John Perlin

John Perlin – The History of Solar Energy

This is an historic episode of Clean Power Planet. It’s historic because our featured guest is John Perlin, author of Let It Shine: The 6,000 Year Story of Solar Energy. It’s also historic because Clean Power Planet is one year old.

John Perlin - Author of Let It Shine: The 6,000 Year Story of Solar Energy
John Perlin – Author of Let It Shine: The 6,000 Year Story of Solar Energy

So, happy 1st birthday to Clean Power Planet. If you’ve listened to the first episode then you may remember that I made some pretty big claims. Something about a fundraiser to install solar on low income homes. I may have even mentioned a community solar movement.

Was I really that confident? Actually I was pretty nervous about starting a podcast. What if it was horrible? What if I couldn’t get anybody to interview? What if my daughter got fed up with helping me produce it? What if I couldn’t find the time to keep it going? I was sure that was going to be the hardest part.

I thought about starting the podcast for a long time. When I finally decided to do it I gave myself an extra incentive to keep it going by announcing that I was going to do a solar fund raising project in that very first episode. I was daring myself to quit.

The history of a renewable energy podcast

So now that the show has been around for a year I want to take a look back and give myself a report card. First of all I haven’t done a solar fundraiser. I get an F on that one but we’ll come back to it. I have kept the show going. It’s not weekly yet so I’ve got a ways to go there, C+. I think Keaton has done a great job of editing and producing the show and she hasn’t gotten fed up with me yet. She gets an A+. I’m sure that she would rather I just paid her. I have gotten a lot of interesting people to interview. That went better than I could have hoped. I’ll give myself a B+.

A lot of amazing things have happened in the last year. I went to the state capital to join in a lobby day for friendlier solar legislation. I managed to get a press pass for a solar finance conference in San Diego even though I only had two episodes posted. I got to interview some of the most prominent speakers. I also got to talk with Nicole Capretz, head of San Diego’s Climate Action Plan.

I ran for a position on the board of the Kentucky Solar Energy Society. I didn’t get elected but they asked me to be an ad hoc member and I got to travel to Penn State to represent the society at the American Solar Energy Society’s annual conference. I got to interview a lot of interesting people including many of the ASES board members and Dave Renne, president of the International Solar Energy Society.

In October the Kentucky Solar Energy Society hosted six solar tours all across the state as part of the National Solar Home Tour. I organized the tour for my hometown of Lexington, Kentucky. I recorded my conversations along the way and produced a solar tour podcast episode.

All in all I’m very happy about how the show is going so far but I’m disappointed that I haven’t done a solar fundraiser yet. So it’s time to get to work and make that happen. I will keep you up to date in the coming weeks.

It’s good to take a look back every so often and see where you might need improvement. But it’s not nearly as useful as honest feedback from other people. If you have some ideas about how I could improve the show please take a second and send me an email at david at

John Perlin, author of Let it Shine: The 6,000 Year Story of Solar Energy

My featured guest today is John Perlin, author and solar historian. It’s kind of fitting that he’s on our one year anniversary show. I’m excited that Clean Power Planet has made it to the one year mark and John is excited about telling the world that solar energy has been around for 6,000 years.

He’s written four books on solar energy and forestry. His current book is Let It Shine: The 6,000 Year Story of Solar Energy. Mr. Perlin works at the University of California, Santa Barbara, Department of Physics and Student Affairs. He worked with Nobel Laureates Walter Kohn and Alan Heeger to produce the film, “The Power of the Sun,” which shows how Einstein’s discovery of the photon helped lead to the development of today’s booming photovoltaic industry. He also consults for UC Santa Barbara Student Affairs on solar energy and energy efficiency for its buildings.

JP: I heard someone say, Oh, you think solar’s new. Why I heard my granddad had solar on his roof in Los Angeles and so I decided to start examining the real roots of solar energy that none of our history books teach us, that none of our classes teach us, that not even any of these conferences teach us, the hidden story of solar energy, that in fact makes solar the most used energy resource for the longest time after firewood.

DB: Wow, I did not know that.

