Background Art Solar panels transform sunlight into electricity using photovoltaic cells connected together in series. Such cells may be constructed of semiconductor materials which generate an electric current when exposed to certain frequencies of light.

Solar panels are often used on mobile platforms such as boats and land vehicles to maintain the charge of a battery. The solar panels are normally fixed to an upper surface of the platform. They can also be mounted in a way that enables their orientation to be manually adjustable.

The power output of a solar cell is related to the amount of sunlight that reaches the surface of the cells. To maximise the power output of a solar panel, the heading and inclination of the solar panel are often manually adjusted throughout the day.

Disclosure of Invention In a first aspect, the invention is a method for automatically tracking the sun from a mobile platform, with a solar panel being mounted to a mechanism operable to rotate the panel about two orthogonal axes, the method comprising the steps of : calculating the heading of the panel using a compass associated with the panel ; calculating the inclination of the face of the panel from the horizontal ; calculating the azimuth and altitude of the sun in reference to the geographical location of the panel; using the azimuth of the sun to calculate a first degree of rotation required to rotate the panel about a vertical axis to substantially align the heading of the panel to face the sun ; using the altitude of the sun to. calculate a second degree of rotation required to rotate the panel about a horizontal axis to substantially incline the panel normally to the sun; and operating the mechanism to rotate the panel through the first and second degrees of rotation.

It is an advantage of at least one embodiment of the invention that by tracking the sun, the panel is able to maximise its output even though the heading of the panel changes as the mobile platform that the panel is attached to moves.

The latitude and longitude of the panel may also change as the mobile platform that it is attached to moves. The mobile platform may be a land or water going vehicle such as a car or boat.

The step of determining whether the step of operating the mechanism should be performed may comprise a consideration of whether output from one or more ambient light sensors associated with the solar panel is less man a predetenoained value.

The step of determining whether the step of operating the mechanism should be performed may comprise a consideration of whether the amount of power currently generated by the panel is less than a predetermined value.

These considerations prevent power from being used unnecessarily by rotating the panel in bad weather conditions when the amount of light reaching the panel is small.

The step of determining whether the step of operating the mechanism should be pexfomed may comprise a consideration of changes in the heading of the panel. When the mobile platform is swinging side to side, this consideration may further comprise the step of calculating a first heading and second heading at the extremes of the swing.

The mechanism may not rotate if the difference between the average of the first and second heading and the azimuth is less than a ptedeterined value If the rate that the change in the heading is more than a predetermined value, the panel may not rotate. Preferably, the predetermined value is 4S°. Desensitising the mechanism helps to prevent using power unnecessarily by rotating through small degrees when the additional power to be gained by the panel in its new orientation is small.

The step of calculating the heading of the panel may comprise taking into consideration the degree of pitch and roll of the panel and/or the variation of the magnetic north from true north.

The configuration of the mechanism may be used to calculate the inclination of the face of the panel and may be dedved from a reading taken from a gear sensor. The step of calculating the inclination of the face of the panel may also comprise taking into consideration the calculated heading, and the degree of pitch or roll, or both, of the panel.

The geographical location of the panel may be defined by the current latitude and longitude of the panel. The method may further comprise the step of deriving the

latitude and longitude from the heading of the panel when it is known to be substantially aligned to face the sun. The panel may be substantially aligned to face the sun by manually rotating the heading of the panel. Alternatively, the panel may be Substantially aligned to face the sun by automatically rotating the panel to seek the position that exposes the panel to the highest level of sunlight, The heading of the panel that results in the highest level of sunlight may be determined from readings from one or more light sensors. One light sensor may be a placed in a tube, where the axis of the tube. is normal to the face of the sun.

The pitch may be determined using a two axis accelerometer associated with the paneL The step of calculating the azimuth and altitude of the sun may use the current date, time of the day, latitude and longitude of the panel.

The panel may be mounted to allow complete rotations about the vertical axis in both a clockwise and anticlockwise direction.

