Technical Field

The present invention relates to a two axis solar tracker and solar power collecting device Such a device could be used to track the sun and/or to collect the power from solar radiation falling on the device and store it for later use. Such devices are primarily for use in domestic, commercial and industrial sites

Background Art

Solar collecting devices at present are generally of a type that is stationary, allowing collection of energy from the sun's rays as sun light falls on the solar panels of the device

Alternatively, there are devices that have a limited ability to track the motion of the sun through the day thus rendering the device more efficient, as sunlight falls on the solar panels for a greater time each day. A mosaic of parabolic reflecting surfaces can be used for heating liquids to obtain elevated temperatures.

Another known type of solar collector is one that includes strips of a material with a mirror finish, which strips are arrayed in a parabola. Light can be both absorbed and reflected for collection However the parabolic reflector requires water cooling, where water may not always be available Also, the addition of water reticulation for the cooling water further complicates the component parts of the collector.

Disclosure of the Invention

An object of the present invention is the provision of a solar tracker or solar power collector that overcomes many of the disadvantages outlined above and provides a useful alternative to the trackers/collectors already known. A further object of the invention is the provision of a portable tracker/collector that is suitable for supplying heating and/or some of the power requirements of a commercial, industrial or domestic operation

The present invention provides a solar tracker and sunlight collector which includes a base and supporting frame; a framework movably connected to said frame and supported thereon, whereby the means of connection allows for movement of the framework relative to the frame in two

directions; a plurality of collecting mirrors, each mirror including a mirror support which is pivotally connected to said framework such that each mirror can be arranged to direct light to a focal point of the device; a target, placed at a focal point of the device, said target including the capacity to have liquid circulated therethrough by a pump, said target being secured to the framework; a photovoltaic panel rigidly connected to said framework, whereby direct sunlight striking said panel generates electricity for operation of a control means; two electric motors each connected to drive means, one motor being for rotation of the framework in the azimuth plane about an azimuth pivot point, and one motor for the elevation of the framework about a horizontal pivot point, each plane of rotation being relative to the base, control means which includes a battery, a time based control system (including a clock) which causes the framework to rotate through the sunlight hours when the sun is not directly striking the mirrors and to reset the framework to a start position for each day, and two light sensing systems, each of which is capable of operating the two motors to align the framework so that sunlight is reflected to the target; whereby one system is an alternative to the above time based control system and for tracking the sun's position and the second system can control the change over from the time based tracking to the light sensing tracking; and insulated storage means to store said liquid, when it is not in the target, and pipes for connection of the storage means to said target.

Preferably said battery is a 12 volt battery that is used to operate the electric motors if there is no sunlight falling directly on the mirrors (i.e. when it is cloudy). Preferably, when it is cloudy, the time based control system rotates the framework at approximately 15° per hour, tracking the sun's position.

Preferably the electric motors are each connected to a drive on the framework that rotates the framework about the respective planar pivot points Preferably also the azimuth pivot point is within the dimensions of the base and the horizontal pivot point is between the mirrors and the target, but adjacent the mirrors. Preferably each mirror is concave or parabolic about one axis and the mirror support rigidly retains said mirror in this shape, without distortion of the surface The mirror is preferably a metal alloy of low polish with a highly polished reflective film smoothly secured thereto

Preferably said control means also incorporates controls to move the collector off the sun if the liquid temperature exceeds a maximum preset temperature ("over temperature

control")

Brief Description of the Drawings

By way of example only, a preferred embodiment of the present invention is described in detail with reference to the accompanying drawings, in which:-

Fig. 1 is a diagrammatic side view of the present invention; and

Fig. 2 is a perspective view of a collecting mirror of the present invention.

Best Mode for Carrying Out the Invention

Referring to Fig. 1 , a solar tracker/collector 2 is thereshown The collector 2 includes a base 3 and support frame 4, a framework 5 and target 6. The framework 5 is pivotally connected to the frame 4 through a pivot point 10 which is forward of the framework 5 and approximately half way up the framework 5, so that the pivot point is in the space between the target 6 and framework 5 but adjacent the framework 5

The framework 5 includes a mirror supporting frame arm 7, a base arm 8 which is rigidly connected at one end at right angles to the frame arm 7, and a target support arm 9 which is rigidly connected to the second end of the base arm 8 The target arm 9 rigidly supports the target 6. The base arm 8 acts as a counterweight to the weight of the frame arm

7 and attached mirrors 1 1.

The supporting frame arm 7 has secured thereto a plurality of collecting mirrors 1 1 The mirrors 11 are pivotable to a limited degree about their point of securement to the frame arm 7 (for example, by the use of a universal joint at the back of the supporting bracket (12, Fig. 2) Thus the or each mirror 11 can be pivoted to provide a focus for that mirror 11 on the target 6.

