Non-stop energy harvesting

Energy harvesting is developing fast, supporting innumerable applications and devices

By Morand Fachot

There is a rapidly increasing range of applications using energy harvesting (EH), the process of collecting low-grade energy from sources such as ambient or waste heat, solar, thermal and kinetic energy and converting it into electrical energy. The increase is driven by the need to enable an ever expanding range of sensors to run and communicate independent of an external power source and by the need to meet the power requirements of a wide variety of mobile and wearable devices. It is seen as one of the main techniques that will allow the Internet of Things (IoT) to develop.

Kids playing football of field made with pavegen tiles
Pavegen tiles work day and night alongside solar panels to power lights of this Rio football pitch (Photo: Pavegen)

Growing importance in industry

Drawing off energy from low-grade sources is seen as an attractive solution for many low-power electronic devices such as sensors. Increasingly these are being deployed in various industrial environments where they can operate independent of power networks and batteries (although the latter can be used for backup power).

Depending on the type of environment and application, different types of energy sources can be tapped using specific EH technologies such as thermoelectric (TE, for heat recovery), piezoelectric (for kinetic energy), or photovoltaic (PV, for solar power).

Industrial processes require monitoring and communication of a variety of parameters, including temperature, vibration and signs of potential failure. This is best done using sensors and, increasingly, wireless sensor networks (WSNs). 

Going wireless – a no-brainer

Employing a wide range of wireless communication protocols allows the transmission of data from sensors to control hubs. Advances in EH have made it possible to extend the range of applications for remote instruments as installing these and tying them to power networks or batteries is both expensive and labour-intensive.

Over 50% of instrumentation installation costs in industry are related to planning, wiring and cabling (installation, routing and protection of cables), mounting and connection of devices (junction boxes, access), etc. Wireless devices and networks can significantly reduce installation costs and implementation time.

The IEC is closely involved in the development of International Standards for WSNs through the work of one of its Subcommittees, IEC SC 65C: Industrial networks, which prepared the widely-used IEC 62591:2010, Industrial communication networks - Wireless communication network and communication profiles - WirelessHART™. This Standard, which provides the specification, definitions, and profile for a wireless communication network, complements the IEC 61158 series and other IEC Standards on industrial communication networks.

Wide range of industrial applications

Energy harvesting is already widely used for powering sensors and actuators, such as those found in certain types of microelectromechanical systems (MEMS). These are increasingly deployed in industry and in other sectors, such as automotive or aerospace that often rely on kinetic energy (impact, pressure, vibration). 

International Standards for MEMS are prepared by IEC Technical Committee (TC) 47: Semiconductor devices, and they are tested by IECQ (IEC Quality Assessment System for Electronic Components) testing and certification.

In industry, wireless vibration monitoring systems have improved ways of detecting faults and reduced the need for maintenance of electric motors and other rotating equipment.

Most kinetic-based EH systems depend on piezoelectric transducers. International Standards for these are developed by IEC TC 49: Piezoelectric, dielectric and electrostatic devices and associated materials for frequency control, selection and detection.

Autonomous temperature transmitters, which rely on TE energy harvesting, are also widely used in industrial applications to monitor abnormal temperatures and prevent equipment failure.

In addition to EH, some wireless sensors also depend on primary and secondary batteries for backup or low energy intensive applications.

In industry, wireless sensing is now a proven and mature technology. It is made possible by various sources of EH which improve its flexibility and reliability.

Endless potential

Energy harvesting is also seen increasingly as offering the potential to power sensors in the medical field. Research has been ongoing into devices that can convert the movement of body parts such as the heart, lungs and diaphragm into energy that could be used to power health monitoring wearables or implantable devices – for instance, pacemakers. A project is underway to harvest energy from body heat and motion to provide a compact, long-lasting power source for nanoscale body metric sensors. IEC TC 113: Nanotechnology standardization for electrical and electronic products and systems, prepares International Standards for such applications.

Energy harvesting from impact and motion can also be implemented in large schemes, in particular to power lights or signs in places that see great numbers of people moving and walking through every day.

