Power Management
Giving developers of self-sufficient energy systems a helping hand
A new energy harvesting platform from Future Energy Solutions looks to help developers seeking to create self-sufficient energy systems. CIE finds outs how
M
any developers of applications in building automation, medical electronics and industry are
looking to energy harvesting as a means to provide their designs with energy self- sufficiency. While the basic technologies for scavenging energy from light, changes in temperature, vibrations and other sources of ambient energy have existed for some time, the challenge for the designer is to match the available energy with the application’s demand for power. Future Energy Solutions is now looking to offer a new form of support to development engineers with the introduction of its Energy Harvesting Platform, a ready-made development system which includes a useful tool for measuring energy flows. Self-sufficient energy systems offer users considerable cost savings, since they require no cabling and avoid the expense in terms of maintenance associated with the use of battery-powered equipment. As well as benefiting existing types of device, energy harvesting can also open up new kinds of applications that were not previously financially viable. Examples include the deployment of sensors in places that are difficult to reach, and of portable wireless sensors which can be moved from one location to another. To justify the cost of investment in energy harvesting, the developer must aim at producing an end product with a longer lifespan and lower total system and operating cost as any device it replaces, as well as providing savings in power consumption.
34 September 2012
“It is not about creating as much energy as possible, but about providing the right amount of power for use under the prevailing operating conditions. Therefore designing for the intended operating environment is crucial to success in energy harvesting,” according to Paul Donaldson, EMEA Sales Director of Future Energy Solutions. The Energy Harvesting Platform has been designed to enable developers to evaluate a design blueprint and then test it in representative operating conditions.
Energy efficiency is the key Whether a system is powered by light, heat or kinetic energy, the total amount of power that can practically be derived from ambient sources is tiny. This means that every part of an energy harvesting device must operate at very high efficiency. This affects not only the energy production device, but also the energy storage and discharging systems. An ultra-low-power microcontroller will also play an important part. And in specifying a battery or supercapacitor, the charging characteristics and leakage current in particular must be taken into account. Fortunately, across the domains of energy production, conversion and storage, the technology has advanced to the point at which working energy- harvesting systems are able to be
successfully deployed in the field. The key to success is testing prototypes in the field, and making adjustments, either to cost- reduce the system if it generates more energy than required, or to increase the generation or storage capacity (or reduce losses) if insufficient energy is available.
Determining the available energy Photovoltaic (solar) panels deliver a higher electrical yield than any other harvesting technology available today. The sun provides up to 100mW/cm2 of radiated power. By contrast, artificial light in buildings can only provide around 100µW/cm2. But even this yield is sufficient for some building automation applications, using solar cells with a conversion efficiency of between 10% and 25%.
For instance, wireless sensors available today can be controlled with this yield, enabling measurements of temperature or humidity to drive air-conditioning controls. Outside, systems powered by solar energy are already being used for lighting or roadside signage, and for the monitoring of rail traffic and bridges. Applications in logistics and process automation are also being driven by wireless sensors powered by ambient energy.
Light is not the only ambient energy
source in use today. Electro-thermal transducers based on the Peltier effect use differences in temperature to generate energy. Only a small voltage is obtained and conversion efficiency, at around 3%, is low. But thermo-electric generators that, for example, are powered by the waste heat from machines can achieve an output of between 150µW and 10mW. Piezoelectric energy from machines can be used by vibration transducers to scavenge energy. These transducers today can generate an output of up to 100mW
Components in Electronics
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