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Let It Shine
The 6,000-year Story of Solar Energy
By John Perlin
New World LibraryCopyright © 2013 John Perlin
All rights reserved.
Chinese Solar Architecture
When discussing millennia-old techniques for building homes and palaces in a way that permitted the Chinese to take advantage of the sun's position relative to the earth throughout the year, the seventeenth-century Chinese philosopher Yu Li compared a correctly built structure to a person who dresses appropriately according to the changing seasons. "As it is true that clothing should be cool in summer and warm in winter, the same holds true for a house," Yu Li wrote in his book Xian qing ou ji. Most important, for warmth in winter, the philosopher explained, "a house must have the correct orientation. It has to face south to catch the heat and light" of the winter's sun. This simple awareness of how to site a home is the first principle of solar-oriented architecture, and no other civilization can boast of having had predominantly solar-oriented houses for as long as China has.
Principles of Solar Architecture
About four thousand years ago, the ancient Chinese began to track the changing position of the sun in relation to the earth by watching the sun throughout the year through openings in a kind of solar observatory. Sometime later, their successors developed a more accurate way to keep track of the sun. They invented the gnomon, a stick or square piece of wood or stone planted perpendicularly (at a right angle) in the ground. Over time, as the sun moved across the sky relative to the earth, they could record the shadow cast as the sun's rays struck the gnomon. In this fashion, people could mark the solstices and equinoxes. The great philosopher of science Thomas Kuhn credits the gnomon for allowing "systematic observations of the motion of the sun ..., [which] harness[ed] the sun as a time reckoner and calendar keeper."
The long shadow cast by the gnomon in winter would have quantified for the Chinese their observation that, at this time of the year, the sun remained relatively low in the sky throughout the day. That the shadow's direction did not fluctuate very much all day was a result of the sun staying in the south from the time it rose until it set, confirming an observation by an ancient Chinese astronomer: "On the day of the winter solstice, in the exact direction of the east and the west, one does not see the sun."
In summer the gnomon shows the opposite is true: the sun spends the majority of the day in the northeast and northwest, and from 10 AM to 2 PM it is high in the sky toward the south. Knowing the location of the sun throughout the year allowed the Chinese to perfect the art of designing homes and whole cities so that all people could warm their houses with the sun's heat in winter and, during summer, keep the sun out of their houses so they could stay cool and comfortable.
The first account of the use of the gnomon for building comes from the Zhou dynasty, which was established sometime before the twelfth century BCE. Zhou government officials considered proper orientation too important to be left to chance, and so they instructed builders to establish the cardinal points of the compass for exact siting. The book Zhouli, which contained the rituals and rules established by the dynasty, explained how this would be accomplished. Builders first had to determine when the equinoxes and solstices occurred, which could be pinpointed by studying the shadows cast by the gnomon. The longest and shortest shadows of the year would mark the winter solstice and summer solstice, respectively. When the shadow cast was half as long as the two solstice shadows, the observer would know that one of the two equinoxes had arrived. At either equinox, the shadow cast by the rising sun would point west, and the shadow cast by the setting sun would point east. Taking note of where the noon shadow fell, the observer would learn where true north and south lay. In this way, sometime in the seventh century BCE, Duke Wan "began to build the Palace at Ts'oo, orienting it ... by means of the sun."
How It Worked
In Yu's day, most houses in northern China, whether opulent or simple, conformed to the traditional courtyard style that had prevailed for thousands of years. This type of architecture had either walls or subsidiary buildings surrounding a courtyard; the rectangular main house was recessed into the back of the court, and all its openings faced south. Poet Ban Gu, who lived in the second century CE, saw Chinese solar architecture at work when the palace's south-facing "Door of Established Brightness" was opened in wintertime. "The sun's radiance would flare brilliantly into the palace, heating the rooms inside."
