Praise for Let It Shine

"The authoritative background story behind the worldwide solar revolution, Let It Shine is a story of human ingenuity and perseverance told with clarity and depth. The next chapter is ours to write."

— David W. Orr, professor of environmental studies and politics at Oberlin College and author of Down to the Wire: Confronting Climate Collapse

"Let It Shine makes it abundantly clear that solar energy has a long and glorious past — a prologue, in fact — that is as bright and diverse as its future will be. Far from being a disruption of the current energy economy, solar power can be harnessed in thousands of ways, making it easy to embrace and integrate into our future, as this book brilliantly demonstrates."

— Daniel M. Kammen, distinguished professor of energy at the University of California, Berkeley

"John Perlin is the historian of solar energy. He now takes the history back thousands of years to early Chinese architecture and the yang-sui, the little bronze mirrors boys used to start the family fire, to nineteenth-century inventors who feared that coal supplies were about to run out, to modern passive solar buildings and today’s falling costs and growing use of photovoltaics. He does all this with a penchant for the diverse characters along the journey and with remarkable illustrations that vividly capture the six-thousand-year story of solar energy."

— Daniel Yergin, Pulitzer Prize–winning author of The Quest: Energy, Security, and the Remaking of the Modern World and The Prize: The Epic Quest for Oil, Money, and Power

With remarkable depth, breadth, and precision, John Perlin lays out humankind’s long reliance on the sun before the carbon era and points the way to a healthy, comfortable, productive, resilient solar-powered world. There is more intelligence and common sense in this volume than in all the federal reports on energy of the last quarter-century combined.

— Denis Hayes, former director of the federal Solar Energy Research Institute and founder of the Earth Day Network

Praise for A Golden Thread, the previous edition of Let It Shine

Western man has been using the sun’s rays for useful purposes since the days of ancient Greece, as this comprehensive, carefully researched, clearly written history of solar architecture and technology makes abundantly clear. The illustrations and diagrams that illuminate the text on almost every page are especially fine examples of modern graphic presentations.

— New York Times

"It is a humbling book. Handsomely illustrated and lucidly written, A Golden Thread is a rich mine of information."

— Los Angeles Times

The history of mankind’s efforts to use the sun’s energy is a fascinating story, one told in a lively yet scholarly manner here…. The triumphs and defeats of solar pioneers help us appreciate what a solar future may yet hold.

— Christian Science Monitor

This book is sorely needed in the solar publication field, for although there are any number of how-to books on solar technology, few if any examine the history of this much-neglected energy source in any depth.

— Denver Post

"I just happened to be carrying A Golden Thread in my suitcase at Princeton. On my way home, I devoured it. Richly illustrated and thoroughly documented, it is a feast for the most critical historian’s mind and eye."

— Technology Review

This book will provide hours of reading pleasure and, at the same time, humble anyone who thinks that solar architecture is a new thing under the sun.

— American Institute of Architects (AIA) Journal

This informative and sobering book traces the evolution of solar applications. Excellent graphics and a highly readable style make this book the best survey available.

— Library Journal

Praise for A Forest Journey: The Story of Wood and Civilization by John Perlin

Outstanding… This book takes one of those bold imaginative sweeps through world history that leaves you full of excitement, as suddenly events seem to fall into a pattern for the first time. Perlin not only presents us with a bold hypothesis profusely documented and illustrated, he does it with a storyteller’s pace and ability to surprise.

— BBC World Service

‘Delight’ is not a word one expects to use in connection with deforestation, but John Perlin has certainly written a delightful book…. It deserves to be a classic and should make a welcome present for anyone who enjoys a good read.

— Forest and Conservation History

Well documented and illustrated, it is history at its best.

— American Forests

Perlin deftly combines a balance of social and ecological values as well as lessons for the immediate future.

— Booklist

Like some Greek epic poem spanning 4,000 years of civilization . . . an impressive array of research and a novel topic.