JP: Yeah see that’s the thing. It’s really interesting, people all talk about how we’re approaching the solar age. We’ve been in the solar age for the last 6,000 years and this is what my book, “Let It Shine: The 6,000 Year Story of Solar Energy” shows. And it’s all based on documents that are in archives all over the world or in archeological digs, or for example a transcript, of Socrates giving a lecture on solar passive architecture to his students and it was transcribed by Xenophone who wrote, he was an acolyte of Socrates and he was an even more prolific writer of Socrates’ statements than Plato. And it’s all in the library.

DB: Well tell me a little bit about the history of solar. I guess you’re primarily talking about passive solar.

Passive solar was just the beginning

JP: Oh no, I’m talking about all the technologies. For example, passive was the beginning. But very soon the Romans in about 1st century A.D. discovered that glass traps solar heat as we know. And so they applied that knowledge to not only to their buildings but to heating their baths, to forcing their plants to grow out of season, vegetables, things like that. And also the Chinese in the Bronze Age developed solar concentrators which troves have just been found in the last ten years. Confucius said that every eldest son should carry a solar igniter, which is a solar concentrator, because it was his duty to light the evening cooking fires.

DB: What did they look like? What were they made of?

JP: Well they were made of, I have a picture here in the book, they’re made of bronze and they look like a wok but the only difference is they have a handle. So when people first found them they said, they can’t be a wok because you wouldn’t have a handle on the other side because if you held a wok when it was cooking you wouldn’t have a hand right? So what they did was they restored one. They polished it. They focused it on a combustible material and in 15 seconds they had a fire and this was dating back to about 900 B.C. and so here we have the beginning of concentration. And concentration became a very popular mode of scientific experimentation in the renaissance. And science began as a spectacle. And what could be a greater spectacle than melting metals with the sun with concentrators? And even solar water heating began in the 1880s, commercial. But also using glass in a solar heat trap in a small box was developed in the 1700s and it became the model for the discovery of carbon dioxide in 1856 as the most intense absorber of heat of all of the atmospheric gases. So just on the Cleantechnica website and in the book, the story of the discovery in the middle of the 19th century using solar apparati to discover the greenhouse effect, the carbon dioxide in the 1850s and that was, once again, well documented but nobody ever looked at it before.

DB: So can you explain in a little more detail how they did that, what this looked like?

JP: Basically, two layers of glass in an insulated box. Okay, the glass allows the shortwave radiation in but then when it’s transformed into heat waves they’re too long so they can’t escape. So the heat gets accumulated inside the box up to about 300 degrees Fahrenheit. So that explains why the atmosphere protects us from extreme cooling. However, a scientist in the 1850s Eunice Foote took the various components of the atmosphere, the gaseous components, in one of these hot boxes and saw that carbon dioxide actually makes things a lot hotter and keeps that heat in a lot longer than hydrogen, helium or plain old atmosphere.

DB: And when did you say she discovered this?

JP: 1856. Published in Scientific American. Published in the Journal of American Science. No big secrets. No conspiracies. It was well-published, well-deduced, and then a scientist named Arrhenius showed that with the burning of coal during the 19th century, not only had they offset all the carbon sinks but they were actually increasing the carbon dioxide exponentially with increased industries. In 1767, Fourier used de Saussure’s model to show how the atmosphere works. In the 1820s. Eunice Foote showed that carbon dioxide was indeed the most potent of all the heat storing gases and then Svante Arrhenius did the mathematics to show to what extent it is. And it was all done before the 20th century.

DB: And our United States Congress has not reviewed this cutting edge research.

JP: Cutting edge research! Well that’s the amazing thing about the entire book is all this cutting edge research that everyone talks about has been known for, if not thousands of years, hundreds of years. Because I show in this book too how photovoltaics begin in the 1870s but science could not explain what was happening because science was based on thermodynamics, heat, and these people showed that it wasn’t the heat of the sun that was creating the electricity it was light and it had to wait for Einstein’s 1905 paper on photoelectricity that showed that light itself, as photons, carries energy that’s inversely proportional to the wavelength. And so that’s why we design today our solar photovoltaic PN junction, which is the heart of the solar cell, very close to the surface because the shorter wavelengths, as Einstein showed in 1905, which he won the Nobel Prize for, it carries the most energy, the greatest amount of energy. So that’s why the heart of the solar cell is always kept very close to the surface to capture those very powerful photons coming from the shorter wavelengths. And that’s why at the dental office you wear that lead protector because X-rays are the shortest waves. And so they contain the strongest photons that will do damage to your body. So all of this is very firmly based scientifically. Global warming, everything solar is all based on very firm scientific ground and it’s been known and known for a long time these principles and yet the irony is the longest known energy resource is considered bleeding edge.

