Imagine being able to power a device with a grape. It may sound absurd but, according to John Blyler, an adjunct assistant professor of systems engineering at Portland State University in Portland, Oregon, it is already possible.
“Today, a few tiny grapes can drive ultra-low-power electronics,” Blyler said. “A few years ago, global semiconductor company Texas Instruments demonstrated a grape-powered digital clock. The 16-bit microprocessor in the clock required so little energy that it could run off of a few grapes. The miniscule amount of acidity in the grape, when teamed with a zinc metal contact, created a battery to power the clock.”
The same pH-based chemical reactions that allow several grapes to power a digital clock can also be used to enable crops in the field to power a small radio frequency (RF) circuit that can send a report of soil conditions wirelessly to a farmer’s computer. “This is just the start of how energy harvesting can be used to provide alternative power sources,” Blyler said.
POWERING THE INTERNET OF THINGS
Finding alternative sources of power for difficult-to-wire devices has become a priority for researchers, largely because of the rise of the Internet of Things (IoT), also known as the Internet of Everything. According to Cisco, a global leader in networking technology, the world will have 10 times as many Internet-connected devices as connected people by 2020, with more than 5 billion connected people and 50 billion connected things.
“TODAY, A FEW TINY GRAPES CAN DRIVE ULTRA-LOW-POWER ELECTRONICS. THIS IS JUST THE START OF HOW ENERGY HARVESTING CAN BE USED TO PROVIDE ALTERNATIVE POWER SOURCES.”
“As we move toward a world filled with a large number of IoT devices distributed all around us, the means to power these devices is becoming a huge problem,” said Vamsi Talla, a doctoral candidate in electrical engineering at the University of Washington in Seattle. “Imagine a scenario where a room is filled with hundreds, if not thousands, of sensors. These sensors are great because they can facilitate a multitude of applications – enabling a smart home or a smart city, monitoring the temperature of soil in a farmer’s field, tracking the flow, level and viscosity of goods in a manufacturing plant – there are unlimited possibilities.”
However, Talla said, providing power to these sensors is a challenge. “Wires are impractical and batteries require constant replacement and add cost, size and weight. This is a big stumbling block. So, if we can eliminate batteries and instead power devices using harvested energy, IoT devices will achieve mass adoption and deployment and, ultimately, fulfill the IoT dream.”
By 2020, Cisco predicts the world will have more than 50 billion connected things.
To date, self-powered devices rely on three main sources of energy. “These are kinetic energy – whereby lateral movement, rotation or vibration can generate electrical energy using electromagnetic or piezoelectric harvesters,” said Matthias Kassner, a product marketing director at EnOcean, a company located near Munich that develops patented, self-powered wireless technology. “Thermal energy – close-distance temperature differences – can be converted to electrical energy. (The third is) ambient energy sources such as light, electromagnetic waves, as well as chemical and bioelectric systems.”
ENERGY FROM VIBRATIONS
Researchers have made significant advances in all three areas. In the field of kinetic energy, for example, Southampton, UK-based Perpetuum, a leader in vibration energy harvesting, has developed the technology to convert vibrations into electrical energy that can be used to perpetually power autonomous, maintenance-free industrial wireless sensor nodes. These sensor nodes are being used on trains to monitor the condition of their bearings – a task previously done manually.
“Today there are fleets of trains across the world using Perpetuum’s vibration energy-harvesting-powered sensors,” said Roy Freeland, the company’s president, who is chairman of the Innovate UK’s energy harvesting steering committee and a member of the European Union’s ZEROPOWER Scientific Advisory Committee.
“IF WE CAN ELIMINATE BATTERIES AND INSTEAD POWER DEVICES USING HARVESTED ENERGY, IoT DEVICES WILL ACHIEVE MASS ADOPTION AND DEPLOYMENT AND, ULTIMATELY, FULFILL THE IoT DREAM.”VAMSI TALLA
DOCTORAL CANDIDATE IN ELECTRICAL ENGINEERING, UNIVERSITY OF WASHINGTON
“I can pull out my smartphone while I’m on holiday and examine, in real time, the condition of the bearings on the 10:37 London to Brighton train. It’s a great example of a high-volume IoT application of energy harvesting.”
Vibration sensors also are being widely used in process manufacturing plants. “Gas, chemical and power stations, including GE’s Bently Nevada, (plus energy equipment companies) Emerson and Honeywell, are using vibration energy harvesters to power wireless sensing systems in their process plants,” Freeland said. “This means that central operations have complete visibility over the status of their equipment, wherever it is in the world.”
