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Installation of thermal solar energy

Solar power plant
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Solar furnace

Solar furnace

A solar furnace is an optical system to provide concentrated solar radiation. The concentrated energy of sunlight can be used for simple heating of a material, aging experiments of plastics or paints, endothermic chemical reactions or for charging experiments with mechanical or electrical components.

The solar furnace system is widely used in solar thermal power plants.

The principle of the solar furnace is also used to build cheap solar solar cookers, and for solar water pasteurisation. Solar furnace can be used to supply a Stirling engine, as well.

The difference between the solar furnace system and a solar panel is that the solar panel captures and converts solar energy directly, whereas the solar furnace only reflects and concentrates it in one point.

Operation of the solar furnace

The concentration component of a solar furnace works in principle like a burning glass. For technical reasons, however, a hollow or parabolic mirror is used, which concentrates the incident solar radiation at a focal point. The reflective surface of this concentrator can be from one square meter to several 100 square meters. If larger areas are required, a heliostat field is generally used, in which several flat mirrors assign light to a single point.

To ensure optimum illumination of the concentrator, it is necessary to continuously follow the heliostat to the sun. This is done through software that constantly calculates the current position of the sun in the sun path, or a sensor is used, which determines the position of the sun and, therefore, provides a follow-up of the heliostat. For a solar furnace with a concentrator, three possible geometries have been realized in practice:

  • direct tracking hub,
  • stationary on the concentrator axis with traced heliostat,
  • stationary outside the concentrator axis with traced heliostat.

For larger concentrators, these are composed of individual flat mirrors, or in a Fresnel arrangement, of individual focusing mirrors.

The reflective components must meet certain qualitative criteria. Therefore, it is important that the reflectivity be as high as possible, or exactly known, as well as the scattering of the reflective surface. The wavelengths to be reflected are also an important criterion, if, for example, one wishes to make use of the UV (A, B) components of sunlight.

The precondition for an effective concentration is directed direct sunlight. Therefore, the climatic conditions in the location of a solar oven play an important role.

Solar furnace uses

The rays of the solar radiation are focused on an area the size of a pot and can reach a temperature of 4,000 ° C, depending on the installed process, for example:

Approximately 1000 ° C for metal receivers producing hot air for the next generation of solar towers.

Approximately 1400 ° C to produce hydrogen by breaking up methane molecules.

Up to 2500 ° C to test materials that will be used in extreme environments such as nuclear reactors or space vehicles for atmospheric reentry.

Up to 3500 ° C to produce nanomaterials by solar induced sublimation and controlled cooling, such as carbon nanotubes or zinc nanoparticles.

It has been suggested that solar furnaces could be used in space to provide energy for industrial uses.

Its dependence on sunny weather is a limiting factor as a renewable energy source on Earth, but it could be combined with thermal energy storage systems for energy production during cloudy days or at night.

There are also small scale solar furnaces, in these cases the temperature at the point of concentration is not so high. They are used, for example to feed small Stirling engines, solar cookers or solar ovens.

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Last review: May 17, 2018

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