The Fresnel Lens.
Fresnel lens is an optical part with a complex stepped surface. The use of a Fresnel lens as a concentrator in solar cells increases the efficiency of silicon cells to 45 %.
Fresnel lens is an optical part with a complex stepped surface. At this stage of such a lens can be delimited, usually concentric, spiral or linear grooves.
Fresnel lens is a compound lens. It comprises separate adjoining each other concentric rings (if steps lens demarcated concentric grooves) of small thickness, which in cross section have the shape of a prism of a special profile or cone with curvilinear profile. Each concentric ring of the lens Fresnel is an element of the surface of the solid lens.
The construction of lens was created by Augustin Fresnel in 1819 He designed it for the marine beacons that their light could be seen for many tens of kilometers. The invention, developed by Augustin Fresnel increased range lighting marine beacons several times. Subsequently, the lens was called by the name of the inventor.
Due to its design , the Fresnel lens has a small thickness and light weight even with a large angular aperture.
Fresnel lenses are circular and waist. The annular concentrated light beam in one direction waist in all directions in a certain plane.
Cross-section of the annular rings of a Fresnel lens is constructed in such a way that reduces its spherical aberration, the rays from a point sourceplaced at the focus of the lens, after refraction in the rings of the lens come almost parallel beam.
Fig. 1. The cross section of the annular Fresnel lens (2) and a conventional lens (2).
The dotted line in the figure shows the optical axis of the lens lenses
Waist Fresnel lens is a hollow rotational body. Its shape arises due to the rotation of the cross section of a Fresnel lens around the axis perpendicular to the optical axis of the lens. At the point of intersection of both axes is the source of light. Waist lens refracts the light in the plane perpendicular to the rotation axis and radiate it evenly in all directions.
Fig. 2. Waist Fresnel lens in the lighthouse Makapu (Hawaii, USA).
The Fresnel lens can replace both spherical and cylindrical lenses and other optical parts, for example, prisms.
She can concentrate the flow of light in one direction (in this case the light beams emerge parallel to each other), and focusing the beams of light at one point.
The diameter of the Fresnel lens may be from a fraction of a centimeter to several meters. The Fresnel lens can be made of glass or of plastic.
Fresnel lens used in lighting and optical devices and appliances.
Promising is the use of a Fresnel lens as a concentrator of solar energy for solar panels (solar PV installation) that allows to increase the efficiency of the solar silicon elements to 45 %. Fresnel lenses can concentrate the solar light on the solar silicon elements with a ratio of almost 500:1. This reduces the active surface of the solar silicon element, lowering the cost and allowing you to use these elements more efficiently.
Also, the Fresnel lens can be used in solar collectorsto generate steam and to power the Stirling engine.
Note: © Photo , , https://ru.wikipedia.org/wiki/Линза_Френеля, http://hawaiiansunrisewaimanalo.blogspot.com/2010/11/makapuu-lighthouse.html