Light and solar energy: life and progress

The laws of cosmology placed Earth, the Blue Planet, in third place in order of distance from the Sun, a location that allowed physical and environmental conditions suitable for the appearance of life. The Earth receives 174 petawatts (10¹⁵ watts) of solar energy. Thanks to it, the water cycle, the movement of air masses, ocean currents are produced, and photosynthesis takes place, the biochemical reaction essential for the development of primary producers, the basis for the rich and complex food chains of the biosphere. But what has the relationship between human beings and the star king been like? Who were the pioneers of the study of light and solar energy? From Aristotle to Fuller, through Newton or Einstein, in this post we will provide, in a pedagogical and entertaining way, brief keys to this fascinating story, a thrilling journey from the chloroplasts of cells to the photovoltaic panels that will give us the energy of the future.

Light, a gift from the gods

Solar energy has always been present in the history of the human species and, over time, we have been improving strategies and technology for more efficient use. Already in the Neolithic period, after the Agricultural Revolution, the peoples of that time sensed the inexorable importance of the sun for plant growth and the obtaining of crops, considering it synonymous with life and prosperity, which sparked an extensive mythology of worship and worship that turned our star into a divinity for all the civilizations of the ancient world; Utu in Mesopotamia, Ra in Egypt, Apollon for Greece and Rome or Itzanma for the Mayans, to name a few examples.

Light, Photosynthesis and Life

The birth of philosophy and the emergence of logos and knowledge in the face of myths, pushed human beings to interpret the light and heat of the Sun as an object of study and no longer of worship. In Physics, the most renowned work of Aristotle, the man who wanted to know everything, suggested that the green appearance of vegetables was directly related to sunlight. This statement, based more on intuition than on deduction, slept the dream of the righteous until well into the 18th century, specifically until the summer of 1778, when Jan Ingenhousz, a Dutch doctor who dedicated his holidays to the study of botany, carried out numerous experiments aimed at investigating the phenomenon of photosynthesis.

Ingenhousz applied scientific foundations to Aristotle's intuitions, his greatest finding being the demonstration that when plants were illuminated with sunlight they released oxygen, as well as the conclusion that photosynthesis could not be carried out anywhere in the plant, such as in roots or flowers, but only took place in the green parts of the plant. The path was already open so that, almost a century later, in 1882, Theodor Wilhelm Engelmann, one of the great German botanists of the 19th century, published his studies on the function of chloroplasts: “green bodies act as light collectors, inside which chemical reactions take place that convert solar energy into chemical energy”. Simply mind-blowing. What if human beings could use sunlight in a similar way? It is undeniable that until now it has been naturalists, biochemists or biologists who have worked the most to study light as an essential resource for photosynthesis and, therefore, for life. But what about physicists? What do they have to say? Let's go with them now.

Light in the Ancient World

The appearance of the first sundials was a milestone in that they were the first gadgets that used sunlight to work. This allowed human beings to measure time and establish schedules and routines according to different times of the day. Euclid, The father of geometry, (s. IV a. C.) was the first to make a treatise on light based on its physical properties: displacement and reflection. Almost a century later —and although it may be a legend—, the chronicles spoke of large mirrors that Archimedes (3rd century BC), one of the great physicists of Ancient Greece, had devised to defend Syracuse from the attack of Rome. Supposedly, these large auditory mirrors set fire to the sails of enemy ships, reflecting sunlight onto them. After the Greek scholars came Rome, the civilization of the 2,000 years, a culture that was based more on pragmatics than on the abstract, on engineering than on theory, so this search for praxis would lead them to build the first greenhouses during the term of Tiberius, the second emperor (1st century BC), mainly intended for a rich and varied cultivation of vegetables.

The Scientific Revolution and the Study of Light

Euclid's perspective had such predicament in the following centuries that no scholar dared to question its principles. We had to wait for the emergence of the scientific method at the beginning of the 17th century, the age golden of science, to once again approach the study of light. The decades of this century will see with amazement the passing of Descartes, Hook, Newton, Leibniz or Fraunhofer. The movement in which all of them were included, rationalism, obsessed them with studying the nature of light: what it was made of, how it formed or how it behaved from a physical point of view, but none ventured into the study of energy, not even Newton, the greatest scientific genius that the human species has illuminated in the millennia of history. In this way, Descartes enumerated the 12 properties of light, Newton dissected its rays obtaining colors, Leibniz delved into optics and Fraunhofer discovered the lines of his spectrum, perhaps the latter, the one that came closest to the study of its energy.