The step of determining whether the step of operating the mechanism should be performed may comprise. a consideration of the current weather conditions, such as the amount of wind.

If a determination is made not to operate the mechanism, the method may further compdse the Step of rotating the panel to stow it away in a position where possible damage to the panel is reduced.

It should be appreciated that although both vertical and horizontal have been used they are not necessarily used in an absolute sense, but may be used in a relative sense. For instance when the invention is used on a sailing ship vertical and horizontal relative to the ship may be offset from vertical and horizontal relative to the horizon.

In a second aspect the invention is a solar Cracking system for attachment to a mobile platform, the system is operable to automatically track the sun to maximise the power output, and the system comprises: a mechanism operable to rotate about two orthogonal axes ; a solar panel mounted to the mechanism ; a battery connected to me solar panel to store the power generated by the solar panel ; a computer to calculate the following : i. the heading of the panel using a compass associated with the panel, ii. the inclination of the face of the panel from the horizontal, iii. the azimuth and altitude of the sun in reference to the geographical location of the panel, and

iv. first degree of rotation about a vertical axis required to substantially align the heading of the panel to face the sun and a second degree of rotation about a horizontal axis required to substantially incline the panel normally to the sun.

The computer may operate to perform the considerations as to whether to operate the mechanism as described above.

The mechanism may be operable to poxfoun the rotations described above.

The computer means may utilise readings provided by an electronic compass and two axis accelerometer associated with the, panel.

The system may also further comprise auxiliary devices connected to the solar panel to use any excess power generated by the battery using an excess power delivery circuit.

It is an advantage of at least one embodiment of the invention that electricity is produced from the solar panel is reliable, efficient, environmentally friendly and low maintenance.

Brief Description of Drawings An example of the system will now be described with reference to the accompanying drawings; in which : Fig. 1 is a pictorial view of a solar tracking system ; Fig. 2 is a detail of the mechanism for rotation about a vertical axis ; Fig. 3 is a detail of the mechanism for rotation about a horizontal axis ; Fig. 4 is a schematic diagram of the circuitry ; Fig. 5 is a flow diagram for the operation ; and Fig. 6 is a diagram showing how the system can derive its current location.

Best Mode for Canying Out the Invention Fig. 1 shows a solar panel 10 mounted to a mechanism indicated generally at 20.

The mechanism is mounted to a vertical pole 30. The entire mechanism 20 is able to rotate about vertical axis 40 in both directions as indicated by arrows 45. Furthermore the panel 10 is mounted for rotation about axis 50 in either direction as indicated by arrows 55. Inside the housing of mechanism 20 there are various sensors, controllers and drive mechanisms to achieve the desired output.

Referring to Fig 2 the vertical drive mechanism is indicated in more detail. This mechanism can be seen to include a rotatable assembly indicated generally at 100 mounted to the top of the vertical pole 30. A high reduction gear motor linked to the vertical pole 30 via a pulley and belt drive 60 serves to drive the assembly 100 around

pole 30. The speed and distance of rotation is controlled by a micro controller which receives readout from an encoder 340. When rotation is effected the entire mechanism 20 rotates about the pole 30.

A high reduction gear box is used so as to prevent rotation unless it is driven by the motor. The pulley and belt 60 are adjusted to slip and prevent the high reduction gearbox from. taking the full force of any excessive unwanted external rotational force exetted on the assembly 100. This provides a looking function against unwanted movement, such as movement resulting from wind or tilt. It should be noted that the locking function is achieved without the use of any power by the system.

Additionally, mechanical limits 120 and 121 provide a physical stopper to the amount of rotation the assembly 100 can rotate around pole 30, either in a clockwise or anti-clockwise direction. Optical limit sensors 130 and 131 indicate to the micro controller the extent that the assembly 100 has rotated around the pole 30.

Electrical conducting wires, indicated generally at 170, are positioned both outside and xsi. e e pl 3. Thse wirs allow connection to external batteries, and loads. These wires also allow communication connections to an external computer, or GPS.

