Energy harvesting (EH) is also known as power harvesting or energy scavenging. It is the process by which ambient energy is captured and, if necessary, stored to provide electricity for small autonomous devices, such as satellites, laptops and nodes in sensor networks. Usually the power is stored as electricity but sometimes it is stored as other energy as with springs storing mechanical energy later converted to electricity as needed. Energy harvesting is a substantial business already and it will become a multi billion dollar business within ten years because, increasingly, it hits so many of the hot buttons - environmental, safe, secure, affordable, more convenient, brand enhancing and making new things possible. So far, the main commercial successes include such things as photovoltaics on space vehicles, road furniture and consumer goods, electrodynamics in bicycle dynamos and wristwatches and piezoelectrics in light switches, indeed many forms of EH in building controls.
Energy harvesting is used for many reasons from providing long life, maintenance free devices to saving cost. Examples are given below:
Table Examples of the primary motivation to use energy harvesting by type of device
The environmental argument
Primarily, the environmental argument for energy harvesting is not saving power stations and their attendant pollution directly. After all, we define EH as powering small electronic devices not acting as a heavy power source for heating, motive power and so on. Information and communication technology ICT represent only two percent of the energy consumption in the world but they can lead to huge environmental savings if deployed more widely and appropriately to optimise heavy power creation and handling by utilities and others. Most notably, 38% of energy is consumed in buildings but it would be much less if electronic controls were cheaper and easier to install. More affordable building controls of longer life are the focus of most of the 70+ companies in the EnOcean energy harvesting alliance. For example, EnOcean, presenting at a recent event, described how they have installed 4200 wireless and battery-less light switches, occupancy sensors and daylight sensors in a new building construction in Madrid. These are powered by energy harvesters and embedded in the building. This saved 40% of lighting energy costs by automatically controlling the lighting in the building, 20 miles in cables, 42,000 batteries (over 25 years) and most of the cost of retrofitting. Batteries usually contain poisons, so the environmental benefits are wide ranging and substantial. Indeed EH is likely to replace many of the 30 billion button batteries sold yearly, many containing poisons. That will involve the exciting new laminar rechargeable batteries and supercapacitors for storage of the harvested energy and sometimes the electronics will accept the input from energy harvesting with no storage at all.