Electronic nanodevices for energy harvesting: a novel approach to thermal-energy conversion

Every hot body emits a large power in the form of infrared radiation. Electronic equipment, appliances, car exhausts and high-temperature industrial processes, can thus provide an untapped -and currently wasted- energy reservoir. The amount of power is startling: an object at a temperature of 600 C emits 33 kW/m2, while an adult human body approximately 100 W. The proposed work explores the application of a rectenna (RECtifier + antENNA) for harvesting this thermal radiation and converting it into useable electrical power, with potential to develop a disruptive technology. Rectennas consists of a microantenna that captures infrared thermal radiation connected to rectifier, which converts the radiation to DC electrical power. The concept is not new, and it was already investigated by Brown in the 1960s at microwave frequency to transmit power wirelessly, with efficiencies above 80%. However, thermal radiation is located at much higher frequencies in the electromagnetic spectrum, tens of terahertz (THz), which means that the rectifiers must be more than ten thousand times faster. The rectifier proposed in this work is based on the self-switching nanodiode (SSD), a novel semiconductor nanodevice consisting of an asymmetric nanochannel, whose room-temperature operation in the THz range was pioneered by Dr Balocco. Planar microantennas will be integrated with an array of approximately 1000 SSDs connected in parallel, in order to reduce the internal resistance of the rectenna, and hence increase their output power. Because of their compact structures, slim form factor and absence of moving parts, electrical generators based on these new devices will find application in industrial waste-heat scavenging, and where space is at premium, such as smart sensors, mobile and combined heat-power (CHP) systems. For industrial applications, where space might not been a concern, the use of rectennas enables the recovery of the low-grade energy lost during high-temperature processes. The solid-state nature of these devices and their robustness requires little maintenance, and are easy to install. Smart sensors operating in an environment where hot bodies, or other sources of infrared radiation, are available, can take advantage of rectennas' compactness. Even if a low electrical power is converted, this is sufficient to intermittently power the sensor. Combined heat-power systems and microgeneration in general, can couple rectennas to recover the lost thermal power radiated by the gas burner assembly. A more ambitious application is indirect solar-energy conversion, where the heat stored in a medium during the day (such as molten salt at ~500 C) is used during the night to produce electrical power. Here, rectennas may provide an alternative solid-state approach to the steam-turbine technology currently in use.

* Social and economic impact
The academic and social benefits that will be generated as part of this proposal can be divided into two categories;
1. It will provide advancement in knowledge about ultra-fast electronic nanodevices for THz and mid-infrared applications, exploring novel structures integrated with microantennas.
2. It will establish a new experimental platform for characterising rectennas and their efficiency. This will also determine their viability for harvesting the thermal energy wasted in industrial processes as well as envisaging their application in microgeneration system.

The proposed approach to energy harvesting may develop into a disruptive technology. Investment in adventurous research in the field of renewable energy is of crucial importance to the UK to meet the 2050 CO2 reduction targets (as clearly highlighted in the recent RCUK energy report), and to strengthen the international profile and leading position of the UK, something that cannot be taken for granted in the long term (10-50 years), due to increasing international competition. Beside the main scope of the project, the development of fast electronic devices operating at tens of THz is critical for future communication systems, which will require a much higher transfer rates, and operate at THz frequencies, an area that EPSRC is expecting to grow in its portfolio.

* Outreach
The proposed research involved novel nanodevices with application in renewable energy, and, as such, it will certainly stimulate the curiosity of the general public. The project's outcomes will be disseminated to a wider public through the active outreach programs organised by the Durham University's Science Outreach Department and the Durham Energy Institute (DEI).

* People
This project will benefit directly the PDRA. She/he will have the opportunity to develop skills in fabrication and characterisation of electronic devices relevant to the UK industry, and work with state-of-the-art micro- and nano-fabrication techniques. Since this research covers areas of strategic importance in the EPSRC's portfolio and fits in general field of renewable energy, the gained experience will also benefit her/his career prospects.

* Renewable energy
This work focuses on a fresh approach to energy harvesting, with clear links to renewable energy. Dr Balocco will take advantage of the unique opportunities offered by the Durham Energy Institute, or DEI, to communicate the impact of outcomes. The DEI is a research institute that facilitates cross-disciplinary research with the ultimate aim of integrating energy science with society. This focus on industry and society is reflected in the membership of its advisory board that includes the energy industry, local government and advisors of the national government. DEI engages with both government and industry to disseminate knowledge regarding renewable energy, and it is through these opportunities that Dr Balocco would demonstrate the implications of the proposed research upon renewable energy and, once rectenna technology will be more mature, on industry.