What is energy harvesting?
The energy problem
Fossil fuels are finite and environmentally costly. Sustainable, environmentally benign energy can be derived from nuclear fission or captured from ambient sources. Large-scale ambient energy (eg solar, wind and tide), is widely available and large-scale technologies are being developed to efficiently capture it.
At the other end of the scale, there are small amounts of ‘wasted’ energy that could be useful if captured. Recovering even a fraction of this energy would have a significant economic and environmental impact. This is where energy harvesting (EH) comes in.
What is EH?
Energy harvesting, or energy scavenging, is a process that captures small amounts of energy that would otherwise be lost as heat, light, sound, vibration or movement. It uses this captured energy to:
- Improve efficiency – eg computing costs would be cut significantly if waste heat were harvested and used to help power the computer
- Enable new technology – eg wireless sensor networks
EH also has the potential to replace batteries for small, low power electronic devices. This has several benefits:
- Maintenance free – no need to replace batteries
- Environmentally friendly – disposal of batteries is tightly regulated because they contain chemicals and metals that are harmful to the environment and hazardous to human health
- Opens up new applications – such as deploying EH sensors to monitor remote or underwater locations
Successfully developing EH technology requires expertise from all aspects of physics, including:
- Energy capture (sporadic, irregular energy rather than sinusoidal)
- Energy storage
- Material science
- Systems engineering
Where can energy be harvested?
Energy is lost in every industrial process and everyday technology that you can think of, eg:
- Power stations – nearly all of the world's electrical power is generated by heat engines. These are gas or steam-powered turbines that convert heat to mechanical energy, which is then converted to electricity. Approximately two-thirds of the energy input is not converted to electrical power but lost as heat
- Computers and microwaves (in fact all our electronic gadgets) – lose energy through heat and/or vibration
How can we harvest waste energy?
Different types of waste energy can be captured using different EH materials. The most promising microscale EH technologies in development include:
- Vibration, movement and sound can be captured and transformed into electrical power using piezoelectric materials
- Heat can be captured and transformed into electrical power using thermoelectric and pyroelectric materials