The Technology of Thermionic Energy Conversion

The Process

Thermionic energy conversion is a method of direct energy conversion where heat is directly converted to electricity with no moving parts. This works by getting a metal hot enough to boil off its own electrons. These electrons then traverse a small gap through a cesium plasma where they are collected on the other side. The only way for the electrons to get back to their starting point is to travel through a load and the system looks like a heat-powered, DC battery.


The process of thermionic conversion has been known for almost 100 years but it was not until the 1950s that it was pursued seriously. At that time the US and the former Soviet Union began extensive development of thermionic nuclear reactors for space due to the technology’s high reliability, compactness, and power density. This research culminated in the flight of two, fully operational 5kW electric thermionic reactors by the Soviet Union in the late 1980s. However, with the termination of space nuclear power programs in the 1990s, much of the thermionic converter development halted completely and the technology never found a foothold in terrestrial applications; despite being proven extensively in combustion-fired and concentrated solar systems.


We are adding new materials, novel converter designs, and advanced manufacturing techniques to the proven cesium thermionic converter of the 1970s. Our innovations can offer improved power density, increases efficiency, and drastically reduced cost compared to previous generations. Our devices are specifically designed to be manufactured by the thousands at a time; allowing thermionic converters to be commercially viable for the first time in history.

Key Numbers

We are in the process of manufacturing our first production units. These devices are expected to have an efficiency of 8-10%, power density of 10W/cm^2, and an operational lifetime of 2-3 years at a temperature of 1700K.

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