Harvesting Ambient Energy from Surrounding Sources

Frank Schmidt of EnOcean looks at methods of harvesting energy for the surrounding environment and the new developments that are taking place.

Energy harvesting is a technology that has made huge progress in recent years and this is attributable to the major benefits available to installers, architects, contractors, developers and property owners alike.

Since self-powered wireless devices eliminate the need for a power source, maintenance requirements such as battery replacement become a thing of the past. Also, as they communicate via radio frequency signals, they are freed from the cost and complexity of conventional wiring.

The last few years have witnessed the commercial delivery of these benefits and now, after three generations of evolution, energy harvesting is enabling entirely new, energy-saving application possibilities in building and industrial automation.

Sophisticated scavenging

The first requirement for designing self-powered wireless products was the ability to scavenge energy from the surrounding environment. Energy harvesting has been around for centuries: after all, windmills, tide mills and water turbines have been extracting raw energy from the environment to generate power since ancient times. The second requirement was to use this energy for efficient communication between different devices. Again, likely solutions have been assumed for some time, with low power radio systems such as Bluetooth or Wi-Fi.

Bringing these two needs together was the challenge that researchers in Siemens laboratories took up in the late 1990s, when they turned their attention to scavenging tiny amounts of energy to power wireless systems. It was apparent from the start that existing technologies were not efficient enough to make them work reliably. What was needed was to bring three key elements together: effective energy transducers, sophisticated electronics and software.

Having successfully identified the opportunity and potential solutions, in 2001 a new company - EnOcean - was established out of Siemens in order to exploit the new technology. EnOcean's wireless technology harvests the required power from the energy resources in the surroundings: motion, light or differences in temperature. The amount of energy obtained in this way is enough to transmit a wireless signal and turn on a light, for instance.

These radio telegrams, just one millisecond in duration, use an optimum data rate of 125 kilobits per second. To eliminate transmission errors, each telegram is typically repeated twice in the space of 30 milliseconds. Furthermore, data packets are transmitted at random intervals, so the probability of collision is extremely small. Using the 868MHz and 315MHz frequency bands, this technology can be used just about anywhere in the world.

Wireless transmission distances can reach approximately 300m in the open and up to 30m inside buildings. A refinement with new self-powered wireless modules is their individually attributed 32-bit identification number, which provides over 4billion unique IDs, to exclude any possibility of overlap with other wireless devices. Power conversion and radio transmission are complemented by sophisticated electronics and, most importantly, by intelligent software stacks that make it simple and straightforward to integrate the technology across a large variety of user applications.

In 2003, EnOcean commercialised its first generation of energy harvesting radio sensors based on piezoelectric powered modules. The second generation in 2007, which consolidated energy transducers, electronics and software, added the option of a new, more efficient means of mechanical power conversion - this time using miniature magnetic coils instead of piezoelectric devices.

Early acceptance in buildings

Examples abound in the sector that recognised the advantages earliest - building automation. Building automation optimises energy savings and reduces operating costs by lowering total cost of ownership. Essential to the success of building automation projects, self-powered wireless technology gives architects, contractors and property owners the freedom to install all the sensors they need, of whatever type, wherever they like. Installation time is minimised and overall system costs are significantly reduced owing to device placement flexibility.

With conventional battery-powered sensors, the cost of monitoring, replacing and recycling batteries increases as more units are installed. Energy autonomous, battery-less sensors remove these headaches. The same advantages also apply to industrial plant installations. Having no batteries means zero maintenance and the wireless technology creates new possibilities to locate sensors in previously inaccessible areas or remote storage vessels.

New advances increase adoption

Now, with the third generation of EnOcean wireless modules, there are even more compelling reasons why the building and industrial industries are adopting devices incorporating energy harvesting technology.

For OEMs developing new products, the fact that all sensor electronics are now integrated on a single chip brings more frugal power consumption, better performance and lower manufacturing costs. Furthermore, EnOcean's software now provides straightforward building blocks to make it simpler to design new products for automated mass production and bring them quickly to market.

Energy converters have also been developed further. For instance, the new electro-dynamic energy converter can generate more electrical power than ever from a single press of a switch; improved solar cells can garner light energy in dim indoor as well as outdoor installations; and the thermal energy harvester has been upgraded to power wireless sensor nodes from temperature differences of only a few degrees Celsius.

Additional new energy sources are setting the scene for a broad expansion of opportunities. Scavenging energy from small temperature fluctuations is one such area. EnOcean envisages rapid growth in the use of thermal gradient energy harvesters, especially in industrial plants where heat dissipation from machinery provides significant temperature differences.

For example, a sensor powered by thermal gradients can be optimally sited for condition monitoring purposes - such as cool-chain monitoring in cold stores and mobile refrigeration units. They are ideal for status monitoring in aircraft, too, and even small temperature differences between day and night time can be used to power a sensor.

Innovative applications

Another key area for energy harvesting technology is the possibility to link industrial, building and home automation networks with other infrastructures, such a cellular phone networks, Wi-Fi or home entertainment networks. The result is a world where you are able to switch lights on and off via a mobile phone, check your security systems over the internet, adjust heating, ventilation and air conditioning via wireless LAN and monitor plant machinery from anywhere in the world.

Energy harvesting wireless networks of interoperable switching devices and sensors are integral to the advancement of this connected world and will continue to turn innovative opportunities into reality far into the future.

Frank Schmidt is CTO and Founder of EnOcean. As Chief Technology Officer he is responsible for the overall technical orientation, patent related activities as well as the relationship management with educational, research and scientific organizations. Before joining EnOcean he was at the Central Research Department of Siemens AG where he created the self-powered wireless sensor technology as early as 1995. He has been granted more than 40 patents for his energy harvesting inventions and is the author of numerous technical publications in this field. Frank is a Physicist and studied at the Technical University of Chemnitz, Germany.

EnOcean GmbH has pioneered and patented many new self-powered wireless technology ideas. Headquartered in Oberhaching near Munich, the company manufactures and markets maintenance-free wireless sensor solutions for use in buildings and industrial installations. EnOcean solutions are based on miniaturized energy converters, ultra-low-power electronic circuitry and reliable wireless. Combining these elements enables EnOcean and its product partners to offer sensor systems that are fundamental for energy-efficient buildings and innovative industry. Today wireless modules from EnOcean are chosen worldwide by more than 100 manufacturers to enable their system ideas for buildings and industry. Wireless components are already in use in over 100,000 buildings. EnOcean GmbH was founded in 2001 as a spin-off from Siemens AG. The company currently employs over 50 people in Germany and the USA.