— Los Angeles Times

The new edition of Perlin’s landmark work again brings needed attention to one of the primary concerns of the modern era.

— Forest History Today

This work… captures the significant impact of wood on past and present civilizations…. Well written and well illustrated.

— Choice

A journey through time — a sort of Western Civ. 101 with a focus on the crucial role of wood in the rise and fall of states and cultures… Solid survey that adds significant dimension to our picture of the current crisis.

— Kirkus Reviews

Perlin has accumulated what seems every reference to the use and misuse of forests in the period beginning with Gilgamesh and ending with the 1880 U.S. census. In between, he chronicles the deforestation of Asia, the Mediterranean, Europe, the West Indies, and the United States by kings, warlords, and robber barons for purposes ranging from building navies to smelting iron to clearing land for cash crops. The research is exhaustive.

— Library Journal

Praise for From Space to Earth by John Perlin

John Perlin’s book gives a taste of the tremendous difficulties that early pioneers had to overcome to turn Charles Fritts’ 1885 invention of a selenium-based solar module to today’s booming photovoltaic business. Perlin gives a vivid and fascinating account of the advances of photovoltaics on Earth. Presenting the development of photovoltaic cells in such a personalized manner makes it a much more lively and interesting read than a mere technical account would have done.

— Nature

"The step-by-step progress of photovoltaics has elicited little fanfare. It is my hope that From Space to Earth will end the silence. The book is gripping to read and its themes long overdue in book-length form."

— Photon magazine

This ‘just in time’ story of the development of photovoltaics merits the most serious attention and cannot fail to stimulate the reader’s interest in both the episodes recounted and their interdisciplinary applications and prospects. The author has provided us with a ‘good read,’ and the illustrations enhance one’s enjoyment. It is a fascinating story, told so that even an individual without technical training can comprehend the breakthroughs which led to today’s widespread and ever increasing adoption of solar power.

— Interdisciplinary Sciences Review

John Perlin’s delightful tour through the development of photovoltaics (PV) answers not only the question of what is new under the sun, but most importantly, how we got there. Perlin charts the evolution of the photovoltaic industry from its beginnings to the present. It’s the best and most readable book on photovoltaic research, policy, and market growth.

— Whole Earth

"Twenty years ago John Perlin published A Golden Thread, a comprehensive and authoritative history of solar energy that remains today one of the best books on the subject. Perlin’s present book is an equally impressive story of the twentieth-century solar photovoltaics industry. Even diehard opponents of solar energy should find it compelling."

— Isis, the official journal of the History of Science Society

Also by John Perlin

A Forest Journey: The Story of Wood and Civilization

From Space to Earth: The Story of Solar Electricity

Copyright © 2013, 2022 by John Perlin

An earlier version of this book was published under the title A Golden Thread: 2,500 Years of Solar Architecture and Technology by Cheshire Books / Van Nostrand Reinhold and Company in 1980.

All rights reserved. This book may not be reproduced in whole or in part, stored in a retrieval system, or transmitted in any form or by any means — electronic, mechanical, or other — without written permission from the publisher, except by a reviewer, who may quote brief passages in a review.

Some of the material in Let It Shine appeared in a different form in the Pacific Standard magazine.

An earlier version of the foreword by Mark Z. Jacobson, No, We Don’t Need ‘Miracle Technologies’ to Slash Emissions — We Already Have 95 Percent, was published in The Hill on May 20, 2021.

The permission acknowledgments on page 499 are an extension of the copyright page.

Text design by Tona Pearce Myers

Library of Congress Cataloging-in-Publication Data

Perlin, John.

[Golden thread]

Let it shine : the 6,000-year story of solar energy. — Fully revised and expanded / John Perlin.

pagescm

Revision of: A golden thread / by Ken Butti and John Perlin. — Palo Alto : Cheshire Books ; New York : Van Nostrand Reinhold, ©1980.

Includes bibliographical references and index.

