Solar power today is mostly photovoltaic technology that converts sunlight into electricity, with some concentrating solar power, solar hot water heaters, and solar ovens. Today, even for every small uses, we use sunlight in ways we might take for granted. In some countries, sunlight is used to disinfect water. Clotheslines are used to dry clothing with a combination of sunlight and exposure to fresh air. Some people make sun tea by placing water and tea bags in a glass container and putting the container in sunlight for several hours. When we expose our eyes to sunlight, doing so is a cue to increase serotonin, a neurotransmitter associated with mood.
We humans have been using sunlight for thousands of years, long before solar power technology was developed. Our ancestors used sunlight to heat their homes and to start fires, among other uses. When we recognize that sunlight has many free benefits and that it has been used for thousands of years, we can let go of the contemporary framing of solar power vs. Fossil fuels and all the politics that go with it, because we will continue to use sunlight in multiple ways and long after we stop using fossil fuels. The physicist, researcher, and author John Perlin wrote a book about the history of solar power titled, Let it Shine, which was recently updated. He generously answered some questions for CleanTechnica about the fascinating history of solar power.
How were Chinese people using sunlight during the Stone Age, and how many years ago was that?
Over six thousand years ago, entrances to the homes at the archaeological site Banpo were deliberately oriented toward the midday sun so that it would receive the maximum solar heat during winter. Overhanging thatched roofs kept the unwanted much higher sunrays off the house during the hotter months. Submerging the main living space underground moderated interior temperatures throughout the year. From the Bronze Age until 1949, when the Communists took over, the traditional Chinese house followed this example, facing the main part of the house to the south with eaves to allow the low sun in winter to enter the structure while shading it during the summer when the sun is high in the sky.
How did the Greeks plan cities in relation to sunlight, and when did they do that?
Major Greek cities built in the fourth century BCE were laid out in a checkerboard fashion with their main streets running east-west so all houses, no matter large or small had a south exposure — relying on the same strategies as in ancient China — enabling the population to stay warm in winter and cool in summer. Aristotle commented that such rational planning was based on the ideas of his time, allowing the convenient arrangement of homes so that they could take maximum advantage of the course of the sun to assure them of comfort throughout the year.
Socrates and Leonardo da Vinci were solar power proponents. What solar solutions did they support?
In typical Socratic fashion, the great sage conducted workshops in how to build a solar house. He began the course by stating the accepted principle of the day that “the same house must be both beautiful and useful.” His pupils agreed. Then he asked the question, “When someone wishes to build the proper house, must he make it as pleasant to live and as useful as it can be?” After the attendees answered in the affirmative, the master then asked, “Is it not pleasant to have the house cool in summer and warm in winter?” When his students assented to this as well, Socrates then set the criteria for accomplishing these goals, stating, “Now in houses with a southern orientation, the sun’s rays penetrate the covered porches” to enter the living spaces faced onto them, 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 season…is at once the most useful and the most beautiful.”
In contrast, Leonardo da Vinci’s interest focused on solar concentrators. He observed that in his adopted city of Florence, metal workers used concave mirrors for soldering and ordinary citizens relied on them to kindle fuel for cooking their main meal of the day. That is why to this day in Italy have their principal dinner in the afternoon. In an age without matches, where fire could be ignited only by laborious friction, solar concentrators made sense. But Leonardo, as a child of his time, wished to achieve immortality by building a greater mirror than the much-admired Archimedes constructed, as legend suggested. Its purpose though, would not be military but to heat water for industry and recreation. He proposed building a mirror with a 4-mile radius that could “supply heat for any boiler in a dyeing factor or a [swimming pool].” Although such a piece of construction never saw the light of day, Leonardo’s pinchant for solar concentrators — as his notebooks show — did not achieve his objectives, he learned from their use that Aristotle was wrong, which his contemporaries had accepted, in believing the sun got its heat through its motion. Rather, da Vinci proved that it is hot by nature. For “the sun, which being itself warm, in passing through these cold mirrors, shows great heat,” Leonardo observed.
In 1875, two British scientists generated an electrical current using a solar cell. How strong was the current and could it be used practically? What was their solar cell made of?
In the late 1860s, scientists discovered that the conductivity of the semiconductor material selenium was affected by light. An amazed James Clerk Maxwell, probably the most highly regarded scientist of his time, wrote to a colleague that when he put the material next to a heater nothing happened. But when he placed it out in the sun, the action of the sun had a powerful effect. From his observation, William Grylls Adams and Richard Evans Day, placed bars of selenium an inch away from a candle. The needle on their measuring device reacted immediately. Screening the selenium from light caused the needle to drop to zero, instantaneously. These rapid responses ruled out the possibility that the heat of the candle flame had produced the current, a process known as thermoelectricity, because when heat is applied or withdrawn in thermoelectric experiments, the needle always rises or falls slowly. “Hence,” the investigators concluded, “it was clear that a current could be started in the selenium by the action of the light alone.” They had discovered something totally new: that light could cause “a flow of electricity” through a solid material. Adams and Day called current produced by light “photoelectric.” Today, we us the term, “photovoltaic.”
