GB2489219A

GB2489219A - Solar concentrator with orthogonal elements

Info

Publication number: GB2489219A
Application number: GB1104489.8A
Authority: GB
Inventors: Peter Ernest Lockley
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-03-17
Filing date: 2011-03-17
Publication date: 2012-09-26
Also published as: GB201104489D0

Abstract

A solar concentrating arrangement that does not rotate about a vertical axis has a primary linear focusing element 101 able to rotate 104 about a horizontal axis 103 and a linear array of secondary focusing elements 107 able to rotate about an axis 108 which is orthogonal to that of the primary element. The elements can be parabolic or Fresnel mirrors or cylindrical lenses that focus light on target areas 302 of an energy convertor 105. Extra mirrors 303 help reflect light when the sun is considerably off-axis. The secondary elements 107,303 can also be curved in a transverse direction, depending on the focal length of the primary element 101.

Description

DUAL -AXIS SOLAR TRACKER AND CONCENTRATOR

The present invention relates to apparatus for concentrating solar radiation for use in the generation of heat or electricity.

Solar power generating systems utilise concentrator optical systems which are designed to focus solar radiation on areas which act as heat exchangers with a working fluid, or upon photovoltaic cells, so as to generate electricity directly. Two forms of focusing systems are in use, those which produce a linear focus, such as cylindrical mirrors of parabolic or hyperbolic form, cylindrical lenses or linear Fresnel lenses/mirrors, or those which produce a point focus, such as concave mirrors or Fresnel lenses. Also known are solar energy convertor systems which employ two linear focusing optical elements, which are so arranged that their linear foci are orthogonal, so that, in combination they produce a focal spot at which is situated a solar energy convertor. Examples of such solar energy convertors are disclosed in patent specifications W02008/046l87 Al, US2007/l81 173 Al, US4439020A, JP59135778A, 0B941813A and GB2148525A. In order to maximise the efficiency of solar power generators it is common practice to cause the concentrator optical systems to follow the apparent diurnal motion of the sun so as to face the sun directly at all times during daylight hours. In order to achieve this, as shown, for example in patent specifications W02008/04617 Al and US4439020A above, the concentrator optical systems are rotated about both horizontal and vertical axes. In so doing, each optical concentrator creates a relatively large swept area, which is wasteftil in terms of land usage. The problem is particularly acute with arrays of linear focusing optical concentrator optical systems.

It is an objectof the present invention to provide a linear focusing optical concentrator system which can allow for the diurnal motion of the sun without the need for the optical concentrator system to rotate about a vertical axis.

According to the present invention there is provided an apparatus adapted to enable a linear focusing solar radiation concentrator to follow the apparent diurnal motion of the sun without rotating about a vertical axis, comprising a linear focusing primary optical element adapted to be capable of rotation about an horizontal axis only, a linear array of secondary focusing optical elements positioned in front of the primary focusing element and adapted to be capable of rotation about parallel axes orthogonal to the axis of rotation of the primary optical element and control means adapted to cause the primary optical element to rotate about the said horizontal axis so as to follow changes in the azimuth of the sun and the secondary optical element to rotate in concert about the said axes orthogonal to the axis of rotation of the primary optical element so as to cause solar radiation proceeding from the primary optical element to remain focused on a target area regardless of changes in the declination of the sun.

Preferably, the primary optical element is a concave cylindrical mirror of parabolic or hyperbolic form and the secondary optical elements are concave with respect to the primary optical element in a plane parallel to the optical axis of the primary focusing element.

The secondary optical elements may also be curved in a plane orthogonal to the optical axis of the primary optical element.

The secondary optical elements may be mirrors of the Fresnel type.

The invention will now be described, by way of example only, with respect to the accompanying drawings, in which Figure 1 is schematic view illustrating the principle of the present invention, Figure 2 is a schematic representation of an embodiment of the present invention, Figure 3 is a plan representation of the apparatus of figure 2 showing the positions of the secondary optical elements when the apparatus is pointing at the sun directly Figure 4 is a plan representation of the positions of the secondary optical elements when the sun is off-axis relative to the primary optical element, Figure 5 shows cross-sections of various configurations of secondary optical elements in a plane perpendicular to the optical axis of the primary optical element and Figure 6 shows an apparatus in which the secondary optical element is a lens of elliptical cross-section.

Referring to Figure 1 of the drawings, which illustrates the principle of the present invention only, a solar radiation concentration apparatus 100 consists of a primary optical element 101 in the form of a cylindrical mirror 102 of parabolic form which is so mounted as to be capable of rotation about an horizontal axis 103, as shown by the arrows 104, which in the figure is also the axis of a solar energy converter 105.

