Harvesting Energy for Low-Power Devices

The concept of harvesting energy—either from readily available natural sources or from nearby equipment—to power simple devices such as sensors has been getting a lot of attention recently. Last spring at the ABB annual conference, I spoke with Peter Terwiesch about ABB’s research into this area involving the harvesting of energy from process temperature, flow and vibration and converting it for use by low power devices via electric materials and piezo motors (to access this article, click here).

Today came an announcement from TPL Inc., a New Mexico-based research and development company, that its patented EnerPak energy harvesting power management systems have successfully completed two years of field testing.  The EnerPak is controlled via the “ultra-low-power” MSP430 microcontroller from Texas Instruments.

According to TPL, several EnerPak systems are powering a network of wireless measurement sensors that monitor the performance of sulfur hexafluoride (SF6)-insulated components at a power substation owned by Public Service of New Mexico (PNM), New Mexico’s largest electric utility, in Albuquerque, N.M.

Because of the potential environmental danger associated with SF6 (it is considered one of the worst greenhouse gases), PNM developed a wireless measurement and reporting system to continuously measure the integrity of the components that use SF6.  The sensor network deployed by PNM 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.

When the utility first tested the system, using conventional batteries for sensor powering, it found the batteries failed within a few weeks.  PNM then turned to TPL to determine if TPL’s EnerPak could provide reliable, long-term power for its 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 reportedly performed as required.  In fact, the power supplies and sensors have been operating continuously since the trial began, achieving tens of thousands of discharge-charge cycles from the EnerPak systems. During the trial, the EnerPak systems have experienced heavy rain, strong winds and dust, and snow.  Summer temperatures have exceeded 100°F, with winter temperatures dropping as low 5°F.