Energy Resilient Manufacturing 2: Enabling Practical TPVs for Waste Heat Recovery

An efficient, practical and cost-effective means for directly converting heat into electricity is a very appealing concept. In principle, thermo-photovoltaic (TPV) cells could form the critical component of various systems for generating electricity from different types of heat sources including combustion processes, concentrated sunlight, waste process heat, and radio isotopes. This opens up a wide variety of possibilities for technology uptake and so TPV systems can be envisaged for use in applications ranging from small power supplies to replace batteries, to large scale co-generation of electricity.
However, existing TPV cells are based on GaSb and are spectrally matched to heat sources at temperatures of ~1800 oC which limits their practical implementation and widespread uptake. GaInAsSb TPV cells with bandgap 0.53 eV have exhibited excellent performance with internal quantum efficiency near 95%. But, currently these are lattice-matched on GaSb substrates making them too expensive for practical implementation except in specialist high value or space applications. TPV development on larger format GaAs substrates will enable effective technology uptake through cheaper volume manufacturing of TPV cells. Consequently, there is a need to transfer the GaInAsSb cell architecture to GaAs.
In this project we shall build on existing UK based world class III-V semiconductor materials expertise to fabricate novel low bandgap InGaAsSb TPV arrays on inexpensive GaAs substrates, capable of efficient electricity generation from thermal waste heat sources in the range 500-1500 oC commonly encountered in industrial processes. These monolithic arrays will be validated on-site together with our industry partners at Pilkington and MPIUK (Tata steel). The project will demonstrate the next step towards fabrication of large area TPV arrays essential for the commercial viability of TPV heat recovery, and will enable their widespread implementation in a wide range of high energy consumption industries such as glass, steel and cement manufacture, oil/gas and energy generation.

We shall enable the development of efficient, affordable thermophotovoltaic (TPV) arrays for electricity generation from radiant waste heat resulting in major energy savings and reduction in CO2 emissions. The project will demonstrate the next step towards the commercial viability of TPV heat recovery, and will enable their widespread implementation in a wide range of high energy consumption industries such as glass, steel and cement manufacture. Productive use of waste heat by conversion into electricity offers obvious environmental and economic benefits. An extrapolation of NSGs findings would suggest a potential reduction of 0.15 GigaTons in the global annual emission of 37GigaTons (2014). This should be viewed in the context that the total CO2 output of UK industry in 2014 was 0.1GTons (DECC, Committee on Climate Change). Hence there is no doubt that the headline potential environmental gains possible with waste heat recovery technology are vast, and the impact of such technology can be maximised by mass deployment in China and emerging Asia. We also envisage wide-ranging impacts through; enabling development of new products and procedures that will generate major socio-economic benefits for the UK; scientific advancement leading to substantial generation of new knowledge as well as effective training and professional development of researchers.

After validation and appropriate IP protection we envisage that IQE together with CSC and CST would develop pilot production; since IQE has substantial epitaxy facilities and together with CST would be able to directly address the challenges in scaling up the existing technology from our initial single wafer concept, before moving towards larger array panels to realize the efficient and cost effective conversion of radiant heat into electricity. NSG Pilkington and MPIUK would become the primary adopters of the technology. This will stimulate a valuable new energy technology for the future which will have a significant impact on utilisation of waste heat and CO2 reduction in process industries. One cannot overestimate the attractiveness of accessibility to a 'home-grown' renewable energy industry in being able to attract future manufacturing inward investment to the UK in the light of predictions of the rising cost of energy.

Low bandgap TPV arrays will recover energy losses from waste heat and reduce CO2 emissions in many situations including; glass and steel manufacturing furnaces, oil and coal combustion, etc. More generally, there is interest in both miniaturizing TPV systems for powering small electronics systems, and scaling-up TPV for large applications such as power plants, submarines and microgeneration in buildings. Small TPV-based systems could replace battery power supplies for communication devices, laptop computers, and portable lighting. Other advantageous features are: TPV systems are modular, quiet, safe, pollution-free, and low-maintenance. The uptake of current technology is limited by cost, size and complexity. We shall foster UK competitiveness and develop impact in these areas through direct interaction with our industrial partners.