Low cost approach to Heliostat construction

Abstract

A free-standing heliostat 1 comprises a mirror 1 and its supporting structure 2 which is mounted on either side of a pair of bearings 3. These bearings are mounted on a frame 5 attached to a vertical

Description

Patent Application Title: Low cost approach to Heliostat construction Background: Concentrated Solar Power (CSP) is one of the most promising forms of renewable, pollution free energy, with huge untapped potential globally. However, currently the set up costs for CSP are significantly higher than for fossil fuel power plants, and development to the sort of scale required to make a significant impact on global carbon dioxide emissions seems unlikely to occur in the foreseeable future. Central Tower CSP is considered to be one of the most promising methods: vast arrays of dual-axis mounted mirrors (heliostats) reflect the sun’s rays onto a receiver situated at the top of a central tower, and the high temperatures generated are used to create electricity, most commonly via the creation of steam which then powers a conventional steam turbine. The angle of each mirror is adjusted very slightly but frequently by a computer utilising complex algorithms, incorporating the exact position of the heliostat and the predictable, though ever changing position of the sun, at any time of day. This computer controls motor driven gear systems, which must be extremely precise, but also be robust enough to withstand the significant strains imparted by winds on the large mirror. Manufacture, installation, calibration and maintenance is a highly specialised and expensive field. The heliostat field usually makes up more than 50% of the total cost of the Central Tower CSP plant. The costs of heliostats are generally presented as cost per square metre of mirror, and the most economical conventional heliostats currently cost around US$100 per square metre of mirror to manufacture. Reducing the cost of the heliostat field is essential to make this method of electricity generation more competitive, when compared to the more environmentally damaging ones. Statement of invention: This invention would allow heliostats to be produced, installed, calibrated and maintained at a dramatically lower cost, by taking a completely different approach to the existing designs. This design allows a human operator to make the small, intermittent but frequent adjustments that would be required to maintain the rays of the sun on the central receiver, very precisely, but also very rapidly. This would allow one operator to control a large number of heliostats, and a team of human operators to be able to control an entire field of many hundreds of heliostats. General Heliostat design The mirror {i} and its supporting structure {2} are mounted on either side on a pair of bearings {31 that allow the angle of elevation around the midline {4} of the mirror to be adjusted freely. These bearings are mounted on a frame {3} that is attached to a vertical foundation post {&}, by way of a single horizontal bearing {7} that rotates freely around the azimuth. Hence the mirror can be orientated to face in virtually all directions. A similar arrangement is seen in a traditional shaving mirror or a theatre spotlight. It is designed such that the two axes of rotation intersect in the plane of the mirror, and at the precise point of this intersection, a small round hole {¥1 is placed in the mirror, which allows an image of the sun {3} to be projected beneath the mirror, as with a pinhole camera. As the pinhole is situated at the intersection i i{}i of the two axes of rotation, it does not move when the orientation of the mirror is adjusted, meaning that the location of the projected image of the sun {¥{ is only affected by the change in position of the sun in the sky. A rigid translucent or transparent hemisphere {11} is attached to the underside of the mirror, situated so that the pinhole is located at the geometric centre of the hemisphere, and the ‘equator’ of the hemisphere is adjacent to the rear of the mirror. Given that the pinhole is located at the intersection of the axes of rotation of the heliostat, and so does not move when the angle of the mirror is adjusted, although the hemisphere will move when the mirror is adjusted, the outline of the hemisphere does not change, rotating as it does about its geometric centre. The image of the sun is projected onto this translucent hemisphere, and is thus clearly visible to the operator {121 standing beneath. Figure bb Perspective drawing showing basic hehostat design, showing the winery and supporting frame, and demonstrating the axes of rotation and the location of the pinhole and hemisphere, The geometric pole {13} of the hemisphere is clearly and precisely marked. When the sun’s rays are reflected by the mirror onto the central receiver | 14}, by definition the angle {13} between the incident sun’s rays and the normal {16} of the mirror, must be equal to the angle {17} between the reflected sun’s rays and the normal of the mirror. A line joining the geometric pole {13} of the hemisphere and the pinhole {&} at the geometric centre of the hemisphere will by definition be parallel to the normal of the mirror. Between adjustments, the angle of the mirror is maintained by a robust brakes {18}, fixing the elevation and azimuth bearings, kept in the default applied position between adjustments by powerful springs. Calibration of the heliostat After each individual heliostat has been installed on site, a one-off calibration is required: 1. The spring loaded brakes {18} arc rclcased, allowing free movement of the mirror. 