Geometric Blackness — Shape-Based Light Trapping for Solar Absorbers

Directly relevant to this KB: a cheaper, coating-free way to make a high-absorptance solar-thermal absorber feeds the desorption heat that drives adsorption and absorption chillers. The project is run by the 601 Delaware roastery team (the sibling KB this wiki cross-links), aimed at sustainable cooling.

The core idea — two ways to make something black

There are two ways to make a surface black:

1. Material-based — pigments/coatings that absorb light chemically (selective paints, black chrome, etc.).
2. Geometric-based — shape that traps light through multiple bounces, regardless of the base material’s color.

“Geometric blackness” is the second: specially-angled cavities catch incoming light in repeated reflections so little escapes, producing blackness from geometry, not pigment. Natural and engineered examples cited: vinyl records, moth eyes, razor blades, and black-silicon solar cells — all dark by structure rather than dye.

The hypothesis and experiment

• Buckminster Fuller geometry: test whether 60° equilateral cavities create superior light-trapping vs flat or arbitrary-groove alternatives.
• Application: improve solar-thermal collectors — a better absorber raises collector efficiency, which is the heat source for heat-driven (adsorption/absorption) cooling.
• Method, staged by cost: from simple ~$65 cardboard prototypes up to thermal measurements of metal absorbers.
• Open science: all findings — including failures — published open-access.

Why it matters here

The whole heat-driven cooling thesis of this KB depends on a cheap, abundant heat source. A material-efficient, coating-free absorber that hits high absorptance by geometry alone would lower the cost of solar-thermal collectors feeding the chillers — and it is being developed by the same 601 Delaware team behind the roastery waste-heat cooling strategy.

See also (for compile)

• Relates to solar-thermal (the collectors this absorber improves)
• Relates to radiative-cooling / selective surfaces (the material-based counterpart to geometric trapping)
• Sibling project: 601 Delaware cooling strategy