# Energy harvesting and storage

ISSN: 0305-6120

Article publication date: 20 November 2009

## Citation

Ling, J.H. (2009), "Energy harvesting and storage", Circuit World, Vol. 35 No. 4. https://doi.org/10.1108/cw.2009.21735dac.007

## Publisher

:

Emerald Group Publishing Limited

## Energy harvesting and storage

Article Type: Conferences and exhibitions From: Circuit World, Volume 35, Issue 4

In 2009 brings the 800th anniversary of Cambridge University and the birth of a new conference from IDTechEX. Based upon the need for energy harvesting for use as ambient energy to power small electronic or electrical devices, interest in this sphere is burgeoning, as the presence of some 140 delegates bore witness. Held at the new Gillespie Centre at Clare College, the four-day event on 2-5 June showed that the timing was right. The first and last days were devoted to master-classes and local company visits, with the middle two to the conference itself.

Day 1 – 3 June

Dr Peter Harrop, IDTechEX Chairman welcomed those attending. They are looking at a market worth $611 million now, which within the next 10 years will be worth a staggering$4,000 million. Almost everything will be transparent, apart from the growth rate. Transparent lighting, transparent batteries, transparent solar cells, transparent flexible electronics, transparent memory. The world players are led by the USA, with Germany 2nd at 33 per cent market share and the UK with 25 per cent and growing. Most of the work in energy harvesting is aimed at the industrial sector, and whilst the use in healthcare will grow slowly, the military application will be significant. For the time being at least photovoltaics and electrodynamics will retain their dominant position in market values, but the move to ubiquitous electronics for energy conservation will be a deciding factor.

Richard Percival is the Sales Director of Infinite Power Solutions. They have a micro-energy cell built from solid-state materials by vacuum deposition of lithium cobalt oxide/lithium phosphorus oxy-nitride. It is called Thinergy™ and it is the thinnest production battery in the world. It has a loss of 1 per cent per annum, can withstand a temperature range of −40°C to +85°C, retains 90 per cent of its capacity after 15,000 recharging cycles, and has a 10 year storage and use life. Produced in 1 in. and 0.5 in.2, 170 μ thick, they incorporate the Schottky diode which allows the cell to clamp over-voltages and convert them into currents which can directly charge the cell. AC coupling for recharging is very efficient; the cell has 20 h complete autonomy, which means that it can work around the clock. Also in the range is the MEC™ (micro-energy cell) where harvested energy is stored with>99 per cent efficiency; recharge methods include piezo-electrics, thermo-electric, photovoltaic and inductive near field. Embedded in a PCB, this becomes a self-powered structure.

Dr Samuel Haque is with the Research Staff at Nokia in Cambridge. With 1 billion wireless broadband subscribers by the end of this year, and with up to 90 per cent of the 6 billion people on this earth having mobile telephone coverage, Nokia are busy. Cambridge is one of their six research laboratories, and here they concentrate on Nanosciences, and one of the key areas is energy harvesting. Whilst mobile driven energy needs increase annually, battery development is not keeping pace, and the need to recharge, with attendant difficulty, is being challenged by the use of sensitised solar cells that will fully meet the need for mobile telephone power in the near future.