ISBN 978-1-60868-132-7 (hardback) — ISBN 978-1-60868-133-4 (ebook)

1. Solar energy—History. 2. Architecture and solar radiation—History. I. Title.

TJ810.B88 2013

First printing, September 2013

First paperback printing, February 2022

ISBN 978-1-60868-791-6

Ebook ISBN 978-1-60868-792-3

Printed in Canada on 100% postconsumer-waste recycled paper

10 9 8 7 6 5 4 3 2 1

Contents

Foreword by Mark Z. Jacobson

Preface to the Paperback Edition: The Age of the Sun Begins Again

Introduction

Part I. Early Use of the Sun

Chapter 1. Chinese Solar Architecture (6000 BCE–)

Chapter 2. Solar Architecture in Ancient Greece (500 BCE–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–)

Epilogue

Acknowledgments

Notes

Illustration Credits and Permission Acknowledgments

Index

About the Author

Foreword

In May 2021, U.S. Climate Envoy John Kerry stated, I am told by scientists that 50 percent of the reductions we have to make to get to net zero are going to come from technologies that we don’t yet have.¹ This comment echoes statements by Bill Gates that solar, wind, and batteries are not enough, so we need miracle technologies to decarbonize our global economy.² They also mimic the statement in a 2021 International Energy Agency (IEA) report that, in 2050, almost half the reductions come from technologies that are currently at the demonstration or prototype phase.³

One might argue that, in all three cases, new technologies means improved existing technologies, such as improved batteries, solar panels, wind turbines, electric vehicles, and so on. However, hidden in a 2021 U.S. economic revitalization proposal is a call to fund CO2 capture and storage, CO2 direct air capture, and small modular nuclear reactors.⁴ Similarly, Gates has funded and argued for these technologies plus modern bioenergy, and the IEA report explicitly proposes the use of all four of these technologies for a decarbonized world.⁵ Ironically, the IEA acknowledges, all the technologies needed to achieve the necessary deep cuts in global emissions by 2030 already exist, but astonishingly, they then say that those technologies and their improvements are not enough to reach 2050 goals.

Let’s examine the claim that we need new technologies such as carbon capture, direct air capture, modern bioenergy, and modern nuclear energy to sufficiently reduce energy and nonenergy emissions. The four main energy sectors are electricity, buildings, transport, and industry, and we’ll consider each one.

For electricity, the main clean, renewable electricity-generating technologies are wind, solar photovoltaics, concentrated solar power (CSP), geothermal, and hydroelectricity.⁶ Collectively, these are known as wind-water-solar (WWS) technologies. All are heavily commercialized. In fact, wind and solar are currently the lowest-cost electricity-generating technologies around.⁷ Wind and solar are also so plentiful that they could each supply the world’s all-purpose energy many times over.⁸

But storage is needed to provide backup energy. Existing electricity storage technologies include batteries, pumped hydropower storage, hydroelectric dams, CSP with storage, flywheels, compressed air storage, and gravitational storage.⁹ In many places, solar plus batteries is already cheaper than coal or nuclear and is replacing both.¹⁰ In fact, battery costs declined nearly 90 percent between 2010 and 2020.¹¹ No miracle is needed in this area, just more rapid deployment. Thus, we have no need for modern bioelectricity, nuclear, or carbon capture attached to fossil-fuel electricity or bioelectricity.

Do we need miracle technologies to clean up energy in buildings? Emissions from buildings arise from natural gas for air heating, water heating, cooking, and clothes drying plus gasoline use in lawn mowers and leaf blowers. Electric replacements for these are commercially available with dropping costs. They include heat pump air heaters, heat pump water heaters, electric induction cooktops, heat pump dryers, electric lawn mowers, and electric leaf blowers. Heat pumps use one-fourth the energy of their natural gas equivalents, so they cost less than gas heaters over their lives. No miracle is needed.

