How to Harvest Infinite Power!
By: Henry Wadsworth
9th May 2019
6 minute read
Wouldn’t it be amazing if an electronic device could run forever, for free, on an unlimited supply of energy? No batteries to replace and no plug socket to be tethered to. This might seem like a flight of fancy, but with modern energy harvesting techniques, it is a much more realisable dream.
Energy harvesting is the capture and storage of energy from the environment which can be used to power an electronic device. This is not a new idea, we are all familiar with the idea of using solar panels to charge a battery, but there are many other energy sources to take advantage of such as kinetic, thermal, and electromagnetic energy. Kinetic energy such as that produced by wind can easily be harvested using a turbine, but even vibrations can be converted into a voltage using a piezo-electric transducer so any form of movement has the potential to power electronics. Thermal energy can be converted into electrical energy using a thermoelectric generator (TEG) which is able to produce energy from heat which would normally be lost to the environment. Electromagnetic energy is present all around us, for example, in the form of radio waves and microwaves which we rely on for wireless communications from WIFI to FM radio. In most circumstances this amount of energy is so small that it cannot readily be captured and stored, however, if a device is located within a reasonable distance of a powerful transmitter, it is possible to provide enough energy to keep a low-power device alive.
This is especially the case with modern integrated circuits designed for power harvesting which are enabling increasingly tiny amounts of energy to be gradually accumulated over time in a battery, or super-capacitor in order to power a low-power device almost indefinitely while the energy source is present. In many cases it is also possible to combine multiple energy harvesting sources, which can be useful in environments where the energy sources may be changing, such as if the device is moving through different environments. For example, solar could be combined with piezo-electric, so that the device can harvest sunlight when the sun is visible, and vibration energy when the device is being moved (perhaps the device is worn by a human, or transported on a vehicle).
Energy harvesting typically refers to small scale harvesting of energy as described above, however, larger power sources can also be harnessed. For example, the power flowing through a cable can be harnessed by placing a current transformer around the cable. We recently developed a system using this technology to supply energy in an underground environment where no other power supply was reliably available. This can be a useful way of retro-fitting a device where power cables already exist, but with no other convenient way to tap the energy from the cables. This method has the potential to supply large amounts of power to a device, depending on the amount of current flowing through the cables.
Energy harvesting is a particularly valuable technique for circumstances where it is not possible to carry out maintenance on a device to replace a battery. For example, the device may be inaccessible or just impractical and expensive to access if there are a large number of devices – which is likely to become an increasingly significant problem as inexpensive IOT devices are used for large monitoring networks.
Energy harvesting techniques are becoming increasingly sophisticated which, coupled with a low power microprocessor makes it possible to power devices with energy sources which previously would be considered impractical.