2. The orientation of the mirror is adjusted manually by the operator { i2{ such that the reflected sunlight is focussed onto the optimal point on the central receiver { 141, 3. The spring loaded brakes { i &} are reapplied. 4. Viewing the underside of the hemisphere {1}, the operator is able to observe the relationship between the geometric pole {i3} of the hemisphere, and the projected image of the sun ($1. 5. The unique ‘calibrated anchor point’ {1%} for that heliostat corresponds to a point on the hemisphere {11} on the same meridian as the image of the sun {&i, on the opposite side of the pole {13}, and exactly equidistant from the pole. 6. The exact location of this ‘calibrated anchor point’ {i%i is then marked permanently, by fixing a marker directly adjacent to the above point on the hemisphere, but not attached to the hemisphere itself, instead secured to the immobile central supporting post {&i. Figwre 20 Cross section of mivvor and henusphere demonstrating In two dimensions the relationships between the geomet pole of the hemisphere, the projected mage of the sun and the “calibrated anchor point, The sun and central receiver are included for clarity and are not to scale. and not in ons section, As the position of the sun in the sky changes with time, so will the position of the sun’s image {%} on the hemisphere {11}, and the sun’s reflected rays will start to spill over, and eventually completely leave, the central receiver | 14] whereby the overall efficiency of the plant will begin to decline. In order to readjust the heliostat, all that is required is for the pole {13} of the hemisphere to be returned to the exact midpoint of the meridian line joining the ‘calibrated anchor point’ {1%} and the new position of the projected sun’s image {$i on the hemisphere {i ii. Performing this task purely by visual judgement would be unlikely to be adequately precise, and some additional apparatus is likely to be required to assist the operator in this regard. Apparatus to assist rapid and precise alignment Including the following apparatus in the design would greatly simplify the process of adjusting the position of the heliostat and would greatly reduce the time needed to adjust the mirror and also the precision with which it can be adjusted. At the geometric pole {i:} of the hemisphere {ii}, on the external surface, a freely rotating circular cog {20} is attached. On either side of this cog {20}, two arms {21} are attached, which follow the curvature of the hemisphere {11} in opposite directions. These are are both equal in length to the distance from the pole to the rear of the mirror, and are kept in the same meridian line by partially enclosing parallel tracks {22}. These tracks also follow the curvature of the hemisphere {11} and are attached to the pole {i3}, but are able to rotate freely around the pole, independently of the cog {20}. Teeth {23} on the inside of each arm {21} interlock with the teeth on the opposing sides of the rotating cog {2{1, so that as the cog turns, the two arms move in opposite directions, with the interlocking teeth on the cog ensuring that this is always by precisely the same distance, with the parallel tracks {22} ensuring that they remain in the same meridian. A two dimensional version of this is scen in the paper trays of most printers, used to ensure that the printer paper is kept central, whatever size of paper is used. The end of one arm is attached such that it is able to rotate freely around the previously described ‘calibrated anchor point’ {19} which will always remain in the same position, directly adjacent to the hemisphere, but not attached to it. At the end of the opposite arm, precisely equidistant from the pole in precisley the same meridian as the ‘calibrated anchor point’, a circular cross-hair {24{, of similar size to the projected image of the sun {3} is attached. Hence, the cog {2{}} mechanism at the pole ensures that the distance from the pole to the ‘calibrated anchor point’, {1%} and from the pole to the cross-hair {24}, will always remain equal, regardless of the alignment of the heliostat. Hence the angle {23} subtended at the pinhole {§} between the normal of the mirror { {&} and the ‘calibrated anchor point’ {i} and the angle {36} between the normal of the mirror and the cross-hair {24} will always be equal. Importantly, this apparatus (as well as perhaps the hemisphere) is the only part of the heliostat that would require any specialist manufacturing. Figure 3 Close op of the ahgoment apparatus viewed from the underside of the hemisphere, with the “calibrated anchor pola” and crosshair both situated close © the pole cog for clarity. With this arrangement, when the angle of the mirror adjusted, the pole of the hemisphere will move, as will the cross-hair, however the ‘calibrated anchor point’ will remain static, as it is rigidly and permanently fixed to the immobile central pole. To align the mirror, the operator merely needs to adjust the heliostat so that the cross- hair lies exactly over the image of the sun on the hemisphere. This not only increases precision, but greatly simplifies the process of adjustment, essentially transforming what was already a fairly simple task into one requiring virtually no skill at all, and reducing the time required to align the mirror to mere seconds. The angular precision with which this can be achieved will be greater, the larger the diameter of the hemisphere. Larger hemispheres could perhaps be used for more distant heliostats, though it is likely that using a uniform size would end up being more economical from a manufacturing perspective. Figure 4 Alignment apparatus viewed frog the anderside of the hemisphere, demonstrating the approach ased to mirror adjustment, whereby the angle of the wirer by adhested such thar the cross-halr woves fo He divectly over the projected nnge of the sun on the hemisphere. Optimal target point on central receiver Assuming the reflected rays of the sun focus to a point smaller that the total size of the central receiver {14}, the most efficient target point {29} on the receiver would be the point at which the natural drift of the reflected light {27} between adjustments in orientation, would result in the longest period of time before the reflected light starts to spill over the edge of the central receiver {4}, which corresponds to the point at which the overall efficiency of the system would start to reduce. Although possible to calculate, it could more easily be determined simply by observing the direction of drift {28} of the reflected sun’s rays across the receiver, which would remain the same regardless of the time of day for that heliostat, but would of course vary between heliostats in different positions surrounding the central receiver { 14}. This would add significantly to the overall efficiency, as the number of operators required for the same number of heliostats would be significantly reduced. Figure § Schematic drawing of the contral receiver, showing three examples of how g ¢ 3 the optimal inital target point on receiver is determined, following observation of the direction of drift of the reflected sunlight. Frequency of adjustments Although the angular velocity at which the sun appears to move through the sky is stable throughout the day (approximately 0.25 degrees per minute) the speed at which the reflected sun’s rays would move across the receiver would be greater, the further the heliostat is situated from the central receiver. Hence, less time would elapse before the light began to spill over the edge of the receiver, necessitating more frequent adjustments. Although this would be easy to calculate, knowing the distance from mirror to the central receiver, the size of receiver, the size of the focussed sun’s rays and the angular velocity of the sun in the sky, in practice it would be even easier to simply observe while in use, and record the time at which the light starts to spill over the edge of the receiver, which would correspond to the point at which efficiency will begin to decline. If the heliostats are arranged in a concentric circular formation around the tower, which is the conventional arrangement near the equator (semicircular at more Northerly and Southerly latitudes) the maximum time between adjustments would be the same for all of the heliostats situated in the same circle. Therefore, the time between adjustments would only need to be observed for one heliostat in each circle of heliostats. The average time taken for one operator to walk between heliostats and to make the small adjustment to refocus the rays to the optimal position could be observed and recorded. Hence the number of operators required for each circle of heliostats, in order to maintain optimal efficiency, could easily be calculated. One operator would be able to effectively operate a larger number of heliostats situated in the proximal rings, compared to the rings more distant from the central tower. Importantly, as long as all heliostats are adjusted with the appropriate frequency, the power output of the plant as a whole would be exactly the same as a conventional automated plant, using an equivalent central receiver and the same