and characterize the bedrock beneath the ice.

 

 

Custom Solutions

In the harsh clime of Antarctica, hybrid power supply solutions are often utilized for wireless devices. For example, during summer months, certain instruments can be powered by energy harvesting by combining solar arrays with lead-acid batteries. In winter months, the power source switches over to bobbin-type LiSOCl₂ battery packs that also provide emergency backup.

Every remote wireless application is unique, demanding individualized power management solutions. As a result, careful due diligence is required to identify the most cost-effective solution that will prevent premature battery failure, lower the cost of ownership, and protect data integrity.

Brett Baker is the president of EVS Supply.