GB1562912A - Automatic heliostat mechanism - Google Patents

Description

(54) AUTOMATIC HELIOSTAT MECHANISM (71) We, STANDARD TELEPHONES AND CABLES LIMITED, a British Company, of 190 Strand, London, W.C.2R, lDU, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment : - This invention relates to heliostats having arrangements for tracking the sun. The present invention provides improvements in or modifications of the heliostat arrangement of our application number 1960/76 (Serial No. 1,556,381).

In certain cases, e.g. in a solar power generator, it is required for an optical image of the sun to be projected on to a desired object, and for the projection system to enable the sun to be followed so that power generation continues throughout the day. The above mentioned patent application describes such an arrangement, and the present invention has as its object the provision of a heliostat which is simpler than that described in that application.

The above mentioned application claims a heliostat arrangement, including a receiver device for solar energy mounted within a housing, said receiver device incorporating conversion means for deriving electrical energy from solar energy incident thereon, means for focussing the solar energy which is incident from a particular direction relative to the housing on to the receiver device, fluid reservoirs within the housing and located adjacent to the receiver device so that when the direction of incidence of the energy from the sun is misaligned with respect to said particular direction that energy falls on one or more of said reservoirs dependent on the direction of that misalignment, and control means associated with said reservoirs and so connected thereto that the arrangement is balanced when the sun's energy is focussed on the receiver and that when the sun's energy falls on one or more of the reservoirs the changes in volume of the contents of the reservoirs influence the control means such that the arrangement is moved to re-orientate the housing such that the sun's energy is caused to fall on the receiver means.

According to the present invention there is provided a heliostat arrangement as claimed in claim 1 of Application No.

1960/76 in which the housing is substantially spherical or partly spherical in shape, and in which said control means includes for a single co-ordinate; a tube of a facile plastics material which interconnects two of said reservoirs which are diametrically opposed with respect to the receiver device said tube extending along the inner surface of the housing, a body of a magnetic material bearing on the tube at or near to its mid-point to constrict the tube at that mid-point, and a stationarv magnet on the outside of said housing with which said magnetic body tends to align; in which when the sun's energy falls on one of said reservoirs the expansion of the fluid therein fills the portions of the tube between that reservoir and the magnetic body, thereby displacing the magnetic body so as to produce relative rotation between the housing and the stationary magnet, said relative movement tending to reset the arrangement to a position wherein the sun's energy falls on said receiver device.

In one of the arrangements described herein the control means referred to includes a tube of a squashable material which interconnects a pair of reservoirs and has a magnetic body bearing on its mid-point so as to produce a constriction thereat. As the fluid on one or other side of the constriction expands, the change in volume within the tube attempts to move the magnetic body. However, the body is located by a magnet with the result that the whole housing moves to redirect the solar energy onto the receiving means.

According to the present invention there is further provided a heliostat arranment as claimed in claim 1 of application No.

1960/76 in which said control means in cludes a plurality of inflatable bags on which the housing, which is spherical or part-spherical, rests, said bags being normally deflated, in which each said bag is coupled by a tube to one of said reservoirs, and in which when the sun's energy falls on one of said reservoirs the heating of the fluid therein causes the bag coupled thereto to inflate, the inflation of one or more of said bags functioning to reposition the heliostat arrangement.

Embodiment of the invention in which the receiver means is a solar cell will now be described with reference to Figures 1 to 3 of the drawings accompanying the Provisional Specification, and the accompanying Figure 4.

As will be seen from Figure 1, the general arrangement is similar to that of the above application, in that it uses a Fresnel lens 1 to focus solar energy on to a Solar Cell 2, and fluid reservoirs 3 and 4 power a Servo mechanism which causes the heliostat to follow the sun's azimuth path. The whole assembly is encased in a plastics sphere 6 and floats on frictionless bearings, e.g. by being supported in a water bath. Note that in the present context, the term fluid embraces both liquids and gases.

The reservoirs 3 and 4 arranged on either side of the solar cell 2 are linked by a thinwalled plastics tube 7, which may be made from two thin strips of a facile plastics sheet seam-welded together. The link tube 7 follows the inside contour of the sphere 6 and is located therein by a part-circumferential channel 8. The channel 8 also serves as a guide for a soft iron cylindrical armature 9 which bears on the tube 7, under the attraction of the magnetic field of an external fixed magnet 10, the armature squashing and thereby locally sealing the tube 7. A small quantity of a ferromagnetic fluid can be introduced into the tube to enhance the sealing characteristics of the tube.

