Solar Energy: A Comprehensive Guide
Solar Energy
What is Solar Energy?
The Sun is 93 million miles away. The tiny fraction of the Sun’s energy which hits the Earth is enough to meet all our power needs and more. The sun provides more energy in an hour than the U.S. uses in a year. We call the energy from the sun, solar energy.
Solar energy is transmitted to the earth in the form of radiant energy. It is vital to us because it provides the world—directly or indirectly– with almost all of its energy. In addition to providing the energy that sustains the world, solar energy is stored in fossil fuels and biomass, and is responsible for powering the water cycle and producing wind.
How Does the Sun Produce Energy?
Under extreme pressure, and at extremely high temperatures, nuclei of atoms and their electrons can separate, forming plasma. In this extremely high energy state, nuclei can get close enough to each other to fuse. When they fuse, they release tremendous amounts of energy. This is what happens in the sun’s core.
The energy produced by fusion can be reabsorbed by other nuclei and re-released in future fusion reactions. Energy released in the core of the sun can take thousands of years to find its way to the surface of the sun. Once the energy has left the sun, it is radiated as electromagnetic radiation toward space at a speed of 300 million meters per second, or 186,000 miles per second. At that speed, the energy needs only 8 minutes to reach the outer atmosphere of the earth 93 million miles away.
Once it reaches the earth, the incoming solar radiation, or insolation, is absorbed and reflected. The greenhouse effect, a naturally-occurring phenomenon, allows the energy from the sun to remain trapped near the earth’s surface, keeping the temperature of the earth in a comfortable range at night. Without the greenhouse effect, life on earth would be impossible.
Passive Solar Design
Passive solar design involves using specific shapes, angles, and building materials to maximize the amount of solar energy allowed into the interior of a building during cold months. Overhangs are used to shield the home from the high, summer sun, but are designed to allow the low, winter sunlight to enter the windows.
Materials, such as concrete and stone, are used to absorb the sun’s energy and store it, releasing it into the home at night after the sun has set. This is called direct gain.
Other features, such as sunspaces and trombe walls, can be used.
- A sunspace uses glass to trap heat like a greenhouse. The heated air within the sunspace is allowed to circulate throughout the building.
- A trombe wall is made of absorbing material and is often painted black or covered with glass (or both) to maximize the amount of energy absorbed and keep it locked inside. The thermal energy is released to the building slowly over time, providing warmth throughout the night.
Maximizing Natural Light
Using skylights, tube lights, and large windows on the sunward side of a building help maximize the amount of light reaching the interior of a building and reduce the need for artificial lights.
Solar Thermal Systems
The people living in this house enjoy heated water using a solar thermal system.
Flat plate solar collectors are usually large flat boxes with one or more glass covers. Inside the boxes are dark colored metal plates that absorb heat. Air or liquid, such as water, flows through tubes and is warmed by heat stored in the plates. These systems are particularly useful for providing hot water to households.
Solar Drying
Crops such as wheat and rice have been allowed to dry in the fields for centuries. Hay is mown and allowed to dry in the field before being baled. A small solar collector is used to dry herbs. Agricultural products can be dried in a special tower that uses a solar collector to heat air and channel it through perforated trays of crops, which dries them and carries the moisture out through the top.
Concentrating Solar Power (CSP)
Concentrating solar power (CSP) is used in special power plants that use mirrors to convert the sun’s energy into high-temperature heat. The heat energy is then used to generate electricity in a steam generator.
Photovoltaic (PV) Systems
Exelon City Solar in Chicago, IL – this tracking flat-panel installation has 32,292 panels rated at a total of 10 MW capacity (DC). Tracking solar panels rotate as the sun moves through the sky to maximize the amount of electricity they can produce.
The photovoltaic cell is the basic building block of a PV system. Individual cells can vary in sizes from about 1cm to about 10 cm across. Most cells are made with silicon today. Silicon must be purified. This is one of the biggest expenses in the production of solar cells.