Daily Cleantech

Daily Cleantech: Aleksandr Stoletov and the First Solar Cell

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On August 10, 1839, the eminent Russian physicist Aleksandr Grigorievich Stoletov is born (August 10, 1839-May 27, 1896).  Stoletov built the first solar cell based on the outer photoelectric effect (discovered by Heinrich Hertz in 1887).

Born to the family of merchants in 1839, Alexander’s early life was one of study. He learned to read by the time he was four.  Between 1849 and 1860 Stoletov studied physics and mathematics at Moscow State University, where he would become a teacher in 1865.  As a professor worked to establish a physics laboratory for the school (which opened in 1872), so students would not have to go abroad to preform research. By his mid life, Stoletov was a world renown physicist, having developed a theory of “electro-techniques” and discovered important patterns in the magnetism of iron.

In 1888, he turned his attention to the photo effect, which was discovered by Hertz the year before.  He built the first solar cell based on Hertz’s theory and earlier solar technology developed by Charles Fritts in 1883.  Stoletov’s cell was more stable and reliable than the highly inefficient Fritts model.  But it was not until Russell Ohl patented the idea of the junction semiconductor solar cell in 1946, that the modern day solar panel was born.

Additional Stoletov contributions to solar energy also includes the fact that solar cells decrease in efficiency as they age and the direct proportional link between the intensity of electromagnetic radiation acting on a metallic surface and the photocurrent induced by this radiation.  This became known as Stoletov’s Law.

Daily Clean Tech: John Ericsson and His “Sun Engines”

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John EricssonOn July 31st, 1803, Swedish inventor John Ericsson was born (July 31, 1803 – March 8, 1889).  Most famous for his design of the USS Monitor, Ericsson explored commercial applications for solar power and build seven “sun engines” between 1868 and 1875. 
The “sun engines” were powered by steam or hot air and fueled by solar energy.

After inventing in England and being forced to give up all of his English patent rights to pay off his debts, Ericsson immigrated to America in 1839.  He is most well known for his engines and maritime propulsion systems, such as the first marine “screw” propeller-driving iron steamship, the USS Princeton (the first propeller driven warship), and the ironclad Civil War warship the USS Monitor

While his maritime inventions brought Ericsson fame and success, he found himself deeply distressed about the rapid consumption of coal as a fuel source.  He and his contemporaries already feared it was running out.  To provide society with alternatives, Ericsson explored renewable energy sources such as solar, tidal, wind and gravitational power. 

In one of his many scientific papers on the commercial use of solar energy in the 1870’s Ericsson wrote, "a couple of thousand years dropped in the ocean of time will completely exhaust the coal fields of Europe, unless, in the meantime, the heat of the sun be employed... the skillful engineer knows many ways of laying up a supply when the sky is clear and the great store-house is open, where the fuel may be obtained free of cost and transportation."

In the book Contributions to the Centennial Exhibition (1877, reprinted 1976) Ericsson presented his "sun engines.”  They collected solar heat for a hot air engine.  He built the first one in New York in 1872 and had intended Californian farmers to use the sun engine for irrigation purposes.  However, nothing came of the project.  Several designs later, Ericsson’s engines were a commercial success, but the heat was supplied by methane gas, instead of the sun.

Despite this design modification, Ericsson’s life contributed to the exploration of renewable energy and his efforts paved the way for the advancement of clean technology. 

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Photoelectric Effect Discovery Leads to Photo Cell Development

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Wilhelm Hallwachs

June 20th in clean tech history honors the death of German physicist Wilhelm Hallwachs (b. Darmstadt Germany, 9 July 1859; d. Dresden, Germany, 20 June 1922).  As an experimental physicist, he laid the foundations for research on photoelectric processes and in 1904 discovered that a combination of copper and cuprous oxide is photosensitive. Modern photo cells are based off of his discoveries.

Hallwachs wood cut

At Leipzig in 1888, Hallwachs investigated photoelectric activity.  He followed the model of Heinrich Hertz’s studies, of whom he was a student.  Hallwachs established that through absorption of ultraviolet light, negatively charged metal plates discharge and uncharged metal plates become positively charged.

This process, which is called the photoelectric effect or Hallwachs effect.  The photoelectric effect is a phenomenon in which electrons are emitted from matter (metals and non-metallic solids, liquids or gases) as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light.  Electrons emitted in this manner may be referred to as "photoelectrons."

Photoelectric EffectThe photoelectric effect forms the basis for the physics of the photoelectric cell and was theoretically interpreted in 1905 in Einstein’s work on light quanta.  Hallwachs’ observations laid the foundation for the later development of photo cells, TV camera imaging and other light-sensitive electronic devices.