Energy harvesting pavements or surfaces have been installed in some heavy pedestrian traffic locations such as train stations, office buildings or sports installations for powering energy-efficient lights or other systems.

A shortcoming of the plethora of energy-hungry mobile devices like mobile phones and tablets or smart watches is the constant risk they face of running low on battery power. Harvesting energy from natural or artificial light to top up or charge their batteries is emerging as a possible answer. An innovative solution for this, among many others, is the Wysips® (What You See Is Photovoltaic Surface) technology that embeds into glassa thin PV surface with a network of micro-lenses that renders the cells invisible to the naked eye. Wysips can also be used in other applications such as automotive (windscreens) and housing (windows).

Not just for small devices

Energy harvesting is no longer perceived as useful for powering only small devices. It is increasingly finding new uses in demanding energy-intensive sectors such as transport, in particular when associated with innovative or improved storage systems.

The industrial trucks and urban public transport sectors above all offer great potential for energy harvesting.

Regenerative-charge braking and energy-harvesting shock absorbers are being fitted to buses to charge batteries and the supercapacitors that provide extra power.

A combination of a sealed maintenance-free battery and a capacitor that stores energy from regenerative actions such as braking or lowering loads so as to be able to feed it back when needed, was introduced in the first fully-electric hybrid forklift in May 2007.

This system allows for up to 80% of regenerative energy stored in the capacitor to be reused, against at most 2-3% for conventional battery forklifts, giving this truck the capacity to work a full 11-hour shift with a single one-hour charge in mid-shift.

IEC TC 21: Secondary cells and batteries, prepares International Standards for lithium-ion batteries.

IEC TC 40: Capacitors and resistors for electronic equipment, has already published International Standards for supercapacitors, or electric double layer capacitors (EDLCs). It has now earmarked hybrid EDLCs, which combine an EDLC and a battery, as being in need of appropriate standardization.

Making its mark on the racing track

A high-profile example of the potential of energy-harvesting and associated storage systems for energy-intensive applications was provided again at the punishing 2015 24-hour Le Mans car race in France. This year, all cars that finished in the top eight positions were hybrid machines, as required by regulations for this category of vehicle. However, since the rules do not specify the type of hybrid system, the method for storing recovered energy or the power transmission concept, different energy-harvesting and energy storage systems were used in each of the three types of cars that finished in the lead.

Three of the cars, including those that came first and second, were fitted with a front-axle-mounted electric engine generator that recovers kinetic energy under braking and transfers it for storage in a lithium-ion battery. During acceleration, the stored energy delivers a power boost via the front wheels, giving the cars an all-wheel drive capacity. Two of these vehicles also had an additional turbine generator unit in the exhaust system, working in parallel with the turbocharger to convert waste heat energy from the exhaust-gas stream into electricity. These cars recover energy not only when braking but also when accelerating.

Another three cars also had a regenerative braking system that recovered the car's kinetic energy under braking and stored it in a flywheel energy-storage system. The recovered energy is then used in acceleration phases to provide an additional boost.

Two more vehicles in the top eight also relied on regenerative braking: storing the recovered energy in banks of supercapacitors which then released it to provide boost to the rear wheels through an electric motor.

These advances are unlikely to remain confined to the motor sports world, as car racing is often a means of introducing technologies that eventually find their way into production vehicles.

Using energy-harvesting technologies to power a very wide range of devices and systems – anything from tiny sensors to industrial trucks – is beginning to offer opportunities in countless applications as well as lucrative commercial opportunities. This is reflected in the figures for global EH markets which stood at USD 131,4 million in 2012 but are projected to increase to USD 4,2 billion in 2019, according to a December 2013 report.

The IEC is set to play a central role supporting the expansion of the EH sector and of associated technologies such as storage or nanotechnologies, by the means of standardization work from a number of TCs.

Kids playing football of field made with pavegen tiles Pavegen tiles work day and night alongside solar panels to power lights of this Rio football pitch (Photo: Pavegen)
WYSIPS Wysips® Crystal technology allows mobile devices to be charged from natural and artifical light sources
wireless temperature sensor WirelessHART temperature sensor TSP300-W with Energy Harvester (Photo: ABB)