The beginning of solar thermal energy

It is often said that science is the result of the concerns of its time, and the fact that none of these great physicists noticed the energy use of light was due to the fact that, at that time, human societies did not have a great demand for energy, and industries were well supplied with coal, an abundant and very cheap fuel that guaranteed energy supply. Thus, seventeenth-century physics would tip-toe the energetic study of light. Everything would change at the end of the 18th century, when the restless mind of the Swiss Horace Bénédict De Saussure, inspired by the solar cannon of Archimedes, devised the solar collector (1762), which will have a decisive impact on the development of low-temperature thermal energy. The system consisted of a glass cover and a black metal plate enclosed in a box with its corresponding insulation and whose purpose was to cook food that was inserted into the cylinder.

The Saussera collector was rudimentary and inefficient, so a few decades later Lavoisier, the father of modern chemistry, devised his prototype of a solar furnace (1792), more efficient and evolved than the previous one. It was already, in 1865, when the French inventor Auguste Mouchout, extending his previous studies, created the first machine that converted solar energy into mechanical energy. The device was capable of generating steam using a solar collector and moving an engine thanks to the pressure generated. His invention was awarded a medal at the Universal Exhibition of 1878, but unfortunately, high costs prevented his invention from being used commercially, but these inventions were the embryonic germ of current solar thermal plants.

One more step; photovoltaic solar energy

Science is insatiable, and for the women and men who practice it, the challenges always outweigh the achievements, so what comes next is prodigious. The 19th century will experience the Second Golden Age of science and scientific eminences and discoveries of enormous scope will appear everywhere, like mushrooms in autumn: Dalton and the first atomic model (1803), Faraday and electromagnetism (1821), Maxwell and the mathematics of light (1871), Nico Tesla and alternating current (1891) or J.J. Thompson and the discovery of the electron (1897). In the heat of this scientific eruption, in 1839 the French physicist Alexandre Edmond Becquerel discovered the photovoltaic effect for the first time. Becquerel was experimenting with a platinum electrolytic battery and found that exposing it to the sun increased electrical current. It would be an essential advance for the design of subsequent photovoltaic cells.

The next step would be taken in 1873. The English engineer Willoughby Smith discovered the photoelectric effect in solids, in this case selenium. A few years later, in 1877, another Englishman, William Grylls Adams, professor of Natural Philosophy at King's College London, together with his students, discovered that when they exposed selenium to light, electricity was generated. In this way, they created the first selenium photovoltaic cell. Only a few years later, in 1883, New York inventor Charles Fritts devised the first solar panel in history by spreading a layer of selenium on a metal plate and coating it with a thin film of gold leaf. Although its effectiveness allowed only the first use of sunlight, it was the first time that human beings were able to convert solar energy into electricity.

The advances of the 20th century

Science is to advance and improve previous research, and in this sense, Albert Einstein was able to mathematically calculate the energy produced by the photoelectric effect using the famous Planck equation: E= h· v. His studies won him the Nobel Prize in Physics in 1921, a contribution that finally opened the door to photovoltaic cells. The results would not be long in coming. In 1954, at Bell Laboratories, Calvin Fuller, Gerald Pearson, and Daryl Chapin, invented the silicon solar cell, a new device that produced greater potential and was efficient enough to operate small electrical devices. A few days later, on April 26, 1954, the New York Time would publish an article entitled: “The enormous energy of the Sun is harnessed by a battery that uses an ingredient from sand”. The use of the sun for uses of civilization would no longer be the exclusive heritage of plant chloroplasts.

The first use of silicon cells was not long in coming. Just a year later, in 1955, Americus, a small town in Georgia (USA) would witness the first installation of an autonomous telephone system that operated with photovoltaic cells. But the main application of these panels was aimed at the space race. In 1958, the Vanguard I artificial satellite was launched, equipped with a sophisticated solar battery system, and in 1962 the Telstar I was the first satellite to emit telephone and television signals between the United States and Europe, fully operating with energy from the sun.

The momentum of solar energy increased during the 1973 oil crash, after the Yom Kippur War, but the subsequent fall in prices and the reduction of fossil fuels slowed down its implementation again. It would be as early as 1992, during the Persian Gulf War, at a new and complicated economic and political juncture, when Western countries re-promoted renewable technologies seeking energy independence and mitigating the effects of pollution.

Conclusions

In 2019, solar energy systems produced 630 GW, the equivalent of 600 nuclear power plants (Martil de la Plaza, I). The future of solar energy is bright, allowing humanity sustainable, clean and cost-effective energy that will considerably reduce the effects of global warming. His story is simply prodigious, it is the journey of many scientists who climbed on each other's shoulders to advance and progress, in a vital example of overcoming, restlessness, ingenuity and effort. A prodigious journey from ancient myths to photosynthesis, through batteries and solar ovens to the photoelectric effect. It is the energy that will make us move from utopia to hope.