In the broadest sense, solar energy supports all life on Earth and is the basis for almost every form of energy we use. The sun makes plants grow, which can be burned as 'biomass' fuel or, if left to rot in swamps and compressed underground for millions of years, in the form of coal and oil.
Heat from the sun causes temperature differences that produce winds that can power turbines. But solar energy usually refers to ways the sun's energy can be used to directly generate heat, lighting, and electricity.
The amount of energy from the sun that falls on Earth's surface is enormous. All the energy stored in Earth's reserves of coal, oil, and natural gas is matched by the energy from just 20 days of sunshine.
By the time it reaches the Earth's surface, the energy in sunlight has fallen to about 1,000 watts per square meter at noon on a cloudless day. Averaged over the entire surface of the planet, 24 hours per day for a year, each square meter collects the approximate energy equivalent of almost a barrel of oil each year, or 4.2 kilowatt hours of energy per day.
This figure varies by location and weather patterns but arid deserts with little cloud cover, receive the most sun - more than six kilowatt-hours per day per square meter. Northern climates, such as that of Boston, get closer to 3.6 kilowatt-hours. Sunlight varies by season as well, with some areas receiving very little sunshine in the winter. Seattle in December, for example, gets only about 0.7 kilowatt-hours per day.
Most of us are familiar with solar panels for home and water heating. But a very simple and fast growing trend in harnessing sunlight is via eco-architecture: designing buildings to maximize sun use. If properly designed, buildings can capture the sun's heat in the winter and minimize it in the summer.
Eco-friendly buildings utilize passive solar energy - a resource that can be tapped without mechanical means to help heat, cool, or light a building. South-facing windows, skylights, awnings, and shade trees are all techniques for exploiting passive solar energy. Buildings constructed with the sun in mind can be comfortable and beautiful places to live and work.
Residential and commercial buildings account for more than a third of U.S. energy use but better insulation, solar design and more efficient appliances could reduce this demand by 60 to 80 percent.
Besides using design features to maximize their use of the sun, some buildings have systems or solar collectors that actively gather and store solar energy for space heating, water heating, and space cooling.
Solar collectors were quite popular in the early 1980s, and today, less than one percent of Americans use them. In other countries, solar collectors are much more common; Israel requires all new homes and apartments to use solar water heating, and 92 percent of the existing homes in Cyprus already have solar water heater.
According to the U.S. Department of Energy, water heating accounts for about 15 percent of the average household's energy use and as natural gas and electricity prices continue to rise, the costs of maintaining a constant hot water supply will increase as well.
Homes and businesses that heat their water through solar collectors could end up saving as much as $250 to $500 per year depending on the type of system being replaced.
On a personal level, there are ways you can make solar energy work in your daily life. According to Green Living, these are some money saving tips for taking advantage of what the sun has to offer:
Black and other dark colors absorb sun warmth; white and light colors reflect that warmth. Assuming you live where it gets cold in the winter, darker colors for your house exterior, particularly your roof, will pass more of the available heat from the sun to your house.
Naturally, the windows of your house, and especially those facing south, can admit a lot of heat from the sun. Storm windows will impede the passage of sunlight very little, but they do keep in more of the heat once it has entered your house.
Take advantage of the solar greenhouse concept in your house. Most conventional greenhouses have glass on four sides and a glass roof that, unfortunately, allows heat to escape at night. A solar greenhouse usually has a large, sloped south-facing area of glass to receive the light the plants need to grow with good insulation to reduce the heat loss to the outdoors.
Take advantage of this concept throughout your house by having solid objects with an ability to store heat standing in the sunlight to store warmth that will be radiated after the sun goes down.
One good heat collector is a windowsill row of flowerpots or an indoor window box. The dirt will store warmth during the day, helping the plants to grow and warming the room at night.
In your house, can the low-lying winter sun slant across the room to warm a brick-fronted fireplace, a slate entryway, or a similar solid surface? Be sure the drapes are pulled back to take advantage of these solar collectors. Close drapes at night to keep in warmth.
Light-colored shades or slatted blinds drawn across a sunny window will reflect the sun's warmth right back outdoors again. During daylight hours, keep the sunny windows in the clear to let that warmth in.
The first step into solar power for many people is a solar hot water system. Such systems are available for new homes or for retrofitting on older homes. They will furnish 50 to 100 percent of your hot water requirements. Look at your current cost of heating hot water and talk to a contractor about the costs and possible savings of a solar system. Ask your contractor for references so you can get a better idea of how much people in your area save with their solar hot-water heaters.
Sunshine is not only a source of warmth but also a source of light at the same time. Turning on the light switches in the daytime may be a habit you can break just by rearranging the furniture or opening the blinds more often.
Next time you're ready to repaint or repaper a room, think about how the room is used before you choose the colors. Light colors in a room will bounce the daylight around, making it a pleasant and cheerful place without extra illumination. This is a less important factor in bedrooms, which are used primarily at night.
Window light can be scarce in the kitchen because you often want a lot of storage, rather than windows, on the outside walls. It's even more important, then, to choose light colors for the kitchen walls.
Whenever possible, place daytime reading and working areas where window light will be sufficient on all but the most overcast days. Specifically, consider the location of the sewing machine, the chair with the magazine rack, the play table for the children, the workbench, and items like an artist's easel or a computer. Light also means heat, so you'll be warmer as you work.