Nonreciprocal STPV Emitter to Eliminate Solar Back Emission
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Solution Overview
Problem
Traditional solar thermophotovoltaic (STPV) systems suffer from intrinsic inefficiencies due to reciprocal optical components, leading to unavoidable thermal emission towards the sun, which cannot be harvested and results in significant energy loss.
Innovation Solution
A nonreciprocal solar thermophotovoltaic (NSTPV) system with an absorber and an emitter having nonreciprocal radiative properties, where the emitter absorbs heat from one side and emits radiation from another, effectively redirecting all photons to a photovoltaic cell, eliminating back emission towards the sun.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a reciprocal optical component is used as the intermediate layer in STPV, then the system structure is simple and follows Kirchhoff's law, but thermal emission towards the sun cannot be eliminated resulting in significant energy loss
Solution Approach 1:
The patent applies asymmetry by using a nonreciprocal optical component where the optical properties differ for different directions of propagation. Specifically, the component has different transmission and emission characteristics for photons traveling toward the sun versus photons traveling toward the photovoltaic cell, enabling directional control of thermal radiation to eliminate back emission while maintaining structural feasibility
Solution Approach 2:
The patent changes the fundamental parameter of optical reciprocity by employing materials or structures that violate Kirchhoff's law of thermal radiation. This involves using magneto-optical materials or nonreciprocal photonic structures that exhibit different emissivity and absorptivity for different propagation directions, thereby transforming the system from reciprocal to nonreciprocal operation
2Loss of energy
If spectral control of emissivity is applied to the absorber, then emission towards the sun can be reduced, but the back emission cannot be completely eliminated due to reciprocity
Solution Approach 1:
The patent inverts the conventional approach by placing the nonreciprocal optical component on the photovoltaic cell side rather than the absorber side. This inversion allows the component to selectively transmit photons from the absorber to the cell while blocking thermal emission from the cell back to the absorber, achieving complete elimination of back emission through reverse directional control
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The NSTPV system achieves efficiencies significantly higher than the Shockley-Queisser limit, reaching the Landsberg limit of 93.3%, by eliminating entropy production and maximizing photon flux to the photovoltaic cell, thereby enhancing energy conversion efficiency.
Implementation Method 1
The front side of the intermediate layer, i.e., the side facing the sun, is designed to absorb all photons coming from the sun. In this way, the solar energy is converted to the thermal energy of the intermediate layer and elevates the temperature of the intermediate layer.
Implementation Method 2
The backside of the intermediate layer is designed such that it only emits photons that have higher energy than the bandgap of the STPV cell.
Implementation Method 3
a photovoltaic cell configured to convert radiation from the emitter to electrical energy
Data Source
AI summary
A nonreciprocal Solar thermophotovoltaic (STPV) system includes an absorber configured to absorb broad-spectrum solar radiation and generate heat an intermediate emitter, and a single-junction photovoltaic cell configured to convert solar radiation to electrical energy. The intermediate emitter includes nonreciprocal radiative properties. The nonreciprocal radiative properties include absorbing light from the front side but only emitting light to the backside.