Meanwhile, GreenPeak Technologies, a Utrecht, Netherlands-based provider of RF communication technology for wireless connected home applications, has developed a light switch that can operate without batteries. “Just flicking the switch generates enough energy to transmit a signal to a lamp,” said Cees Links, founder and CEO.
THERMAL AND AMBIENT POWER
In the field of thermal energy, EnOcean has created a technology that can power sensor nodes using small fluctuations in temperature. This principle is already being used by farmers to collect in-field data, including temperature, humidity, soil moisture, pH levels and macronutrients.
“Our technology has led to the emergence of self-powered heating valves, which can automatically regulate the heating based on room temperature and occupancy,” Kassner said. “This enables a reduction of heating cost – usually the biggest share of energy cost in private homes – by around 20%-30%, without any user intervention.”
Advances in ambient energy harvesting include the ability to broadcast power to remote devices with Wi-Fi signals, using a modified router that broadcasts noise and maintains constant energy to provide power. “Recently, our group has shown that you can power devices from Wi-Fi access points to a distance of up to 30 feet (9 meters),” Talla said. “For example, we have recently demonstrated the ability to power a surveillance camera using the energy harvested in this way.”
Solar energy is another form of ambient power. Fujitsu in Kawasaki, Japan, for example, has developed a solar-powered beacon that, at just 2.5 millimeters (0.09 inches) thick, can be attached to curved surfaces, corners – even clothing. Meanwhile, two engineers in the electrical engineering department at the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts, have developed a small-scale converter chip that can convert up to 80% of solar energy into electricity. Dina El-Damak, a doctoral student, and her professor, Anantha Chandrakasan, point out that this is a substantial improvement over traditional solar cells, which can convert at most half of the solar energy they collect into usable electricity.
PUTTING IT INTO PERSPECTIVE
While the potential of energy harvesting is promising, experts caution that it’s important to remain realistic about the extent to which these solutions can be applied in everyday life.
“The biggest challenge with energy harvesting techniques is that they provide extremely small amounts of energy,” said Hrishikesh Jayakumar, a doctoral student at Purdue University in West Lafayette, Indiana. “What’s more, the power you get from them is dynamic – it can be in short bursts or a continuous trickle – quite the opposite of what you get from a battery.”
For now, applications are limited to devices that require only small amounts of energy, Kassner said. “Not only this, but they need to implement very efficient sleep modes so that only a very tiny amount of energy is consumed when the system is not active,” he said.
Freeland advises consumers not to believe everything they read. “I recently read an article in a national future our mobile phones will be using energy harvesting to get power from ambient radio frequency signals,” Freeland said. “This is nonsense. Some of the research out there seems to bypass the fundamental laws of physics. If you’re going to make progress in energy harvesting then you need to be realistic. The fact remains that you can only harvest very small amounts of power using these techniques.”
The power limitations of energy harvesting are why GreenPeak has turned its attention to creating new, more efficient forms of battery power. “We spent three years pursuing the energy harvesting market,” Links said. “While there are several areas with great potential, for us it just wasn’t economically feasible. So we’ve instead set about creating a low cost, ultra-low-power battery which has a life expectancy of over 10 years.”
HARVESTING FOR THE FUTURE
Despite the limitations, new ways of applying harvested energy offer huge IoT potential, and the industry shows no signs of slowing. According to WinterGreen Research, an analysis and forecasting company based in Lexington, Massachusetts, the global energy harvesting market – which was worth US$131.4 million in 2012 – is projected to increase to US$4.2 billion by 2019.
One area where increased adoption seems inevitable is in smart cities. “More than half of the growing world population lives in cities,” Kassner said. “Intelligent control will be needed to coordinate people’s daily life and protect the environment and resources at the same time. The concept of a smart city intends to provide automated control of traffic, streetlights, energy supply or transportation of needed goods as well as waste disposal. This can only be realized with billions of wireless sensor nodes collecting and delivering the data needed.”
Portland State’s Blyler predicts: “We’ll see progress in a number of IoT applications, including everything from smart buildings, where the energy could be generated locally and transferred without wires, to recharging a hearing-aid battery. We’ll also see advances in the wearables space; consumers show a very low tolerance for devices that constantly need to be recharged.”
“Overall there’s a very exciting future ahead,” EnOcean’s Kassner said. “We expect a wave of IoT sensor developments as radical as we’ve seen with computers and mobile phones.” ◆