Photon Enhanced Thermionic Emission (PETE)

Solar conversion is usually divided into two classes: quantum-based conversion, such as photovoltaics (PV), and thermal conversion, such as solar dishes and power towers. Because these two processes operate at very different temperatures, they have remained separated. While traditional fossil fuel power conversion technology can enjoy the benefits of a combined cycle approach to reach greater than 50% conversion efficiencies, this has not been possible for solar technology. An ideal combination would be to first absorb sunlight in a PV panel which could operate at very high temperature, and use the waste heat from this process to drive a thermal engine. However, due to PV physics they cannot operate at the high temperatures necessary for thermal systems. Here we describe a new physical mechanism that combines both photon and thermal energy sources, and can operate at high temperatures (200-1000ºC).  This new mechanism, called photon-enhanced thermionic emission (PETE), uses similar materials as traditional solar cells, yet the mechanism is fundamentally different. Theoretical estimates of the PETE process show it can be more efficient than a single junction solar cell, yet its true importance is that it could work in tandem with a thermal engine. Estimated efficiencies of combined cycles reach over 50%, though are still quite a ways from being demonstrated. We will show the first proof-of-concept results from the PETE process showing the mechanism is valid, and discuss what the current obstacles to obtaining high efficiency are.

Speaker: Nick Melosh, Department of Materials Science and Engineering, Stanford University