When, as a result of the sun's diurnal movement, the focussed solar energy falls on one of the reservoirs 3 or 4 the fluid content thereof is heated and expands and inflates the corresponding side of the link tube 7. As the tube 7 inflates it displaces the cylindrical armature 9 in a mode similar to that of a peristaltic pump. Since the armature 9 is maintained in its absolute position by the magnetic field of the external magnet 10 a reaction between the armature 9 and the inflated tube 7 provides a drive to align the sphere 6 with the sun.

The drive mode is only maintained whilst the sun's energy is focussed on the reservoir 3 or 4, and as soon as the light leaves the reservoir the fluid therein return to ambient temperature and the link 7 collapses.

In the quiescent state fluctuations in ambient temperature are unlikely to be a problem since the link tube 7 would readily accommodate any such fluid expansion, Alignment of the sphere can be automatically locked by a brake shoe 11 bearing on the armature 9 and operated by a temperature-responsive diaphragm spring capsule 12; such a capsule is an integral part of the heatsink 1-3 upon which the solar cell 2 is mounted. With the solar energy focussed on the solar cell 2 and its heatsink 13, the diaphragm capsule 12 responds to the temperature change to operate the brake shoe 11.

Note that such location arrangements are needed for both x and y co-ordinates, although only shown for one coordinate. In some cases it may be desirable to provide a location arrangement of a different type for the other co-ordinate.

When the reservoirs are gas-filled, as in Fig. 1 it may be desirable to provide vents from the reservoirs with valves via which the fluid in the reservoir has access to the inside of the housing. Thus when the heliostat has been re-positioned as described above, the heated gas in the reservoir which caused the re-positioning has to be released, since otherwise it may tend to return the heliostat to its previous position as the heated gas cools. This cooling, of course, takes place because the sun's energy no longer falls on the reservoir. The venting action which thus occurs results in a so-called ratcheting action of the heliostat as it follows the sun.

The armature need not be of a round section, but could be elliptical as shown at Fig. 2, or roughly triangular. In this case a locking system may not be required, as the armature 14 would come to rest with its flat side adjacent to the magnetic field and would therefore resist any further movement.

The armature 9 or 14 could be replaced by a spherical armature 15, Fig. 3, provided the adjacent surface 16 of the link tube 7 is corrugated or ribbed so as to maintain its linear flexibility but prevent lateral distortion. This facilitates the second motion required, that of elevation.

A bimetallic strip 17 attached to the side of the heatsink 13 at one end and to a double fence 18 at the other end would be influenced by solar energy focussed on the bimetallic strip 17 instead of the solar cell 2. The bimetallic strip may have to be duplicated, on either side of the heat sink.

Such a bimetal strip and fence arrangement provides the means to move the armature 15 in a lateral mode relative to the link tube 17. As the armature is main tained in its absolute position by the external magnet 10 a reaction between the armature 15 and the fence 1?8 provides the drive to align the focus of the solar energy in the elevation mode. A braking system will not normally be required as the corrugations of the surface of the link tube would locate the armature.

This arrangement using a bimetallic strip initiates movement in the elevational mode, but the full movement in that mode is completed by the reservoir-link tube system appropriate to the elevational mode.

Thus the cooling of the bimetallic strip after the solar energy leaves it will have little or no effect from the point of view of oscillation as the strip cools after the solar energy leaves it.

The venting arrangements referred to hl connection with the arrangement shown in Fig. 1 may also be needed in the device of Fig. 3.

We now turn to Fig. 4 which also shows a heliostat embodying the features of the above mentioned aDDlication. As in the device of Fig. 1, a Fresnel lens 21 focuses solar energy onto a solar cell 22 to produce electrical energy and an arrangement of three or more fluid reservoirs 23 around the solar cell provide the effort to motor the device into correct azimuth and elevation orientation i.e. to seek the sun.

Once again the Fresnel lens 21, Solar cell 22 and fluid reservoirs 23 are housed in a spherical or partially spherical envelope 24.

