Active & Passive Solar Systems

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Solar Systems - Active, Passive, Cost

Solar - energy from the SUN. There are two primary types of solar systems; Passive and Active.

Passive Solar Design

Passive solar design refers to the use of the sun's energy for the heating and cooling of living spaces. The building itself or some element of it takes advantage of natural energy characteristics in materials and air created by exposure to the sun. Passive systems are simple, have few moving parts, and require minimal maintenance and require no mechanical systems.

Passive solar systems rules of thumb:

  • The building should be constructed on an east-west axis.
  • The building's south face should receive sunlight between the hours of 9:00 A.M. and 3:00 P.M. during the heating season.
  • Interior spaces requiring the most light and heat should be along the south face of the building. Less used spaces are located on the north.
  • An open floor plan optimizes passive system operation.
  • Use shading to prevent summer sun entering the interior
While Passive Solar implementations offer virtually free heat and cooling, for best results these features must be designed into the building at the start or will require major renovations to an existing structure. As a result, Active Solar systems are quiet common as they are more readily added to existing buildings.

Active Solar Designs

Active solar technologies are employed to convert solar energy into usable heat, cause air-movement for ventilation or cooling, or store heat for future use and for the production of electricity. Active solar uses electrical or mechanical equipment, such as pumps and fans, to increase the usable output of a system.

Solar Thermal - Domestic Hot Water and Electricity

Domestic Hot Water

Most solar hot water systems, except those based on the thermo siphon, use pumps or fans to circulate water, an anti-freeze mixture, or air through solar collectors, and are therefore classified under active solar technology. The solar collectors can be non concentrating or 'flat-plate', or of various concentrating designs. Most solar-thermal collectors have fixed mounting, but can have a higher performance if they track the path of the sun through the sky. Solar trackers, most often used to orient photovoltaic arrays, may be driven by either passive or active technology.

Solar Thermal Electricity

Primarily for large commercial operations, solar thermal collectors heat a liquid, which is then used to drive a turbine to produce electricity. These units are VERY efficient and cost competitive with more traditional methods of producing electricity such as coal fired generators. However, they do not produce the smog and greenhouse gases, emitted by coal fired electrical generating stations! With present technology, a 100 square mile section of solar thermal arrays, could produce all of the electricity used by the USA. One of the issues with this option, is transmission of the power to the end user.

See our section on Solar Thermal for more information.

Solar Photovoltaic (P.V.)

Solar photovoltaic systems convert sunlight into electrical current. The solar panel or array, converts sunlight into direct current (DC) which can be used to charge batteries or directly by DC appliances. An Inverter converts DC current into AC current for household use or for delivery to the electrical power grid. PV systems need clear access to sunlight as even small shadows can have a large impact on the total output of power.

Solar PV allows the electricity to be produced where it's needed. This get around most of the transmission issues. The three larges producers of PV cells are Japan, Germany and China, with China increasing it's production rapidly. In India, the government pays the FULL COST for all solar projects in non-electrified areas.

There are several companies developing new ways of manufacturing solar cells that hold promise to huge price reductions. Nanotechnology for example, reduces the amount of silicon required per watt of energy, from 15 grams, down to just 0.04 grams!

See our section on Solar Photovoltaics for more information on these advances in technology.

Average Cost for Small Solar Thermal and Solar Photovoltaic Systems

Solar Therval and Photovoltaic System Costs

These average costs for small solar thermal and solar PV systems are taken from a presentation put on by OSEA (Ontario Sustainable Energy Association and Go Solar.


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