Energy harvesting

As energy harvesting (literally energy crops ) refers to the recovery of small quantities of electric power from sources such as ambient temperature , vibrations or air currents for mobile devices with low power. The structures used for this are also referred to as nanogenerators . With wireless technologies, energy harvesting avoids restrictions due to wired power supply or batteries .

Energy harvesting is important for the energy supply of miniature devices in the digital world . National standardization in Germany is handled by the German Commission for Electrical, Electronic and Information Technologies, and international standardization is handled by Technical Committee 47 "Semiconductor Devices" of the International Electrotechnical Commission .

Energy harvesting options

Micro effects
- Piezoelectric crystals generate electrical voltages when a force is applied, for example through pressure or vibration

Macro effects (mechanical with or without induction)

Some watches are powered by the movement of the wrist. In most cases, a strong imbalance on an axis is caused to rotate involuntarily by the wearer and the rotational energy is fed mechanically or electromagnetically to the core function of the watch. Variations with electric linear generators can be found e.g. B. in flashlights, where the acceleration of the moving core due to the rather high energy requirements of a flashlight mostly has to be very intense and thus arbitrary.
Floor slabs generate energy from pedestrians walking over them. The weight of the person lowers the plate by up to 1 cm and the system absorbs up to 50 watts of power. In Toulouse / France there is the Trott-Elec project (Trott-Élec; Trottoir Électrique - electric pavement). The energy generated is to be used to illuminate the street. Something similar was implemented for dance floors and small electrical appliances by a company from Rotterdam.
Backpacks produce electrical energy when moving up and down on the back to charge a cell phone.

Energy conversion through the piezoelectric effect

The direct piezoelectric effect converts mechanical pressure into electrical voltage . Piezo igniters, in particular, are known as energy generators, which convert the mechanical energy introduced into the button into an ignition spark. More recent applications in this area are radio switches , in which the energy required for the coded radio signal is also provided by manually operated piezo elements. In the field of self-sufficient sensors , piezo elements can generate the energy required for the measurement process and any radio transmission by converting the vibration energy present in the “environment”, similar to the principle of self-winding clocks.

Energy conversion through the thermoelectric effect

In 1821 Thomas Johann Seebeck discovered that an electrical voltage is generated between the ends of a metal rod when there is a temperature difference ( temperature gradient ) in the rod . With suitable materials, it is possible in Peltier elements to generate electrical current from temperature differences.

Advantages are:

no moving parts
maintenance-free due to the materials used
possible use of natural heat sources or residual heat

A disadvantage of thermoelectric generators is their low efficiency of less than 10%. Thermoelectric generators are available for petroleum lamps.

Energy conversion through photoelectric effect

When using the photoelectric effect in photovoltaics , light energy is made directly usable for electrical consumers by means of solar cells . It is the most widespread method of self-sufficient energy supplies and operates e.g. B. Parking meters, traffic control systems, night lights and calculators.

Circuit technology

The voltages and powers that are available from thermoelectric generators are usually very small and require appropriate electronics . An integrated circuit developed for thermoelectricity requires e.g. B. only 20 mV input voltage. Even amateurs try their hand at simple means, for example with photodiodes as a supply voltage source.

On the other hand, photovoltaically operated devices are well established and often only require a battery in addition to a solar cell. To avoid overcharging, excess current from the solar cell must be diverted - unless the accumulator is sufficiently overcharge-proof.

literature

Klaus Dembowski: Energy harvesting for microelectronics: energy-efficient and self-sufficient solutions for wireless sensor systems . VDE-Verlag, 2011, ISBN 3-8007-3234-3 .

Olfa Kanoun, Jörg Wallaschek (Hrsg.): Energy Harvesting - Basics and Practice of Energy Self-Sufficient Systems . Expert-Verlag, 2008. ISBN 978-3-8169-2789-1 .

Norms

DIN EN 62830 Semiconductor components - Semiconductor components for energy harvesting and energy generation
(2014)
- Part 1: Vibration-Based Piezoelectric Energy Harvesting
- Part 2: Thermal voltage-based thermoelectric energy harvesting
- Part 3: Vibration-Based Electromagnetic Energy Harvesting