Singapore’s Nanyang Technological University (NTU) is hoping that the appointment of Professor Michael Grätzel (often spelled “Graetzel”), will result in advancements in the manufacture of cheaper, more efficient solar cells.

The Swiss professor is the pioneer of applying artificial photosynthesis principles to solar technology

The University says Professor Graetzel will take the lead as Chairman of the Scientific Advisory Board of the Energy Research Institute at NTU and has established a new Centre for Nanostructured Photosystems aimed at further developing and commercialising Graetzel’s dye-sensitised solar cells; along with other innovations in solar technology.

A dye-sensitised solar cell mimics the ability of plants to absorb sunlight and produce energy. Special dyes are added to the surface of the cells which capture photons from different light wavelengths, like chlorophyll in plants. Also known as Graetzel cells, NTU say they “represent an exciting breakthrough and show great promise as an inexpensive alternative to costly silicon solar cells.”

The Professor’s work won him 2010 Millennium Technology Prize, and to honour the appointment of their VIP chairman, NTU have awarded Graetzel a Doctor of Engineering degree.

At the launch of the Energy Research Institute, NTU President Professor Bertil Andersson said it was vital to foster growth in alternative fields of solar cell technology in an environment of growing concern among governments and industry groups about the sustainability and security of global renewable energy supply.

“The new Centre will be, literally, “taking a leaf from nature” to produce energy harnessed from the sun. Development of sustainable energy solutions is today a sunrise industry, with solar energy being the most abundant and promising renewable energy source on our planet.”
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boosts efficiency of solar cells

In order for a solar cell to be as efficient as possible, the last thing it should be is reflective – after all, light should be getting absorbed by it, not being bounced off. With that in mind, a few years ago a group of Japanese scientists set out to create an antireflective film coating for use on solar cells. What they ended up creating utilizes the same principles that are at work in one of nature’s least reflective surfaces: moth’s eyes.

The moth-eye film was developed by Noboru Yamada, a scientist at Nagaoka University of Technology Japan, who collaborated with researchers at Mitsubishi Rayon Co. Ltd. and Tokyo Metropolitan University. Using anodic porous alumina molds, they were able to nanoimprint the microstructure of moth’s eyes into acrylic resin – this provided a high throughput, large-area/low-cost method of producing the film.

Based on the results of indoor and outdoor tests of crystalline silicon solar panels coated with the film, the team’s computer models indicated that use of the film could boost the annual efficiency of solar cells by five percent in Tokyo, and six percent in the “sun belt” city of Phoenix. “People may think this improvement is very small, but the efficiency of photovoltaics is just like fuel consumption rates of road vehicles,” said Yamada. “Every little bit helps.”

They are now working on improving the durability of the film, and optimizing it for use on different types of solar cells. They are also looking into using it to reduce glare on surfaces such as windows and computer screens, although in that area they may be facing some competition – Germany’s Fraunhofer Institute for Mechanics of Materials has already developed an anti-reflective coating for use on displays and eyeglasses, which was also inspired by moth’s eyes. In Franuhofer’s case, the coating is incorporated into the viewing surface during the molding process, instead of being added afterward in the form of a film.

The reasons that moths have anti-reflective eyes, incidentally, is to allow them to gather as much light as possible in the dark, and to avoid being seen by predators.

The moth-eye film research was recently published in the journal Energy Express.

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Powering Up

the Battery-Free World

The amount of electricity generated by vibration is proportional to the frequency and amplitude of the vibrator, which means that maximizing both will easily increase output. Because of the way vibration-based generators work, however, fine adjustment is needed to ensure they resonate at a particular frequency, and the inherent vibrational frequency must be matched to the application.

A look at the vibration parameters for the announced prototypes reveals just what application each firm is aiming at. Sanyo Electric, for example, plans to having people wear its device and set the frequency to 2Hz ^Note . Murata Manufacturing chose 10Hz to 20Hz, which is a neat fraction of the 50Hz/60Hz frequency of commercial power. Their decision, explains a source at the firm, was that the large number of vibration sources in that range would provide a wide range of applications. Omron, on the other hand, comments that “about 30Hz is common in factories, vehicles and bridges, for example.”

Note Sanyo Electric is now developing a prototype measuring 23mm x 42mm x 6mm, capable of generating 120?W.

