Questions and Answers by John Perlin, Author, Let It Shine: The 6000-Year Story of Solar Energy

How and when was the photovoltaic effect discovered in a solar cell?

In 1872 British engineer Willoughby Smith published a paper on the photo­­-sensitivity of selenium. The article led English scientists William Grylls Adams and Richard Evans Day to further experiment with the material. In one of these trials they lit a candle an inch away from same bars of selenium that Smith had used. The needle on their measuring device reacted immediately. Screening the selenium from light caused the needle to drop instantaneously. The rapid response ruled out the possibility that heat from the candle’s flame was the cause, because when heat is applied or withdrawn in thermoelectric experiments, the needle always rises or drops slowly. “Hence,” the investigators concluded, “it was clear that a current could be started by the action of light alone.” They wrote that they had discovered a completely new phenomenon – that light had caused a flow of electricity through a solid material. Adams and Day called current produced by light “photoelectric.” Today, we call it “photovoltaic.”

 

So why didn’t photovoltaics take off in the nineteenth century?

American inventor Charles Fritts did put together selenium modules and placed a test array on a New York rooftop in the mid 1880s. He optimistically predicted that soon his modules would compete on the market place with the new electric power plants established by Thomas Edison. Europe’s Edison, Werner von Siemens, called photovoltaics to be “scientifically of the most far-reaching importance,” and the world’s leading physicist of the nineteenth century, James Clerk Maxwell, called Adams and Day’s discovery as “a very valuable contribution to science.” But the science of the nineteenth century lacked the wherewithal to explain the direct transformation of light into electricity. The rejection by Adams and Day of a thermal effect producing the electricity from the selenium bars led most to dismiss the discovery as heretical as the science of the day believed that only heat could produce power.

So how did the scientific community come to accept photovoltaics as a legitimate area of study?

Einstein’s new understanding of light combined with the late nineteenth-century discovery of the electron uncovered the secret of photovoltaics: light consists of packets of energy, according to the new science, capable of setting electrons into motion whose orderly movement is electricity. 

Did scientific acceptance lead to practical developments?

Scientific acceptance led to a flurry of activity in the photovoltaic field. But try as they may, no one could construct a solar cell efficient enough for everyday power needs. As one scientist lamented in 1949, “It must be left to the future whether the discovery of materially more efficient cells will reopen the possibility of harnessing solar energy for useful purposes.”

So what happened?

The semiconductor revolution began at Bell Laboratories that started with the discovery of the transistor and took silicon electronics from theory to working device led to the great breakthrough that we are celebrating this year. Serendipitously, Gerald Pearson, a Bell scientist, took one of the first silicon transistors and applied light to it. To his surprise, he recorded an efficiency of almost six times greater than any other solar cell had ever produced. Like Archimedes, he ran down the hall at the lab, shouting to a colleague, Daryl Chapin, who was working with selenium at the time for a remote telephone power project, “Don’t waste another moment on selenium!,” and gave him his piece of doped silicon. So began the Bell Solar Battery project that a year later in 1954 produced the most significant breakthrough in solar history and perhaps, the history of electricity – a solar cell capable of converting enough sunlight directly into electricity for useful purposes.

What was the reaction of the world to the Bell discovery?

The day after Bell executives presented the first practical solar cell to the world at a press conference on April 25, 1954. The following day The New York Times noted on page one, that the Bell solar cell “…may mark the beginning of a new era, leading eventually to the realization of one of mankind’s most cherished dreams – the harnessing of the almost limitless energy of the sun for the uses of civilization.” U.S. News and World Report came out with a story as full of hope as the Times’ piece with the title: “Fuel Unlimited,” exclaiming that the silicon solar cells “may provide more power than all the world’s coal, oil and uranium…Engineers are dreaming of silicon powerhouses. The future is limitless.” 

Why didn’t the silicon solar cell immediately take off?

First, its price was an obstacle. One watt cost $286. More importantly, at the moment of the solar breakthrough, the Eisenhower Administration, to counter worldwide anti-nuclear protests, initiated the Atoms for Peace program, to give nuclear a happy face. Subsidies and funding for nuclear ran into the billions. There was no parallel Solar for Peace program despite that the Bell breakthrough happened at the same time. Selling the peaceful atom as the world’s future energy source had become America’s number one priority. The nuclear dream eclipsed any consideration of solar development. Newsweek judged "the sun's diffuse radiation" as "paltry" when compared with what nuclear could do. The best solar enthusiasts could hope for, according to the prevailing wisdom of the middle and late 1950’s, was to plan for far-off energy needs. The New York Times best articulated this point of view, predicting in an editorial, "Electricity from the atom will keep industry turning and homes lighted for centuries in the future. And the energy of the sun...will be available after the last atomic fuel is gone."

What happened to the Bell solar cell?

After such high expectations, the inventors could not help but wonder, “What to do with our new baby.” Desperate to find commercial applications, solar cells found their way powering novelty items such as toys and transistor radios. Then the space race came. The first two sputniks went dead after several weeks in space as they ran on battery power alone. No one could go up and recharge or replace them. For the same reason fuel-powered engines were ruled out. Any satellite that had to function for more than three weeks or so on solar cells appeared to be the perfect source of power. The first solar-run satellite – the Vanguard - went up in March, 1958. It kept on transmitting data over the next six years. The success of solar on the Vanguard led engineers and scientists working with satellites to accept the solar cell as one of the critically important devices in the space program since they provided the only practical power source for long-term missions. The urgent demand for solar cells above the earth opened an unexpectedly large and lucrative business for manufacturing them. Locked into the space race with the Russians, the American government poured millions into solar cell research and development. As solar-cell pioneer contends, “The onset of the Space Age was the salvation of the solar-cell industry.”