Referring to Fig. 2, each mirror 1 1 includes a supporting bracket 12. The bracket 12 includes two longitudinal braces 13 and cross braces 14. Boxing 15 centrally situated between the longitudinal braces 13 allows for ease of handling the mirror 1 1. A universal joint (not shown) is secured to the centre 16 of the back of the boxing 15 to permit the movement of each mirror 11 (for initial alignment of the mirrors 11 ) once secured to the frame arm 7

The mirror surface 17 is of a bendable sheet of a metal alloy. In practice it has been found that aluminium sheeting, appropriately cut to a rectangular size and secured to a bracket 12, is appropriate for small run production. The supporting bracket 12 and surface 17 may also

be formed by injection molding of plastics or a similar suitable material The surface 17 can be secured to the bracket by any known means (for example gluing, spot welding, etc). The curve on the front of the longitudinal braces 13 is concave or parabolic, and the resultant shape of the front of the mirror 1 1 is concave about one axis A thin foil of film of highly reflective paper or foil (not shown) is then secured to the front of the surface 17 such that there is a smooth surface to the mirror 1 1 Alternatively, if so desired, the surface 17 of the mirror 1 1 can be highly polished to act as the reflective surface Each mirror 11 is mounted on the frame arm 7 and angled so that the focal point for each mirror 11 is on the target 6 The target 6 is a box with a surface of highly absorptive material The target 6 includes means for the circulation of a liquid The target arm 9 is shown in Fig 1 as extending upwardly from the base 8. If so desired, the target 6 may be supported from above, via an upper frame which extends from the top of the frame arm 7 over the base 3 This arrangement could be used advantageously to increase the options available for over temperature control. A pump (not shown) pumps the liquid from a bulk storage container (not shown) Two high temperature sensors (not shown), one attached to the target 6, are used to activate the motor controlling elevation if the measured temperature rises above the desired temperature In areas where air temperatures may fall below 0°C, a suitable antifreeze compound may be used in the liquid. If an antifreeze is used, a heat exchanger (of known type) must be used to transfer heat from the liquid containing antifreeze to another liquid (in known manner)

The control (not shown) of the framework 5 about the elevation pivot point 10 is by means of an electric motor (12 volt dc) and appropriate gearing to a chain drive connected to the framework 5 An alternative drive may be used, eg belt drive, if so desired The motor is connected to a 12 volt battery which can run a motor intermittently (as described below) for up to 7 days without direct sunlight

The framework 5 also rotates about the azimuth axis 18 A second small electric motor (not shown) with appropriate gearing and a similar drive is used to rotate the support frame 4 (and thus the framework 5) about the axis 18 As with the above-described motor, the 12 volt battery is connected to operate the second motor Both motors, gearing and drives are all of known type and operating in known manner

The two motors and the pump are operated by use of electronic controls, a light sensor ("magic eye") and a photovoltaic panel (not shown) The photovoltaic panel is rigidly connected to the frame arm 7 and positioned at the top thereof This is connected, along with the magic eye, to a control panel with electronic control circuitry that permits the operation of the motor

pivoting the collector 2 about the axis 18 when there is no direct sunlight falling on the mirrors 1 1. When there is direct sunlight falling on the mirrors 11 the magic eye operates in conjunction with the two motors to cause the collector 2 and mirrors 1 1 to track the sun. The controls are set appropriately so that the mirrors 11 are rotated so that they always catch the maximum amount of direct sunlight that can fall on them. The pump operation and the change over of the rotational control from the time based system to the magic eye is controlled by a manually adjustable light sensing system (of known type). The control system also incorporates controls connected to one of the two high temperature sensors to move the collector 2 off the sun if the liquid temperature exceeds a maximum pre-determined temperature. This allows for over temperature control of the collector 2 to be effected.

The above described solar collector 2 works as follows: the supporting frame arm 7 of the framework 5 is filled with mirrors 11 set at an appropriate angle to provide a focus on the target 6. The battery is connected to the pump and the two electric motors and the controls are set so that the framework 5 will move by a controlled amount of approximately 15 ^ϋ per hour about the axis 18 when it is cloudy. When the sun falls directly on the collector 2 the magic eye and control panel operate the two motors so that the collector 2 tracks the sun and the pump starts circulating the liquid. If the sun is clouded over, the time based movement of the collector 2 takes over. The pump circulates the liquid through the target 6 where it is heated by the conduction of heat from the surface of the target 6. At the end of the day the control panel reverses the operation of the second electric motor to reverse the collector 2 back to its starting position and the pump switches off. If so desired, and with the addition of appropriate electronic controllers, the movement of the sun for each individual day at the location of the solar collector 2 could be pre-programmed from the operation of the control panel, thus obviating the need for the magic eye. Differing movements in the northern and southern hemispheres and at different latitudes can thus be catered for.

The solar collector 2 can include means for the protection of the controller 2 and the circulating liquid against frost or freezing at very low temperature. For example an antifreeze can be added to the liquid to depress the natural freezing point of the liquid. If an antifreeze is used, the liquid may need to be circulated through a heat exchanger before the collected energy may be used.

The liquid in the target 6 and for the storage of heat is preferably water, but can be any other appropriate liquid, as is desired.

In practice it has been found that twelve to fifteen mirrors 1 1 with a surface area of approximately 0.75m ² and 5000 litres of water can store the heat energy requirements for the

average domicile for a period of five days without the sun. This is at approximately 45° latitude. It is anticipated that 6 kilowatts or more energy could be generated under direct sunlight.

If so desired, the frame arm 7 can be dismantled from the base 3 and frame 4. Thus if so desired, the solar collector 2 can be disassembled into sections for travel and re- assembled with relative ease without needing high technical skills. Thus the solar collector 2 can be moved to reasonably remote locations to provide the heating needs for a remotely located domestic, commercial or industrial location. Additionally , the collector 2 can be used as a heat source to drive desalination of salty water, domestic heating requirements, and /or commercial heating (for example greenhouses), etc. Also, if so desired, the collector 2 may be used to provide steam for a generator for energy generation.