At 93 million miles from Earth, our sun is a middling star that provides nearly all the energy on Earth. The only energy sources we have on Earth which do not come from the sun are the tides caused by the moon’s gravity, radioactive materials and geothermal energy. The sun provides everything else. All the energy embodied in fossil fuels and biomass is actually the sun’s energy stored as carbon.
Each minute of every day, enough sunlight falls on the Earth’s surface to meet the world’s energy demand for an entire year; and it’s free. There are two types of solar energy that enter our atmosphere: light energy and thermal energy (or heat). We can use both types of solar energy to improve our energy efficiency.
The simplest way to capture solar light energy is called “daylighting.” Just open the curtains, turn off the lights and let the sun light the room. To take advantage of daylighting, new homes and buildings strategically place windows and skylights to bring sunlight into every room where it may be needed. The savings on electricity can be dramatic.
Photovoltaic or solar electric systems use the sun’s light energy to generate electricity. When sunlight strikes a chemically treated silicon photovoltaic cell, electrons inside become excited and move through the silicon. This “photovoltaic effect” results in direct current (DC) electricity. We have all seen solar calculators, battery chargers and other devices. Photovoltaic systems have no moving parts. They are virtually maintenance free and can have a life of 20 to 30 years. Photovoltaic cells respond to any light energy, not just direct sunlight, so they even generate some electrical power on cloudy days.
There are several types of photovoltaic systems. Flat plate photovoltaic collectors have become more efficient and less costly than they were just decades ago. One recent advance is the development of Building Integrated Photovoltaics (BIPV). A BIPV unit serves a dual role in a building. It acts as a functioning part of the building structure and produces electricity for use in the structure. Some types of BIPV products include : roofing shingles and tiles, semi-transparent curtain walls and skylights, awnings and entire roofing systems. As the cost of photovoltaic cells continues to drop, the use of BIPV will advance in the building market.
Photovoltaics are cost effective and practical for use in many remote locations. They are used to generate power for traffic control systems, crop irrigation systems, bridge corrosion inhibitors and radio relay stations. They provide electricity to remote cabins, villages, medical centers and other isolated sites.
Solar Thermal Energy
Thermal energy from the sun can also be used to make a home or building more energy efficient. Solar thermal systems collect and store solar heat. That heat can be used for many purposes, such as warming spaces, heating water, generating electricity, destroying pathogens, drying or cooking. There are two basic types of thermal solar systems: active and passive solar systems.
Active Solar Systems
Active solar systems are those that rely on electrical or mechanical devices to collect and store solar heat. A solar water heater is an example. Glass-covered panels collect heat from the sunlight. Air or a fluid is pumped through the heated panels. The heated air or fluid is pumped to a heat exchanger (a reverse radiator) where it warms water. The hot water is then pumped into a storage tank for later use in the home. The active parts of solar water heaters are the electrical pumps and fans that move heated air or fluids through the system. However, the electricity needed by the fans and pumps is far less than the electricity required to heat a tank full of cold water. When a photovoltaic panel is used to power the pumps, the electricity costs are zero.
Another similar active system can be designed to provide radiant heating to a home. In this system, the fluid heated by the solar panels is run through piping in the floors of the home. The hot fluid radiates heat up through the floor providing a very comfortable, even heat.
Other more complex active solar systems include those that use reflectors to concentrate the solar energy for use in generating electricity or heating large building complexes.
Passive Solar Systems
Passive solar systems use no electrical or mechanical assistance to capture energy from the sun. A greenhouse is an example of a passive solar system. Sunlight enters the greenhouse and warms the air and surfaces inside. The glass then prevents the heat from escaping. In fact, the property of glass that allows sunlight in but traps the resulting radiated heat is known as the “greenhouse effect.”
A beneficial application of passive solar systems and the greenhouse effect is the solar home. In Minnesota, a solar home is situated facing south to allow the winter sunlight to enter through double and triple-paned glass windows and skylights. The building materials are selected to store the solar heat and radiate it to warm the interior spaces. The home is well insulated to hold in the solar heat during the cold winter months.
In the summer, the design of the home keeps the direct sunlight out. Strategically placed windows also encourage convection currents that draw cool air into the home and vent out warm air. A well-designed passive solar home will use the sun’s energy to heat and cool itself.
Passive solar homes are beautiful, comfortable and healthy living spaces that can be built for no additional cost and provide savings through lower utility payments. They are better for the environment while contributing to an energy-independent, sustainable-energy future.
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