Energy Harvesting Technology


Energy Harvesting

Energy Harvesting (EH) is the process of capturing and accumulating energy from an energy source as energy from it becomes available; storing that energy for a period of time, and conditioning it into a form that can be used later, for instance to operate a microprocessor within its operating limits. In many common cases, EH is associated with capturing residual energy as a by-product of a natural environmental phenomenon or as a by-product of industrial processes. Often these residual energy were not previously captured, but instead were released into the environment as waste. Common target energy harvesting sources for EH are mechanical energy resulting from vibration, stress and strain; thermal energy from furnaces and other heating sources, even biological; solar energy from all forms of light sources, ranging from lighting, light emissions and the sun; electromagnetic energy that are captured via inductors, coils and transformers; wind and fluid energy resulting from air and liquid flow; and chemical energy from naturally recurring or biological processes.

In most cases, these sources provide energy in very small packets that have been difficult to capture for use. New opportunities in Energy Harvesting are being enabled by new EH circuits that can finally provide the overall Energy Management to capture and store these small energy packets and condition them to provide a useful output. The Energy Management provided by these EH circuits needs to include high Energy Efficiency to capture and accumulate these small energy packets, high Energy Retention to store the energy for long periods of time, and the proper Energy Conditioning to perform the desired task. The Energy Management must be well defined even starting at 0.0V operation and must tolerate a wide range of voltage, current, and waveform inputs, including over-voltage, over-charge, and other irregular input conditions.

Energy Efficiency

The Energy Management of capturing, accumulating and storing small packets of electrical energy requires High Energy Efficiency. The net captured energy is a direct function of energy available for capture minus the energy the EH circuit must consume to stay in the active mode. The circuit must stay in the active mode and be ready to perform the energy capture whenever harvestable energy becomes available and be ready to provide an output as the application design requires it.

For example, let's say the energy is vibration from someone walking on a surface embedded with a vibration energy source with an EH circuit and a temperature sensor and wireless transmitter. The small energy packets provided from the possibly infrequent pedestrian must power the EH circuit in the active mode for a long period of time until the EH circuit triggers the transmitter to send the temperature data. The Energy Efficiency must be very high so that the energy consumed by the EH circuit is much smaller than the small energy provided by the vibrations.

Energy Retention

A second key component of Energy Management is High Energy Retention to store the captured energy for as long as possible with minimal leakage or loss. In the example of the pedestrian, if pedestrian activity is low, it may be many hours before enough energy has been stored by the EH circuit to trigger the data transmission or many hours before the application design wants the data transmitted. Therefore, the EH circuit must have extremely high Energy Retention.

Energy Management

Energy Conditioning is a third key component of Energy Management. The EH circuit must Condition the stored energy to provide the output necessary for the desired application, such as operating a self-contained wireless sensor network node. In the prior example, the EH circuit conditions collected small packets of energy to provide the required voltage-output and current output conditions to operate the temperature sensor and the wireless ZIGBEE transmitter.