How Did We Learn about Solar Energy? – Isaac Asimov

When people think about solar energy, they often think about the panels on rooftops and the sun shining brightly in the sky. However, it was the development of tools to study the sun that taught us about solar energy and changed how we use it. Here’s how we learned about solar energy, and how you can become an expert in this emerging field.

Early Research

While studying nuclear physics at the University of Manchester, Isaac Asimov spent a lot of time working on his own experiments. One of these experiments was to measure the solar constant – the total amount of solar radiation that falls on a square meter of Earth’s atmosphere – and see how it varied over a year. As expected, the solar constant fluctuated over the year, going up in the summer and down in the winter. This fluctuation was due to the fact that the Earth orbits the sun, and the seasons change as a result.

Determining the Solar Spectrum

The next step was to try to determine what wavelengths of light were absorbed by the atmosphere. At the time, no accurate measurements of the solar spectrum existed, so Asimov decided to create one himself. To do this, he took a spectrometer – which measures the intensity of light as a function of its wavelength – and set it up in the mountains near his home in California. With this setup, he was able to identify the wavelengths of light that were absorbed by the atmosphere and use this information to plot the solar spectrum. What he found surprised him: not only was there a wide range of wavelengths that were absorbed by the atmosphere, but there was also a strong peak in the ultraviolet range.

Interestingly, the solar spectrum does not match what we see on Earth. The atmosphere filters out some of the visible wavelengths, shifting the spectrum to the longer wavelengths. In addition, the amount of light in the ultraviolet range is greatly diminished due to the ozone layer in the stratosphere. This is why when people think about solar energy, they often think about the panels on rooftops – the majority of the sun’s radiation is visible light, which can be used directly for illumination purposes.

The Importance of Calculating Energy Yield

In his experiments, Asimov learned that the amount of energy a substance releases when it is irradiated by sunlight is known as its energy yield. When he calculated what this energy yield was for various elements, he was surprised to find that some elements produced more energy than others. For example, the sun’s energy yield per mole of carbon is about 12 times that of hydrogen. This means that when carbon is converted into energy, it releases 12 times as much energy as hydrogen.

While the energy yield of various elements varies, it is usually the case that the heavier the atom, the greater the energy it releases. For example, nitrogen has about the same energy yield as hydrogen, whereas oxygen has about 16 times the energy of hydrogen. This is because the nucleus of an atom contains a great deal of energy, which is transferred to the electrons as the atom gains angular momentum due to the force of the sun’s radiation. The energy released during this process is known as nuclear fusion.

Helium Is the Key to the Energy Future

The information gleaned from Asimov’s experiments would prove invaluable. One of his observations was that the element helium, which is mostly made up of two hydrogen atoms bonded together, has the highest energy yield of any element. This is because helium nuclei are the lightest of all nuclides, and as a result, they are the most affected by the sun’s radiation. This made helium an excellent choice for powering future nuclear fusion devices.

What is also interesting is that Asimov’s observations about the importance of helium would later be supported by other scientists. For example, William Happer, a physicist at the Lawrence Berkeley National Laboratory, observed:

“It always amazes me how many people think that carbon and hydrogen are the most important elements in the universe. They are only important because they can be used to make other elements. But helium, which is 10 times more abundant than carbon or hydrogen, is the key to the future of energy production. Once we have harnessed helium, we will have the energy to solve all our energy problems.”

Solar Energy and the Environment

When people think about solar energy, they often think about the benefits that it provides to humanity. However, there are also concerns about the environment. Asimov’s observations about the effect of the sun on the atmosphere would prove valuable, and his experiments with carbon would later be extended to study the effect of solar energy on the environment. In fact, it was Asimov’s experiments with carbon that led directly to his groundbreaking book, The New Physics, in which he describes the process of photosynthesis. In this book, he makes the case for a biologically-based economy rather than one based on fossil fuels.

One of the key findings of The New Physics is that “[e]very plant transforms solar energy into organic compounds, which are the building blocks of living things.” This process has profound environmental benefits. For example, plants use water indirectly through photosynthesis, allowing them to thrive in arid climates. In essence, the energy provided by the sun is essential to life as we know it.

Looking Toward the Future

Asimov’s findings about the potential of solar energy for powering the future were not met with universal acclaim. Many physics journals at the time were skeptical about his claims, instead seeing solar energy as a possible source of energy for weapons. Fortunately, the field of solar energy would not be derailed by these concerns. In the decades that followed, scientists would build on Asimov’s findings, and further discoveries would open up the doors to a field that would change the world.

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