Limit of efficiency for photon-enhanced thermionic emission vs. photovoltaic and thermal conversion

Abstract

a b s t r a c tConversion of sunlight by photon-enhanced thermionic emission (PETE) combines a photonic process similar to photovoltaic cells, and a thermal process similar to conventional thermionic converters. As a result, the upper limit on the conversion efficiency of PETE devices is not the same as the ShockleyQueisser (SQ) limit that corresponds to the bandgap of the absorbing material, nor to the Carnot efficiency corresponding to its temperature. Here we analyze the upper limit on efficiency of ideal PETE devices in several possible configurations, in comparison to ideal photovoltaic cells and ideal solar thermal converters. Isothermal PETE converters are shown to be restricted to less than the SQ limit, but non-isothermal devices can exceed this limit. The limit of efficiency increases with the flux concentration reaching for example 52% at concentration of 1000 suns. Spectral splitting leads to a modest increase in conversion efficiency to 56% at 1000 suns. Addition of a secondary thermal cycle increases the efficiency limit for all PETE configurations, up to 69.8% and 70.4% for the cases of isothermal PETE and a dual bandgap PETE system at 1000 suns.

Selected methods of converting solar energy into electricity - comparative analysis

“…In the case of PETE cells, the cathode work function ϕ K should equal 1.4 eV, similarly as PV cells [6,8]. The work function of anode ϕ A should be as small as possible to obtain the maximum output voltage.…”

An analysis of solar energy conversion systems based on photon and thermal processes

“…Various methods have been proposed for overcoming these technological barriers in the process of designing thermionic diodes that convert thermal energy to electricity (Dragoman & Dragoman 2007, Bell 2008, Snyter 2008, Schwede et al 2010, Baranowski et al 2012, Meir et al 2013, Segev et al 2015.…”

Konwersja Energii Słonecznej W Elektryczną Z Wykorzystaniem Fotonowo Wzmocnionej Termoemisji Elektronowej

“…Dla ogniw PETE wskazane jest by praca wyjścia ϕ K katody wynosiła 1,4 eV, podobnie jak w przypadku ogniw PV [1, 3,7], natomiast praca wyjścia anody ϕ A powinna być jak najmniejsza aby uzyskać maksymalne napięcie wyjściowe. Na Rys.…”