Those living in humble abodes, too, took advantage of the sun's winter location to stay warm. Peasants and workers regarded the southwest nook of the house as "the cozy corner," the most desirable place to nestle, where the warm rays of the afternoon sun poured in, even though it might be freezing outside.
A south-facing building could also stay cool in summer. The Chinese studied the gnomon's shorter summer shadows that resulted from the sun climbing much higher in the sky than in winter. They recognized that eaves, if projected over south-facing windows and doors, would keep the high, hot summer sun from entering the buildings throughout the day yet still let in the low winter sun. As Ban Gu observed at the palace complex of the Western Capital in summer: "Their upturned eaves provide a covering mantle [for they] intercept the sun's rays."
The Chinese, Ban Gu noted, immensely appreciated solar architecture for helping to maintain mild temperatures indoors throughout the four seasons, so necessary, the ancients believed, for a long life. The sun's warming rays also reduced people's dependence on charcoal heaters, in this way saving a lot of money. For as temperatures dropped, the price of charcoal would always shoot up.
Deforestation and Solar Architecture
Solar architecture and the relentless war against forests went hand in hand as China's long history unfolded. Unlike Western notions of paradise, where trees and human beings and animals happily coexisted before the Fall, the Chinese saw only chaos in primordial times, when "vegetation was luxuriant and birds and beasts swarmed." Paradise on earth began, as far as the Chinese were concerned, when the legendary Shun brought order to nature and civilization to China. Under his orders, the forests were "set fire to and consumed, opening up the Middle Kingdom for cultivation." In the four thousand years since then, the Chinese have continued Shun's work, chopping their way to new lands, leaving most of China to resemble the slopes of Niu Mountain, once covered with lovely woods but by 300 BCE so bare that people believed nothing had ever grown there. By the fourth century BCE, if not earlier, it was seemingly axiomatic that wooded areas near large population centers would be deforested. Without easy access to forests, charcoal no doubt became harder to get, changing solar architecture from a matter of choice to one of necessity.
Archaeological Evidence for Solar Architecture
Archaeological discoveries, too, reveal that building with the sun in mind began very early in China. More than six thousand years ago, entrances to the homes at Banpo, in the north, were, according to one Asian scholar, "deliberately oriented toward the mid-afternoon sun when at its warmest a month or so after the solstice," which was the coldest time of the year. Overhanging thatched roofs kept the unwanted sunshine off the structures during the hotter months. Submerging the main living spaces below ground level at Banpo moderated the temperature inside throughout the year.
Recent excavations at Erlitou, also in northern 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 shows it set on the north side of a south-facing courtyard, so that it could face south. Qinhua Guo, the lead archaeologist at Erlitou, states, "The new discovery reveals that many city construction rules [principles] in the later dynasties can be dated back to the Erlitou site. This includes the crisscrossing streets [running perpendicular to each other] and constructions [buildings] facing south."
Though laid out thousands of years after Erlitou, Beijing too was given the same type of grid pattern. "Its streets are all so straight, so long, so broad and well proportioned," remarked a European visitor to Beijing in the 1600s. The perpendicular layout with streets running east-west assured a southern orientation for anyone wishing one. "You shall rarely see a palace or house of any great person which does not face that point of the compass," the visitor remarked.
Early Energy Conservation
Winter in the Middle Kingdom could be very harsh. Dew on grass, leaves, and rooftops began to freeze in late autumn, and heavy snows fell by early December. When putting up a structure such as the palace at Ts'oo, builders had to think of the season when determining the best material for its walls, just like people considering what type of coat would suit them with winter on its way. As the royal residence went up in 1300 BCE, "crowds of [laborers] brought the [wet] earth in baskets" to "dress" it in proper clothing, an onlooker at the construction site reported. "They threw it with shouts into the frame. They beat it with responsive blows.... Five thousand cubits of [walls] arose together." Five hundred years passed, and those putting up a later king's palace still used rammed earth for the walls so they would remain "impervious to wind and rain" for the years to come.
