Lesson Objectives:- Solar energy
- Solar heating
- Producing solar energy
- The future of solar energy
The Solar Constant is the rate at which solar energy reaches the Earth. Solar energy is radiant energy and enters the Earth at 1,366 watts per square meter.
Solar energy ranges from ultraviolet light to visible light and infrared light. About 30% of energy is reflected and 20% absorbed back into the atmosphere. Full sunlight delivers about 700 watts per square meter to the Earth's surface when the Sun is overhead. The Sun can deliver 700 MW of power or the size of one power plant to an area of 390 square miles.
The amount of solar energy reaching the Earth is massive.
40 minutes of direct sunlight striking the land surface of the United States yields the energy equivalent of one year's use of fossil fuel. The Sun delivers 10,000 times the energy used by human beings.
Using solar energy does not change the energy balance of the biosphere. Solar energy is converted to heat energy and usually lost to outer space. If human beings captured and used solar energy, it would ultimately be broken down into heat energy and then dispersed into the atmosphere.
Solar heating has been popular in warm sunny climates for a long time.
A solar collector consists of a thin box with glass or clear plastic at the top and black bottom with embedded tubes. As sunlight gets absorbed by the black surface, it is converted into heat. The black bottom gets hot and the plastic prevents heat from escaping. Solar collectors can help cut down utility bills as heat is collected and moves into the home via passive convection. Solar collectors can also be used to heat water. In this case, a flat plate collector is used again and water circulates through the embedded tubes. As the black bottom heats up, the water circulating through the tubes gets warmer and is sent to a tank for storage.
A well-designed passive solar energy building can reduce energy bills significantly. Excellent solar design can save a lot in oil, gas and electrical power consumption.
The Energy Star Program by the EPA recognizes energy efficiency and well-designed products and buildings. The Program awards the Energy Star Label to public and corporate buildings and products that use less than 40% of energy compared to other products or buildings in the same category and that meet other environmental criteria.
We all use electricity in some form or another throughout the day. Switching to renewable energy sources like solar would require that solar energy produce electricity on a scale like we are used to.
Photovoltaic cells are the most common method of capturing solar energy and converting it into electrical energy. A photovoltaic cell consist of a simple wafer of material with one wire at the top and one at the bottom. As sunlight shines on the wafer, it puts out an amount of electrical energy via a current that is equal to roughly a flashlight battery. PV cells are in use today to power calculators, watches and toys. They also provide power in rural areas for radio transmitters, lighthouses and traffic signals.
The most complicated part of the PV system is the inverter, which connects the solar PV modules with the electric grid or batteries. It connects the direct current from the PV panels to alternating current and acts as a control for the system.
The cost of producing solar energy keeps decreasing. The Sun is a plentiful energy source. More adoption is happening as homeowners add Photovoltaic (PV) systems, especially through government subsidies.
Other methods of capturing solar energy are being explored, such as solar troughs and power towers. Solar facilities do not face the same threats incurred with oil supplies that are vulnerable to terrorist attacks and require diplomatic efforts in volatile regions of the world.