Munich seems to be the place for energy harvesting events with the IDTechEx event Energy Harvesting & Storage Europe and Wireless Sensor Networks & RTLS 2010 being held there on the 26th & 27th May.

This was a successful event with just under 250 delegates. The plenary talks successfully addressed the challenges faced when combining energy harvesting and wireless sensors in different practical environments. A good example of this was the presentation by Thomas Becker from EADS who posed the question: do we need energy harvesting and wireless sensor networks in aeronautical applications? Thomas provided clear motivation for such systems, namely decreased maintenance effort and increased lifetime of aircraft, but also highlighted the challenging requirements particular to the application. For the wireless aspect, the network would require certification and need to be totally reliable. The environment was very challenging with temperatures ranging from -55 to +85 oC, plus humidity variations, icing, exposure to hydraulic fluids, structural aging effects and vibrations. The system would be expected to work for a lifetime of 30 years. EADS has evaluated various types of energy harvesting. Vibration energy harvesting in rotor craft has been demonstrated obtaining mW of power from 17 Hz vibrations. On fixed wing aircraft, thermoelectric harvesting appears more attractive but issues remain regarding their successful integration and no solution is expected within the next 5 years.

Haydn Thompson from Rolls Royce continued the theme with a talk on self powered wireless sensors. The environment within an aero-engine is clearly even more challenging than the standard aeronautical specification with temperature variations ranging from -55 to 1300 oC! The potential for energy harvesting is clear - batteries are okay for test be applications but are totally unsuitable for production systems where there is plenty of vibration and thermal energy available to be harvested. Both vibration and thermal energy harvesting had been demonstrated with 100 mW and 200 mW being demonstrated form each approach respectively. The size of the energy harvesters remains an issue and much work remains to be done to develop harvesters for this application.

Other interesting talks on energy harvesting included a presentation from Pavegen Systems Ltd who have developed an energy harvester than looks like a conventional paving slab but that is able to develop between 2 and 3.75 W from an average footfall. They are seeking to licence the technology to act as a localised power supply for low level lighting and operation of systems at bus stops for example.

After the plenaries there were two parallel streams on energy harvesting and wireless sensor networks and an exhibition from various organisations and companies involved in energy harvesting. These included presentations form Microstrain, Cranfield University, University of Southampton, US Space and Naval Warfare Systems Command (SPAWAR), EnOcean, IMEC Holst Centre, Arveni, Humdinger and Meggit Ferroperm. These talks focused on the more technical issues relating to energy harvesting including aspects of piezoelectric vibration energy harvesters, MEMS implementations, increasing vibration bandwidth and thermoelectric energy harvesting. The talk from Cranfield on modelling of piezoelectric energy harvesting was, for me at least, very interesting. They have successfully modelled piezoelectric harvesters using ANSYS and we at Southampton have benefited from this research which has improved the accuracy of our simulations. The talk from Humdinger was on the novel topic of energy harvesting from airflows by exploiting aeroelastic flutter. They have developed a small harvester able to harvest about 1% of the wind energy obtaining 200 micro Watts at 3.5 m/s airflows. The research into MEMS energy harvesters mentioned at this conference was technically interesting but, as is often the case, felt like investigating solutions without a problem. The laws of physics do not favour microscale vibration energy harvesting and applications for low power, high frequency, albeit small, harvesters are not yet obvious. As power requirements fall and MEMS technology and materials evolve I'm hopeful this won't remain the case.

The next two energy harvesting events organised by IDTechEx will be held on the 13-14 October in Hong Kong and 16-17 November in Boston. A discounted rate will be available to Network members and further details will be available on the website.