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Energy harvesting answers increasing demand for high power

Posted: 02 Dec 2015     Print Version  Bookmark and Share

Keywords:IDTechx  energy harvesting  thermoelectrics  Imec  piezoelectrics 

With the noise generated by the Internet of Things (IoT) and related technologies, energy harvesting has little choice but to take the back seat. However, one analyst claimed that the future may be bigger for energy harvesting.

"Energy harvesting nowadays doesn't just apply to a whisper of electricity. It's used up to the megawatt level, off grid," said Peter Harrop, chair of IDTechx. "There's only limited success with low energy in the microwatts up to milliwatts."

The energy that's actually being harvested in test or in market, Harrop said, powers larger devices such as construction vehicles, boats and planes. The low-power market is a $100 million business but still not a huge success; Harrop claimed that even when low power energy harvesting has its day, it will only be accountable for one-hundredth the business of higher-power devices.

High-power devices, particularly those in industrial markets, are often early adopters because OEMs and customer companies have the volume/pricing power to reduce the cost of purchasing new technologies. Moreover, industrial equipment is often inaccessible and requires power management that doesn't require heavy monitoring.

There are several forms of energy harvesting available or in research today: photovoltaic, piezoelectric or vibrational harvesting, RF/near field, and thermoelectric or heat differential harvesting. Harrop suggested that while thermoelectrics are presently No. 4 in the line-up of energy harvesting contenders, it will soon eclipse piezoelectric power.

Available options abound for energy harvesting

"Piezoelectrics are great as sensors and transducers, but in creating electricity there's a lot of broken promises," he said, adding that ceramic-based piezoelectrics often break under tension. "Thermoelectrics have no moving parts and they last virtually forever. They've been used for powering sensors on remote oil terminals and pipelines. They are being prepared for use in hybrid cars [in Japan] where can generate a kilowatt or more on tailpipe of a car."

Researchers at North Carolina State University's Centre for Advanced Self-Powered Systems of Integrated Sensors Technologies (ASSIST) are studying thermal harvesting at non-elevated temperatures for a wider set of applications. One of the biggest challenges in this space is maintaining the proper temperature differential, between the thermoelectric system and device it sits on, said Tom Snyder, the lab's industry liaison.

"We want something to be thin, so we need some advances in heat rejection and cold seeking on the device. We're doing some research there but there's still a ways to go," he noted.

Texas Instruments' engineer Ajith Amerasekera, a TI and IEEE fellow, said energy harvesting still has generally low efficiency at 10-50 per cent. Photovoltaics for the industrial segment is plagued by issues related to driver and inverter inefficiency on a high voltage platform, while thermoelectrics often have too low of a pressure differential.

"You only get a few per cent of the actual energy that's incident," Amerasekera said. "The biggest challenge is to not to waste any of the energy when we deliver it to the component."

To increase efficiency, TI has integrated low power SRAM into its microcontrollers. Low-power memory allows for a lower duty cycle that can support various energy harvesting methods.

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