How about transportation? Electric vehicles are commercially available to replace fossil-fuel vehicles of all types and weights, aside from long-distance aircraft and ships, the longest-distance trucks and trains, and heavy military vehicles. Such long-distance, heavy vehicles are part of the last 5 percent of energy technologies that may take until 2035 or 2040 to commercialize. However, such vehicles can and likely will run on hydrogen fuel cells.¹² To produce hydrogen, we will use existing and improved electrolyzers powered by renewable electricity. Thus, no biofuel, such as ethanol, biodiesel, or bio-jet fuel, is needed.

What about industry? Energy for high-temperature processes will come from existing electric technologies: arc furnaces, induction furnaces, resistance furnaces, dielectric heaters, electron beam heaters, heat pumps, and CSP steam. No miracle is needed.

How about nonenergy emissions? Steel and cement manufacturing emit process-CO2. Biomass burning emits CO2, black and brown carbon (the second-leading cause of global warming), and more. Rice paddies, landfills, and manure emit methane. Halogens, used as refrigerants and solvents, leak. Fertilizers emit nitrous oxide.

These all have current solutions. For steel, the hydrogen direct-reduction process reduces CO2 during steel production by 97.2 percent.¹³ Replacing concrete with Ferrock, an alternative composed of iron-rich waste steel dust, eliminates process CO2 from concrete production. Recycling concrete helps further. Strong policies are needed to slow biomass burning. Collecting methane from rice paddies and landfills with pipes is an existing technology, as is the digester for trapping methane from manure. Policies to substitute less-damaging halogens for more-damaging ones and to strengthen seals to reduce halogen leaks have worked in the past. Using less nitrogen-based fertilizer and cultivating leguminous crops that don’t require fertilizers help reduce nitrous oxide emissions. None of these techniques requires a miracle.¹⁴

Some argue that we need direct air capture to reduce CO2 levels beyond those obtained from stopping emissions. However, we can obtain 350 parts per million CO2 by stopping 80 percent of emissions by 2030 and 100 percent by no later than 2050.¹⁵ Also, direct air capture is an opportunity cost, just like carbon capture, so it is always better to spend on a different mitigation method.¹⁶

In sum, we have 95 percent of the technologies we need today and the knowhow to get the rest to address both energy and nonenergy emissions. Therefore, no miracle technology — particularly carbon capture, direct air capture, modern bioenergy, or modern nuclear power — is needed.

By implementing only clean, renewable WWS energy and storage and implementing nonenergy strategies, we will address not only climate change but also the 7 million annual air pollution deaths worldwide and energy insecurity. None of the miracle technologies addresses all three.

We at Stanford’s Atmosphere/Energy program, along with seventeen other research groups, have shown that we can do it with renewables alone in the fifty United States and worldwide.¹⁷ This transition will reduce energy costs and land requirements while creating jobs.¹⁸ The key is to deploy, deploy, deploy existing clean, renewable, safe technologies as fast as possible.

To that end, Let It Shine focuses on one of the pillars of the energy transition, solar energy. Solar is an essential energy needed to move us away from fossil fuels to a clean, renewable energy future. It has provided warmth and energy for societies in the past and will continue to do so for societies in the future, but to a much greater degree. This book gives us a view of the past and present so that we can learn from it for the future.

— Mark Z. Jacobson, PhD

Professor of Civil and Environmental Engineering at Stanford University

Director of Stanford University’s Atmosphere/Energy program

Preface to the Paperback Edition

The Age of the Sun Begins Again

The publication of the paperback edition of Let It Shine could not have been better timed. It comes out as the sun remerges as a significant source energy for humanity, as it was from deep antiquity to classical times in the Chinese, Greek, and Roman world, with houses commonly designed to scoop up sunlight for heating during winter yet avoid the scorching summer sun. During the time of Confucius, and probably much earlier, almost every Chinese household relied on concave mirrors to concentrate the energy of the sun onto kindling to start the family dinner fire, as did Europeans in the time of the Renaissance, when welders also used such devices to solder metals. Now, centuries later, a goodly portion of people in China, Cyprus, and Israel have come to rely on solar energy for hot water, just as others had in the waning years of the nineteenth century and into the first decades of the twentieth century in southern California, and then from the 1920s until World War II in Florida. And as far back as the 1870s, scientists and technologists experimented with certain solid-state materials to convert sunlight directly into electricity, culminating in the discovery of the world’s first practical solar cell in 1954. All of these developments are richly covered in the chapters you’ll read in Let It Shine.

