Solar energy is all around us. No, I am not talking about the silicon based solar panels that are cropping up around the globe, but rather I am talking about the actual light coming from the sun. The true ‘solar power’. The thing that made life on this planet and at the end of the day, the reason for, well, everything.
Solar radiation is amazingly abundant and fascinating and yet most people have very little knowledge about what light actually is, how much energy hits earth, and just why the sun keeps on keeping on like it does.
Although I may not go into every detail, in this article I want to touch upon some of the topics related to our very own Helios- the sun.
First thing is first: the sun is not a giant flashlight aimed at earth for 12 hours and then rotated. At its core, the two are fundamentally different, and yet to many people, that is the end all be all when it comes to our star.
The sun is a giant ball of burning gas constantly undergoing fusion processes. These fusion reactions create and expel photons, or light particles. We can think of a photon as a tiny ball that travels along a wave. The wave has a certain frequency, which determines its energy as well as visibility. For humans, we are only able to see photons that travel within the visible spectra. Interestingly, the visible spectra accounts for only about 40% of the total light that reaches earth. This helps to explain why people get sunburned on cloudy days.
Energy is generally measured in BTU’s or British Thermal Units. The sun sends anywhere between 600 to 2000 BTU’s of photon based energy per square foot to earth. Intuitively, the places that get a bit more energy is the ones that are ‘closer’ or see a more direct line to the sun. This includes the Sahara, the South West United States, and other clear, equatorial desert systems.
However, before the sun’s rays even reach the surface of the earth, they must undergo a rigorous and intensive “selection” process. For close to 31% of the sun’s rays, they are simply reflected away by clouds, water vapor, or other reflective atmospheric surfaces. The reflected light is known as earth’s albedo and is the reason why earth, when viewed from the moon, is so bright and illuminated.
Another 19% is absorbed into atmospheric gasses such as CO2, O2, and N2 which later emit the absorbed energy (this is the cause of the well-known ‘greenhouse effect’).
From these statistics, it is relatively easy to conduct a radiation based energy balance for the earth’s surface. We can see, that from the absorbing nature of the airborne chemicals coupled with the delicate balance of terrestrial exposure, the earth’s atmosphere is finely tuned to regulate temperature with a mix of cloud cover and chemic reemission.
Interestingly, the amount of sun that hits the Northern Hemisphere during the summer months should induce a far greater temperature alteration than is generally experienced by the earth’s terrestrial climate. This buffering a combination of increased cloud cover (got to love those afternoon thunder storms) resulting from an increase in evaporation. However, the cloud cover also serves as an insulation increase and in some ways keep terrestrial temperatures stable.
Knowledge of solar fundamentals is crucial when determining if solar energy is appropriate for a certain situation. Although it may sound intuitive, places further north often are not ideal candidates for solar cells simply due to the decrease in sunlight exposure. Pockets of New Hampshire and Vermont only get around 1100 BTU/ ft^2 whereas Arizona and Nevada see closer to 1900. That means a solar cell in NH may be close to half as effective as one in NV (temperature efficiencies aside).
All in all, it is crucial to understand how the sun’s immense power offers great potential to solve the world’s energy issues. After all, all of the energy we currently have (hydro, oil, coal, etc…) is at its core just a trapped form of the sun’s energy. At the end of the day, we owe it all to that big yellow orb in the sky.
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