Solar Energy

It is no understatement that solar energy is the lifeblood of our planet. Weather, oceanic circulation, and life owe their existence to the energy output of our sun. Although it is true that solar energy is responsible for heating up our planet, there is a common misconception that solar energy and thermal infrared energy are synonymous. In fact, only a small proportion of the direct solar beam is composed of thermal infrared energy.

The sun is a star that has natural variation in output but the variations are currently insignificant enough to maintain life on Earth. The evolution of the sun and certain prehistoric output changes has been known to force climate change, but the present status of the sun is not such that we do not expect large changes in the next thousands of years. Sunspots are dark features on the sun’s radiating photosphere some 1,500°C cooler than their surroundings. They are caused by disturbances in the interior solar magnetic field. These disturbances are tube-shaped and sometimes pop above the photosphere. Sunspots occur where the magnetic field lines leave and enter the photosphere. These areas can grow until some reach sizes exceeding 30,000 km with individual sunspots usually lasting a few days to a few months. Numbers of sunspots cycle over 11–13 years, and increased numbers of sunspots are associated with increased solar activity. It has been conjectured that solar cycles influence weather and climate but this relationship is unclear because of all the other factors influencing Earth’s atmosphere. Prominences, coronal mass ejections, and flares are other output variations related to sunspots. However, the measured year-to-year solar variability at the top of Earth’s atmosphere is about 0.1 percent of the average. 

The sun is able to emit huge amounts of energy through space because its gases are heated as a result of fusion. The hotter a substance, the more energy it radiates because of the greater intensity of molecular vibration. The vibrating electrons of the gases’ molecules emit electromagnetic energy, and this energy is propagated through the void of space and through our atmosphere. In space, the speed is about 300,000 km per second with the speed of transmission through our atmosphere being negligibly slower. Solar energy can penetrate some Earth materials. Solar output is a staggering 3.31 × 1031 joules per day. Of course, Earth is small and 150 million km distant and the sun radiates in all directions, so we receive only about one two-billionths of the total solar output. The mean instantaneous solar input is 1.74 × 1017 joules per second at the top of the atmosphere; compare this figure with the “measly”1.5 × 1013 joules per second consumed by human activity on the planet.