Three or more fluid reservoirs 23 are linked by separate tubes 25 to inflatable envelopes 26 upon which the sphere 24 rests. When the focussed solar energy falls on one of the reservoirs 23, it causes its fluid content to expand and thereby inflate its corresponding envelope 26, and as one or more of the envelopes 26 inflate they displace the sphere 24 in a mode similar to that of a peristaltic pump. Once the sphere is aligned with the sun correctly the reservoirs cool and in consequence the envelopes collapse, obviating interference by fluctuating ambient temperatures. A heavy amorphous ballast 27 in the base of the sphere provides a means to maintain alignment with the sun after the envelopes 26 collapse. This mass is free to move to maintain this alignment.

The coolant drawn through the heatsink 28 of the solar cell would provide an additional benefit of heating.

This heliostat arrangement may also need a venting arrangement such as described for use with the arrangement of Fig. 1.

WHAT WE CLAIM IS: 1. A heliostat arrangement as claimed in claim 1 of Application No. 1960/76 (Serial No. 1,556,381) in which the housing is substantially spherical or partly spherical in shaape, and in which said coil- trol means includes for a single-co-ordinaLe, a tube of a facile plastics material which interconnects two of said reservoirs which are diametrically opposed with respect to the receiver device, said tube extending along the inner surface of the housing, a body of a magnetic material bearing on the tube at or near to its mid-point to construct the tube at that mid-ooint and a stationary magnet on the outside of said housing with which said magnetic - bod tends to align) in which when the sun's energy falls on one of said reservoirs the expansion of the fluid therein fills the portions of the tube between that reservoir and the magnetic body thereby displacing the magnetic body, so as to produce relative rotation between the housing and the stationary magnet said relative movement tending to reset the arrangement to a posittion wherein the sun's energy falls on said receiver device.

2. A heliostat arrangement as claimed in claim 1, in which the receiver device is mounted on a heat sink formed by an enclosed chamber with a diaphragm mounted on it, and in which when the sun's energy falls on the receiver disc the gas in said enclosed chamber is heated and moves he diaphragm which moves a brake to lock the magnetic body.

3. A heliostat arrangement as claimed in claim 2, in which said brake includes an arcuate strip-like member which is adjacent to and parallel to said tube, one of its ends being anchored by a pivot to the underside of one of said two reservoirs and its other end being anchored by a spring to the underside of the other of said reservoirs, and a finger extending from the mid-point of said strip-like member to the diaphragm via which the movement of the diaphragm is communicated to the strip-like member, and in which said strip-like member when moved by the diaphragm bears on the magnetic body.

4. A heliostat arrangement as claimed in claim 1, 2 or 3, and in which said magnetic body is cylindrical in cross section.

5. A heliostat arrangement as claimed in claim 1, 2 or 3 and in which said magnetic body is elliptical or roughly triangular in cross-section.

6. A heliostat arrangement as claimed in claim 1, 2, 3, 4 or 5, and in which a small quantity of a ferromagnetic fluid is introduced into the tube to enhance its sealing characteristics.

7. A heliostat arrangement as claimed in claim 1, in which said magnetic body is spherical and in which the surface of the tube onto which it is urged by the attrac

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. tained in its absolute position by the external magnet 10 a reaction between the armature 15 and the fence 1?8 provides the drive to align the focus of the solar energy in the elevation mode. A braking system will not normally be required as the corrugations of the surface of the link tube would locate the armature. This arrangement using a bimetallic strip initiates movement in the elevational mode, but the full movement in that mode is completed by the reservoir-link tube system appropriate to the elevational mode. Thus the cooling of the bimetallic strip after the solar energy leaves it will have little or no effect from the point of view of oscillation as the strip cools after the solar energy leaves it. The venting arrangements referred to hl connection with the arrangement shown in Fig. 1 may also be needed in the device of Fig. 3. We now turn to Fig. 4 which also shows a heliostat embodying the features of the above mentioned aDDlication. As in the device of Fig. 1, a Fresnel lens 21 focuses solar energy onto a solar cell 22 to produce electrical energy and an arrangement of three or more fluid reservoirs 23 around the solar cell provide the effort to motor the device into correct azimuth and elevation orientation i.e. to seek the sun. Once again the Fresnel lens 21, Solar cell 22 and fluid reservoirs 23 are housed in a spherical or partially spherical envelope 24. Three or more fluid reservoirs 23 are linked by separate tubes 25 to inflatable envelopes 26 upon which the sphere 24 rests. When the focussed solar energy falls on one of the reservoirs 23, it causes its fluid content to expand and thereby inflate its corresponding envelope 26, and as one or more of the envelopes 26 inflate they displace the sphere 24 in a mode similar to that of a peristaltic pump. Once the sphere is aligned with the sun correctly the reservoirs cool and in consequence the envelopes collapse, obviating interference by fluctuating ambient temperatures. A heavy amorphous ballast 27 in the base of the sphere provides a means to maintain alignment with the sun after the envelopes 26 collapse. This mass is free to move to maintain this alignment. The coolant drawn through the heatsink 28 of the solar cell would provide an additional benefit of heating. This heliostat arrangement may also need a venting arrangement such as described for use with the arrangement of Fig. 1. WHAT WE CLAIM IS:

