TPL EnerPak Energy Harvesting Power Management System Completes Two-Year Performance in Wireless Sensor Network Trial for Utility

September 28, 2010 by Jeff Shepard

TPL, Inc. announced that the patented EnerPak™ energy harvesting power management systems have successfully completed two years of field-testing. Several EnerPak systems are powering a network of wireless measurement sensors that monitor the performance of sulfur hexafluoride (SF6)-insulated components. These components are at a power substation owned by Public Service of New Mexico (PNM), New Mexico’s largest electric utility, located in Albuquerque. According to TPL, this significant milestone demonstrates the performance and reliability of self-powered wireless sensors and networks using the EnerPak power management system. The EnerPak leverages the ultra-low-power MSP430™ microcontroller (MCU) from Texas Instruments Inc. (TI).

SF6 is one of the worst greenhouse gases in existence. PNM developed a wireless measurement and reporting system to continuously measure the integrity of the components that use SF6, to reduce the potential damage to the environment. When the utility first trialed their system, using conventional batteries for sensor powering, they found the batteries failing within a few weeks. PNM then turned to TPL to determine if TPL’s EnerPak could provide reliable, long-term power for their wireless sensor network. The EnerPak power systems replaced the conventional battery power system in September, 2008.

In the two years of operation at the Albuquerque substation, the eight EnerPak power supplies, each integrated with a small photovoltaic array, have performed reliably and consistently. In fact, the power supplies and sensors have been operating continuously since the trial began, achieving tens of thousands of discharge-charge cycles from each of the EnerPak systems.

In addition to traditional product testing, this real-world field-evaluation continues to demonstrate the long-term performance of the EnerPak supercapacitor-battery power management system and TI’s ultra-low-power MSP430 MCU. The sensor network includes both sensor node-to-sensor node wireless communications as well as wireless transmission of data to a central gateway processing station, both requiring sizeable power bursts. During the trial, the EnerPak systems have experienced heavy rain, strong winds and dust, as well as snow. Summer temperatures have exceeded 100°F, with winter temperatures dropping as low as 5°F.

Steve Willard, PNM’s engineer responsible for the development of the SF6 monitoring system, said the performance of EnerPak "... continues to meet all of the powering requirements demanded by the sensor network." Willard added that the use of wireless sensor networks demand a long-term power management solution like EnerPak because of the costs associated with the frequent replacement of conventional batteries.

EnerPak optimizes the combined performance of supercapacitors and rechargeable batteries, in order to deliver the best power management for autonomous devices like industrial sensors, wireless gateways and video surveillance. Through a unique microprocessor/charge pump configuration, the harvested energy is either used by the sensor or efficiently stored for later use. Also, the supercapacitors very efficiently provide high pulse power. The rechargeable battery, because of its high energy density, serves as the primary energy storage source, acting as a reserve when the energy harvesting source is not able to provide enough system power.

Using TI’s MSP430 MCU for system control, the EnerPak delivers the most harvested energy for each application load. The system is also capable of extracting energy from a variety of energy harvesting devices such as photovoltaic arrays, thermoelectric generators, vibration harvesters, and other generator devices.