Solar Energy: Solar Production and Radiation

Abstract

173 000 000 GJ of energy from the Sun enters Earth's atmosphere in the form of electromagnetic radiation every second. This is more than 10 000 times the rate at which the human race uses energy. Almost all the energy we use originally arrived on Earth in the form of solar radiation – the exceptions being nuclear, geothermal, and tidal energy. The energy released when we burn fossil fuels was stored away long ago by plants that used photosynthesis to convert solar energy into chemical energy. The energy in the food we eat has a more obvious solar origin in photosynthesis by the plants that we consume, or that were consumed by animals. Solar energy evaporates water, and heats ocean and land masses, generating wind currents from which power can be harvested.Winds, fueled by solar energy,move evaporated water above mountains and plains where it falls and gathers into rivers and reservoirs from which hydropower is derived. While most energy we use is solar energy in one form or another, direct use of solar energy still represents a very small piece of all human energy use. Solar energy is used in many places for some fraction of water and space heating, but in the critical areas of electrical and transport energy, use of solar energy is still marginal. For example, in 2015 the world derived about 1.3% of its total electrical energy from direct solar sources (over 97% photovoltaic and the remainder solar thermal electric conversion) [129, 130]. Although this is a small percentage, it has increased rapidly from a mere 0.065% in 2008. One of the greatest challenges of large-scale solar energy use is the diffuse nature of the resource. Unlike fossil fuels or nuclear power, which have very high energy densities, solar energy is broadly distributed across the entire planet. Even in arid deserts near the equator, a substantial land area is needed to gather industrial-scale quantities of energy. Most of the solar-derived energy used by humankind up to the present has been gathered and concentrated by natural systems into other more readily usable forms such as wood, coal, and petroleum. It may be, however, that in the long term direct use of solar energy will be the simplest and most efficient way to sustainably power our extensive and still-growing energy needs.