Lesson 68: Putting Solar Energy to Work
In this lesson, we will talk about the potential energy that
could be harnessed from the sun, and the current methods being used for solar
heating and solar energy production. We will also look at the bright future
ahead for 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.