Professor Haydn Thompson is the Programme Manager at Rolls-Royce Control and Systems. This large and diverse company is very interested in energy harvesting, as it can be used in the massive monitoring programme of wireless monitoring equipment that is essential. He illustrated the myriad uses of such equipment, such as a Bluetooth system for monitoring the position of water-jet positioning in marine propulsion units; the use on vibration table testing, and equipment being tested in hostile environments. The video clip of a $17 million jet engine blowing up during testing as a result of as loose turbine blade underlined the need for the tortuous route taken by Rolls-Royce during the adoption of any new technology. Florence Fusalba works with the French Atomic Energy Commission also as Programme Manager, and explained about the workings of the CEA at Liten. Of the three departments there one is entitled Nomad, where people wander collectively to develop new materials for micro-processing systems. Here, they have produced lithium-ion electrode coated cells as small batteries, 14.5 m/Al, 2.3 V, used as medical implants, in smart cards, in packaging, in E-Books. They have also produced lithium-ion electrode inks adapted for thick layer application to a range of substrates, and are now embarked upon liquid thin film batteries powering temperature measurement devices on clothing, as well as the FACESS (FP7) project for complete printed battery cores for embedded sensors, this is a large market that will eclipse the smartcard market by 2015. Dr Ivan Sham spoke about his work with ASTRI, the Hong Kong Applied Science and Technology Research Institute. Here, 420 people with HK$1.7 billion funding through to 2011 are working to keep Hong Kong as a competitive technological centre. They have four main areas of activity – consumer electronics; communication technologies; materials packaging and analog signal devices. Under their advanced packaging technologies they are now looking at energy harvesting, which they estimate will be a $164 million market by 2015. Dr Sham was of the view that price-based energy harvesting is the most competitive approach for battery-less TPMS applications working in many areas to support industry. Frank Schmidt is the Founder of EnOcean Alliance. This company produce wireless sensors for sustainable buildings. What a sustainable building is exactly was not made clear, but apparently they move, so they need sensors, so that the degree of movement may be known. These sensors will also measure light, temperature and humidity, and monitor doors and windows, CO2 and gas. Energy sources of such sensors are solar, displacement and thermal. The fact that they have now been installed in over 400,000 buildings via 150 companies, offer energy savings of between 40 and 60 per cent, and have a ROI of <12 months, speaks volumes for products that have more to do with energy saving whilst operating via energy gathering. Oliver Schneider is the Creative Director of The Facility in the UK. This is an architectural company who convert dissipated environmental elements into tenable and sustainable buildings. Given that 50 per cent of carbon emissions come from buildings, and half the buildings in the UK give off carbon emissions, the problems are severe. Through his company energy harvesting is being vigorously pursued. He illustrated how a pedestrian walkway in the new Olympic park in East London was using the building vibrating movement as energy harvesting, yielding 2.1 W/m, sufficient to power 400 m of EL lighting. The forecasts indicate that by 2018, 100 per cent of communications will be by WiFi and broadband, 100 per cent will be by smart metering and by 2016, 100 per cent Level 6 CSH. Albert Nardelli is a Director of SAVI, a Lockheed Martin company, who operate the world's largest RFID network, monitoring the movements of 35,000 shipping containers every day. Within the next 10 years tracking conveyances and their contents will be done wirelessly, and towards this end their GlobalTag system, which incorporates RFID, GPS and SATCOM will form part of a “SmartChain” to provide accurate asset location and status. Batteries to power the tags work fine if the container is moving and is exposed to light, but what about a container that is buried under others on a dockside for three months? Albert let it be known that SAVI need to partner with an energy harvesting company to resolve this issue, and fairly quickly too. Dennis Hohlfeld from IMEC in Belgium spoke about creating energy harvesters using MEMS under a programme entitled WATS – wireless autonomous transducer solutions – where micromachining is the key, and so far record levels have been obtained from MEMS harvesting from sources such as photovoltaic, vibration, electromagnetic, electrostatic (yields poor so far) and piezo-electric (which looks more promising. Aluminium nitride is the main material, giving 60 μW@572 Hz. Miss Lauriane Thorner from Imperial College intrigued the delegates with her paper on EH for marine-based wireless sensor networks using ocean-wave energy. She told us about the Mobesens FP7 project, which incorporates sub-surface monitoring, river, lagoon, estuary and coastal monitoring via moored buoys. Energy to power the sensors comes from waves, current, tide, solar and thermal and powers their propulsion and communication systems. She described the Archimedes wave swing, the Limpet, the Sea Anchor, the Wave Buoy (that contains a polymer spring that converts stress into electricity and the work done to produce a realistic maximum power point tracker (MPPT) for electromagnetic generators. Day 2 – 4 June Professor Neil White of the University of Southampton is the Head of Electronics Systems and Devices Group, and Deputy Head of School (Enterprise). He looked back to 1998, when they were working on self powered microsystems, using screen printing on to a variety of substrates to produce a screen printed energy harvester. Industry was interested, but could not see any application back then! However, this work continued, and found that the electromagnetic version produced more power, which led to the birth of Perpetuum Ltd Professor White mentioned that to have gone from concept to commercialisation within 12 months must have been something of a record. Vibration Energy Scavenging is developing an energy aware wireless condition monitoring sensor node powered by very low-vibration levels. The piezoelectric generator was described, where dielectric with piezo-electric and electrode layers are screen printed on both sides of a tapered cantilevered beam of stainless steel. But this was found not to be as good as the electromagnetic system. Freestanding structure from Ag/Pd-PZT-Ag/Pd sandwich over a carbon sacrificial layer, which disappears after firing, leaving a cantilever, which harvests energy from vibration. Here, bandwidth size and integration are important. They have also produced a plug and play energy aware sensor node, which uses a multiplexer to obtain energy from various sources, and has a sensor node which can model and predict the future energy availability and uses the stored power accordingly. They have shown that wireless sensor networks can be powered by harvesters and thus have an extended lifetime. Much work done down in Southampton, it seems, and whilst energy harvesters are commercially available, there are challenges, and the systems are bulky. Let us see what happens in 2010. The energetic Shashank Priya from Virginia Tech in Blacksburg, USA, told us how they were working with Clemson University and the University of Texas Arlington on MEMS scale wireless sensor nodes. They have used novel chemistries to lower the crystallisation temperature, and use vacuum deposition of thick film. Energy harvesting circuits were described, showing how energy from various sources could be stored; this is chip size circuitry, produced on reel-to-reel flexo printers. Within his own group of talented people, many projects are under way. He described how they had harnessed wind power to charge storage media via a very small piezo-electric windmill to power sensors on the USA/Mexico border. He also spoke about a micromachined PZT harvester with a 3D package; how electromagnetic harvesters could be used via clothing; how vibration energy from a car engine could be used to power sensor nodes used elsewhere in the car; 40 mW are readily available from this source, more than enough to power the sensor nodes. Dr Simon Aliwell of Sensors and Instrumentation KTN spoke about using energy harvesting in powering wireless sensors, a subject upon which they had now published a report. He described how they had set about the project, and of their findings. Main points – Europe was leading the way in EH, with strong expertise. Photovoltaic cells have the most potential, thermoelectric and vibrational energy are moist available in industrial settings. Hybrid devices are more efficient just to store. Whilst it may be possible to harvest vibrational and thermal energy, it might be easier just to scale up the individual device. It is likely that there will be issues with integration on chip, e.g. CMOS with MEMS processes for piezoelectric. Under a charming heading (graceful degradation) he mentioned that no one was working on how to detect impending failure, or insufficient energy, to minimise impact on a monitoring system. Field reliability is still something of an unknown, too, with only accelerated aging tests being performed. In comparing energy harvesting with batteries, EH devices were priced according to perceived benefit, generally savings £100's. One perhaps needs to compare the cost of changing batteries – people, disruption, access. Apparently, it cost$1 million to change a battery on an oil rig in the middle of an ocean; they had to hire a submarine. Developing wireless sensors requires very different and rare skills, and many large companies have yet to show interest, although Texas Instruments and INTEL have got their hands up. Energy harvesting is here, at macro system level, but at micro system level there is still some way to go.

