Did you know that the amount of sunlight that falls on the earth’s surface in one and a half hours is enough to drive the energy consumption of the entire world for a full year? Solar energy has incredible potential to power our daily lives thanks to ever-improving technologies.
Solar power systems come in all shapes and sizes. Residential systems are on rooftops across the United States, and businesses are also choosing to install solar panels to offset their energy costs. Utility companies are also building large solar power plants to provide cleaner power to all customers connected to the grid.
There are two main types of solar energy technologies: photovoltaic (PV) and concentrated solar power (CSP). You are probably most familiar with photovoltaics, which is used in panels. When the sun shines on a solar panel, photons from sunlight are absorbed by the cells in the panel, creating an electric field across the layers and causing electricity to flow.
The second technology is concentrated solar power, or CSP. It is mainly used in very large power plants and is not suitable for residential use. This technology uses mirrors to reflect and focus sunlight onto receptors that collect solar energy and convert it into heat, which can then be used to produce electricity.
Every place on Earth receives sunlight for at least part of the year. The amount of solar radiation that reaches any point on the earth’s surface varies according to:
Geographic location
Time of the day
Season
local landscape
Local weather.
Because the Earth is round, the sun hits the surface at different angles, ranging from 0° (just above the horizon) to 90° (directly overhead). When the sun’s rays are vertical, the Earth’s surface receives as much energy as possible. The more inclined the sun’s rays are, the longer they travel through the atmosphere, becoming more scattered and diffuse. Because the Earth is round, the frigid polar regions never get high sun, and because of the tilted axis of rotation, these areas get no sun for part of the year.
Earth revolves around the sun in an elliptical orbit and is closest to the sun for part of the year. When the sun is closer to Earth, the earth’s surface receives a little more solar energy. Earth is closest to the sun when it is summer in the southern hemisphere and winter in the northern hemisphere. However, the presence of vast oceans moderates the hotter summers and colder winters one would expect to see in the southern hemisphere as a result of this difference.
The 23.5° tilt in the Earth’s axis of rotation is a more important factor in determining the amount of sunlight striking the Earth at a given location. The tilt results in longer days in the Northern Hemisphere from the vernal (vernal) equinox to the autumnal (autumn) equinox and longer days in the Southern Hemisphere for the other 6 months. Days and nights are exactly 12 hours long at the equinoxes, which occur each year around March 23 and September 22.
Countries like the United States, which are located in the mid-latitudes, receive more solar energy in the summer not only because the days are longer, but also because the sun is almost up. The sun’s rays are much steeper during the shorter days of the winter months. Cities like Denver, Colorado (near 40° latitude) receive almost three times as much solar energy in June as in December.
The rotation of the Earth is also responsible for the hourly variations of sunlight. Early in the morning and late in the afternoon, the sun is low in the sky. Its rays travel further through the atmosphere than at noon, when the sun is at its highest point. On a clear day, the greatest amount of solar energy reaches a solar collector around solar noon.