1. A heliostat arrangement as claimed in claim 1 of Application No. 1960/76 (Serial No. 1,556,381) in which the housing is substantially spherical or partly spherical in shaape, and in which said coil- trol means includes for a single-co-ordinaLe, a tube of a facile plastics material which interconnects two of said reservoirs which are diametrically opposed with respect to the receiver device, said tube extending along the inner surface of the housing, a body of a magnetic material bearing on the tube at or near to its mid-point to construct the tube at that mid-ooint and a stationary magnet on the outside of said housing with which said magnetic - bod tends to align) in which when the sun's energy falls on one of said reservoirs the expansion of the fluid therein fills the portions of the tube between that reservoir and the magnetic body thereby displacing the magnetic body, so as to produce relative rotation between the housing and the stationary magnet said relative movement tending to reset the arrangement to a posittion wherein the sun's energy falls on said receiver device.

2. A heliostat arrangement as claimed in claim 1, in which the receiver device is mounted on a heat sink formed by an enclosed chamber with a diaphragm mounted on it, and in which when the sun's energy falls on the receiver disc the gas in said enclosed chamber is heated and moves he diaphragm which moves a brake to lock the magnetic body.

3. A heliostat arrangement as claimed in claim 2, in which said brake includes an arcuate strip-like member which is adjacent to and parallel to said tube, one of its ends being anchored by a pivot to the underside of one of said two reservoirs and its other end being anchored by a spring to the underside of the other of said reservoirs, and a finger extending from the mid-point of said strip-like member to the diaphragm via which the movement of the diaphragm is communicated to the strip-like member, and in which said strip-like member when moved by the diaphragm bears on the magnetic body.

4. A heliostat arrangement as claimed in claim 1, 2 or 3, and in which said magnetic body is cylindrical in cross section.

5. A heliostat arrangement as claimed in claim 1, 2 or 3 and in which said magnetic body is elliptical or roughly triangular in cross-section.

6. A heliostat arrangement as claimed in claim 1, 2, 3, 4 or 5, and in which a small quantity of a ferromagnetic fluid is introduced into the tube to enhance its sealing characteristics.

7. A heliostat arrangement as claimed in claim 1, in which said magnetic body is spherical and in which the surface of the tube onto which it is urged by the attrac

tions of said magnet is corrugated or ribbed.

8. A heliostat arrangement as claimed in claim 7, and in which the receiver device is mounted on a heat sink which carries one or more bimetallic strips whose deflections when the heat sink is heated also control the position of the magnetic body.

9. A heliostat arrangement as claimed in claim 1 of Application No. 1960/76 (Serial No. 1,556,381) in which said control means includes a plurality of inflatable bags on which the housing, which is spherical or part-spherical, rest, said bags being normally deflated, in which each said bag is coupled by a tube to one of said reservoirs, and in which when the sun's energy falls on one of said reservoirs the heating of the fluid therein causes the bag coupled thereto to inflate, the inflation of one or more of said bags functioning to reposition the heliostat arrangement.

10. A heliostat arrangement as claimed in claim 9, and in which the bottom of the housing contains movable amorphous ballast.

11. A heliostat arrangement substantially as described with reference to Fig. 1, 2 or 3 of the drawings accompanying the Provisional Specification.

12. A heliostat arrangement substantially as described with reference to the accompanying - Fig. 4.