Roy Freeland is the CEO of Perpetuum. He showed an example of an environment where failure would be catastrophic, and where changing batteries would be an absolute no-no; place where energy harvesting would be ideal to power wireless sensors; place inside the Arctic Circle, in fact. The use of Vibration Energy Harvesting was discussed, which could be gathered from various sources, such as AC induction motors, compressors, any rotating machinery, trains, road and off-road vehicles, and transformers. EH needs include enough power, reliable power, no/low maintenance, low costs, able to operate in hazardous environment, and have a mean time to failure of some 440 years. Roy described the Intelligent Harvester Power module which meets the above demands and the need for alternative interchangeable power sources.

Thomas Rödig from the Fraunhofer IKTS in Germany introduced the subject of piezoelectric (PE) generators for low-power applications. In a detailed paper, he explained how this has been most successful with surface mount generators used in aviation and used to check structural integrity all the time. The nodes are based on ultrasound and have a very long life (30 years+). PE can power microsystems, and PE materials and different technologies for low-power generation are available.

Steven Novack of the Idaho National Laboratory is someone experienced with nanoantenna structures, and their use in energy harvesting. In capturing energy, light propagates as an electromagnetic wave captured by a nanoantenna, and absorption occurs at the antenna frequency. He explained that current nanotechnology allows for the creation of antennae small enough to be resonant at the near and mid IR ranges, but large-scale manufacturing is something of a challenge as they move from small prototypes to roll-to-roll production. Photovoltaics address many of the limitations, and can be inexpensively mass produced, and used on many different types of antennae.

