electricity generation » energy harvesting - Overview of key principles of energy harvesting.

Energy Harvesting

Although still in its infancy as a legitimate 'renewable' energy technology, energy harvesting is said to be the way of the future, especially when it comes to providing energy for portable and mobile devices. Energy harvesting, sometimes referred to as energy scavenging, is the science of using ambient, readily available energy that is present all around us for powering devices such as light switches, watches, ignition systems (such as in cars or in gas stoves), sensors (for security or for monitoring data), microphones, and even the identification chips in passports and store security systems.

The energy that this specialized technology harvests can come in several forms, such as the heat generated by machinery or by the human body; the kinetic energy of a human arm in constant movement; the piezoelectric energy created when special crystals are subjected to mechanical force (such as constant foot-fall); or even the electromagnetic energy that surrounds us in the environment, generated by radio and television broadcasts and the rays of the sun.

Small Scale But Wide-Ranging

Whilst many of these sources of energy are only sufficient to power small devices, the combined effect of using 'free', sustainable energy for many small jobs is guaranteed to have a huge impact. Through utilizing energy harvesting technologies for these small devices and jobs, carbon emissions can be reduced (less reliance on mains electricity means a smaller amount of fossil-fuel generated electricity is used), electricity bills drastically cut, and the remaining energy requirements of the building in question can be more easily met by other renewable sources of energy, such as solar and wind power.

Present Uses

While energy harvesting is still a marginalized area of renewable energy, there have been many developments in recent years that should soon mean we can incorporate the energy harvesting technology cheaply and easily into our homes and businesses.

At present the main use for the technology is powering remote sensors and monitoring devices that are not practicable to have wired into a mains power supply or powered by battery. Kinetic, thermoelectric and piezoelectric energy harvesting are all suitable for this type of job, though piezoelectricity seems to be the most common energy source. Piezoelectricity uses the reaction of particular crystals and ceramics that generate an electric charge when submitted to mechanical stress, for instance when they are walked on (experiments have placed the crystals in the soles of shoes and in walkways) or banged together with force (such as in an electric cigarette lighter, a gas ignition for a cooker, or in a light switch).

The electricity that is generated is then used to periodically complete a job - in the case of a sensor or monitoring device, it may regularly update a central system with a stream of data, or be triggered by movement or sound. Most efficient devices are capable of storing energy rather than expending it straight away, constantly being recharged by whatever motion or source is powering them, meaning that the devices can effectively go on 'forever'.

Whilst this technology is presently quite expensive, there are more and more businesses becoming involved in energy harvesting technology and this should inevitably lead to a fall in device costs.

Future Technology

There are several other promising technologies that fall into the realm of energy harvesting which should be incorporated into present devices and appliances in the years to come. It is thought that piezoelectric energy and thermoelectric energy (thermoelectricity being generated by ambient heat, such as that present in the human body) could be used for powering important medical implants such as the modern-day pacemaker.

Electroactive polymers (EAPs) and Radio-Frequency Identification tags (RFID) are other exciting developments - EAPs may become replacement artificial muscles both in humans and in robotics, whilst RFIDs, which are already used as tracking devices in animals and for storing identification in passports, may lead to better personal security as well as rapid information transfer in hospitals and other emergency situations.