As crickets retreated indoors, seeking refuge from the approaching cold and hiding under people's beds, the peasantry knew the time had come to close up the house for winter. No different from getting winter clothes out and fixing any rips or tears a few days before the ugly weather strikes, peasants sealed the cracks and the openings not needed. An ode written more than three thousand years ago gives an account of the preparations. "The windows that face [north]," which had been opened during the hotter months to bring in cool drafts, "are now stopped up," the ancient poet wrote. "And the doors [on the north side] are plastered."
The rich also employed more luxurious methods for keeping out the cold. At night or during bad weather, the Emperor Wu had goose-feather curtains covering his south-facing windows. And while the peasantry slept under plain blankets, the wealthy covered themselves using fabric filled with wadded cotton and, before retiring, had curtains drawn around the bed. The wealthy also used kangs (heated beds) for added comfort — another example of interest by the ancient Chinese in energy conservation. A kang consisted of a platform built of material such as brick or adobe, which has excellent thermal-absorption capabilities. When people cooked their meals in the late afternoon, a flue captured the waste heat and conducted it to the kang, which then radiated sufficient heat throughout the night for the comfort of those who slept in it.
Linguistic and Ritualistic Evidence for the Importance of Orientation of Buildings
As the importance of solar architecture grew, the southern aspect took on great stature in Chinese life. Ancient wisdom associated the south with fire and summer — in other words, with warmth — while the north came to be synonymous with winter and somberness, with things cold and dark. The southwest corner became known as the seat of honor, where "the elder and respected members of the family reside." Ritual also required the emperor to face south whenever in the company of an audience. Sages explained the custom by pointing out that "the diagram of the south conveys the idea of brightness." By facing south the emperor shunned darkness and embraced enlightenment while governing.CHAPTER 2
Solar Architecture in Ancient Greece
Never in history has there been a stronger or more eloquent advocate for the use of solar building principles than Socrates. Xenophon, a disciple of Socrates, presented in a Socratic dialogue the philosopher's belief that the art of "building houses as they ought to be" was firmly based on the principle "that the same house must be both beautiful and useful." In what has become known as the Socratic method, Socrates began his discourse by asking a question: "When someone wishes to build the proper house, must he make it as pleasant to live in and as useful as it can be?" After his student answered in the affirmative, the master then asked, "Is it not pleasant to have the house cool in summer and warm in winter?" And when the student assented to this as well, Socrates then closed the discussion by affirming, "Now in houses with a southern orientation, the sun's rays penetrate into the porticoes [covered porches,] but in summer the path of the sun is right over our heads and above the roof, so we have shade.... To put it succinctly, the house in which the owner can find a pleasant retreat in all seasons ... is at once the most useful and the most beautiful."
The second great sage of Greece, Aristotle, provided additional details not mentioned by Socrates. He, too, started with a question: "What type of housing are we to build for slaves and freemen, for women and men, for foreigners and citizens?" And then he answered, "For well-being and health, the homestead should be airy in summer and sunny in winter. A homestead possessing these qualities would be longer than it is deep; and its main front would face south."
Socrates's father worked in the construction industry as a stonemason, and many believe Socrates followed in his father's footsteps. If he did, he would have known about the remodeling of two houses in downtown Athens — the Agora — where workmen changed the arrangement of rooms so the most important ones would face onto a southern courtyard. The fact that Socrates spent the majority of his life in the neighborhood assures that he knew about the solar project in Athens. And less than 2 miles outside of the city, another example of solar design was built in Socrates's time. This was a large rectangular house that sat on the foot of the northerly slope of Mount Aegaleo, one of several mountains near Athens. According to the archaeologists who excavated it, the farmhouse they discovered, "which faces south and has its entrance and court on this side and its main rooms on the north," corresponds exactly to the ideas expounded by the great philosopher as recorded by Xenophon.
