harvesting Archives

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The Internet of Things holds great potential, and much has been written about the final applications and the possibilities – however one major factor of any device is how it will be powered. It’s all very well to have the latest sensors or interactive devices, if they don’t have a suitable power supply. It’s easy to consider a battery – however there’s many more options that can increase lifespan, reduce maintenance calls and therefore the running costs. Let’s review a few options that can provide a portable power supply for your IoT nodes where mains power or cabled-in power supplies are not available.

First, consider solar photovoltaic – a common choice for sensing, control or measurement devices that are located outdoors where sunlight is available, and that consume a relatively small amount of power. For a small, low-power embedded device that receives a reasonable amount of sun each day, a moderately small solar panel is perfectly capable of supplying sufficient power – on average – to run a small, basic wireless network node consisting of a microcontroller, some sensors and an embedded low-power Wi-Fi, Bluetooth or 802.15.4/ZigBee radio transceiver. However this is assuming that the overall system is designed for a reasonable degree of power efficiency.

However, solar power is intrinsically intermittent and is only available on average for a fraction of the day. To allow the system to have access to the current it needs to function when needed, solar-powered wireless devices almost always need to incorporate a small amount of energy storage in the form of a battery or supercapacitor in conjunction with the solar cell. Furthermore, solar cells or solar panels typically have a relatively low output voltage if a small number of cells are used, and their non-linear V-I curve makes it desirable to employ Maximum Power Point Tracking (MPPT) where practical.

This is necessary to keep the system operating near the maximum power point so that the limited energy available is harvested most efficiently. A solar power supply for a remote wireless system ideally tracks the maximum power point of the cell along the V-I curve and is able to charge a small battery or supercapacitor to fill in the demand when sufficient sunlight is not available.

As an example of a controller IC one may use for the power supply in a small solar powered system, the Linear Technology LTC3105 is a high efficiency step-up DC/DC converter that can operate from input voltages as low as 225 millivolts, with a built-in maximum power point controller (MPPC). As well as solar cells, this device is well suited to other low voltage, high impedance energy harvesting transducers such as thermoelectric generators and fuel cells.

Whilst it is not a true maximum power point tracker, the user-programmable maximum power point setting helps to optimise the efficiency of energy extraction from any energy source, such as a thermoelectric pile or a solar cell, where the voltage across the transducer may vary with changing environmental conditions as well as with the load current. The LTC3105 is capable of supplying 70 mA of output current at 3.3V from an input voltage of 1 volt – this is sufficient power to run a small, well designed basic sensor node consisting of a microcontroller, RF transceiver and a sensor or two.

Another type of power supply is known as energy harvesting, made possible by parts such as the Linear LTC3108, which is designed to accommodate energy harvesting from transducers with extremely low output voltages, as low as 20 millivolts. This makes it particularly well suited for use with thermopiles and thermoelectric generators which can generate a very low potential difference from a realistic temperature difference – a potentially convenient energy source for remote sensing in industrial automation or process monitoring in high-temperature systems where wired communications and power are not convenient.

Energy can also be derived from vibration, and using a part such as the Linear LTC3588 – a piezoelectric energy harvesting power supply controller which connects to a piezoelectric crystal to harvest mechanical energy in the form of vibrations from the ambient environment. This IC incorporates a low-loss, full-wave bridge rectifier and is capable of accommodating the rapidly changing AC voltage output and high source impedance of a piezoelectric crystal subject to mechanical stress and converting this energy into a DC current with relatively high efficiency.

Output voltage selections between 1.8V and 3.6V are available with a continuous output current capability of up to 100 milliamps, compatible with a range of modern power-efficient microcontrollers and RF mesh systems-on-chip.

An electromechanical energy harvester of this sort can be employed to provide a continuous source of a small amount of “free” energy for a small, efficient wireless network mote, particularly in applications such as vehicles and industrial machinery where plenty of vibrational energy is available to be harvested in the environment.

Finally, for some systems it is also practical to use just batteries – for example, lithium-ion, lithium-polymer or nickel-metal hydride batteries – and rely on user intervention to simply
recharge and replace the batteries where needed. The batteries may be left internally, inside the device, with the system being plugged into a power supply via a charging port
– perhaps using a low-power standard power-supplying interface such as USB – when the device requires a recharge, as opposed to the traditional method of removing and swapping the batteries.

In this sort of application, battery management and charging ICs such as the Microchip MCP73833 Li-polymer / Li-ion charge management controller can be of use to control the recharge of a Li-ion cell, as can buck/boost converters such as the Texas Instruments TPS63031. A buck/boost converter like this allows a regulated output voltage to be generated from input voltages both higher and lower than the desired output voltage – an output of 500mA at 3.3V, in this case, from an input voltage anywhere from 2.4 to 5.5 volts. This allows a battery such as a two-cell NiMH, three-cell NiMH, or single-cell Li-ion / Li-polymer to be used efficiently and charged and discharged across the entire usable part of its discharge curve without hitting the minimum input voltage of a LDO or buck regulator.

No matter what your device or where it will be located, finding an appropriate source of power is possible, and easier than you realise. It just takes a little research and a team of dedicated engineers with the experience and knowledge to understand your requirements. Here at the LX Group we have the experience and team to make things happen. With our experience with connected devices, embedded and wireless hardware/software design, and ability to transfer ideas from the whiteboard to the white box – we can partner with you for your success.

