FEATURE PHOTOVOLTAICS


Photovoltaics powered by ambient energy technology


and essentially free, if they can be captured at, or near, the system’s point of deployment. A typical energy harvesting system


requires an energy source such as vibration, heat or light, plus some key


electronic components. These include: • An energy conversion device (transducer) such as a piezoelectric element or solar panel that can translate the ambient energy source into electrical form


• An energy harvesting conversion IC that captures, stores and manages power


• Sensors, microcontrollers and a transceiver to read, record and transmit the data as part of the WSN


Bruce Haug, senior product marketing engineer, power products at Linear Technology, now part of Analog Devices explores how compact solar panels are taking advantage of energy harvesting


R


ecent technical advancements have increased the efficiency of devices in


capturing trace amounts of energy from the environment, transforming it into electrical energy. In addition, advancements in converter technology have not only increased power conversion efficiency but have also reduced their internal power consumption requirements. These developments have sparked interest from the engineering community to develop even more applications that utilise energy harvesting. Energy harvesting from an ambient


source, where a remote application is deployed, and where a natural energy source is essentially inexhaustible, is an increasingly attractive alternative to wired power or batteries. These essentially free energy sources, when utilised properly, can be maintenance- free and are usually available throughout the working lifetime of many applications. Alternatively, energy harvesting can be


used as a secondary energy source to supplement a primary power source such as a battery to greatly extend the life of the battery, reducing maintenance costs. Many real life applications using energy


harvesting as the main power source are now in use. Wireless sensor networks (WSNs), for example, often benefit from energy harvesting power sources. When a


20 WINTER 2017 | MICROMATTERS


wireless node is deployed at a remote site where wired power or a battery is either unreliable or unavailable, energy harvesting can supply the power needed to operate it. In other situations, multiple energy sources can be used to enhance the overall efficiency and reliability of a given system. Some of the more common energy


harvesting sources include: • Mechanical energy – from sources such as vibration, mechanical stress and strain


• Thermal energy – waste energy by- product from furnaces, heaters, motors and friction sources


• Light energy – captured from sunlight or room lighting via photo diodes, or solar cells


• Electromagnetic energy – from inductors, coils and transformers


• Natural ambient energy – from the environment such as wind, water flow, ocean currents, galvanic and solar


• Human Body – a combination of mechanical and thermal energy generated or through actions such as kinetic movement


• Other Energy – from chemical and biological sources It is important to


note that all these energy sources are virtually unlimited


Figure 2:


The LTC3106 is configured as a solar harvester with primary battery backup powering a wireless network node


Figure 1:


The LTC3106 uses either a solar panel or primary battery to provide continuous power to a downstream load


• Optional supplementary energy storage device such as thin-film or primary cell battery or super capacitor It is very important that the power


conversion device has a high efficiency and a low quiescent current so as to allow most of the harvested energy to be used for powering the sensor network or control and monitoring device. Furthermore, it is essential to


understand how much average power is available from the harvestable energy source and how much energy is required to power the device being powered (its duty cycle of operation).


ENERGY HARVESTING IC SOLUTIONS Fortunately Linear Technology has several energy harvesting devices for processing, storage and utilisation of harvestable energy. The LTC3106 is one such device that is a highly integrated, ultralow voltage buck-boost DC/DC converter with automatic PowerPath management optimised for multiple input sources and low power systems. If the primary power source is


unavailable, this device is designed to switch to the backup power source and is compatible with either rechargeable or primary cell batteries and can trickle charge a backup battery whenever there is surplus energy available. If a light source is used, an optional


maximum power point control ensures power transfer is optimised between power source and load. At no load, it draws only 1.6μA while creating an output voltage up to 5V from either input source. Figure 1 shows a typical schematic. The LTC3106 employs a PowerPath control architecture to allow the use of a


/MICROMATTERS


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28