Since the publication of the hardcover edition in 2013, photovoltaics (PV) — the means of direct conversion of the sun’s energy into electricity by semiconducting material known as solar cells, less than the thickness of a human hair — has moved to center stage in today’s power world, crowned as the new king of electricity, by the authoritative International Energy Agency (IEA).¹ The IEA previously was skeptical of the potential of PV, and this change of heart is significant. The story behind PV’s coronation can be found in chapters 21 through 23, chapter 28, chapter 29, and the epilogue of Let It Shine.

The reason for PV’s ascendency lies in its great drop in price from a whopping $286 per watt at its discovery in 1954 to less than 25 cents as of December 2020.² Since the writing of the hardcover edition of Let It Shine, the cost of a large-scale photovoltaic installation has fallen by more than 66 percent, and installed capacity has risen sevenfold.³ As a result, the value of the photovoltaic industry has increased from about $86 billion in 2015 to an estimated $422 billion in 2022,⁴ leading the IEA to conclude, For projects with low-cost financing that tap high-quality resources, solar PV is now the cheapest source of electricity in history.⁵

Continued increased module efficiency has been one driver of the unrelenting drop in price. Recent developments in manufacturing and an improved type of silicon solar cell that can absorb sunlight from the sky and its reflectivity off the ground, as well as apparatuses that allow solar cells to follow the course of the sun, offer even cheaper and more efficient solar cells in the near future and therefore a rapid acceleration of photovoltaics’ growth throughout the world.⁶ With the advent of new materials, solar cells could reach a mind-boggling 90 percent efficiency, that is, the capacity to convert 90 percent of the incoming sunlight into electricity.⁷ More power per cell results in less land area required, as well as less metal for wiring and racking per installation. Reducing the amount of silver used to draw the freed electrons from the modules has also brought down the price. The possibility of replacing the silver with much cheaper copper would bring the price of modules down even farther.⁸ Giant companies, rivaling the size of their fossil-fuel competitors, are financing the technology, while pension funds and investment firms are incorporating solar into their portfolios, all of which allows for easier access to capital at better terms than in earlier times, making solar far cheaper than before.⁹ The price of batteries, too, has dropped precipitously, mirroring the cost decrease of PV and resulting in solar changing from an intermittent to a baseload source of power that produces electricity less expensively than its fossil-fuel or nuclear competition and yet just as reliably.¹⁰ The combination of solar and batteries, and the electronics that allow them to interact seamlessly with the grid, allows for the overflow into insatiable markets throughout the developed world hungry for a noncarbon source of electricity, confirming the thesis that carbon-free power based on solar can provide the world with an equitable yet clean future.

The diffuseness of the solar fuel has led skeptics to argue that solar installations would take up too much land space to generate an amount of power equal to that of fossil-fuel facilities. In reality, when the amount of land required to obtain the fossil fuels is factored in, there is very little difference.¹¹ In fact, PV has the potential to be even less land-intensive, because the modularity of the technology allows panels to be placed on rooftops and carports, floated on waterways, installed alongside highways, and integrated as building material.¹²

In 1977, with only 700,000 watts of PV installed, Allen Hammond, writing in Science, declared, If there is a dream solar technology, it is photovoltaics — solar cells … a space-age electronic marvel at once the most sophisticated solar technology and the simplest, most environmentally benign source of electricity yet conceived.¹³ Today, in 2021, the total worldwide installed PV capacity is almost 800 billion watts.¹⁴ Bloomberg’s primary research service predicts that by 2050 there could be as much as 20 trillion watts of PV in service.¹⁵ The dream technology has definitely awoken, relegating natural gas as the bridge to nowhere, as we enter what will surely be an enduring Solar Age thanks to PV.

