Impacts of propagating, frustrated and surface modes on radiative, electrical and thermal losses in nanoscale-gap thermophotovoltaic power generators

Abstract

The impacts of radiative, electrical and thermal losses on the performances of nanoscale-gap thermophotovoltaic (nano-TPV) power generators consisting of a gallium antimonide cell paired with a broadband tungsten and a radiatively-optimized Drude radiator are analyzed. Results reveal that surface mode mediated nano-TPV power generation with the Drude radiator outperforms the tungsten radiator, dominated by frustrated modes, only for a vacuum gap thickness of 10 nm and if both electrical and thermal losses are neglected. The key limiting factors for the Drude- and tungsten-based devices are respectively the recombination of electron-hole pairs at the cell surface and thermalization of radiation with energy larger than the cell absorption bandgap. A design guideline is also proposed where a high energy cutoff above which radiation has a net negative effect on nano-TPV power output due to thermal losses is determined. It is shown that the power output of a tungsten-based device increases by 6.5% while the cell temperature decreases by 30 K when applying a high energy cutoff at 1.45 eV. This work demonstrates that design and optimization of nano-TPV devices must account for radiative, electrical and thermal losses.

Solar thermophotovoltaics: reshaping the solar spectrum

“…The third kind of loss comes from increased PV diode temperatures, which suggests a need for effective PV thermal management [109]. The combined effect of the three kinds of losses has been studied by Bernardi et al [84]. A unifying solution comes from spectral shaping of the radiator.…”

“…The advantage of this method is that it captures the physical nature of thermal emission from fluctuating thermal currents, and models the emission, propagation and absorption of thermal radiation between bodies [81]. This makes fluctuation thermodynamics particularly important to study near-field thermal energy transfer that is the essence of near-field TPVs (NFTPVs) [81][82][83][84].…”

“…In contrast with far-field TPV power conversion, bringing the emitter closer to the PV cell (nano-or microscale separation distances) allows tunneling of evanescent surface modes. These new channels of energy transfer could potentially enhance thermal emission and overcome the blackbody limit [84,97,98].…”

Near-field thermal electromagnetic transport: An overview

“…In the absence of objects, the (total) electric field is simply equal to the incident field. In the special case that thermal emission by the objects is negligible compared to the incident field, the fluctuating current J fl vanishes and the volume integral equation for the electric field reduces to: (18) which is the volume integral equation used for solving classical electromagnetic scattering problems [54].…”

“…The growing interest in near-field thermal electromagnetic transport is driven by numerous potential applications to thermophotovoltaic power generation [11][12][13][14][15][16][17][18], localized radiative cooling [19], nanomanufacturing [20], thermal emission control [21][22][23] and thermal rectification [24][25][26][27]. In terms of modeling, closed-form solutions of near-field thermal electromagnetic transport have been derived for special geometries such as one-dimensional layered media [28,29], two large spheres [30][31][32], a sphere and a surface [33,34] and an arbitrary number of nanoparticles modeled as electric point dipoles [35,36] using the method of dyadic Green's function.…”