Solar Energy

The sun is a renewable resource. An enormous amount of solar radiation reaches the earth each

year. In fact, if just a fraction of the sun's power could be captured and used as an energy source, the world's energy demands could be met. Human civilizations have used the sun's energy for heat for thousands of years. Advancing techniques to capture and utilize this power will help continue the tradition of utilizing this clean, renewable source of energy.

 

 Passive Solar Power

Passive Solar energy converts sunlight directly into useful energy. It involves designing architecture in a way which capture's and stores heat radiated from the sun. The architectural innovations that are conducive to solar power are typically incorporated in to the initial design. In other words, a house is typically built for solar energy via overall orientation and the construction of large skylights and other south facing windows, enhanced by efficient insulation(this is not always the case though, and passive solar features can be added onto a building). Active solar, on the other hand, utilizes solar electric technologies such as photovoltaic cells to convert sunlight into energy. These are typically "add-on" features. The means of conversion are actively mechanical, versus the receptive nature of passive energy provided via design.

• Passive solar is largely used for space conditioning (heating and cooling areas), in addition to providing light.
• Houses are constructed, in the northern hemisphere, with their long axis in an East-West direction. This orientation maximizes solar gain and minimizes the losses. It also allows for cool summer afternoon to stay cool (for the sun is in the western part of the sky). and warm winters when the sun is to the south.
• a common design feature of solar houses is a greenhouse like addition which is attached to the outside of the building. These "sunspaces" facilitate heat transfer into the house during the day. They cool down rapidly during the night (for the windows allow warn air out just as they allowed it in). For these reasons, they are more storage houses for heat exchanges, but aren't;t normally used as a living space.
• Passive Solar has almost no negative impact on the environment--giving off no air or water emissions at all.
• Thermal masses are used to store the heat radiation. Common objects used as thermal masses are brick . slate, and rock, concrete, and water. Optimal thermal storage can take place by increasing the mass of these material son the inside of a building.
• Every buildings has some of its heating requirement met by windows, the primary tool in passive solar heating. Window glass is virtually transparent to solar radiation. Placing windows facing south maximizes these

 

Active Solar Power

 

Photovoltaic Cells as means of transforming sunlight into energy, actively.

We have already addressed some of the basic difference between passive and active solar. While passive solar is just that, passive, active solar uses growing technological innovations to capture the sun's energy for use. The beginning of such technology can be traced to the mid 1950's in Bell Laboratories in the United States. The use was largely limited to powering satellites in space. The oil crisis in 1973 served as an impetus for expanding these uses into the private sector.

Because passive and active solar both look to the sun for power, both share the same free, renewable source and costs are therefore in the installation and maintenance. Another perk they both share: their demand curbs the demand and thus the extraction of nonrenewable, polluting fossil fuels.

Active solar power can supply energy to the power grid. It is therefore a viable option for a grid-wide switch to renewable energy sources.

Understanding the Photovoltaic Reaction

The Photovoltaic Reaction (PV) produces direct current electricity (the same kind which is produced by a battery). The basic building block for this reaction is a cell wherein a reaction produces energy currents via the following steps:

 Looking at Figure one, as provided by www.iclei.org, one can see the basic set of processes that are involved in the PV reaction. PV cells are made out of a semiconducting material (this Figure uses silicon, but it could be a variety of different substances. When these cells are exposed to light, the electrons within the crystalline silicon are knocked from their crystal structure. Due to "impurities" added to the cell material, the negatively charged electrons are unable to fall back into the p-region (the positively charged area) and are then follow the path of least resistance into the negatively charged are (labeled here as n-type region). The accumulation of these electrons in the n-region creates a strong negative charge on the cell's surface. These electrons can only travel to the p-type region if an outside path is created, as is done via a wire in Figure 1. The result is an electric current, which can be used at that moment or stored for later.

 

Environmental Impacts

• PV cells use no fuel during operation (other than sunlight of course)
• Emit no atmospheric or water pollutants
• require no water for cooling processes
• do not contribute to global warming or acid rain
• The ONLY negative environmental impact relates to the potentially toxic chemicals required for PV cell production. Proper handling and storage of these chemicals, however, will mitigate any environmental hazards. Additionally, most of the toxic materials can be recycled.

THE FUTURE: Active solar power has enormous potential as a widely used energy source in the United States (as well as abroad)! Costs have declined twenty-fold since 1970--a trend which will only continue in the future with growing technology and an increasing demand for its services. Many energy suppliers are investigating the feasibility of active solar as a contributor into typical grid power. In fact, there are several right here in New England (with an increasing list of customers as electric companies are becoming deregulated. In fact, 22 states have deregulated --a step towards diversifying energy sources which feed into the energy grid).

CHECK IT OUT:  Central Vermont Solar and Wind, a local company dedicated to promoting renewable energy systems

www.

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