What Hammond and other seers realized is that the price of photovoltaics is based on the learning curve of its microelectronic peers: the more you make, the less costly it becomes. No other power generator — whether coal, concentrated solar power, natural gas, nuclear, or wind — enjoys this advantage because the construction relies on huge amounts of cement and steel. It’s like comparing a gargantuan 1950s computer run on vacuum tubes with a 2021 desktop relying on silicon — the same material that dominates today’s photovoltaic market. In fact, as early as 1956, at Bell Laboratories where the semiconductor revolution began, engineers predicted that the two Bell inventions [the transistor and practical solar cell] will be closely linked in many future developments that will profoundly influence the art of living.¹⁶

As Bloomberg News observes, America needs to do its part to allay the global carbon crisis, of course. But also, renewable energy technologies have become massively cheaper over the past two decades, to the point they’re now competitive with fossil fuels in most regions. Making the transition will thus deliver not only environmental value, but solid dollar value as well.¹⁷ A new review by Oxford University academics reveals that a fast, decisive shift to solar and other zero-emissions technologies would yield significant economic benefits, likely saving trillions in energy costs!¹⁸ Red tape and the inertia created by special interests remain the only barriers. The world has to realize that the objective of the entire planet’s population living well is, according to The Economist, unachievable if it is based on an economy powered by coal, oil and natural gas.¹⁹

— John Perlin

November 2021

Introduction

Charles Pope explains that he wrote his book Solar Heat, published in 1903, because SOME CALL TO THE PEOPLE is needed… to arouse interest…[in] ‘catching the sunbeams’ and extracting gold from them. To accomplish his goal, he tells his readers, he has endeavored to trace the history of attempts and successes in the utilization of solar heat[;]… discuss ways and means; and attempt to arouse his readers to give to the matter their energy and invention, their brain and capital; that we may very soon see solar enginery take its place by the side of steam enginery and electrical enginery and gas enginery in the public estimation, in technical schools, in mechanical journals, and in myriads of practical, labor-saving constructions.¹ More than one hundred years later I have attempted the same by writing Let It Shine.

Many believe that solar energy is a late-twentieth-century phenomenon, yet six thousand years ago the Stone Age Chinese built their homes so that every one of them made maximum use of the sun’s energy in winter. So begins the story of the genesis of solar energy told in Let It Shine: The 6,000-Year Story of Solar Energy, the world’s first and only comprehensive history of humanity’s use of the sun. Because so few have attempted a comprehensive history of solar energy, page after page of this book brings to light information never before unearthed.

Twenty-five hundred years ago, for example, the sun heated every house in most Greek cities. Years later Roman architects published self-help books about using solar energy to show people how to save on fuel as firewood became scarce and as fleets scoured the known world for much-needed supplies of wood. During the Renaissance Galileo and his contemporaries planned the construction of solar-focusing mirrors to serve as the ultimate weapon to burn enemy fleets and towns. Leonardo entertained more peaceful applications. He aimed at making his fortune by building mirrors a mile in diameter to heat water for the woolen industry. Much later, during the Industrial Revolution, engineers devised sun-powered steam engines to save Europe from paralysis should it run out of fossil fuels. In 1767 a Swiss polymath modeled global warming by trapping solar heat in a glass-covered box in the same way that carbon dioxide traps solar heat above the earth. Using the same type of glass-covered box to harvest solar energy, enterprising businessmen established a thriving solar water-heater industry in California beginning in the 1890s! And as electricity began to power cities, the first photovoltaic array was installed on a New York City rooftop in 1884.

A hundred and thirty years later, Let It Shine brings to light documents suppressed by the Nixon, Carter, and Reagan administrations that, had the public and Congress known about them at the time, would have permitted solar energy to assume a much larger role in the American energy mix.

