I wanted to learn more about solar energy and I decided to start from the sun because that's where it all starts. The sun, our star is central to all life on Earth! Current theories state that the sun and everything else in the solar system formed from the leftover clouds of gas and dust from a massive star that went supernova. The cloud was mostly hydrogen and helium with trace amounts of other materials.
The sun formed from the coalescing of the materials in the clouds due to their mutual gravitational attraction. After a period of time as the proto-sun continued accumulating more material, it started to collapse under its own weight and build up pressure at the core. As the pressure increased, the temperature at the core started to rise. The pressure at the core is 340 billion times that of the earth at sea level and temperature is approximately 13,600,000 ºC. The present state of the sun is such that the inward pressure of all the material in the outer layers is matched by the outward pressure at the core.
The sun formed from the coalescing of the materials in the clouds due to their mutual gravitational attraction. After a period of time as the proto-sun continued accumulating more material, it started to collapse under its own weight and build up pressure at the core. As the pressure increased, the temperature at the core started to rise. The pressure at the core is 340 billion times that of the earth at sea level and temperature is approximately 13,600,000 ºC. The present state of the sun is such that the inward pressure of all the material in the outer layers is matched by the outward pressure at the core.
The sun is enormous: it's diameter is approximately 864 million miles and equal to about 109 earths; it's volume is equal to approximately 1,300,000 earths. It is so massive that it comprises approximately 99.9% of the total mass of the solar system including that of the planets, moons, proto-planets, asteroids and comets. It is comprised of about 75% hydrogen, 24% helium and small quantities of other elements like oxygen, neon, iron, carbon and silicon.
At the very center of the sun, the pressure and temperature conditions are favorable for nuclear fusion to occur. Nuclear fusion is the process by which atoms are able to overcome their repulsive electrostatic force and bind to another atom by their attractive nuclear force and release tremendous amounts of energy in the process. The only place this can happen is at the core of stars.
In this process the mass of four hydrogen atoms fuse into a single helium atom and release roughly 0.7% of the combined mass as energy per Einstein's famous equation E=mc2, where E is the energy released, m is the mass lost in the conversion process and c is the speed of light in a vacuum. In one second, the sun converts 600 million metric tons (tonnes) of hydrogen into 595.8 million tonnes of helium; the missing 4.2 million tonnes are converted into energy. Every second, the sun releases approximately 386x1026W of power; the sun releases more energy in one second than used by man in our entire existence!
In the mass-energy conversion process at the core, photons or "packets of energy" are released. It takes anywhere from 10,000 to 170,000 years for the photons to get from the core to the outer edge of the sun called the corona. This is due to the photons continuously being deflected from their path by electrons. Once free of the corona, the photons reach the earth, about 93 million miles away, in about 8.3 minutes. The photons are received by the earth as light and heat.
The sun also emits charged particles (electrons and protons) through its corona as the solar wind. Every second a million tonnes of these charged particles are emitted by the sun as the solar wind; we detect these particles as they interact with the earth's magnetic field as polar auroras or the northern and southern lights. The matter-energy conversion process also release neutrinos, inert particles that aren’t affected by and pass right through matter.
The sun has so much mass that even with the tremendous mass loss through the matter-energy conversion process and through the solar wind, it is estimated it has enough material to last for another 5 billion years. And it is estimated our sun has been in existence for approximately 4.6 billion years!
The photons or sunlight received by the earth is used by plants for energy in synthesising carbon into sugars and releasing oxygen, a process called photosynthesis. We can also use sunlight to create energy using various techniques. The estimated amount of power that the sun deposits on the earth is approximately 1300W/m2; however, due to atmospheric effects, the power is approximately 1000W/m2. It is estimated that amount of energy that falls on the earth for an hour could satisfy the entire energy needs of the world for a year!
As this abundant source of energy will be available for a very long time, we should find ways to utilize it. It is free, clean and with our ingenuity, could satisfy all of our energy needs. My next post will discuss some of the ways in which we can use this energy to create usable power.
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