Rotation about the horizontal axis 50 will now be described with reference to Fig. 3. The upper end of panel 10 bears a rearward extension 200 to the end of which is connected a wire 210. Wire 210 passes over wheel 220 and is driven by it. The lower end of panel 10 is cotmected to a second wire 230 which passes over wheel 240 and is captured by it In use wheels 220 and 240 are driven in counter rotation so that as one feeds out wire 210/230 the other reels in wire 230/210.

Referring now to Fig. 4 two ambient light sensors 300 and 301, such as an LDR (Light Dependant Resistor) are used to determine the strength of the sunlight falling on the panel and send this information to the micro controller via A/D converter (see below).

An electronic circuit board 310 has connections to the following devices : External electrical connections 320 Motors 330 and 31 Rotary encoders 340 and 341 Ambient light sensor 300 and 301 Solar panel 10 Limit Sensors 130 and 131 Site tube 52

A voltage regulator 350 is included on the circuit board. The electronics requires a +5 volt supply, as the batteries are +12V this device provides the necessary voltage.

A micro controller 355 is also included on the circuit board. This is the computer of the panel that is loaded with a program that perfoms the required tasks which are described below.

A serial interface 360 and a USB (Universal SeriaJ Bus) interface 361 are included on the circuit board which allows an external device to communicate with the micro controller serially over the connected wiring. Connecting another computer via the serial or USB interface can easily change the software, allow diagnostics, or change the parameters of the panel, such as the current latitude and longitude. Alternatively, a keypad and display screen could be attached to the device to allow for the direct entry of information.

A Real Time Clock (RTC) 370 is also included on the circuit board and maintains the current time and date. It is independent of the micro controller as it has a small Lithium battery allowing it to keep time even if the main battery is not connected.

Field Effect Transistors (FETS) are used by the Micro Controller to switch things on and off. The motors are actually turned on and off rapidly to control their speed. The FETS also allow the panel to be connected to one or the other battery or other auxiliary device.

The DC motors are driven-by the circuit board via Field Effect Transistors (FETS). The FETS form an H bridge configuration allow the motors to be driven in both directions. FETS are also used to charge the batteries and drive the connected loads. FETS use very little power to operate and have a very low on resistance.

An analogue to digital converter (A/D) 380 is included on the circuit board. The A/D measures voltages and gives to the micro controller a digital value that represents that voltage. The A/D converter is used for the following, as these are analogue devices : X, Y, Z axis of the compass Battery voltages Auxiliary device voltages Ambient light sensor (s) The micro controller 355 is a 64. Motorola GR260, the oontroller has 64 Kbytes of FLASH Ram forprogram alld data, and 512 bytes of RAM for transient data It executes machine code created using a C compiler.

An electronic compass 390 is also associated with the circuit board. The compass consists of a magnetic sensor and an accelerometer. This device calculates the heading of the solar panel and is used in conjunction with a two axis accelerometer, which provides roll and pitch information.

An 4 single axis and a dual axis linear magnetic field sensor, for example the HMC 1021Z and the HMC 1022 by Honeywell are used. Magnetic sensors basically provide information about the strengtTn of the earth's magnetic field that they are experiencing at any one time. The trigonometric function ARTAN (X, Y) is used to derive a compass heading between 0 and 359 degrees. Where X and Y are numbers converted from voltages in the A/D converter after the output of the sensor has been amplified.

As the device can be tilted a further magnetic reference called Z is required.

This can be considered as a third magnetic device however it is in the vertical plane and points down. In this case the formula is XH-X * cos (pitch) + Y sin (ro ! l) sm (pitch)-Z*cos (roll) *sm (pitch) YH = Y * cos (roll) + Z * sin (roll) Heading is then AU. CYAN (YH/XH) The two axis accelerometer, such a$ the ADXL202E, is affected by gravity as the device leans over, this movement is reflected as data in the form of a digital output.