DB: Yeah, it’s all very novel.

JP: All very novel. And if people read the book Let It Shine, they’ll see how this all transformed the whole evolution of energy from the sun and also very well-documented from multiple archives throughout the world that I was the first person to ever have the curiosity to visit.

DB: Well that’s exciting. That’s a great topic for a book. How long has it been out now?

JP: It’s been out for about 14 months. And it took about, an accumulation of about 20 or 30 years of research.

DB: So tell me where can people find the book.

JP: People can find the book on Amazon. They can order it from their bookstores or I don’t know if you have my card but if they want signed copies they can send me a check for $25.

DB: And you’ll send them one?

JP: Send them one.

JP: Okay great.

DB: Tell me about some of the… I know this is not your first book so tell me about some of the other projects you’ve worked on.

The history of photovoltaics

JP: Well I did a book before on the entire history of photovoltaics, which is abridged in this book, but also since I did that I gave a lecture, two lectures at Oxford. And so I had time to stop off in London to put my hands on the first solar collector, I’m sorry, the first solar module, that was developed in the 1870s, which now I have in the book.

DB: And what does that look like?

JP: It’s basically a glass covered box just like a modern module and it has cylindrical pieces of selenium. And they shine a candle flame on the selenium and because the electrical measuring device, the needle jumped immediately they knew it wasn’t thermal because if it was thermal it would be very slow.

DB: Yeah it would ramp up gradually right?

JP: It would be a very gradual ramp up. So suddenly they said they were dealing with something totally unseen before by science and that was energy from light. Because you have to understand. Science was all based on heat during the 19th century. They thought that light was divided into light rays and heat rays and the heat rays is what activated anything solar. So William Grylls Adams and Richard Evans Day, the two discovered that light did not contain heat waves or light waves. They contained something else, which they didn’t know that cause the direct conversion of sunlight into electricity, which is probably the most amazing thing that’s ever happened in science. When you think of transforming light into electricity without any moving parts, without any change at all in the material. When you think about it, nobody talks about it like this. And I talk about it because it’s the most transformative idea ever introduced to humanity, to take the sun rays and suddenly have electricity, without any. You know people have always come to me and like where’s the solar panel because we don’t hear it. Or people say “Wow, it’s only made of a few microns. It sure must be real weak electricity.” And what I tell people is, all electrons are created equal, it was written in the declaration of independence. So you know it’s probably the most transformative, amazing technology because it’s greater than the attempts, and they all failed, changing lead into gold. This really works. And so these guys, they saw that there was something different in light than anybody knew. But it took Einstein’s genius to make the big leap and this was extremely disruptive to science because they all thought that light was a wave. And suddenly Einstein said, “Well, light’s not only a wave but it’s also a particle.” And the whole problem was science thought they had solved that problem because Huygens suggested light was a wave, Newton suggested it was a particle. And they thought they had proven in the 1800s that light was a wave. Pillar of science. And this guy Einstein from nowhere, he hadn’t even written his PhD thesis shows that light is also a particle. Then the greatest scientist of the time, Milliken, tries to prove Einstein wrong, calls him bold and reckless in the scientific papers. And the more and more exacting his experiments became, the more it showed that Einstein was right. And suddenly you had this whole new science called quantum mechanics. And this is why photovoltaics are so interesting to me, because it’s always been a disruptor of the way we think, but in a positive way. You have to understand that in the 19th century people believe that we had discovered everything and suddenly Einstein introduces this whole new science. And suddenly we think we have this solution to all the ways of producing electricity and suddenly the ideas of Einstein show that we can do it in a much better way. We can do it on our rooftops. We can do it anywhere in the world.

DB: Now the fellows that were experimenting with the glass box with the selenium cylinders, they probably didn’t anticipate this right? What were they looking for?