Olynthus: A Planned Solar City
Socrates surely also knew about the solar district planned and built as part of the city of Olynthus, northeast of Athens, since its creation was a consequence of a revolt against his beloved city-state. People from neighboring towns participating in the break with Athens in 432 BCE moved to Olynthus for protection against Athenian retribution. The increase in population forced the Olynthians to establish a new district, which its excavators called North Hill. The latitude was approximately that of New York City and Chicago, and the temperature often dropped below freezing in winter. Approximately twenty-five hundred people settled there.
North Hill was a planned community from the beginning. Starting from scratch, the settlers could more easily implement the principal ideas of solar architecture. The town planners situated the new district of Olynthus atop a sweeping plateau and built the streets perpendicular to each other, just as the Chinese had, with the main streets running east-west. In this way, all the houses on a street could be built with a southern exposure, assuring solar heating and cooling for all residents — in keeping with the democratic ethos of the period. Aristotle later commented that such rational planning was the "modern fashion," which allowed the convenient arrangement of homes so that they could take maximum advantage of the sun.
Olynthian builders usually constructed houses in a blocklong row simultaneously. The typical dwelling had six or more rooms on the ground floor and probably as many on the upper floor. These houses were usually a standard square shape and shared a common foundation, roof, and walls with the other houses on the block. The north wall was made of adobe bricks, which kept out the cold north winds of winter. If this wall had any window openings, they were few in number and were kept tightly shuttered during cold weather.
Excerpted from Let It Shine by John Perlin. Copyright © 2013 John Perlin. Excerpted by permission of New World Library.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents
ContentsForeword by Amory B. Lovins,
Part I. Early Use of the Sun,
Chapter 1. Chinese Solar Architecture (6000 BCE–),
Chapter 2. Solar Architecture in Ancient Greece (500 bec–300 CE),
Chapter 3. Ancient Roman Solar Architecture (100 BCE–500 CE),
Chapter 4. Burning Mirrors (400 BCE–1700s),
Chapter 5. Heat for Horticulture (1500s–1800s),
Chapter 6. Solar Hot Boxes (1767–1800s),
Part II. Power from the Sun,
Chapter 7. The First Solar Motors (1860–1880),
Chapter 8. Two American Pioneers (1872–1904),
Chapter 9. Low-Temperature Solar Engines (1885–1915),
Chapter 10. The First Practical Solar Engine (1906–1914),
Part III. Solar Water Heating,
Chapter 11. The First Commercial Solar Water Heaters (1891–1911),
Chapter 12. Hot Water, Day and Night (1909–1941),
Chapter 13. A Flourishing Solar Industry (1923–1950),
Chapter 14. Solar Water Heating Worldwide, Part 1 (1930s–1960s),
Chapter 15. Saving Airmen with the Sun (1943–),
Part IV. Solar House Heating,
Chapter 16. Solar Building during the Enlightenment (1807–1850),
Chapter 17. Solar Architecture in Europe after Faust and Vorherr (1850–1939),
Chapter 18. Solar Heating in Early America (1200–1912),
Chapter 19. An American Revival (1931–1950s),
Chapter 20. Solar Collectors for House Heating (1882–1962),
Part V. Photovoltaics,
Chapter 21. From Selenium to Silicon (1876–),
Chapter 22. Saved by the Space Race (1971–),
Chapter 23. The First Large-Scale Photovoltaic Applications on Earth (1968–),
Part VI. The Post–Oil Embargo Era,
Chapter 24. Prelude to the Embargo (1945–),
Chapter 25. Solar in the 1970s and 1980s,
Chapter 26. America's First Solar City (1920s–),
Chapter 27. Solar Water Heating Worldwide, Part 2 (1973–),
Chapter 28. Photovoltaics for the World (1978–),
Chapter 29. Better Solar Cells, Cheaper Solar Cells (1955–),
Illustration Credits and Permission Acknowledgments,
About the Author,