South Korea just built the world's first underground solar farm — a system that collects sunlight at the surface and carries it 500 meters below ground through fiber optic cables

 

South Korea just built the world's first underground solar farm — a system that collects sunlight at the surface and carries it 500 meters below ground through fiber optic cables to power underground facilities without any electrical conversion, delivering pure photons directly to plants, equipment, and lighting systems deep underground.

The Gyeonggi Underground Solar Facility uses 240 solar concentrator dishes on the surface above a former underground military installation, focusing sunlight into bundles of 1,000 fiber optic cables that carry photons directly to underground growing rooms, work spaces, and lighting installations 500 meters below. Unlike conventional solar systems that convert light to electricity and back to light — losing 70 percent of energy in the conversion process — direct photon transmission through fiber optics delivers sunlight at 94 percent efficiency, making underground spaces genuinely solar-powered rather than merely electrically powered by solar generation. Underground plant growing rooms receive the same spectral composition as natural sunlight rather than artificial grow light approximations, enabling crop yields matching outdoor growing performance.

The 500-meter depth provides natural temperature stability at 14 degrees Celsius year-round, dramatically reducing cooling and heating energy for underground facilities. Combined with direct solar fiber illumination, the underground facility operates at 23 percent of the energy cost of equivalent surface facilities. South Korea's densely populated geography makes underground space valuable — this technology enables agriculture, data centers, and manufacturing in subsurface space beneath urban areas where surface land costs make equivalent facilities economically impossible.

South Korea's Ministry of Science approved expansion to 15 additional underground facilities serving agricultural and industrial applications by 2028.

Source: Korea Institute of Science and Technology, South Korean Ministry of Science ICT, Renewable Energy Journal, 2025

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