Omron is planning to wait until the market scale becomes a little clearer, and ship product in 2011, according to Masashi Doi, manager, core technology centerof the firm. The company has already shifted its development target from boosting generating performance to assuring reliability. Many wireless sensor networks are expected to be “plug and forget,” capable of running for at least five years without needing anything, so reliability assurance is critical.

Troubling Patents

Patents could pose a thorny problem for practical applications, though. Basic patents do exist for energy harvesting, and some people in the industry have warned that care will be needed when launching business in the field. They are held by EnOcean ^{Note 9)}, and already eighteen key patents in energy harvesting have been identified in the firm’s portfolio.

Note 9) EnOcean began research into energy harvesting in 1995, when it was still a research arm of Siemens AG of Germany. It became an independent venture business in 2001, acquiring all related patents from Siemens in return for 19% of its issued stock.

Fig. 10 Patents held by EnOcean

The patents are for “transmitting collected data using power acquired through energy harvesting technology,” which covers a wide range of applications.

Of these, the strongest is said to be international patent WO 98/36395 (Fig. 10), which covers a very wide scope. It has been granted in a number of nations already, including Germany, the US and China. The patent was filed in Japan in 1998, but patent examination was refused and as a result the patent has not been granted. EnOcean refused to accept the judgment, requesting reconsideration in 2008.

A number of manufacturers planning to ship products using energy harvesting technology as early as 2011 are worried about possible patent issues, but EnOcean Chief Executive Officer (CEO) Markus Brehler has said “Our business is shipping products, not arguing about patents.” In any case, though, care will be needed in export sale.

1) Harrop, P. et al., Energy Harvesting and Storage for Electronic Devices 2010-2020, IDTechEx Ltd., July 2010.

2) Innovative Research and Products, Inc., ULTRA-LOW POWER (MICROWATT) ENERGY HARVESTING FOR WIRELESS SWITCHES AND WIRELESS SENSOR NETWORKING TYPES, APPLICATIONS, NEW DEVELOPMENTS, INDUSTRY, April 2010.

3) Roundy, S. et al., “A study of low level vibrations as a power source for wireless sensor nodes,” Computer Communications 26, Issue 11, pp. 1131-1144, July 2003.

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Powering Up

the Battery-Free World

One of the reasons that overseas manufacturers have pulled so far ahead of Japan in practical application is that domestic manufacturers are overly concerned with generating electricity. Many firms in Japan have been developing power generating devices for years, but the thrust of research and development has been boosting output. European and American firms more interested in combining the most useful characteristics of peripheral circuits, on the other hand, have taken the lead in market development.

Table 2 Energy Harvesting Consortium Members

The situation is beginning to change, however, as companies swing into action to make businesses out of the new technology. One symbol of the change is the establishment of the Energy Harvesting Consortium, which was established in May 2010 by thirteen companies (Table 2). With the addition of eight latecomers, the group is already collecting related industry information and stimulating discussion and exchange between member firms.

Corporate Aim Revealed through Frequency

Japanese companies are finally making the transition from competing to make a better generator to actually refining products. Some firms, for example, are actively working on products to generate electricity from vibration: Omron Corp. of Japan, Sanyo Electric Co., Ltd. of Japan and Murata Manufacturing Co., Ltd. of Japan are developing prototypes with very specific applications in mind (Fig. 9) ^{Note 7)}.

Note 7) The three companies are developing vibration-based generators utilizing a material called electret. When the areas of two opposing electrodes change as a result of vibration, it causes a change in induced charge, producing a current.

Fig. 9 Corporate Objectives Apparent in Waveband

Scope of application shown for vibration generators. The optimal target frequency varies with application, revealing each firm’s goals. (Diagram by Nikkei Electronics based on material courtesy Omron, plus papers presented by Sanyo Electric and Murata Manufacturing)

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Up the Battery-Free World

The idea behind wireless sensor networks is old, but a battery-free design would vastly expand its range of application. Voltree Power LLC of the US, a spin-off from the Massachusetts Institute of Technology (MIT) of the US, has been contracted by the US Department of Agriculture to construct a temperature sensor network in mountainous, forested regions of California ^{Note 6)}.

Note 6) The power source is based on technology developed by MIT utilizing the electric potential difference between the tree trunk and surrounding area, which is between 50mV and 200mV.

