Science: Modest energy generation linked to outer space cold

A Science article describes a Stirling engine that is powered by an energy-creating contraption with the engine mounted on it. The contraption, which is super simple in design, emits energy at Earth's surface warmth to the super cold of low-energy space. It has two layers, a top and a bottom layer. Energy at the Earth's surface is transmitted to space by the contraption's top surface, which is painted with a coating that efficiently emits infrared light (heat) into space. The emitted light has a wavelength range of 8–13 μm, which is in the “atmospheric window”. Light in that wavelength range can escape through the atmosphere to outer space rather instead of being re‑absorbed.  

In other words, the contraption passively sends Earth heat directly into space cold by sending out heat energy in the form of light. As heat is emitted from the top plate, it cools down. That creates a temperature difference between the cool top and warm bottom plates. The Earth keeps the bottom plate warm and light emission keeps the top plate cool. 

A Stirling engine then converts a temperature difference between its top cold and bottom warm plates into mechanical work by cyclic compression and expansion of a working gas between the engine's reservoirs. In this setup, the “cold of space” enters only via radiation: energy leaves the top plate as mid‑infrared photons into space, lowering its temperature relative to the ground. That sustains the heat gradient that keeps the Stirling cycle running.

Sounds nutty, right? Yeah, but it isn't. This thing actually works.

That temperature differences >10°C between the two plates are sustained during most months of the year. That is enough difference to generate of >400 milliwatts per square meter of mechanical power by the Stirling engine. A theoretical >6 watts per square meter is the upper limit of how much power can be produced this way, so this early version might be amenable to major efficiency increases. For comparison, modern silicon solar panels typically produce on the order of 150–230 watts per square meter under full noon sun.

The researchers tested the contraption for air circulation, and got an air flow of >0.3 meters per second with a potential volumetric flow rate that greater than 5 cubic feet per minute (cfm). That amount of air flow is enough for CO₂ circulation in greenhouses and for thermal cooling in residential buildings.

Stirling engine mounted on the 

center of the two plates

How a Stirling engine runs

Blue = cool

Red = warm

Stirling engine showing its simplicity. Unlike the steam engine or internal combustion engine, it has no valves or timing train. The heat source (not shown) would be placed under the brass cylinder.

This can be scaled up, but the realistic ceiling is modest power densities of ~3-6 watts per square meter. It will thus be viable in niche mechanical uses, not grid‑scale power generation. Global weather modeling shows the best radiative power densities will be attained in arid regions, high plateaus, and some Antarctic conditions. That suggests arrays of such engines could be deployed over fairly large areas such as rooftops, greenhouses, and remote sites.

By Germaine: Fascinated by the idea of linking Earth's warmth to the cold of space by transmitting heat through the atmosphere -- very cool idea, so to speak