Dr Harry Zervos is the Technology Analyst at IDTechEx, and continued the theme of PVs. In 2007, 14 per cent of energy in Germany was produced from renewable sources, of which 4 per cent was from PVs, and the market is changing fast. Thin film solar energy systems are produced by companies such as Heliovolt, Honda Soltec, and Solindra who have a cylindrical energy harvester that works from direct, diffuse and reflected sunlight. DSSC have Dyesols, organic PVs used as power for lamps in Africa, which has been headed by a G24 project. Blue Earth from Samsung is a solar powered system; there are portable solar chargers, solar powered camping tents for the military, and indeed solar powered water bottles which charge a light in the base. By 2019, the thin film PV markets will be worth \$50 billion, and will give rise to all manner of innovative products.

Professor Amin Song of the University of Manchester specialises in ultrafast nano-diodes for EH. PV may have enjoyed 50 per cent growth per annum, but they have limited efficiency, have high cost and large energy loss, with 27 per cent efficiency at best even with triple junction Gas solar cells. Optical rectanna are the answer, he maintained, they have 91 per cent efficiency, are very fast, and do not rely upon sunlight angle, they use extremely fast zero-threshold diodes, and are very low cost being nano-imprintable and capable of operating at different wavelength bands. Given that sunlight falling to earth will yield 1 KW/m2, rectenna can offer 56 KW/m2. Based on GaAs semiconductors he is experimenting with producing nano-diodes as ballistic rectifiers and as self-switching diodes using a free electron laser, as both spiral and bowtie antennae which have been demonstrated at room temperature to be an effective THz diode. Of THz 100 s might be possible through design and the use of lithography for imaging.

Dr Leo Poll from Philips Research in Cambridge came down the road to talk about smaller sensor nodes. Wi-Fi tags are used in hospitals to track equipment, which means that some bulky rigid and expensive equipment has to be used. The aim is for a for a low cost sensor node, with a smaller footprint/profile. They started by optimising energy consumption, by designing a radio transceiver from scratch, optimising all layers. Or you could reduce the form factor, or you could reduce the costs – lower BoM. Architecture and circuit, baseband & uP, and \protocol, are all part of a redesign. As result Philips have a radio that only uses 2.7 mW Peak power including embedded CPU, sand measures 4 mm2. With data rate of 90 kb/s with only 4 external components, an energy course, antenna crystal and saw filter. Has a range of 10 m and operates at 898/9,125 MHz running on a supply voltage of 1.2 V. Prototype proven to work, they are now looking for licensees. This proves that wireless nodes need to become smaller and cost less.

Ciaran Connell is the CEO of DecaWave in Ireland focussing on producing low cost wireless sensors for real time location systems, using received Signal Strength for distance between transmitter and receiver for consignment monitoring; these are Time of Arrival based systems. Ciaran went on to explain IEEE 802.15.4a which is a standard for ultra-low complexity, ultra low cost, ultra low-power consumption alternative for IEEE STD. This system can be deployed worldwide; his company's system is called ScenSor, and its performance is better than Wi-Fi, with a range 500 m outdoors, 40 m, indoors. Scensor can be used for tags – precision RTLs, using wireless connectivity, with ultra low power, great flexibility; realising wireless sensors that are compact low cost and with a very long life.

Peter Spies from the Fraunhofer Institute for Integrated Circuits in Germany spoke about the challenges of micro-electronic power management in energy harvesting applications. Power consumption decreasing, efficiency of energy transducers is increasing; power management is the enabling technology for energy harvesting power supplies. He listed the challenges of microelectronic power management which included minimum start-up/supply voltages, minimum leakage currents, etc. and commended the low voltage DC-DC up convertor for Tags; the ASIC design of this convertor works with 20 mV.

Mr Yen Kheng Tan came to the UK from the Department of Electrical and Computer Engineering at the National University of Singapore, and energy harvesting is the subject of his PhD A smart environment relies upon wireless sensor networks. But sensor nodes have a limited energy supply. It is hard to replace batteries, once deployed, and the number of nodes in a network is high, and in difficult locations, so batteries are not practicable. To find longer operational lifetime you need a greater energy supply and higher energy storage, and we have no doubt, having listened to Mr Yen Kheng and his detailed technical paper, that he will not only obtain his Doctorate but will have found a way to successfully harvest energy from four energy sources for long-term storage.

IDTechEx will need to find larger premises for their conference in 2010, which they want to hold in June in the UK somewhere, but if the next conference is anything like the first one then they can assured of a full house. This is a subject that draws a great deal of interest on a global basis, and the level of expertise addressing EH in its many formats is inspiring, the application for it is exciting, and the coming year will see some rapid advances.

J.H. LingAssociate Editor