The objective is to detect forest fires and minimize damage. Considering the damage cause by such fires, and the cost of firefighting personnel, equipment and supplies, the economics of constructing and operating a wireless sensor network are clear indeed.

One application attracting considerable attention of late is health monitoring. Sensors are mounted on buildings and bridges, detecting structural change. The amount and speed of these changes are used to diagnose the health of the structure, with acquired data utilized in guiding maintenance and component replacement.

There is considerable demand for health monitoring in the motor and engine sectors, as well. Automobiles use a large number of sensors to detect the conditions of various components, and as a result use vast quantities of wire harnesses. If engine and motor heat and vibration energy can be used to drive wireless sensors, it would be possible to dramatically cut the number of wire harnesses needed.

Another application in the health monitoring field is the life recorder, managing people and animals. Mounted on livestock or wild animals, for example, it can provide not only position information, but also data such as body temperature and pulse. If they can be powered by animal body heat, then there is no need for battery replacement.

Simple Enough for Everyone

Energy harvesting technology is the key behind the popularity of wireless sensor network, and with continuing development and wider recognition, a host of new applications will no doubt be pioneered. One major change in the environment is that companies getting into the energy harvesting field can now pick up low-power peripheral components very easily.

A large number of generating devices are already available from companies like AdaptivEnergy LLC of the US and Perpetuum Ltd. of the UK. For wireless technology, modules on the market eliminate the need for specialized knowledge of high-frequency waves. Alps Electric Co., Ltd. of Japan, which is volume producing a sensor network module using GainSpan’s wireless transceiver IC, has received inquiries from over thirty firms already.

Japan “A Decade Behind”

While the technology seems to be taking off, there are some worries for Japan: Japanese industry is almost invisible in the field energy harvesting field. Some people in the field warn that Japan is a decade behind Europe and America.

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Powering Up

the Battery-Free World

Though the thermoelectric conversion device is small, the heat exchanger used to attain the high efficiency for a given temperature differential is relatively large. This component is expected to account for the majority of module cost. The heat exchanger is critical in determining electric conversion efficiency, and can as much as double output. Research in this area is sparse, and it is likely to develop into a major battleground for peripheral components.

Expanding Application in Wireless Sensor Networks

Advancement in high-efficiency peripheral circuits and generators with low power consumption has finally made energy harvesting a practical technology. And now that the foundations are in place, the applications are beginning to take shape. The technology is likely to be used diversely, not only in existing switch applications for lighting and such (Fig. 7).

Fig. 7 New Ideas Pioneer New Applications

There is a wide range of possible applications. Especially promising ones include health monitoring for bridges and vehicles, and implementations in animal husbandry and agriculture. (Illustration: Reiko Kusumoto)

One of the most promising applications is wireless sensor networks. Data acquired by the sensors only has to be transmitted a few times an hour, which means power consumption is low. This level is quite possible for an energy harvesting system (Fig. 8).

Fig. 8 New Wireless Sensor Node

The “Mr. Shoene” wireless sensor node released by Seiko Instruments (SII) in Sept. 2010 uses the firm’s proprietary special low-power wireless technology. Power consumption is low and the device is non-directional, making it possible for signals to route around obstacles.

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Powering Up

The Battery-Free World

Sensors and Microcontrollers, Too!

Sensors are another type of peripheral components evolving rapidly. Sensors designed to acquire information such as temperature and humidity are shrinking and consuming less power. The brightness sensors used to control lighting, for example, are being mounted on mobile phones now, and over the past few years current consumption has droppedto one-fifth. A source at Avago Technologies, Inc. of Japan says “We’ve confirmed that we can maintain sensitivity while suppressing noise, even running on low voltage.”

The microcontrollers used to control energy harvesting circuits and sensor drive are also showing up in lower-power versions. One widely used design is the MSP430, from Texas Instruments Inc. (TI) of the US, which sells for as little as US$0.25 apiece.

Fig. 5 Standby Current a Key Point

In applications such as wireless sensor networks, standby time is significantly longer than actual operation time. (Diagram by Nikkei Electronics based on material courtesy Renesas Electronics)

The key points in microcontrollers are a low standby current consumption, and a very short wake-up time. Operation is intermittent in almost all wireless sensor networks, so standby current consumption is crucial. A comparison of this characteristic alone shows that 16-bit microcontrollers from Renesas Electronics Corp. of Japan have current consumption low enough to put them at the very top of the list for candidates (Fig. 5).