Light-sensitive selenium cells provided many practical applications. Alexander Graham Bell’s first telephone was the photophone, using the varying intensity of light to reproduce words. Another application was the automatic control of light buoys, as well as by astronomers as an automatic detector of comets. They were also used as burglar alarms. But most importantly, as they demonstrated the possibility of directly transforming light into electrical energy without any intermediary mechanism, a writer as early as 1886, the selenium solar cells “foreshadowed a scientific revolution of first importance,” “the inevitable Solar Generator.”
Who was Maria Telkes, and what did she do with solar power?
Maria Telkes was one of the leading scientists working on solar thermal projects in the 1940s and 1950s. During World War II, she came up with one of her most important inventions of the war — a device that used solar heat to make seawater drinkable. Both sailors and airmen carried her foldable solar desalinator. When adrift, the solar still saved the lives of many sailors and airmen. The famed aviator, Eddie Rickenbacker, and his crew, shot down in the early days of the war and temporarily lost at sea, describing the importance of her invention, stating, “The story of my own experience as a survivor would have been stripped of Much of its aura of stark tragedy had it occurred a year later than it did… We would have not known thirst. The solar still, which uses the energy of the sun to produce more than a pint of water a day, would have obviated it.”
Why do you think it’s important to study the history of solar power?
When I told someone I was writing a book on the history of the uses of solar technologies, the person replied that it will be a very short book. 520 pages later shows the ignorance most hold regarding the subject, which I hope the book corrects. Let It Shine is basically an idea book regarding the many ways solar energy have proven very helpful to the benefit of humanity much of which we have forgotten to our detriment. By giving an in-depth account of past successes and failures in applying the sun’s energy to the art of living, the reader gains 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 it can be done. Showing that in many instances over the last six thousand years, our ancestors took such steps, enabling us to realize that the sun can again become a major source of power that moves humanity toward living in a world that moves humanity toward living in a world that operates in a carbon-free world.
Why did you become interested in solar power and what motivated you to write your solar power history book?
My interest in solar power began when the Santa Barbara County Board of Supervisors decided to consider the oil giant Exxon’s request to build an on-shore oil processing facility on the grounds that fossil fuels were the only way to solve the fuel crisis of the 1970s. Curious as to the validity of its arguments, I devoted more than half a year researching alternatives. As a consequence, I came to the conclusion that thermal and photovoltaic solar could go a long way to solve the energy crisis if only the powers at hand would explore the options with an open mind. I shared my work at the public meeting of the Board. My presentation so impressed the news director of the most popular radio station of Santa Barbara that he offered me unlimited radio time to market a write-up of what I had stated. The result: a mimeographed reader called Solar Energy Fact Sheetshowing readers all the ways solar energy could make life better.
Thanks to favorable reviews in several international publications, I gained a wide readership and an invitation to present at several conferences, where after one of the talks a member of the audience came up to me and said, “You think solar energy is new. But I’ve got something to tell you — back when I was a youngster, the roof of our house in LA had a solar water heater, as did most of our neighbors.” Suddenly, it dawned on me, here set before me was an opportunity of a lifetime to explore and write about something in the information age that few, if any, knew about. At first, I thought I was going to write a breakthrough book about the history of solar water heating in southern California. But the deeper I dove, I found that the uses of solar energy ran deep in the annals of human history, all the way back to the Stone Age. The final result: Let It Shine: The 6000-Year Story of Solar Energy.
What is your snapshot view of what is happening with solar power now, and where do you think it is going?
It all depends on the route we choose. Dr. Mark Z. Jacobson, in his foreword to the new paperback edition, shows that adopting solar is the leading pillar to a 100% clean, renewable future. Already, photovoltaic generation has proven to be the cheapest producer of electricity in most parts of the world, with many future materials that might even hold greater promise. One example still in its infancy, solar cells becoming part of an architectural structure, oriented as in times past to make optimum use of sunlight in winter and its avoidance during the hotter months. Or, as Mark points out, corporate greed could lead to dreams of carbon capture to perpetuate a fossil-fuel future that can only lead to even greater global warming disasters, not to mention the chimera of nuclear energy, proven as a Trojan Horse in the ongoing Ukraine tragedy.
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