Positioned in front of the mirror 102 is a secondary optical element 106 in the form of a section of a second cylindrical concave mirror 107, which is so mounted as to be capable of rotation about a vertical axis 108. The combination of the two mirrors 102 and 108 and their respective axes of rotation 103 enables solar radiation to remain focused upon the solar energy convertor 105 throughout the apparent diurnal motion of the sun.

Referring to Figures 2 and 3 of the drawings, which illustrate schematically an apparatus embodying the invention, in which those components already described with reference to figure 1 have the same reference numerals, a plurality of secondary of secondary mirrors 107 are mounted in a housing 300 which is positioned in front of the primary mirror 102 by means of struts 301. The secondary mirrors 107 are linked together by a mechanism within the housing 300 so that they move in concert. This mechanism can be of any convenient form and is not shown in the drawings. Each secondary mirror 107 receives solar radiation reflected from the primary mirror 102 and brings it to a focus as a rectangular area 302 on the solar energy convertor 105.

These areas are hereinafter referred to as targets. The solar energy convertor 105 may be a heat exchanger with a working fluid circulating through it, or each of the targets 302 may be photovoltaic devices, which convert solar radiation into electricity directly. The secondary minors 107 are of two types, main ones, which are within the bounds of the primary mirror 102 and two extra ones 303, which extend beyond the primary mirror 102 and redirect onto the targets 302 solar radiation, which, otherwise when the sun is considerably off-axis with respect to the primary mirror 102, would not be re-directed by the secondary mirrors 107 onto their respective targets 302, as shown in Figure 4. The movements of all of the mirrors 102, 107 arid 303 are directed by a controller 304 in response either to signals generated by a separate sun-seeker of any known type, or by monitoring the power generated by the solar energy converter and maximising this by means of a feed-back loop of appropriate type.

Normally, the primary mirror 102 focuses solar radiation in a direction normal to the axis of the primary mirror 102 and the secondary mirrors 107 and 303 focus solar radiation along the axis of the primary mirror 102. However, the secondary mirrors 107, 303 may be curved also across their width so as to influence the focal length of the primary mirror 102. The transverse configurations of the secondary mirrors 107, 303 are related to the positions of the secondary mirrors 107, 303 in relation to the focal length of the primary mirror 102. If the separation between the primary mirror 10 and the secondary mirrors 107, 303 is less than the focal length of the primary mirror 102, then the transverse curvature of the secondary mirrors 107, 303 is negative (convex) if the separation between the primary mirror 102 and the secondary minors 107, 303 is greater than the focal length of the primary mirror 102, then the transverse curvature of the secondary mirrors 107, 303 is positive (concave) as shown in Figure 4.

Figure 5 shows an apparatus in which the secondary minors 107, 303 are replaced by cylindrical lenses 501 of elliptical cross-section, only one of which is shown in Figure 5, which are adapted to be capable of rotation about axes which are orthogonal to that of the primary mirror 102. The control mechanism is as before. In this case the solar energy convertor 105 is located in front of the primary reflector 102 and the lenses 501, as shown in Figure 5.

Claims

CLAIMS1. An apparatus adapted to enable a linear focusing solar radiation concentrator to follow the apparent diurnal motion of the sun without rotating about a vertical axis, comprising a linear focusing primary optical element adapted to be capable of rotation about an horizontal axis only, a linear array of secondary focusing elements positioned in front of the primary focusing element and adapted to be capable of rotating about parallel axes orthogonal to the axis of rotation of the primary optical element and control means adapted to cause the primary optical element to rotate about the said horizontal axis so as to follow changes in the azimuth of the sun and the secondary optical elements to rotate in concert about the said axes orthogonal to the axis of rotation of the primary focusing element so as to cause solar radiation proceeding from the primary optical element to remain focused on a target area regardless of changes in the declination of the sun.
2. Apparatus according to claim 1 wherein each secondary optical element is a mirror which is concave with respect to the primary optical element in a plane parallel to the optical axis of the primary focusing element.
3. Apparatus according to claim 2 wherein each secondary element is curved in a plane orthogonal to the optical axis of the primary optical element.
4. Apparatus according to any of claims 1 to 3 wherein the target area is positioned beyond the focus of the primary optical element and the secondary optical elements are cylindrical lenses of elliptical cross-section adapted to rotate about an axis orthogonal to that of the primary optical element.
5. Apparatus according to claim 1 wherein the secondary optical elements are mirrors of the Fresnel type.
6. Apparatus adapted to enable a linear focusing solar radiation concentrator to follow the apparent diurnal motion of the sun without rotating about a vertical axis substantially as hereinbefore described and with reference to the accompanying drawings.