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Active Solar

It may seem that active solar systems are less efficient than passive solar systems, but this would not be accurate. In passive systems, thermal energy only begins to flow once it reaches a critical threshold. This means that a great deal of energy must be invested in and maintained in the system just to get it up and running. Active solar, on the other hand, only requires enough energy to run a pump or other electrical device. This means the threshold for moving energy can be lower and thus more energy can be obtained from the system. So, even though active solar uses some of the energy invested to power and control the system itself, the ultimate end can mean more energy is extracted overall and can offset the small investment. The major benefits of passive solar are its lower cost and reduced complexity.

Components of Active Solar

Active solar systems are generally broken down into three parts: Collection, Storage, and Distribution. Whether the form of energy utilized is heat or electricity, the components of an active solar system are basically the same.

Collection

The collection aspect of any solar system can be classified as either solar concentration or photovoltaic. In photovoltaic systems, light energy is used to excite electrons in a special blend of materials that create a semiconductor. These electrons then flow through wiring as electricity, which either powers devices immediately or is stored for future use.

In solar concentration, energy from the sun is collected and focused on specific device that uses the heat to produce either hot water or electricity. In the case of hot water, the solar collector usually consists of a flat box filled with piping that contains water or another liquid used for heat collection and transfer. These systems generally are not used to create electricity. The other type of solar concentrator is often referred to as a parabolic collector. In this type of system a mirrored dish, often shaped like a satellite dish or half of a tube, is used to collect light and reflect it onto a very concentrated area where it superheats a liquid. This liquid is then used to drive a turbine that can produce electricity.

Storage

Storing solar energy is one of the most challenging aspects of any system. For electrical systems, batteries are often used. They are easy and convenient, but they also wear out rather quickly and are one of the most expensive components of the system. In photovoltaic systems, batteries are the only alternative unless the solar system is being used to supplement energy delivered from the electrical grid.

In solar concentration systems, the key to storing the solar energy is to store the heat that is generated. To that end, a number of alternatives have been tried. In large scale systems, molten salt is often stored in large tanks that are highly insulated. The molten salt can then be used to heat water when solar is not available. This works well for larger installations, but is generally not feasible for smaller, consumer applications. For consumers, the heat is generally converted to electrical energy that is then stored in batteries. Storage of solar energy is a major branch of investigation in solar as an advanced method would not only allow storage of electricity for stationary applications, but would also make solar (or electric) powered vehicles more feasible.

Distribution

Distribution refers to the devices and controls used to regulate how solar energy is consumed. For liquid systems, this refers to pumps, pipes, ducts, and fans. For electrical systems, this refers to the switches, regulators, wiring, and other controls used to determine when, where, and how electrical energy is used. Distribution is the simplest of three components of any solar system.
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