This represents the angle that the device is inclined in two directions. This takes the form of + or - 90 degrees of pitch and + or-90'degrees of roll.

This information is used to calculate the heading as described above, and also for calculating the inclination of the face of the panel, see Figure 5, 501 and 502 In use, the micro controller 355 calculates the current azimuth and altitude 400 of the sun using an astronomical formula, 503 and 504. The formula's inputs are current values for the : latitude of the panel (set at installation) longitude of the panel (set at installation) time of day from the RTC 370 date (day, month year) from the RTC 370 The latitude and the longitude of the panel can be set at installation. In many cases this is a simple suitable solution as the panel will be installed in similar area as the boat will be used. In order for the solar panel to rotate one degree the boat will need to move approximately 1001ou towards North or South and 60kan East and West.

So even if the boat did move that far from its initial installation location, the lack of precision caused will not prevent the solar panel from operating efficiently.

Alternatively, if the current latitude and longitude is not known, or the latitude and longitude is likely to change significantly, current values could be communicated to the micro controller and the required rotations calculated accordingly. The communicating of current values could be achieved by attaching a GPS system to the boat or system in such a way that it was able to provide the micro controller with the current latitude and longitude of the panel.

The current latitude and longitude could also be derived by the micro controller.

As the GMT is known due to the RTC that has its own battery backup, the. azimuth and altitude of the sun could be derived if the solar panel was known to be facing the sun.

For example, at installation the user sets the latitude and longitude by aiming the panel to face the sun and informing the macro controller that the manual adjustment has been made, such as by pressing a button, that the panel is now pointing to the sun. From this position of me panel, the micro controller could determine its current: inclination heading from the compass, and the pitch and roll.

The current time is also known. Using these values the micro controller can calculate the cuzrezt longitude and latitude of the panel. Further, the magnetic deviation. may also need to be factored into the calculation to ensure a more accurate result The magnetic deviation remains substantially constant over large areas, and its value should be provided to the micro controller. The calculated values for latitude and longitude could then be stored and used by the microprocessor for all future rotation calculations.

This manual adjustment could be repeated whenever the user desires to reset the latitude and longitude, such as when the panel changes significantly in location.

Another method of providing the microprocessor with the current values of latitude and longitude would be to enter the known latitude and longitude of the panel at installation or any later time. Then, when me location of the panel changes, such as a certain number of kilometres from that location in a certain direction, then the micro controller could be provided information of the change and the stored latitude and longitude values could be amended accordingly.

Yet a further method of providing the latitude and longitude involves allowing the panel to seek the sun itself. This would be achieved by using the light sensors attached to the panel and an additional site tube 52. The site tube 52 is a tube of some length, say 100mm, open at one end to the sun and aligned normally to the face of the

panel. Inside the tube at the opposite end a further light sensor is provided. The panel could automatically rotate to determine which position provides the best light reading on the sensor in the tube.

Tho micro controller is programmed to make adjustments to the position of the panel to maximise the readings on the sensors. Readings from the sensors on either side of the panel allow the microprocessor to rotate the panel to set the correct heading.

The tube will be able to provide the microprocessor feedback on the accuracy of the direction. Only when the tube is aimed directly at the sun will strong light fall on the light sensor, as otherwise the walls of the tube will block the sunlight. The position that provides the strongest light to fall on the sensor in the tube provides the orientation of the panel on both axes that is substantially correct.

With this method, the panel can automatically readjust itself to better face the sun. The different derived longitudes and latitude values are then reconciled. Repeated calculations will serve to increase the accuracy of the longitude and latitude recorded, and at the same time allow for changes to the geographical location and magnetic deviation of the panel without requiring the user to input, these values. For example, refemjig to Fig. 6, the panel automatically adjusts itself to face the sun when the sun is in position A, the micro controller is able to infer the altitude but not the magnetic deviation. The compass reading allows the micro controller to deduce that the panel is located at A on the arc 1, but the panel could actually be at any point on arc 1. The size of arc 1 would be equal to the greatest amount of magnetic deviation on earth. From this single collaboration, the solar panel uses the derived latitude and longitude to automatically track the sun. However, it is possible that the derived latitude and longitude are not as accurate es they could be.