JP: It’s hard for us to accept that, sometimes failures are the best things that ever happen in life because they were laying the transatlantic cable, they were proposing to use selenium to test the cable’s quality control because they were putting it underneath the ocean, right? So they wanted to make sure the cables were good. And it was very resistive. It turned out that it was very changeable in its resistivity, depending on, they didn’t know whether it was sunlight or heat. But when it was exposed to sunlight, suddenly it became an extremely good conductor. So what they did was, the guy who discovered this put the selenium in water and then exposed it to sunlight. And he discovered that it wasn’t the heat because it was being cooled. It was the rays of the sun alone. So these two scientists, in fact all the scientists of Europe were just amazed. For the first time a material could be changed by light and so they started all sorts of experiments. Then they decided, well let’s see if we connect the selenium to an electrical measuring device called a galvanometer, bring a candle next to it and see what happens. And voila they get this jump in the needle then when they put the curtain between the flame and the selenium material it just dropped immediately. That makes it, we’ve discovered something totally new. Light producing electromotive force. And suddenly the greatest scientist of the time, Maxwell is amazed by this. Nobody wanted to publish the paper because they thought it was just too out there, right? Too heretical. Science is interesting because scientists are what’s called conservative revolutionaries. They try to maintain the status quo until proven otherwise, but once it’s proven otherwise they all capitulate.

DB: Now what were the names, what was the name of the fellow who put the selenium under water?

JP: His name was a very funny name, Willoughby Smith.

DB: Okay. And what about the guys that had the glass box? What were their names?

JP: William Adams and Richard Evans Day and they discovered that light could produce, when light shined on the selenium you could create an electromotive force and it wasn’t the heat of the sun but the light of the sun. And this is really hard for most people to imagine today. They think that somehow you need hot sun. So that’s why in Pennsylvania people say in the winter time it won’t work. But you’re not working with the heat. In fact solar cells are more efficient as the temperature drops. So you’re only dealing, and I can’t make more emphasis with this and this is what they said in 1875, we’re dealing with light. And that’s what tripped up all of the scientists at the time, was that in the 19th century everyone thought that the only way you could drive an engine was through heat. You couldn’t do it with light. But then Einstein changed all that when he showed that light indeed has energy on its own called photons and actually photons are light. One scientist really didn’t like this at all. He said, “What do we have to think that light is a particle on Monday and Tuesday and Wednesday and a wave Thursday and Friday and Saturday”, right?  And that’s how it is. That’s how nature is. You can’t force nature to be something it isn’t if it doesn’t conform to your need for order.

DB: It’s a shame, um, I’d say it would be a shame if you were a scientist around the time of Einstein and one of your most memorable accomplishments was a sarcastic remark you made about Einstein.

JP: Actually nobody believed in the reality of the photon for 18 years. Then Arthur Haley Compton took a Gamma ray, which is a short wave and it carries photons, shot the photon at an electron. And you had a deflection like in a billiard ball game. There was no question after that because that particle from the gamma ray deflected the electron and also that collision caused the gamma ray itself to slow down. And they have a thing called a cloud chamber where you can see the changing wavelengths and as you go from blue to yellow to red the wavelength gets longer and the photons get less powerful. So that demonstration in 1923. There was no way you could not think of light as a particle.

DB: That’s pretty exciting.

JP: That’s why for me photovoltaics is such an exciting science. It’s the only power source, energy source we have based on 20th century science.

DB: So you started down this road because you were upset about an oil refinery moving into town.

JP: I was just curious if solar could do it. And I spent a half year in the library researching and this was the beginnings and there seem to be so many great ways of using the sun because

  1.      it’s low heat so it’s perfect for house heating
  2.      It carries particles called photons that interact with the most modern materials called semiconductors, which can produce electricity.
  3.      Then it can be concentrated to higher heats, which can be used for various purposes like making steam.

So there’s just so many ways we can use it. Just designing houses properly to use solar energy in wintertime and keep it off our houses in summertime would go a long way in saving the amount of energy we use today.

DB: Alright. Well thank you very much John. I appreciate your time. It was good talking to you.

JP: Yeah.

Where to find more about John Perlin

You can find links to John Perlin’s books and articles as well as his contact information by going to

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