number and size of mirrors. Size of mirror This system would technically work with any size of mirror, with the only limitation being weight, as the operator is required to manually adjust the angle of elevation and orientation around the azimuth, without undue effort. However, with well lubricated hinges, even a very large mirror, or array of mirrors, if its weight is balanced either side of the axis of clevation, would be relatively casy to adjust, particularly if long handles {30} are attached to the supporting frame {2} of the mirror. There are clear advantages with regard to the frequency of adjustments, of having the area of reflected sun’s rays on the receiver, as small as possible in relation to the size of the receiver. Therefore, multiple small mirrors, all attached to a rigid frame on the same heliostat, could have their relative alignment adjusted, so that the reflected light of each is focussed onto the same area on the receiver, as that of the central mirror, carrying the pinhole and hemisphere. Multiple small mirrors would also be much cheaper to manufacture and far easier to transport and install than a single large one. Brake system Between adjustments, the angle of the mirror is maintained by strong brakes {i} fixing the elevation {3} and azimuth {7} bearings, kept in the default applied position between adjustments by powerful springs. The brakes could be released by a foot operated pedal {311 on the ground, attached to the brakes via brake cables {3} using the body weight of the operator, thus allowing the operator to precisely adjust the orientation of the mirror with both hands, and also to hold it in the optimal position while the brakes are being re-applied. The brakes {{%{ would only be released for the one or two seconds required to adjust the mirror, and would revert to the default applied position as soon as the operator releases pressure from the foot pedal {31}. Alternatively, the brakes could be released by hand operated levers attached to the ends of the handles {3{:{, such that the operator could release the levers and return the brakes to the applied position, while also holding the position of the heliostat with both hands. Simple mechanics suggests that the further the brakes {13} are situated from their respective axes of rotation, the less the force will be required to hold the two mobile sections of the heliostat in a fixed position, and the more reliably will the precise position of the mirror be maintained. To this end, for the elevation bearing {3}, a simple disc brake system could be used, with two large semicircular discs {33} attached to the frame {2} supporting the central mirror, and two spring loaded clamp brakes {18} attached to opposite ends of the horizontal supporting beam of the rotating frame {3} which grip these semicircular discs when applied. In order to secure the azimuth bearing, a circular disc {34} could be firmly attached to the top of the fixed central supporting post {¢, with spring loaded clamp brakes attached to the opposite ends of the underside of the horizontal supporting beam of the frame {5} that rotates around the azimuth, which grip the opposite sides of the single circular disc when applied. Having brakes in pairs on the opposite ends of the horizontal supporting beam would mean that any torsional forces created by changes in tension in the brake cables would tend to cancel each other out, and would be less likely to interfere with the precise orientation of the mirror. Unlike the discs and brake pads used in cars and bicycles, which use low friction discs and pads to allow rapidly rotating discs to be slowed smoothly and gradually, these would be made from materials that have high degrees of friction when firmly applied together, so as to prevent any slippage in high winds. See Figure & Perspective drawing showing a possible arrangement for the spring foaded clamp brakes and the respective dises fixing the elevation and seimoth axes of rotation, whereby the brakes are rolcased by a foot operated padal convected via brake cables, to allow reclignment of the mirror, Advantages over existing heliostat design The potential advantages of this design of heliostat over that of the existing technology are numerous, and are listed below: Ease of manufacture The absence of motors, gears, wires, or computers, will make the manufacture of these heliostats vastly cheaper than the current market leaders of conventional computer controlled heliostats. The costs of heliostats are generally presented as cost per square metre of mirror. The most economical conventional heliostats cost around US$100 per square metre of mirror to manufacture. The numbers of these heliostats required for a Central Tower CSP plant are measured in the hundreds or even thousands. This new design would work with any size of mirror, and could also use either concave mirrors, or several plain mirrors, orientated so the focal length of the array on