With a focus on wireless sensors as used within an industrial setting, requiring average power of around 1mW, the ISA100.18 working group will also take into account the needs of wireless systems such as those covered by ISA100.11a, as well as commercially dominant protocols including WirelessHART and ZigBee. But high on the deliverables will be a standard for power module interchangeability that will ensure that any (compliant) application will be able to use batteries, fuel cells or energy harvesters indiscriminately. This, it is hoped, will promote the use of energy harvesting modules within new installations by promoting interchangeability. The first draft detailing a standard connector has recently been published for comment.
A number of companies have now commercialized their energy harvesting technologies and are already seeing success. Typically the underlying technology employs a well-known and well understood electromechanical or chemical effect. For example at least two companies are currently producing harvesters that exploit Seebeck’s Law to create a current flowing between two substrates; one n-type, one p-type. Current flow between the substrates is caused by a thermal differential. The effect itself has been known for many years and is synonymous with the Peltier Effect, which is the reverse effect used to create a heat pump.
All that is needed to generate energy is a relative temperature difference between the two sides of the substrate ‘sandwich’, a significant advantage of this effect is that the n- and p-type pairs can be ‘stacked’ side by side and wired in series to create greater potential differences.
The symbiotic nature of energy harvesting in wireless sensor nodes enables many use-cases, like this thermostatic radiator valve.
Micropelt, which started as a project by Infineon but is now VC funded, employs the effect to create both Peltier coolers and thermoelectric generators (TEGs). It uses MEMS technology to create micro-TEGs which are capable of producing power in the 10mW range, and is currently commissioning its first volume production line in Halle/Saale, Germany, which will eventually produce 10 million parts per year.
The Perpetuum free-standing harvester combines electromagnetic vibration energy harvesting technology with a selectable suite of energy charge, storage and management options.
According to Micropelt’s Vice President of Business Development, Burkhard Habbe, the biggest challenge the company now sees is supporting its target markets and customers through to volume deployment, but that market acceptance will require the energy harvesting industry to further prove its maturity by developing and adopting standards, while educating and supporting system integrators: “Cross-disciplinary consulting and design houses are very desirable and we work on establishing those in our efforts to speed market development.”