Lonnie Johnson, a nuclear engineer who holds more than 100 patents, says he can achieve a conversion efficiency rate that tops 60 percent with a new solid-state heat engine. It represents a breakthrough new way to turn heat into power.

The Johnson Thermoelectric Energy Conversion System has no moving parts. It’s similar to a fuel cell: it circulates hydrogen between two membrane-electrode assemblies. Unlike a fuel cell, however, it is a closed system. No external hydrogen source. No oxygen input. No wastewater output. Other than a jolt of electricity that acts like the ignition spark in an internal-combustion engine, the only input is heat.