SELECTIVE COATINGS FOR POROUS MEDIA COMBUSTION-BASED THERMOPHOTOVOLTAICS
Creators: name: Gentillon Molina, P
name: Taylor, RA
name: Conibeer, G
Publisher: name: UNSW Sydney
Year: 2017

description: Thermophotovoltaic (TPV) systems represent an indirect, and potentially highly efficient, means to convert primary energy into electricity. These technologies can be designed as portable devices, which are able to provide high power density using a variety of heat sources, such as hydrocarbon fuel, solar, nuclear and waste heat. Moreover, efficiencies over 60% can (theoretically) be achieved in the case of high emitter temperatures, which makes this technology quite attractive for military, space, or any stationary/protable electrical generation applications [1]. The working principle of TPV technology is shown in Fig. 1. The concept is based on using an energy source to heat up an absorber/emitter material which then re-emits the energy towards the photovoltaic (PV) cells. With clever design it is possible to tune of the re-emitted spectrum to match with the PV cell’s bandgap [2], i.e. releasing photons with energies higher than the bandgap energy level illuminate the PV cell. One of the major challenges of TPV systems is reducing the waste heat. A large portion of the input energy is typically wasted by convection in the flue gases. One potential way to create these temperatures involves using porous media combustion (PMC), due to the intense heat exchange from the combustion zone throughout the solid, enabling higher temperatures at outer (non-convective) surface of the solid matrix. To reduce un-useful radiative emission, the porous media matrix surface can be coated with a film to produce an emitter that matches to the spectral response to a GaSb PV cell, which has a bandgap energy at λ_gap=1700 [nm]. In this work, we explore key low cost selective coating formulations over alumina (Al2O3) and silicon carbide (SiC) porous foam samples for this application. As such, different powders with selective emitter properties, such as erbia (Er2O3), ytterbia (Yb2O3), magnesium oxide (MgO) and nickel oxide (NiO) are spray and dip coated onto the porous mediums. Since these rare earth materials have a narrow emission bands at different excited state energy levels which are shown in Table 1 [3], it is hypothesised that they will serve as suitable selective emitters. In addition, a 2 wt.% NiO-doped MgO emitter at 1404 [°C] have shown a peak at 1400 [nm] [4]. Using an integrating sphere spectrophotometer, this study will measure total hemispherical reflectance to determine the emissivity of different combinations of these materials over the porous foams in order to have a coating with a high and broad emissivity in the range above the bandgap energy, but low emissivity beyond the bandgap. Finally, the findings of this research will inform and help the development of porous media-based TPV. REFERENCES [1] D. L. Chubb, Fundamentals of thermophotovoltaic energy conversion. Amsterdam, Netherlands; Boston; Oxford, UK: Elsevier, 2007. [2] A. Luque and S. Hegedus, Eds., Handbook of photovoltaic science and engineering, 2. ed., [Fully And updated]. Chichester: Wiley, 2011. [3] C. Ferrari, F. Melino, M. Pinelli, and P. R. Spina, “Thermophotovoltaic energy conversion: Analytical aspects, prototypes and experiences,” Appl. Energy, vol. 113, pp. 1717–1730, Jan. 2014. [4] L. G. Ferguson and F. Dogan, “A highly efficient NiO-Doped MgO matched emitter for thermophotovoltaic energy conversion,” Mater. Sci. Eng. B, vol. 83, no. 1–3, pp. 35–41, Jun. 2001.
description: 9th International Conference on Porous Media &amp; Annual Meeting; Rotterdam, Netherlands; 2017-05-08 - 2017-05-11