Energy from the Sun Solar Energy Power Guide

Many technologies have been developed to make use of solar radiation. Some of these technologies make direct use of the solar energy (e.g. to provide light, heat, etc.), while others produce electricity.

Solar heating systems

Solar hot water systems use sunlight to heat water. They may be used to heat domestic hot water or for space heating. These systems are basically composed of solar thermal collectors and a storage tank. The three basic classifications of solar water heaters are:

A Trombe wall is a passive solar heating and ventilation system consisting of an air channel sandwiched between a window and a sun-facing wall. Sunlight heats the air space during the day causing natural circulation through vents at the top and bottom of the wall and storing heat in the thermal mass. During the evening the Trombe wall radiates stored heat.

A transpired collector is an active solar heating and ventilation system consisting of a perforated sun-facing wall which acts as a solar thermal collector. The collector pre-heats air as it is drawn into the building's ventilation system through the perforations. These systems are inexpensive and commercial models have achieved efficiencies above 70%. Most systems pay for themselves within 4-8 years.

Solar cooking

A solar box cooker traps the sun's energy in an insulated box; such boxes have been successfully used for cooking, pasteurization and fruit canning. Solar cooking is helping many developing countries, both reducing the demands for local firewood and maintaining a cleaner breathing environment for the cooks.

The first known western solar oven is attributed to Horace de Saussure in 1767, which impressed Sir John Herschel enough to build one for cooking meals on his astronomical expedition to the Cape of Good Hope in Africa in 1830. Today, there are many different designs in use around the world.

Solar lighting

Solar lighting or daylighting is the use of natural light to provide illumination. Daylighting offsets energy use in electric lighting systems and reduces the cooling load on HVAC systems (this assumes that daylighting is replacing incandescent lighting, which produces more heat than light). The use of natural light also offers physiological and psychological benefits, although this is difficult to quantify.

Daylighting features include building orientation, window orientation, exterior shading, sawtooth roofs, clerestory windows, light shelves, skylights and light tubes.[13] These features may be incorporated in existing structures but are most effective when integrated in a solar design package which accounts for factors such as glare, heat gain, heat loss and time-of-use. Architectural trends increasingly recognize daylighting as a cornerstone of sustainable design.

Daylight saving time (DST) can be seen as a method of utilising solar energy by matching available sunlight to the hours of the day in which it is most useful. DST energy savings have been estimated to reduce total electricity use in California by .5% (3400 MWh) and peak electricity use by 3% (1000 MW).

Photovoltaics

Solar cells, also referred to as photovoltaic cells, are devices or banks of devices that use the photovoltaic effect of semiconductors to generate electricity directly from sunlight. Until recently, their use has been limited because of high manufacturing costs. One cost effective use has been in very low-power devices such as calculators with LCDs. Another use has been in remote applications such as roadside emergency telephones, remote sensing, cathodic protection of pipe lines, and limited "off grid" home power applications. A third use has been in powering orbiting satellites and spacecraft.

Total peak power of installed PV is around 1700 MW as of the end of 2005. This is only one part of solar-generated electric power.

Declining manufacturing costs (dropping at 3 to 5% a year in recent years) are expanding the range of cost-effective uses. The average lowest retail cost of a large photovoltaic array declined from $7.50 to $4 per watt between 1990 and 2005. With many jurisdictions now giving tax and rebate incentives, solar electric power can now pay for itself in five to ten years in many places. "Grid-connected" systems - those systems that use an inverter to connect to the utility grid instead of relying on batteries - now make up the largest part of the market.

In 2003 worldwide production of solar cells increased by 32%. Between 2000 and 2004 the increase in worldwide solar energy capacity was an annual 60%. 2005 was expected to see large growth again, but shortages of refined silicon have been hampering production worldwide since late 2004. Analysts have predicted similar supply problems for 2006 and 2007.

Solar thermal electric power plants

Solar thermal energy can be focused on a heat exchanger, and converted in a heat engine to produce electric power or applied to other industrial processes.

Power towers

Power towers use an array of flat, movable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target). The high energy at this point of concentrated sunlight is transferred to a working fluid for conversion to electrical energy in a heat engine, or in some instances, stored for night-time usage, in order to provide a more continuous output.

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