Nano-rectennas for heat-to-electricity conversion

This project addresses a new technology to convert radiant heat to electricity, using large arrays of electronic nano-devices known as nano-rectennas. We envisage their use in micro (also known as domestic) combined heat-power (CHP) systems, converting part of the heat generated by the burner into electricity. Unlike thermoelectric devices, our proposed energy converters are neither in physical contact with the hot source, nor require materials with a high toxicity or strict disposal regulations. Our rectennas are fabricated using "green" materials, and are based on common metals (e.g., titanium, platinum and gold), carbon (in the form of graphene) and non-toxic highly-stable organic layers.

The micro, or domestic, combined heat power system (mCHP) is relatively new technology which enables local generation of both heat and electricity by burning gas - effectively replacing the old boiler. A report commissioned to Ecuity Consulting LLP by the major UK energy players and published in 2013 [available at www.ecuity.com] found that mCHP is the most cost-effective method for using gas, and it is uniquely placed for underpinning the UK policies aiming to the 2050 decarbonisation target.

Currently, the gas-to-electricity conversion is achieved using quite bulky systems such as fuel cells, or Stirling engines driven by a gas burner, which require maintenance and/or have moving parts. The only compact, maintenance-free solid-state technology is thermoelectric generation, but, apart from the low efficiency, requires toxic materials which are difficult to dispose of.

In this project, we propose the conversion of radiant heat to electricity using novel electronic nano-devices called nano-rectennas. A gas burner is utilised to heat water using a conventional heat exchanger, while heat radiated by the burner is collected by the nano-rectennas and converted to electricity. Nano-rectennas will be manufactured on a flexible sheet, which can be easily fitted on gas burning systems. Preliminary estimates on the amount of power radiated indicate that it will suffice to power domestic premises.

The main challenge of the project is the fabrication of nano-rectifiers operating at infrared frequencies on large area with high yield, and their connection to the micro-antennas which collect the radiation. Recently, we have experimentally demonstrated a low-efficiency proof-of-concept with a source temperature ranging from 280 C to 700 C [Y. Pan, C. V. Powell, A. M. Song and C. Balocco, Appl. Phys. Lett. 105, 253901 (2014)]. This proposal aims to address the conversion efficiency shortcomings and develop a cost-effective prototype. The fabrication of the nano-rectifiers will be approached with two complementary device concepts: the first based is based on a new type of metal-insulator-metal (MIM) diode, named the self-assembled monolayer diode (SAMD), and the second based on ballistic rectification in graphene, called the graphene ballistic rectifier (GBR).

The generation of electricity using micro combined heat and power systems (mCHP), has been highlighted as the most effective technology for using gas in domestic generation by a recent report commissioned to Ecuity Consulting LLP. A relatively new technology, mCHP has been recently heavily advertised by the major energy-industry players, and it is now an eligible measure under the UK Government's Green Deal scheme, and also eligible for the feed-in tariff.

Despite the promises offered by this technology, current mCHP systems rely on traditional gas-to-electricity conversion devices, such as fuel cells and Stirling engines driven by gas burners. Our alternative, and innovative, approach could dramatically simplify the integration of the heat-to-electricity converters into the design gas burners, which would ultimately reduce costs. Both the end users and manufacturers will thus benefit from it: the former will have access to a more affordable system and gain financial benefit from the feed-in tariff, the latter from the establishment of a larger customer base which is well supported by the UK Government.

In year 2, Q3, we will organise a workshop hosted by Durham University to bring together larger boiler and mCHP manufacturers with companies from the electronic sector, who have the necessary facilities to scale-up our technology to commercial requirements. This workshop will expose the boiler and mCHP industry to a technology they may be unaware of, as well as create business opportunities among the attending partners. This workshop will be organised with the help of Durham University's Business & Innovation Services (DBIS) which is responsible for the facilitation of several projects including knowledge transfer partnerships and secondments, business partnerships with industry, Durham's Enterprise Incubator and the regional blueprint business planning competition. DBIS has an excellent track record in business engagement and research commercialisation; a prime example of this pathway in action is the recently floated nanotechnology spin-out company, Applied Graphene Materials. In less than three years, the DBIS team was able to provide the essential support required to convert an idea into a multi-million listed company.

We will also engage closely with the activities of the Durham Energy Institute (DEI). DEI supports and produces research that tackles the societal aspects of energy technology through a unique interdisciplinary approach. The DEI has developed into a leading UK energy research institute that is differentiated from others on the basis of its focus on both the social and technical aspects of energy. The DEI was responsible for the launch of a multidisciplinary Centre for Doctoral Training (CDT) in Energy (2009-14) funded by EPSRC.DEI addresses energy challenges collaboratively through strong partnerships with industry, international partners, governments, community groups and other academic institutions. This focus on industry and society is reflected in the membership of its advisory board that includes the energy industry (Dong Energy, Eaga and Narec), and advisors of the national government (UK Fuel Poverty Advisory group). The broad range of expertise within the DEI has led to MPs, including the Secretary of State for Energy and Climate change, visiting and consulting the DEI on a range of energy issues. With the support of DEI, we are thus in the unique position to pitch our technology to the key players in the UK and European energy arena, raising its awareness in potential industrial partners.