We can create or tailor just about anything from a wireless temperature sensor to a complete Internet-enabled system for you – within your required time-frame and your budget. For more information or a confidential discussion about your ideas and how we can help bring them to life – click here to contact us, or telephone 1800 810 124.

LX is an award-winning electronics design company based in Sydney, Australia. LX services include full turnkey design, electronics, hardware, software and firmware design. LX specialises in embedded systems and wireless technologies design. https://lx-group.com.au

Published by LX Pty Ltd for itself and the LX Group of companies, including LX Design House, LX Solutions and LX Consulting, LX Innovations.

At the LX Group we say that smart energy is an exciting and important growth technology area, and that it encompasses and enhances a wide variety of existing and new technologies. Although many people consider energy to be a resource only limited by one’s capacity to pay the supplier invoice every three months – the ability to reduce energy consumption in an increasingly complex world is a communal goal.

Smart energy technology can be applied to a wide variety of devices used in the domestic, commercial and industrial areas – and benefits can of course be found in not only reduced energy consumption, but also in some cases by a reduction in the costs of installation and maintenance of smart energy hardware. In saying that let’s examine a variety of smart energy applications and their benefits.

Smart street lighting

Since their first installation, the use of electric street lighting has been a prime candidate for the smart energy devices due to the sheer volume of lamps and their combined energy use. Recenlt the ability to determine the ambient light level and illuminate accordingly provides light when necessary as well as saving energy. Further enhancements include replacement of lamps with lower-power LED equivalents that allow for a wider range of display levels. Finally by taking advantage of Zigbee wireless networking – lamps can not only be controlled remotely, they can also report lighting status data as well as error situations to a central computer. This removes the need for public response to broken lights and regular patrols – saving the utility time and money.

Energy harvesting

As more industrial and commercial applications rely on sensors, wireless transceivers and small microcontrollers for monitoring and data transmission, one of the design challenges has been powering and connecting these items to their required host. With regards to data transmission itself – the challenges have been overcome with the proliferation of low-power wireless mesh and point-to-point networking. And microcontroller manufacturers have reduced consumption by great lengths – in some cases down to micro amps by reducing CPU speed and smart sleep modes. These sleep functions can help when the power harvesting is sporadic, or takes time to generate enough energy for operation – for example when enough is available, the microcontroller can “wake up”, perform an operation such as transmit sensor data, then resume sleep until the energy levels resume at which point the process repeats itself.

Energy to run these devices can be harvested in many ways, however the three prevalent methods are:

Solar energy – a simple solution when the device is outdoors or can be wired to an external panel. A proven technology that can be used to charge various battery types and allows for 24/7 operation when the power drain is matched with an appropriate storage cell.
Mechanical energy – it is possible to transfer the energy from vibration and deformations into electrical currents suitable for low-power devices. An idea solution for constantly moving situations such as line-haul freight trains, mining system conveyor belts, and wave/tidal energy generators. These would also include a rechargebale battery to avoid power loss during short periods of down-time.
Thermal energy – Using sensors that consist of hundreds of tiny thermocouples, energy can be harvested from the difference between the ambient temperature and an external source of heat. These can include waste heat from industrial processes, climate-control systems and engine block heat. For example – with a sensor mounted on an area of 90 degrees Celsius, and an ambient temperature of 25 degrees – 10 mW of energy can be harvested – the equivalent according to sensor producer Micropelt of thirty AA cells per annum.

The Smart Energy Home

Domestic energy consumption is an issue for every householder, apart from rising energy bills the debate over climate change due to fossil-fuel energy sources and global warming has increasingly educated the population to reduce the energy consumption. The requirements to monitor consumption can be detailed due to the time of use and requriements for various appliances. Although utilities are installing smart meters which can offer various tariffs depending on the time of day – more can be done to assist the consumer.

The greatest advantage can be found by replacing appliances with new, energy-efficient units such as heat-pump electric hot water systems, however the cost can be substantial. A cheaper way is to offer real-time monitoring of each appliances’ energy use. This can be provided by a smart meter which can wirelessly transmit data to a receiver linked to a consumers’ PC or device – showing real-time consumption data. An option of increasing popularity is to sense the consumption of each major device in real-time – and in conjunction with time-of-use tariffs a true running cost can be shown – the greatest incentive to reduce energy use. These sensors can be fitted externall between the device and power outlet, or over time hopefully included within the device and working on a common Zigbee wireless standard.

As you can see there are many methods of smart energy use, including generation, intelligent consumption and better devices. All of these methods and more can be harnessed and modified for your individual requirements. Here at the LX Group our team has a range of experience in smart energy key technologies, including:

Displays and various user interfaces
Logging and data management
Remote monitoring and control
Ultra-low power wireless systems including mesh networking topologies
ZigBee-based networking, using Ember, TI, Jennic and Microchip platforms
Low unit cost design and BOM cost optimisation

And the team at LX has won national and international awards for past ZigBee-based systems.

For more information or a confidential discussion about your ideas and how we can help bring them to life – click here to contact us, or telephone 1800 810 124.

Published by LX Pty Ltd for itself and the LX Group of companies, including LX Design House, LX Solutions and LX Consulting, LX Innovations.