a single heliostat is equal to the distance between the heliostat and receiver. It would be suitable for both conventional glass coated mirrors, or the more lightweight stretched membrane design. Materials for the heliostat frame With conventional motorised computer controlled heliostats, there is an obvious economy of scale in having a large surface area of mirror per heliostat. Consequently, the heliostats tend to be very large, and so large amounts of steel are required to build the supporting frame. Although the same economies of scale would apply to some degree, they would be far less critical, given that the costs of the hemisphere, adjustment aparatus and brakes would be negligible compared to the computers, motors and gears in conventional heliostats. The main limiting factors in terms of mirror surface area would be how comfortably and precisely the operator is able to adjust the angle of the mirror by hand. This would allow heliostats of significantly smaller size to be economical, which would make it feasible to use alternative materials of significantly lower cost. For example timber could be used for the central support, frame and mirror mounts, which would be orders of magnitude cheaper in terms of material costs and construction, and would also be much less environmentally damaging overall. Appropriately treated timber has a working lifespan in excess of thirty years, which is the equivalent to the predicted life spans of most existing CSP plants. Other materials such as rigid moulded plastic, or MDF could also conceivably be used. CSP site selection Conventional Power Tower CSP plants require very flat and even ground to enable the computer algorithms to adjust the angle of the mirrors accurately, based on the precise coordinates of each heliostat and the predictable position of the sun at any time of day. This either greatly limits the sites that can be used, or necessitates expensive land preparation and the grading of very large arcas. With this manually operated heliostat design, each heliostat is completely autonomous, meaning that even very steep and uneven ground could be used to site the array of mirrors. Not only does this vastly increase the potential application of this form of renewable energy, it also negates the need for expensive and environmentally damaging land grading. It could very easily coexist with some forms of agriculture, particularly in desert areas where some degree of protection from direct sunlight is actually beneficial. Moreover, naturally occurring amphitheatres or, for example, disused quarries, have significant efficiency advantages over flat ground in that they minimise the shadowing effect of heliostats on each other, and also allow more mirrors to be sited closer to the central tower, which has efficiency advantages, for the reasons previously explained. The central tower would also potentially not need to be so tall, which again could generate additional cost savings. Installation ‘With conventional plants, this is a highly specialised and expensive undertaking, with large amounts of site preparation, land grading and the laying of high specification concrete and steel foundations. In addition, installation of often several miles of underground electrical wiring is required to join the two motors attached to each heliostat to the central computer. With the new design, installing the vast array of upright poles that support the heliostats could potentially be performed by a pair of labourers with shovels, pick axes, some cement and a spirit level. The optimal heliostat array for the planned height of central tower and the given dimensions of the heliostats, in terms of the diameters of the circles of heliostats, and the spacing between the individual heliostats, could be calculated and mapped out in advance using computer modelling. This arrangement could then be very simply translated onsite into the location of each heliostat, using a rope tied to a central post (prior to tower construction) and measuring wheel, with the future location of each heliostat marked on the ground. Furthermore, being imperfectly vertical would not actually have any effect on precision and efficiency, as this approach only relies on the axes of rotation being perpendicular to each other. This would make this design more resistant to land subsidence or earthquakes. Calibration With conventional plants, calibrating the heliostats is a highly specialised task, involving complex computer algorithms. It is very time consuming and requires to be repeated regularly, as one or two degrees of error will have a drastic effect on efficiency of the plant as a whole. By contrast, calibrating each heliostat with the proposed design takes a matter of seconds, and the technique (described earlier) can be taught, learnt and mastered in minutes. Given that large numbers of heliostat operators would be employed at the plant, calibration could even take place daily, though