Conduct a Google search for “the history of photovoltaics” and you’ll quickly run into the name Alexandre Edmond Becquerel. It seems that Becquerel is universally recognized as the father of PV. In fact, the European Commission hands out periodic Becquerel Prizes for outstanding achievements in photovoltaics. But one solar historian thinks Becquerel’s contribution has been overstated.
I was very fortunate to have John Perlin as a recent guest on the Disruption: Solar Energy podcast a few weeks ago for a chat about solar and his new book Let It Shine: The 6,000 Year Story of Solar Energy. While reading Let It Shine, I noticed one glaring omission upon reaching Perlin’s account of the PV epoch in the history of solar. Where is mention of Alexandre Becquerel? When I pressed this, Perlin replies thusly:
“[Becquerel’s] contribution has been overstated because, first of all, he witnessed only a change in EMF (electromotive force), not an initiating of an EMF by the direct conversion of solar energy into electricity. And also he was using not a solid material which we rely on today. Actually, it was in 1876 that William Grylls Adams and Richard Evans Day took a piece of selenium and shined some candlelight only about four feet away from the selenium, and they encountered something no one had ever seen before — the direct conversion of sunlight into electricity.”
Perlin goes on to explain that this observation was the first of it’s kind. The science at that time was that only heat could power an engine. He finally wraps up this part of the interview by revisiting Einstein’s explanation of light as quanta.
After Becquerel’s discovery, a huge gap takes place in PV history. Nothing happens for 40 years or so. Technology is linear. New developments build upon previous concepts. Clearly, Adams and Day did not rely on Becquerel’s knowledge to make their discovery. Their discovery was influenced by James Clerk Maxwell by way of Willoughby Smith. Here’s an excerpt from Let It Shine.
The great scottish scientist James Clerk Maxwell wrote in 1874 to a colleague: “I saw conductivity of Selenium as affected by light. It is most sudden. Effect of a copper heater insensible. That of the sun great.” Maxwell was among many European scientists intrigued by a behavior of selenium that had first been brought to the attention of the scientific community in an article by Willoughby Smith, published in the 1873 Journal of the Society of Telegraph Engineers.
Smith, the chief electrician (electrical engineer) of the Gutta Percha Company, used selenium bars during the late 1860s in a device for detecting flaws in the transatlantic cable before submersion. Though the selenium bars worked well at night, they performed dismally when the sun came out. Suspect- ing that selenium’s peculiar performance had something to do with the amount of light falling on it, Smith placed the bars in a box with a sliding cover. When the box was closed and light excluded, the bars’ resis- tance — the degree to which they hindered the electrical flow through them — was at its highest and remained constant. But when the cover of the box was removed, their conductivity — the enhancement of electrical flow — immediately “increased according to the intensity of light.”
But this time, unlike Becquerel’s discovery, there is a connection of subsequent steps leading up to modern photovoltaics, an historical chain of custody, if you will. From selenium to silicon to thin film, the roots of PV trace back to Adams and Day.
So why does Becquerel’s name show up so much in the history of PV? Can it be explained by the geopolitical circumstances of the time? Did nationalism play a role? Maybe. What I do know is that there should be an Adams and Day Prize instead of, or in addition to, the Becquerel prize. Here are some final words from Perlin sent to me via email on the matter:
“And why isn’t there a Chapin-Fuller-Pearson award for the inventors of the
silicon solar cell, responsible for today’s great solar revolution? Let’s get Adams and Day and Chapin, Fuller and Pearson their rightful recognition as the true progenitors of modern photovoltaics!”
If you’d like to learn more you should read John Perlin’s historical account of solar energy, Let It Shine. The book does not disappoint.