Bid document

Request for Information (RFI)

DARPA-SS-27-01

Solid-State Energy Conversion from Heat to Electricity
Responses Accepted: Until 4:00 p.m. (Eastern) on November 23, 2026 Point of Contact: Mike McDonald, Program Manager, DARPA/DSO Email Address: [email protected]
The Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) is requesting information on the current state of the art and technological limitations of solid-state direct thermal-to-electric energy conversion technologies. We define solid state energy conversion as systems that convert a temperature differential directly into electrical energy without utilizing mechanical moving parts (e.g., pistons, turbines, or rotary alternators). This RFI seeks to identify the best possible solid state heat engine performance across a wide operating temperature range, factors that limit performance, and the most attractive use cases if these highly efficient solid state heat engines could be made today. This survey of limits, challenges and use cases will identify opportunities for research and development to inform potential program(s) in this area.

BACKGROUND

Much energy generation today relies on converting heat to electricity in heat engines using thermodynamic cycles (e.g., Brayton, Stirling, and Rankine cycles). These systems are well characterized and >50% efficient at utility scale (gigawatts, GW) but achieve more modest efficiencies of 30-40% in the strategic (megawatts, MW) and 15-25% in the tactical (kilowatts, kW) power ranges. Mechanical systems introduce vulnerability to friction, seal wear, vibration, lubrication and more, presenting complex maintenance requirements. In contrast, solid-state direct energy conversion uses electronic, photonic, or electrochemical transport to generate electricity directly from a heat source with no moving parts. In principle this allows for higher reliability, favorable scalability across power levels, and near instantaneous start-up and responsiveness. Energy conversion directly from heat to electricity offers the potential for high theoretical efficiencies, due to the ability to leverage operating temperatures far above mechanical creep limits, increasing the Carnot ceiling. Direct thermal-to-electric conversion methods date to the 1800s, and development efforts surged in the mid-late 20th century, yet realized efficiencies have remained stubbornly low, on the order of 3-7% for thermoelectric devices and 5-15% for thermionic systems despite higher theoretical