this would be unlikely to be necessary. Resilience to wind and environment One of the major challenges and one of the factors contributing to the high costs with conventional plants is that the motors and gears have to be sensitive enough to make the frequent tiny and precise adjustments, but must also be strong enough to withstand quite significant strains and torque duc to the significant cffect of high winds on the large mirrors. The new design side-steps this issue entirely, in that there are no gears or motors at all. The heliostats will be very resistant to wind, as powerful spring loaded brakes maintain the position of the mirror firmly between adjustments by the operator. Maintenance Maintaining conventional plants is a specialist and expensive task, given the numerous things that can potentially go wrong with the computers, motors and gears. By contrast, there is very little that can go wrong with the new design, and maintenance would likely be limited to oiling the bearings, cleaning the mirrors, and occasional checks of calibration. Job creation Conventional plants are fully automated, and so only employ a small numbers of highly skilled and specialised engineers. The new design has the potential to create an entirely new cadre of employment, possibly on a vast scale. The work would be low skilled and the training required would be negligible. In countries with high unemployment, demand for the work would be likely to be very high, and the economic benefits of creating large amounts of useful work for unemployed people are obvious. Given the very short learning curve involved in mastering the task of adjusting the mirrors, the work would be perfectly suited to casual shift work, but could also provide full time employment. In countries with low unemployment, where recruiting for menial jobs can be a challenge, many low risk prison inmates would perhaps be happy to volunteer to for paid work manning the heliostats, even if just for the fresh air and exercise. Cost of central receiver and steam turbine With the existing technology the central receiver turns water to steam which powers a conventional steam turbine. Some plants use the high temperatures to create molten salt, which can be stored in tanks, to be used for creating steam at a later hour, in order to allow electricity generation to occur after sunset or during overcast periods. With the new design of heliostat, exactly the same receivers, heat storage systems and steam turbine systems could be used. However, by greatly decreasing the costs of the heliostats, which make up such a significant proportion of the overall cost of these plants, a significantly lower specification of receiver and turbine would be both possible and justified, as a slight reduction in efficiency would be perfectly acceptable from an economic perspective, particularly given that the fuel source is free and renewable. This would further reduce the overall costs of the plants, as the costly pursuit of ever increasing efficiency of receiver and turbine, is subject to the law of diminishing returns. Some CSP plants have experimented with Highly Concentrated Photovoltaic central receivers, and even Sterling heat engines, neither of which require a circulating heat transfer liquid or steam turbine. It is likely that these have been shown to have lower efficiency, given that they remain very uncommon, but with the cost of the heliostat field a tiny fraction of those used in conventional plants, these may well become viable options. This paradigm shift in cconomic viability could potentially stimulate the development of multiple large CSP plants, but would also make small-scale, low technology community level CSP plants a viable option even in remote areas, far from national grids. Using a lower cost central receiver would also allows multiple central receivers, each with its own concentric rings of heliostats, to share a single steam turbine, thus allowing the distance from tower to its heliostats to be kept to a minimum, and therefore significantly increasing efficiency of the plant as a whole. Alternative uses for similar apparatus A conventional thermal CSP plant located near the ocean could conceivably use sea water, with salt and desalinated water produced as very useful by-products. Although electricity generation from solar power is by far the most common use for heliostat arrays, there is potential for the very high temperatures achieved at the receivers to be used for industrial processes such as separating quicklime from limestone in the production of cement, which usually consumes large amounts of electricity or combustible fuel. The high temperatures created at the central receiver could also be used to directly power large scale air conditioning units, for example for an office building or hospital, without the need for conversion to electricity, a process which in itself is inherently significantly less than 100% efficient.

