Using sintered lunar regolith for heat storage, Harbin Institute of Technology researchers demonstrate how a closed Brayton cycle combined with thermoelectric generators could provide uninterrupted electricity for future moonbases
The Moon presents an uncomfortable truth for anyone hoping to live there: its night lasts approximately 354 hours. When the Sun sets on a lunar outpost, temperatures plunge below minus 170 degrees Celsius for two full Earth weeks, and with the darkness goes the primary source of energy. While photovoltaic technology has served space missions well, its inability to generate power during the long lunar night becomes an existential challenge for permanent habitation. Nuclear options are under development, but these carry complexities of launch safety and thermal management. What if the solution lies not in splitting atoms, but in the regolith beneath astronauts' feet?
Published in the journal Planet (Volume 2 Issue 1), a team from the Harbin Institute of Technology led by Academician Hongyuan Mei and Professor Teng Fei has proposed an elegant answer. Their work examines a hybrid power generation system that couples a closed Brayton cycle with thermoelectric generators, using sintered lunar regolith as a thermal battery. During the two-week lunar day, excess solar energy heats a mass of sintered regolith; when darkness falls, that stored heat drives a turbine, with thermoelectric devices scavenging remaining thermal energy when temperatures drop too low for the main turbine to operate.
Using a helium-xenon mixture as the working fluid, the researchers tracked system performance across an entire lunar day. Their results show the closed Brayton cycle thermal efficiency reaches 31.4 percent at lunar noon, when solar radiation peaks at approximately 1365 watts per square meter. However, the cycle cannot operate continuously; during low-solar periods, the turbine generates insufficient power to overcome the compressor's demands. This is where thermoelectric generators become critical. With the cycle's maximum operating pressure set at 600 kilopascals—identified as the optimal balance between operating duration and power output—the combined system generates electricity continuously throughout lunar daytime. When the cycle cannot operate, thermoelectric generators alone produce power, reaching a maximum of 1.8 kilowatts at 0.67 percent efficiency.
While this efficiency appears low compared to terrestrial plants, the researchers offer a compelling explanation: unlike conventional applications where heat transfers through conduction, the lunar system rejects heat to deep space through radiation. The thermal resistance of radiative transfer is so substantial that most of the available temperature difference occurs between the radiator surface and space itself, leaving only a small fraction across the thermoelectric elements—a fundamental insight for waste heat recovery in vacuum environments.
Perhaps most intriguing is the use of sintered lunar regolith as a heat storage medium. With a density of 3000 kilograms per cubic meter and specific heat capacity of 840 joules per kilogram-kelvin, the 10-tonne thermal storage unit absorbs heat during the day and releases it throughout the night. The mass flow rate of the working fluid critically determines how long the system operates after sunset. At flow rates below 0.2 kilograms per second, the cycle functions across the entire lunar night, with thermal efficiency reaching 37.52 percent. Higher flow rates extract heat more rapidly, generating more power initially but exhausting the thermal reservoir sooner—a classic engineering trade-off between peak output and operational duration.
The work also addresses practical engineering considerations. Increasing thermoelectric generator stages from one to four improves power output—the four-stage configuration achieves 1.8 kilowatts maximum—but at a substantial mass penalty: 237.14 kilograms versus 56.24 kilograms, an increase of approximately four times. During the lunar night when the cycle becomes inoperable, the four-stage thermoelectric generator continues generating power, starting at approximately 118 watts and declining as the thermal storage unit cools.
What distinguishes the HIT team's approach is its elegant minimalism. It requires no specialized materials shipped from Earth at prohibitive cost, no nuclear fuel with attendant safety concerns, and no moving parts beyond those already present in a conventional Brayton cycle. The sintered regolith serves simultaneously as radiation shielding, thermal mass, and construction material—a multi-functional solution aligning perfectly with the in-situ resource utilization principles that will define sustainable space exploration.
The publication of this research in Planet signals the growing maturity of lunar engineering. Where earlier work focused on whether humans could survive on the Moon, current research asks how they can live there productively. Continuous power is not merely a convenience; it is the foundation for life support, communications, scientific instrumentation, and processing local resources into water, oxygen, and fuel. Without electricity through the long lunar night, a moonbase becomes little more than an extremely expensive camping trip.
As the HIT team notes, optimal system parameters—operating pressure, flow rate, thermoelectric generator stage count—must ultimately be selected according to practical mission needs. A science outpost may prioritize longevity over peak power; a resource processing facility may make the opposite choice. The value of their work lies not in prescribing a single solution, but in mapping the design space within which engineers can make informed decisions. When the first permanent moonbase finally switches on its lights and watches them stay on through the 354-hour night, somewhere in its thermal management system will be the legacy of this research: a reminder that sometimes the best way to solve a space problem is to use what is already there.
DOI:
10.15302/planet.2025.25006