Let It Shine presents the step-by-step development of solar architecture and technology. By providing the background for and illuminating the process of discovery, this book permits a deeper understanding of how solar-energy applications have evolved and performed. The book is more than a technological treatise, though. It presents the context in which these developments occurred and the people who made the solar revolution possible, revealing a whole new group of unknown technological pioneers, as well as identifying people famous for accomplishments other than in their work as solar-energy advocates and technologists. No one today thinks of Socrates as a solar-energy promoter, for example. Yet the author Xenophon, in his work Memorabilia, records Socrates presenting a basic plan for a solar house. Vitruvius, a Roman still famous today as the architect of architects, transmitted the wisdom of the Greeks on building in relation to the sun. The first aspiring solar-energy entrepreneur was Leonardo da Vinci. And Einstein’s famous treatise on light quanta, which won him the Nobel Prize, reveals the great scientist as the father of modern photovoltaics.

Then there are the forgotten people, such as Gustav Vorherr, who in the 1820s opened the first school of solar architecture, in Munich, and his mentor, Dr. Bernhard Christoph Faust, the first person to write a complete book on using solar energy. Thousands of architects — trained in the work of Faust and educated by Vorherr — fanned out to build solar-oriented homes throughout Europe in the nineteenth century. Sympathetic despots of Bavaria and Prussia actually required their subjects to follow the teachings of these men when building, which resulted in one portion of an urban area becoming a sun city. And who has heard of William Grylls Adams and Richard Evans Day, who discovered in 1876 the photovoltaic effect in solid materials, or Charles Fritts, who put up the first rooftop solar array in the 1880s?

This is but a sampling of what’s to be found in Let It Shine.

Let It Shine’s precursor was A Golden Thread: 2,500 Years of Solar Architecture and Technology, which I coauthored with Ken Butti in 1980. Ken went on to follow other pursuits, and I continued to write, producing, for example, A Golden Thread’s photovoltaic sequel, From Space to Earth: The Story of Solar Electricity. And my book A Forest Journey: The Story of Wood and Civilization examines in great detail the fuel shortages, principally caused by forest devastation, that led many civilizations to turn to the sun to heat water and home interiors. Let It Shine is distilled from the insights I gained while researching and writing these three books and from new research over the past three decades.

Let It Shine presents the core of A Golden Thread, along with twelve new chapters and many additions to the older ones, making it the definitive history of the uses of solar energy throughout time. By giving an in-depth account of past successes and failures in applying the sun’s energy to the art of living, the book offers insights into what the future of solar energy may come to be.

The first and most difficult step in crossing over from today’s fossil-fueled world to a solar future is realizing that it can be done. Let It Shine makes this recognition possible by showing how our predecessors used the sun to better their lives. In doing so, Let It Shine demonstrates that the sun can become a major source of power that moves humanity toward living in a world that operates on carbon-free energy.

PART I

EARLY USE OF THE SUN

[ 6000 BCE– ]

1

Chinese Solar Architecture

Figure 1.1. Path of the sun at noon on December 21 (top) and June 21 (bottom) in the Northern Hemisphere. In winter, the sun is always low in the sky and remains in the south throughout the day, while in summer it is much higher in the sky and spends the majority of the day in the east and west. These facts have important implications in building a home that is naturally comfortable throughout the year.

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.¹ 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.² 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.³ 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.⁴

Figure 1.2. A Chinese family during the Zhou dynasty checking the shadow cast by their gnomon.

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.⁵

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.⁶ 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.⁷

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.⁸

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.⁹

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.¹⁰

Figure 1.3. A typical Chinese house. The main building faced south, protected from the high summer sun by eaves that extended from the roof’s edge on all sides of the building.

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.¹¹ 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.¹²

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.¹³ 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.¹⁴ 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.¹⁵ By the fourth century BCE, if not earlier, it was seemingly axiomatic that wooded areas near large population centers would be deforested.¹⁶ 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.¹⁷ 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.¹⁸ 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.¹⁹