Design and global optimization of high-efficiency thermophotovoltaic systems

Abstract

Despite their great promise, small experimental thermophotovoltaic (TPV) systems at 1000 K generally exhibit extremely low power conversion efficiencies (approximately 1%), due to heat losses such as thermal emission of undesirable mid-wavelength infrared radiation. Photonic crystals (PhC) have the potential to strongly suppress such losses. However, PhC-based designs present a set of non-convex optimization problems requiring efficient objective function evaluation and global optimization algorithms. Both are applied to two example systems: improved micro-TPV generators and solar thermal TPV systems. Micro-TPV reactors experience up to a 27-fold increase in their efficiency and power output; solar thermal TPV systems see an even greater 45-fold increase in their efficiency (exceeding the Shockley-Quiesser limit for a single-junction photovoltaic cell).

Integrated photonic crystal selective emitter for thermophotovoltaics

“…1 Several materials have been proposed for selective emission, including plasmonic metamaterials, 2-4 refractory plasmonic structures, 5 rare earth materials, [6][7][8] and photonic crystals (PhCs). [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] However, realistic selective emitters still have residual low energy emission near the bandgap that can considerably limit the conversion efficiency. Significant improvement can be achieved by the use of cold-side PhC filters, including plasma filters, quarter-wave stacks, 25 and rugate filters.…”

“…[27][28][29][30][31][32] In order to achieve sufficient photon recycling, proximity between the emitter and filter is required. 33 In the typical cold-side filter configurations, where the filter is attached to the PV diode as an entire receiver, this requirement can be quantified by the view factor from the emitter to the receiver, which is the probability that emitted photons reach the receiver. Certain strategies, such as micro-gap or nanoscale-gap TPV, in fact require extremely high view factors to achieve evanescent coupling.…”

“…This approach also sidesteps the difficulties of the nanoscale-gap regime, since no gap is required. Photon recycling and reabsorbed power can therefore no longer be considered as a perturbation; 33 instead, new physical effects should arise in this nonperturbative regime. Finite difference time-domain (FDTD) 38 and current transport simulations have shown that an IPSE enables system conversion efficiencies to reach up to 41.8%, using the realistic model for GaSb PV diodes, by nearly eliminating sub-bandgap emission.…”

“…45 Then the current-voltage ðJ − VÞ relation for TPV cells is calculated from the emittance spectrum assuming zero series resistance, as in previous work. 33 The effect of finite series resistance is considered later in this work. The power output is then calculated by solving for the maximum power point via dðJVÞ∕dV ¼ 0.…”

“…Based on the experimental performance of metalorganic vapor phase epitaxial grown low-bandgap III-V PV diodes from Lincoln Laboratories, an average external quantum efficiency of 82% is assumed. 33 The thermal power input is calculated as the total thermal emission less the power reabsorbed by the emitter. The system conversion efficiency η is then finally given as E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 0 1 ; 1 1 6 ; 4 3 7…”