Ancient Breakthroughs in Solar Energy

Second Major Breakthrough – Solar Architecture and Solar Cities

The second major breakthrough in solar occurred when the Chinese began to apply their knowledge of the changing position of the sun during the year, as discussed in the first installment to this series, to consciously build with the sun in mind for warmth in winter and shade during the hotter months. Conclusive evidence for this breakthrough comes from excavations of the Chinese Neolithic village of Banpo.

The villagers saw to it that their circular dwellings solely opened to the south, “deliberately oriented toward the mid-afternoon sun when at its warmest,” according to David Panenheir, a leading Sinologist. He adds this occurs one month or so after the winter solstice so that sunlight would pour into the houses during the coldest month of winter. Eaves of thatch extended far enough to keep the unwanted heat off the house during the summer months as it is much higher in the sky than in winter.

perlin erlitou image — Erlitou Palace recessed to the north and opening to a large courtyard on the south with overhangs to protect it from the high summer sun

Recent excavations at Erlitou, China show solar architecture in full bloom. Settled two thousand years after Banpo, Erlitou is characterized by a house type and a form of urban planning that would continue basically unchanged for the next four thousand years, well into the twentieth century. A reconstruction of the Erlitou palace reveals a building of rectangular shape, longer than deep to minimize its exposure to the east and west, and recessed to the north so it could face the entire expanse of a south-facing court.

According to the lead excavator, “The new discovery shows that many city construction rules in the later dynasties can be dated back to the time of the Erlitou site. This includes the crisscrossing streets (perpendicular to each other), allowing for all buildings to face south.”

perlin P.38 SiheyuanperspectiveZGGDJZS1984 — The traditional Chinese courtyard house that evolved from Erlitou with main body of the house recessed to the north and opening to a large courtyard on the south with overhangs to protect it from the high summer sun

Though much later in time than Erlitou, Beijing, too, was laid out in the same fashion. “It streets are all so straight, so long so broad and well proportioned,” remarked a European visitor in the 1600’s.

perlin p. 24 Beijing Grid Qianlong — Beijing city plan of the sixteenth century with main streets running east-west so every house and palace could face south.

With main streets running east-west assuring a south-orientation for anyone wishing one, “You rarely see a palace or house which does not face that point of the compass,” the visitor remarked.

Perlin ch1_001lowres — Illustration shows at left the path of the sun at the winter solstice, low in the sky and always in the south; at right, the path of the sun at the summer solstice is significantly higher in the sky throughout the day than in winter and much of the time in the east and west.

Source | Images: “Let it Shine”, by John Perlin.

John Perlin is author of four books: “A Golden Thread: 2500 Years of Solar Architecture and Technology;” “A Forest Journey: Wood and Civilization;” “From Space to Earth: The Story of Solar Electricity;” and his latest book, “Let It Shine: The 6000-Year Story of Solar Energy.” Harvard University Press Chose “A Forest Journey” as one of its “One-Hundred Great Books” published by the press, as well as a “Classic in Science and World History.”