Thermoelectric Conversion Devices through Thinfilm Technology

In addition to merely improving the characteristics of peripheral components, however, other firms are working on the generating devices that are the heart of energy harvesting. For example, a thermoelectric conversion device with high electromotive force has appeared. Slated for volume production start in 2011, the device comes in a small, thin package, and can get 140mV from a temperature difference of about 1°C. Conventional devices measuring several cm on a wide can usually generate only about 50mV.

Fig. 6 Miniature High-Performance Thermoelectric Converters

Micropelt has begun supplying thermoelectric conversion devices, and modules using them (a). Made with thinfilm technology, they can provide satisfactory generating capacity even in small sizes (b). (Diagram by Nikkei Electronics based on material courtesy Micropelt)

The device was developed by Micropelt GbmH of Germany. Wladimir Punt, Vice President, Sales & Marketing at the firm, is confident in the technology: “We are constructing a plant now that will be able to manufacture 10 million modules annually.” Engineers applied thinfilm technology to create a device combining small size with high efficiency (Fig. 6) ^{Note 5)}.

Note 5) In manufacturing, n-type and p-type devices are sputtered individually on separate wafers, which are then sandwiched together in alternation.

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No Power through

Energy Harvesting:

Powering Up

the Battery-Free World

Stepping Up from only 20mV

Co2 to energy

The impact of higher power supply circuit performance is dramatic, because just how efficiently the power supply can handle the minute trickles of power gained through energy harvesting-how little loss there is-is key. Recently, even ultra-low voltages can be harvested efficiently.

Linear Technology Corp. of the US began volume production of the LTC3108 DC-DC converter, offering relatively high step-up efficiency from even an extremely low 20mV, in December 2009. With a thermocouple, the firm says, it can produce electricity from a temperature difference of only 1°C. An engineer involved in power supply circuit development for years is amazed: “They can use voltages a whole order lower than we can as energy sources!” ^{Note 2)}.

Note 2) The LTC3108 uses an internal n-channel metal oxide semiconductor field effect transistor (MOSFET) with external step-up transformer and capacitor, forming a resonant step-up oscillator. A transformer with a 100:1 ratio would boost 20mV to 2.0V.

According to Tony Armstrong, Director of Product Marketing, Power Products at Linear, the firm began development of the LTC3108 in about the summer of 2007, predicting growth in the energy harvesting field.

Ultra-Low Dissipation Wireless ICs

Lower dissipation by wireless transceiver ICs has also had an enormous effect, along with power supply circuits. Standby dissipation, previously about 1?A, has now been slashed to about 0.2?A thanks to smaller geometry and innovations in communications control.

One company that stands out in the energy harvesting field when it comes to wireless transceiver ICs is venture firm EnOcean GmbH of Germany. The amount of power consumed by the firm’s “EnOcean” standard for wireless communication between equipment is one digit smaller thanother methods.

Fig. 4 EnOcean Emphasizes Low Power Consumption and Ease of Use

The single design means a signal is sent only three times in 30ms (a), helping reduce standby current to only 0.2?A (b). The wavebands used vary by nation and region. Ease of use has been enhanced by modularization (c).

Power consumption was slashed by eliminating unnecessary functionality. Frank Schmidt, Chief Technical Officer (CTO) of the firm, stresses the key is simple control. Wireless ICs used in switch applications, for example, send only three 1ms signals every 30ms for on/off control (Fig. 4) ^{Note 3)}.

Note 3) The latest specification further improved convenience by supporting feedback from the receiver to the transmitter.

There are also efforts under way to apply low-power wireless LAN to energy harvesting wireless communication. GainSpan Corp. of the US, with founders including engineers from Intel Corp. of the US, has developed a wireless LAN IC with a standby current consumption of no more than 1?A: between 10% and 1% of standard designs ^{Note 4)}. This is about the same level as ZigBee. It offers an advantage in that existing wireless LAN access points can be utilized. Standardization has also started on ZigBee Green Power, however, a version of ZigBee tweaked for energy harvesting applications. The standard is expected to be finished by the end of 2010.

Note 4) Lower dissipation was achieved in part by frequent clock gating and use of sleep mode.

