Energy harvesting is off-grid production of electricity where it is needed using ambient energy such as wind, tide and waves or just vibration. At power levels of watts to megawatts it is a great success. Examples are the bicycle dynamo, small wind turbine and regenerative braking in vehicles - even conventional ones - nowadays. See the IDTechEx report, Mild Hybrid 48V Vehicles 2016-2031. A host of new inventions will increase the money rolling in for high power energy harvesting in future. Think solar
Energy Independent Vehicles, car tires producing electricity instead of heat, solar roads, power generating kites. The IDTechEx report, High Power Energy Harvesting: Off-Grid 10W-100kW 2016-2026 and Electric Vehicle Energy Harvesting/ Regeneration 2017-2027 give more.
Low power energy harvesting at microwatts to milliwatts is a more troubled area commercially. Academics love it, particularly developing piezoelectrics, one of the least successful approaches commercially due to reliability, performance and toxicity issues.
Vibration harvesting a bridge to something else?
Most of the work on low power movement harvesting consists of vibration harvesting to provide microwatts to milliwatts. This is achieved in many ways but the manufacturers tend to go under or at best create modest businesses of only a few million dollars sales yearly that struggle to make profit. In commercial terms the significance may be that, with the right technologies, vibration harvesting can transition to random movement, high power harvesting, potentially a large market. For example, Witt 6D motion harvesting by electrodynamics started at devices generating up to one watt but it is now being focussed on 10-1000W then more when practicable. It turns rotary and linear movement in any of the three axes into rotation of a shaft powering a generator.
Vibration harvesting is used to provide self-powered sensor/ transceiver units where hard wiring or batteries for wireless would be expensive and/or impracticable to install or service and where photovoltaics would not work. Ironically, that is often where huge amounts of electricity or other energy are being used nearby as with large servo motors in factories and helicopter and train transmission monitoring where Perpetuum has success by using the superior electrodynamic approach instead of piezoelectrics. Here the vibration harvesting is easier and cheaper to install than the alternative of directly tapping mW from what can be MW supplies locally. Another example of this is Textron Bell helicopters where sensors are powered by Microstrain piezoelectric harvesters with no reliability problem but the necessary 1kz vibration is rare elsewhere and Textron Bell tell us they have no plans to use it more widely.
One difficulty in selling vibration harvesting lies in the fact that companies providing hard wired systems in chemical, oil, gas and utility facilities making a lot of money from the complexity of their hard-wired traditional solutions and protect their turf, assisted by the fact that their clients abhor change. Other users prefer the lower cost up front of batteries. For example, Linear Technology, a leader in processing for energy harvesters, has recently noted that, with less power needed these days, many sensor product integrators are using long-lasting lithium thionyl chloride primary batteries.
Many innovations show promise
Vibration harvesting is a niche business and suppliers struggle to profitably attract more than millions of dollars of business yearly. Nevertheless, much research on energy harvesting is specifically directed towards vibration harvesting in the hope that it can be made more affordable, smaller, more standardised and with wider acoustic bandwidth so it is more effective and more widely applicable. Triboelectric TENGs, the most recent energy harvesting technology invention in 2012, offer new formats and materials for vibration harvesting. For example, a rollable paper version has been demonstrated that could be disposable. However, so far it has among the lowest power density figures though rigorous comparison is not available. Like so much vibration harvesting, it is a solution looking for a problem. Read the IDTechEx report, Triboelectric Energy Harvesting TENG 2017-2027 which details the remarkable progress with this option in only four years. TENG researchers have even got a self-powered sensor working in the heart of a living pig and self-powered haptic touch buttons have been made.
Other new approaches
The new start up 8Power, using know-how from Cambridge University in the UK, looks promising with a different approach to electrodynamic vibration harvesting producing tens of milliwatts in the most efficient manner with the best figure of merit. They also have a neat capacitive harvesting approach to the need for integral MEMS energy harvesters. Microgen and IMEC had already demonstrated piezoelectric vibration harvesters using MEMS technology.
A different capacitive approach uses electrets and it was first commercialised in a product by Omron of Japan in 2015. Professor Haydn Thompson of Thhink Technologies showed us his electret capacitive harvester in the form of a shaken device that lights an LED. His initial devices are claimed to be maintenance free and have long life and wide temperature range at 0-60C. They only produce a fraction of a milliwatt at present but that is ample for a lot of low power electronics and electrics nowadays. He adds, "The target for the device is a 2x2cm package for running small sensors but of course you can link modules together to give more power. So basically you go up by about 100uW per 2cmx2cm package. You could imagine a panel such as the floor of a car or a panel on a train generating quite a lot. There is work going on a rotational harvester based on the same electret concept (looks like a DVD but with patterned plates) and this is generating 7.5mW per revolution at the moment. We are looking at this for a small wind turbine concept." He explains that electrodynamic wind turbines do not downscale well and that creates a gap in the market.
Those escaping what has been a dust bowl of low power vibration harvesting by moving to higher power outputs do not have to aim for the hundreds of kilowatts of off-grid Airborne Wind Energy AWE or solar roads let alone the megawatt level of wave power that is the target of some developers of Dielectric Elastomer Generators DEG, 6D motion harvesters and Triboelectric nanogenerators TENG as they escape their origins in low power harvesting. Two huge markets need one watt energy harvesting - mobile phones and Internet of Things nodes. Solve that problem with something affordable, convenient and acceptable and you may match the riches of Croesus. In the meantime, some of the more primitive IOT nodes that rarely transmit could have their batteries charged by mW level vibration harvesters provided these provide fairly continuous output.
For more on energy harvesting at all power levels attend the IDTechEx conference, Energy Harvesting USA 2016 in IDTechEx Show! Santa Clara California November 16-17. It will have over 3500 paying delegates, a 200+ stand exhibition and 23 masterclasses on energy harvesting and allied subjects on the day before and the day after. Star Micronics reveals its new advances in vibration harvesting. Analog Devices, EnOcean, GE, Linear Technology, NTT Data and others look at the IOT opportunity in this and parallel conferences at the event. Others cover different applications and technologies including triboelectric, thermoelectric, electrodynamic and photovoltaic in the Energy Harvesting conference.
Top image: 8Power
Learn more at the next leading event on the topic: Electric Vehicle Materials Europe 2020 on 13 - 14 May 2020 at Estrel Convention Center, Berlin, Germany hosted by IDTechEx.