Later in the day when the sun is now at position B, a second automatic adjustment of the panel is made. From this, the microprocessor deduces that the panel is now located at B on arc 2. These two positions A on arc 1 and B on arc 2 must now be reconciled. By shifting the compass heading a number of degrees in the same direction, both positions will determine that the panel is at thé location D. This amount of shift is equal to the magnetic deviation. This calculated magnetic deviation is then used by the micro controller for any future calculations. This can be repeated as often as desired in order to track the sun more accurately. For example, when the sun is at C the method could be repeated to derive the latitude and longitude and would produce the result that the panel is at C on arc 3. These additional derivations of the latitude and longitude could be reconciled, such as by averaging, in order to account for changes in the location and the magnetic deviation of the panel's position.

The above method assumes that the panel is operating at sea level. If in fact there is any altitude, this could be determined from an altimeter associated with the panel.

The calculated azimuth is the horizontal angular distance of the sun in a clockwise direction from true north in reference to the panel. The calculated inclination is the angular distant of the sun above the horizon in reference to the panel. For example, in Sydney at sunrise or sunset the altitude is zero degrees, and at midday this would be a maximum of 79 degrees in summer, to a lower maximum of 33 degrees in winter.

The micro controller 355 executes software that include polling operations and interrupt operations..

The polling operations include calculating or cheeking the current : azimuth altitude degree of roll of the panel degree of pitch of the panel compass heading of the panel ambient light level from the li « t $ensot ($) battery voltages solar panel voltage serial data current inclination of the panel The micro cos ler 3$5 snakes a decision whether to rotate the panel about the vertical axis based on these values. The degree of rotation is calculated about the vertical and horizontal axes that will point the panel at the sun, 505 and 506.

The compass heading is adjusted ior true north and takes account of the current pitch and roll. This is then compared to the azimuth value. If the value is different then a decision is made to rotate the panel along the vertical axis to make the adjusted compass heading of the panel the same as the calculated azimuth.

Similar comparison is made for horizontal rotation Optimally, the sun's rays should be normal to the face of the panel. For this to occur the angle of inclination of the panel measured from the horizontal and the angle of the altitude of the sun should sum to 90 degrees. If the sun's rays are not normal to the panel, {hen 9 decision is made to rotate the panel along the horizontal axis to make this so. Factors taken into account are : inclination of the panel

degree of pitch and roll of the panel the altitude of the sun Based on the 1st and 2nd degrees of rotation that are calculated, a decision to rotate the panel along one or both axes is made. The decision of whether or not to rotate the panel may include a consideration of various issues that are detailed below.

The output of the light sensors 300 and 301 which returns the amount of ambient light can be taken into consideration. If there is little light, such as heavy overcast days, rotating the panel may have little or no advantage. The value returned by the light sensor is compensated for pitch, roll and the altitude of the sun. If this level remains low for an extended period then a decision can be made to move the panel to a flat horizontal position until the sensed ambient light level increases. If the light level falls below for a short period and then rises again, the timeout can be restarted and the panel re-oriented to face the sun.

The system could be desensitised so that a decision to rotate the panel is only made if the difference between the azimuth and the proposed adjusted compass heading of the panel exceeds a certain value, or the degrees off normal the sun makes with the face of the panel exceeds a certain value. By increasing the allowed differences the system would be made less sensitive, and by reducing the value made more sensitive.

This ensures that during rapid changes in compass heading, pitch and roH the panel will not use more power in rotating the panel than it will gain in its new position.