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Powering Up

the Battery-Free World

The enormous attention garnered by the growing market, in spite of the tiny amounts of power available, is due to the high convenience it promises. The major selling point for energy harvesting is that equipment can use it to eliminate primary battery replacement, wiring and maintenance (Fig. 2). It will mean a switch from low power to no power.

Fig. 2 Battery-Free Design for Enhanced Convenience

The key point is that primary batteries and wiring are no longer needed (a). Vibrator “battery” combines a capacitor and generator (b). The same size as a battery, it can be swapped into a remote control. A remote control for relay truck jacks was jointly developed by NHK Toyama Broadcasting Station and Yuasa (c), driven by the force of the finger pressing the buttons.

The range of applications is gradually expanding as industry makes an effort to realize this convenience. The Hoki Museum in Chiba City, Chiba prefecture, which opened on Nov. 13, 2010, for example, adopted energy harvesting technology for voice guidance switches. The system is already in operation.

Control signals are handled via wireless, eliminating the need for new wiring for the switches. Setting up the power cables and other wiring for frequently changing exhibits has always been a major load for art museums, and energy harvesting’s wire-free strengths are invaluable here.

Changing Peripheral Components

A representative energy harvesting system consists of four major steps, namely (1) detecting the energy source and generating electricity, (2) converting the acquired electricity as needed in a power supply circuit for storage in capacitors or rechargeable batteries, (3) using the stored power to drive microcontrollers and sensors, and (4) using a wireless transceiver to pass information acquired from sensors to the outside world ^{Note 1)}.

Note 1) The price of a unit implementing these four functions, according to Linear Technology’s Armstrong, is “about US$12 in lots of 50,000.”

The concept of energy harvesting is quite old, and research in the field also has a long history. The rapid expansion in application fields of late is due to evolution in the peripheral components to make best use of the generating devices, corresponding to steps (2) through (4) above. This evolution has made it possible to utilize the technology in an increasing range of applications.

Fig. 3 Generated power Exceeds Self-Consumption

The performance of generating devices is rising, while the power needs of peripheral components drops. The appearance of high-tech startups with superior technical expertise is especially significant in radio transceiver ICs, which dissipated the most power.

Peripheral component evolution here refers to significant reductions in power consumption by the power supply circuits needed to efficiently utilize generated power, the wireless ICs that send and receive signals, microcontrollers and sensors (Fig. 3). Until recently, the electricity collected by the generating devices was expended by the peripheral components themselves, making the target function impossible to achieve. Now that there are a number of ICs available with high-efficiency, low-dissipation circuits, energy harvesting has finally entered the realm of the practical.

Received & published by Henry Sapiecha

through Energy Harvesting:

Powering Up

the Battery-Free World

Vibration from people walking or cars crossing bridges, automobile heat, broadcasting waves and more: Energy harvesting makes it possible to utilize the uptapped energy all around us. While the available electric power is small, the world is fascinated by the concept of eliminating the need for primary batteries… More and more applications are becoming possible as the characteristics of peripheral components are improved, and high-efficiency wireless ICs running on minimal power are driving expanded introduction.

Energy harvesting refers to collecting the minute amounts of energy in our immediate surroundings, such as vibration, light, heat and electromagnetic radiation. This concept of efficiently tapping the minute amount of energy that we casually discard today is attracting enormous interest.

“The energy harvesting equipment market will grow from US$650 million in 2010 to US$4.4 billion in 2020,” predicts IDTechEx Ltd. of the UK. ¹⁾ Innovative Research and Products, Inc. of the US adds “The 2009 market is US$79.5 million, but that will grow at an annual rate of 73.6% to reach US$1.254 billion in 2014.” ²⁾

“Battery-Free” the Major Selling Point

Also known as environmental energy harvesting and energy scavenging, energy harvesting offers the advantage of being able to generate power in diverse locations (Fig. 1). The energy gained, however, is extremely small (Table 1), ³⁾ with output power on the ?W order for the majority of generating devices. It is unlikely to be able to provide enough energy to make it unnecessary to charge smartphones, for example.

Fig. 1 Diverse Energy Sources All Around Us

Energy harvesting is a technology to efficiently “harvest” and utilize minute amounts of energy currently being discarded. Energy sources include vibration, light, heat and electromagnetic radiation. (Illustration: Reiko Kusumoto)

Table 1 Common Minute Energy Sources

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