SkyCool cools below ambient by radiating heat through the sky window to deep space

Air conditioning is a big slice of building energy and the main driver of peak electricity demand, so a way to cool without running a compressor would change the load curve.

A Stanford team built a seven-layer HfO2/SiO2 photonic structure that both reflects nearly all sunlight and emits heat through the atmospheric transparency window, so it loses energy to deep space even in the day.

On a rooftop under direct sun the cooler settled about 4.9C below ambient with a cooling power of 40.1 W/m2, a daytime result the field had not previously hit, and SkyCool Systems was spun out to make panels from it.

Radiate heat to deep space through the sky's window

It converts an unlimited heat sink — outer space — into a usable resource for buildings.

The design is passive: no moving parts, no refrigerant, no daytime power input.

It works at the hottest hour, when demand and prices peak, not just at night.

The multilayer film is a manufacturing problem, not a resource problem, so it can scale.

Find a free heat sink nobody is using — the cold night sky actually works at noon.

SkyCool Systems commercialized the panels for refrigeration and building sub-cooling, raising a $5.0M seed round in 2023 and drawing ARPA-E support; the underlying physics remains a reference point for daytime radiative cooling research.