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Methods of Solar Energy Capture

The sun provides solar energy in two main forms, heat and light, both of which are the result of electromagnetic waves. Harvesting those electromagnetic waves is the key to using solar energy from the sun and there are a number of mechanisms for doing so.

Heat or Light

At the very basic level, the decision of how to harness solar energy from the sun comes down to using either heat or light. While the sun emits radiation over a range of wavelengths, those corresponding to visible light and heat are the most abundant and thus the most viable in terms of providing usable energy.

Anyone who has stood in the sun on a summer day knows that the heat can be intense. The intensity of the heat is directly proportional to the number of 'rays' hitting a surface. In the winter, few rays reach the surface of the Earth and so temperatures are cooler. The opposite is true in the summer.

Heat from the sun can be collected using mirrors and magnifying lenses that concentrate the available rays to produce temperatures easily hot enough to boil water, even in the winter. This is probably the simplest way of utilizing energy from the sun because it requires nothing more than simple concentration to heat a substance. The hot substance can then be used directly for heat or hot water or used to produce steam and thus run turbines that generate electricity.

In contrast to heat, at least in terms of simplicity, is light. Collecting light from the sun is much more complicated because visible light must be converted into electricity to be useful for anything other than seeing our way about the world. The conversion of light to electricity is the focus of photovoltaic science; an entire field that studies the phenomenon of how light liberates electrons from certain materials like silicon and copper.

Photovoltaics was helped along in its development by a number of discoveries, including Einstein’s description of the photoelectric effect and materials science that has allowed for complex polymer formation from simpler materials. The net result of this work is solar panels (called photovoltaic cells) that are able to capture upto 50% of the energy from the sun and convert it into electricity.

The most basic choice in solar energy capture comes down to whether a system will capture heat energy or light energy. Of course, even though the methods of capture are different, an entire system can utilize both. It is often the case that both heat and light are used in the same system to increase efficiency.

Active and Passive Solar Systems

Solar systems can manipulate the energy they obtain or they can leave it unchanged. In a passive solar system, a system is built to make the most out of available solar energy without manipulating or changing that energy in any way. For instance, south-facing windows in homes in the Northern Hemisphere are a form of passive solar energy utilization. Passive solar systems are most easily designated by the fact that they use neither mechanical nor electrical devices of any kind.

On the other side of the spectrum is active solar, which uses both mechanical and electrical devices to manipulate the energy from the sun. So, even though photovoltaic panels have no moving parts, their conversion of solar energy into electrical energy makes them active. It is easiest to think of active solar as the process of increasing the usefulness of the energy from the sun, rather than simply allowing it to fall where it may. Thus, solar concentrators are a type of active solar because they collect solar rays and redirect them to a single point of focus. Windows are passive because they do not redirect the rays of the sun.

The distinction between active and passive often becomes blurred, at least occasionally as a result of misapplication of the terms. If a system responds to solar energy changes by altering itself in some way (orientation, speed of function, etc.), then it is generally termed active. If a system simply uses solar energy, but does not purposefully change its function to meet changes in solar energy, then it is passive.

Other Solar Categories

Though many of these technologies can fall into the categories listed above, they are given special status due to their unique importance. Solar lighting, solar chemical, and solar vehicles all make use of the sun’s energy to various extents.

Solar lighting can be both active and passive. Using natural daylight to enhance an indoor space is an example of passive solar lighting. Collecting the sun’s energy and using it to create electricity for light is a form of active solar lighting. In both cases, lighting is given a special status because of the importance it holds in modern life. Without active lighting, humans would be at the mercy of the sun as to when they could accomplish work.

Solar chemical refers to any process that uses the sun’s energy to drive a chemical reaction. These processes are important for a number of reasons. First, they do not require the use of energy from burning fossil fuels, so any reaction that can be performed this way will directly benefit the environment and reduce fossil fuel consumption. Some chemical reactions can only be carried out with light, such as photosynthesis. Solar chemical is a special field that studies the application of solar energy to the field of chemistry.

Finally, solar vehicles command their own category due to their importance in society. Beyond light, heat, food, and shelter, transportation is critical to any modern society and uses fully 40% of all energy in developed nations. Reductions in fossil fuel use are seen to rely heavily on reducing human dependence on them as a means of easy, accessible energy for moving around the world. Solar planes, boats, and cars are all actively underdevelopment.
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