The system could deduce that it is moored by calculating that it is swinging a number of degrees from side to side. The system can take into consideration the fact that it is moored when deciding to rotate. The range of degrees that the system swings can be thought of as an arc of a circle. Of course this arc may never be the same twice however it may be roughly the same for some hours, the tide and wind are of course the governing factors. From any two sequential changes in compass heading experience by the system, the ends of the arc are calculated and temporarily stored. The micro controller then calculates the heading that the system would have if it were in the centre of this arc. If this calculated centered heading is within a predetermined range from the current Azimuth (the sensitivity of this range being the same consideration as described above) then no rotation would be required. The temporarily stored ends of the arc are then cleared for new arc ends to be calculated from the next two changes in direction, and the assessment is repeated.

If the calculated centered heading derived from the arc is out of the allowable range from the current azimuth, then the device can make a decision to move. The advantage of de-sensitizing the device in this manner when it is moored is that it is

based on the centre of an arc that roughly approximates its future movements. Thus regardless of where it is actually currently positioned in that arc, the device will help maximize its exposure to the sun with minimum rotation.

The same arc calculation can be used to effect decisions made during sailing.

The device is able to calculate the size of the arc and how much time expired between each end. From this the rate of change in degrees per second can be determined. Given that a moored boat's heading will never change as rapidly when compared to it being sailed, the system is able to detect that it is in a rapid changing course mode. This being the case, constant movements in the orientation of the device to track the sun may cause more power to be lost than will be gained by rotation to constantly track the sun. To prevent this, once a changing course mode is sensed, the range of allowable degrees from the correct azimuth and altitude when compared with the current position of the panel could be automatically increased.

A boat may hold its course for some time whilst sailing warranting a change in orientation of the panel. As the detection of the"changing course mode"is characterized by rapid changes in direction the device could switch in'and out of changing course mode so as to detect when rapid changes are no longer experienced and warranting rotation of the panel. Once changing course mode is detected, after a time period such as 30 minutes the curent mode can be reassessed and the changing course mode released iffast rate changes are no longer experienced.

The battery voltage (power level) can taken into consideration. For example, if the battery is i11 there is no need to rotate the panel.

The interrupt operations include driving motors ; and counting and timing the gear pulses.

Once a decision is made to rotate the panel on one or both axes, the rotation is effected by'the mechanism, 507 and 508. Instructions to drive the motors include the parameters direction, speed and distance required to rotate the panel to its new orientation. To move the panel the interrupt routine has the ability to vary the direction of the current to the motors and the amount of power delivered to the motors. The amount of power delivered is varied by analysis of the encoder 340 and 341 outputs.

The frequency of pulses from the encoders allows a constant speed to be achieved by measuring the interval between pulses. If the interval is long the power is increased, if the interval is short the power is reduced.

By this same means loading on the panel by wind can be detected by a comparison of the amount of energy normally required to move the panel, if after a

number of movements the amount of energy being required exceeds that of normal, taking mto consideration pitch and roll, a decision can be made to move the panel to a position of least wind resistance, such as a stow away position.

Alternatively, me current weather conditions can be acquired from a wind meter that is external or attached to the system. The current weather conditions could also be acquired from the weather bureau. This information could then be communicated to the micro controller such as wirelessly. If the information about the weather conditions provided to the microcontroller do not justify energy to be expended by the system to track the su, or would make the panel susceptible to damage, the panel would automatically move the panel to a position of least resistance.

These pulses are also used to determine the distance travelled. For example, on the horizontal axis 360 degrees is represented by 4000 pulses, thus to move. say 5 degrees then 55 pulses is used from the calculation 4000fus 5.

These pulses also allow horizontal and vertical position counter to be maintained. The counter is used on a vertical plane to determine the inclination of the panel. And on the horizontal it will allow the device to know the heading of the platform to which it is mounted.

Further variations and modifications to the preferred embodiment also fall within the scope of the invention.

In the event that the battery attached to the solar panel is lw ehargedl ie system may include battery management means such as an excess power delivery circuit that is able to divert any excess generated electricity to another device. For example the device can be a series of fans that use the excess generated electricity to better ventilate the cabin of the boat.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly desired The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.