Claims

1. A heliostat whereby the orientation of the mirror [ 1 ] is adjusted manually by a human operator [12] so that the sun’s rays are directed onto the central receiver [14], and held in this position between adjustments by a spring loaded brake system [18].

2. A heliostat according to claim 1, whereby the mirror [1] is situated such that the intersection of the azimuth and elevation axes of rotation occurs within the plane of the mirror, and a small hole [81 is placed at this precise intersection, thus allowing an image of the sun [9] to be projected beneath the mirror, which can be used to guide the operator in the correct alignment of the heliostat.

3. A heliostat according to claim 2, whereby a translucent hemisphere [11] is firmly attached to the rear of the mirror [ 1], which thus moves with the mirror, and onto which the image of the sun [ 9] is projected, such that it can be easily viewed from beneath by the human operator 114], with the hemisphere attached such that the equator of the hemisphere is adjacent to the rear surface of the mirror, the geometric centre of the hemisphere coincides with the abovementioned pinhole [8], and a line from the geometric pole 113] of the hemisphere to the pinhole [8j is parallel to the normal of the mirror] 16].

4. A heliostat according to claim 3 whereby the orientation of the mirror 11] can be precisely adjusted such that the rays of the sun are reflected onto the central receiver 114], by the operator placing the clearly marked geometric pole 113] of the abovementioned hemisphere at the exact midpoint of a line joining the projected image of the sun [9] and a ‘calibrated anchor point’ 119] which is specific to that heliostat, and which is located by reverse calibration, and whose position is clearly identified by a marker which is robustly fixed to a non-mobile part of the heliostat supporting structure.

5. A heliostat according to claim 4, utilising a device to increase the ease, precision and speed with which the mirror can be correctly adjusted, characterised by a freely rotating circular cog 40]attached to the pole of the hemisphere, whose teeth interlock robustly on opposite sides with the internal teeth 123] of two arms [21] which follow the curvature of the hemisphere [11] in opposite directions, whereby the rotation of the pole cog [20] ensures that the distance between the two ends of the respective arms to the pole is always equal, and kept in the same meridian line by parallel tracks [22] which rotate freely about the pole, with the end of one arm attached to a ring rotating freely around the previously described fixed ‘calibrated anchor point’ [19], directly adjacent to the hemisphere, but not attached to it, and at the end of the opposite arm, precisely equidistant from the pole, a circular cross-hair [2.4], of similar size to the projected image of the sun [9] is attached.

6. A heliostat according to claim 5, whereby the device described in claim 5 ensures that when the mirror orientation is adjusted such that the crosshair [24] lies over the image of the sun [9] on the hemisphere [11], the pole i 131 is always equidistant between the ‘calibrated anchor point’ ] 19] and the image of the sun [9], therefore the rays of the sun are reflected onto the desired point of the central receiver [14].

7. A heliostat according to claim 6, whereby long and sturdy handles [30] are firmly attached to the frame supporting the mirror, thereby facilitating theprecise orientation of the mirror, and allowing larger mirrors, or arrays of mirrors to be used with each heliostat.

8. A heliostat according to claim 7, whereby between adjustments, the orientation of the mirror is fixed by robust spring loaded bakes § 18] which can be released through pressure applied to a foot operated pedal 131] attached to the brakes via brake cables [321, such that the operator’s arms are free to move the mirror to the correct orientation, and to hold it in place while the brakes are reapplied through release of pressure from the foot lever [311.

9. A heliostat according to claim 7, whereby the brake release levers are attached to the ends of the handles referred to in claim 7, such that the operator can release and return the brakes while also holding the position of the heliostat with both hands.

10. A heliostat according to claim 8 or 9, whereby two pairs of spring loaded brakes [18] are attached to opposite ends of the horizontally rotating supporting beam [5], such that the upper pair interfaces with two large diameter, rigid semicircular discs 133] attached firmly to the underside of the supporting frame of the mirror [11, thus preventing any change in the elevation angle of the mirror when applied, and the pair attached to the underside of the horizontal beam, interfaces on opposite sides of a large diameter, rigid horizontal circular disc [34], attached firmly to the immobile central supporting post [6], thus preventing any rotation of the mirror around the azimuth when applied.

11. A heliostat according to any of the above claims, forming part of a large array of heliostats for use in concentrated solar power, whereby a single operator controls multiple heliostats, and the entire array by a team of operators.

12. A heliostat according to any of the above claims, forming part of an array of heliostats targeted at a receiver [14] made from highly concentrated photovoltaic cells, a Stirling heat engine, or used to generate high temperatures for industrial processes or to directly power a large scale air conditioning system.

13. A heliostat according to any of the above claims, using either a single mirror, or multiple mirrors attached to the same supporting frame, orientated such that the reflected sunlight from each individual mirror falls on the same point on the central receiver.

14. A heliostat according to any of the above claims, utilising a parabolic mirror with a focal length equal to the distance from the heliostat to the central receiver.

15. A heliostat according to any of the above claims, utilising one or more stretched membrane mirrors.

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