Energy harvesting is the creation of electricity from ambient energy. "Make electricity where you need it" as Edison advised. At microwatts to tens of milliwatts it is used for sensors, the high end being needed to transmit their data from time to time. Above that we have some microcontrollers with many sensors as used in the Internet of Things (IoT) and at watts to tens of watts we have portable consumer electronics.
Beyond that is energy harvesting typically for electric vehicles by land water and air but now also for conventional vehicles as they become more and more electrical with alternators that work backwards when coasting or braking and the familiar regenerative braking for example. See the IDTechEx report, Electric Motors for Hybrid and Pure Electric Vehicles 2015-2025: Land, Water, Air . IDTechEx has reports on sensors and on all forms of energy harvesting such as a popular one on thermoelectric energy harvesting. It also has the world's largest selection of reports on electric vehicles and their technologies and infrastructure.
Vehicles need all forms of energy harvesting now
Actually, vehicles increasingly use everything because the powerful energy harvesting devices can charge traction and other power batteries whereas the sensors now appear all over a vehicle and increasingly they are wireless to save weight and space and that means they need energy harvesting to avoid changing a lot of largely-inaccessible primary batteries. For example, the value of cars and buses is going from 40% electrical and electronics to 70%. Anyway, all this energy harvesting is one subject often with the same companies involved in buying and the same companies supplying across the spectrum of needs. They all variously harvest light, heat difference and/or movement in the main.
Too much focus on the low power end?
Despite this there has been a tendency to pretend that only the whisper of electricity for sensors is really energy harvesting and this was largely the case at a recent, excellent event in London called "Energy Harvesting 2015," staged by the UK Knowledge Transfer Network. It had space for only 100 delegates so people were turned away. There were about 20 exhibits and about 25 posters of research work and 14 excellent presentations. Here are some highlights to show what is happening.
Research not matching need
Piezoelectrics and thermoelectrics were the main focus though most applications serving sensors and small devices use photovoltaics and electrodynamics. However, these did also get some exposure. Innovate UK presented UK funding support for energy harvesting, showing vibration getting most, followed by thermoelectric (TE) then photovoltaics (PV).
Supercapacitors and fabric energy harvesting
A common factor is the use of supercapacitors most of the time for the power hungry data transmission from sensors. They are longer lived than batteries and provide a sharper pulse when needed. When coated on weavable fiber in the European Powerweave project that was presented, their low series resistance permits connections limited to the ends of fibers.
Exception in using supercapacitors was the Perpetuum electrodynamic vibration harvester now using a Tadiran hybrid battery for higher temperature performance. Incidentally, Powerweave does talk of real power, seeing its woven supercapacitor + DSSC photovoltaic fiber being used in airship fabric generating 1500 kW for propulsion meaning about 10W/ square meter - one tenth of a rigid silicon panel but safely flexible, lightweight and rugged. Another compelling opportunity is 4.5 million square meters of greenhouse covering in the Mediterranean countries and China that could be furlable PV thanks to Powerweave if the project is successful.
Printing electronics is very useful
Professor Beeby of Southampton University prints piezoelectric energy harvesting for cost reduction, speed and flexibility but he also reported thermoelectrics getting better performance up to 400 microwatts per cc. and combinations. He was followed by Professor Rob Dorey of the University of Surrey giving an equally excellent presentation on printed energy harvesting, in this case thermoelectric, piezoelectric and pyroelectric though the latter needs temperature change rarely encountered when needed. European Thermodynamics reported 1 mW from only 5 C temperature differences.
Sharp advocated its 3-5 compounds for indoor photovoltaics because they have 3-6 times the efficiency of conventional silicon panels but they are not printed and the materials can be more expensive. The best was 21.8 microwatts/ sq. cm in LED light with fluorescent giving 18.2. Other PV such as amorphous silicon aSi, CdTe, copper indium gallium diselenide CIGS for Building Integrated Photovoltaics (BIPV) at kW of power, dye sensitised solar cells DSSC ("over 20 yr life demonstrated") and organic photovoltaics (OPV) are all being developed by Sharp for energy harvesting.
Electret energy harvesting
Alternative phenomena are also leading to working devices. For example, Professor Haydn Thompson showed us a working ceramic electret vibration harvester using microW to briefly light an LED. It was developed by one of his companies called THHINK Wireless Technologies Ltd.
Multiple harvesting needed
It was a shame that the urgent need for multiple energy harvesting to remove intermittency and provide redundancy was inadequately addressed. However, standards are now followed that lead to some interchangeability between vibration, thermo etc. modules in a given application such as a vibration energy harvester.
No one knew of a big order for anything at the low power end, in contrast to the huge business in regenerative braking and so on in vehicles and Building Integrated Photovoltaics, but there was the usual rehearsal of UK water companies needing 150k battery powered sensors replacing. In other applications such as aircraft, there was disagreement on the practicality of thermoelectric harvesting. The great success of structural photovoltaics across wings charging traction batteries was not covered but many applications and potential applications of piezoelectric energy harvesting for structural health monitoring sensors in aircraft, not least helicopters, was covered with all manufacturers now following the pioneering work of Microsensys with Textron Bell helicopters years ago.
IDTechEx Show! covers it all in one place
Next comes the much bigger IDTechEx Show! in Berlin 28-29 April with 13 conference streams including energy harvesting and separately Internet of Things using harvesting and a substantial exhibition. 21 optional masterclasses on the day before and the day after that are combined with visits to centers of excellence in the area. Uniquely, all forms of energy harvesting are covered alongside their key enabling technologies such as printed and flexible electronics and conferences on how everything is changing in electric vehicles including all those sensors and that harvesting proliferating.
At the high power end, there are energy-harvesting shock absorbers, photovoltaics across the vehicles and many new types of heat and movement harvesting, even thermoelectrics on range extenders and microturbines in their exhaust pipes. Indeed, Witt presents on its remarkable new 3D electrodynamic energy harvester garnering energy in any direction and claimed to be suitable for everything from a small 10W device on a rucksack charging a mobile phone to wave energy harvesting to propel sea craft.
Pavegen will reveal paving generating electricity and WiTricity remotely charges electric vehicles. At IDTechEx Show! we shall hear about GE Aviation working on energy harvesting in tiny Micro Electromechanical Systems MEMS, Jaguar Land Rover intending to use printed electronics, Daimler AG, Tata Motors, Deutsche Telekom, Augusta Westland, Komatsu and United Technologies developing and using energy harvesting and allied technologies.
Natural allies now: Electric Vehicles + Energy Harvesting
For example both fuel cell hybrid electric vehicles and pure electric battery or supercapacitor-powered electric vehicles have zero pollution at point of use but so does energy harvesting. They are natural allies, joined in the conferences "Energy Harvesting and Storage Europe 2015" and "Electric Vehicles: Everything is Changing" at IDTechEx Show! In Berlin.
Here comes structural electronics
The megatrend of moving from the components-in-a-box approach to electrics and electronics over the last 120 years to structural electronics is the subject of a masterclass and lectures in the conferences. It is analysed in the IDTechEx report, Structural Electronics 2015-2025 and the IDTechEx report series on 3D printing, the subject of its own conference at the event. Other newly hot topics such as autonomous vehicles and even LEDs as energy harvesters are also covered.
The event is end-user focused with needs and experiences aired, latest technology developments and roadmaps and demonstrations, samples and much more. Over 150 exhibitors are expected, with 200 company presentations and 2000 attendees from over 42 countries. www.idtechex.com .
Top image: New electret based vibration harvester by Think Wireless Technologies in the UK, Source IDTechEx