WO2012001649A1

WO2012001649A1 - A system for and method of manually adjusting a photovoltaic panel assembly

Info

Publication number: WO2012001649A1
Application number: PCT/IB2011/052881
Authority: WO
Inventors: Mark Nolan Mitchell; Philip Douglas John Calcott
Original assignee: Thupela Carbon Cc
Priority date: 2010-06-30
Filing date: 2011-06-30
Publication date: 2012-01-05
Also published as: ZA201300372B

Abstract

A system (10; 110) for manually adjusting photovoltaic panels comprising a solar panel assembly (26) secured to a panel support frame (14; 114), the support frame being secured or connected to anchoring means for mounting the system,, wherein the panel support frame defines a horizontal axis of the system and the photovoltaic panels are primarily adjustable about the horizontal axis, with the primary adjustment being defined as adjustment of the panel (or frame) in order that the normal of the panel substantially tracks the movement of the sun over the course of a day and the daily adjustment occurs only about the horizontal axis. The system (10; 110) further comprises means to adjust the elevation of the horizontal axis thereby in effect adjusting the angle of the horizontal axis or elongate support means relative to the horizontal, to accommodate seasonal adjustments of the assembly.

Description

A SYSTEM FOR AND METHOD OF MANUALLY ADJUSTING A PHOTOVOLTAIC PANEL ASSEMBLY

BACKGROUND TO THE INVENTION

The present invention relates to a system for manually adjusting photovoltaic panels, commonly referred to as solar panels. The invention also extends to a method of manually adjusting a photovoltaic panel assembly.

Environmentally friendly and energy saving heating systems are becoming increasingly popular in both urban and rural settings. The use of photovoltaic panels to farm energy is also increasingly being used as an adjunct to supplying populations with energy. In some cases, particularly where spatial constraints are of low importance, solar farm projects are envisaged to replace the use of conventional power stations, which require the burning of coal and the like to generate electricity. These solar farms comprise a plurality of individual solar tracking assemblies, which are connected together to facilitate transmission of the energy generated therefrom. These systems are used, amongst other things, to reduce carbon emissions, reduce conventional energy dependency and to reduce energy generation costs.

Current solar farm projects employ two different approaches to mount the solar panels. Some solar farms employ mechanically driven adjusting solar panel assemblies, which have automated tracking mechanisms to track the movement of the sun through the sky and actuators to adjust the panels to follow the sun, thereby optimising the amount of solar energy generated by the solar panels. The automation of such assemblies requires costly mechanical and electronic devices and is thus usually not an economical option compared to a second approach of simply fixing the panels in one orientation and generating less electricity. It follows that this second fixed panel approach, which has lower capital and maintenance costs, but generates significantly less electrical energy from the same number of panels, is usually the option employed.

The economical barriers to using tracking systems can be overcome in regions where labour costs are low. This is possible because of a critical aspect of the dependence of the electrical power generated by a solar photovoltaic panel and the angle between a normal to its surface and the sun. This angle represents the misalignment of the panel from the optimal orientation pointing directly at the sun. The electrical power generated depends on the cosine of this misalignment angle. The cosine function varies slowly with angle for small angles, so, for example, a 4 degree misalignment of the solar panel only reduces the electrical power generated by approximately 0.25% - an insignificant amount. Even an 8 degree misalignment only reduces the electrical power generation by approximately 1%.

This insensitivity of electrical power generation to small misalignment angles means that a tracking system can generate within 1 or 2% of its maximum theoretical amount of electrical power with only a small number of panel adjustments during the day. In countries with low labour costs, it may thus be plausible, indeed potentially highly economically favourable, to carry out these small number of adjustments manually, rather than by using expensive automated systems.

The basic concept of a tracking system with manually adjusted panels is known. These tracking systems are mechanically driven and may employ a manual adjustment means. These systems employ a vertical axis about which the primary daily rotation is conducted, and a secondary axis perpendicular to this. Such a vertically orientated system suffers from certain drawbacks. If only the vertical axis to which the panels are attached is rotated on a daily basis the system is only reasonably close to alignment when the elevation of the sun matches the elevation of the secondary axis. This results in significant generation losses early in the day and late in the day, and also at midday. These losses are particularly severe in summer. The exact inefficiency of such a vertical tracking system depends on latitude, but will generally be of the order of 5% or more. Additionally the losses early in the day and late in the day correspond to times of peak residential electricity demand, and are therefore additionally undesirable.

The adjustment of both the axis of the vertical system described above on a daily basis has not been deemed a solution as, with such a vertical axis manually adjusted system, the system will be significantly more complex, the time required for adjustment will significantly increase and labour costs will be significantly higher.

The present invention seeks to provide a system for manually adjusting photovoltaic panels with minimal mechanical complexity and operational requirements that at least partially ameliorates the disadvantages associated with the prior art vertical axis systems. In particular, it aims to provide a very simple mechanical system that is easy to operate, and which system enables efficiencies much closer to the maximum possible level obtainable with perfect two-axis automated tracking. Additionally it aims to generate more electrical power early and late in the day at times of peak demand. SUMMARY OF INVENTION

According to the invention there is provided a system for manually adjusting photovoltaic panels comprising a solar panel assembly secured to a panel support frame, the support frame being secured or connected to anchoring means for mounting the system, wherein the panel support frame defines a horizontal axis of the system and the photovoltaic panels are primarily adjustable about the horizontal axis. Primary adjustment is defined as adjustment of the panel (or frame) in order that the normal of the panel substantially tracks the movement of the sun over the course of a day. As such, daily adjustment occurs only about the horizontal axis.

Preferably, the support frame is secured to an elongate support means which defines the horizontal axis of the system.

The elongate support means may be connected with the anchoring means at ends of the elongate support means, or at some point towards its centre.

Conveniently, the panels are rotatable about their horizontal axis independently of the panel support frame. Preferably, the panel support frame is rotatable about the horizontal axis with the panels in a fixed mounted position. Adjustment about the horizontal axis may be accomplished through rotation means such as a jack which is connected between the anchoring means and an intermediate point on the panel support frame between the horizontal axis and a side of the panel support frame.

Conveniently, the system comprises means to adjust the elevation of the horizontal axis, i.e. the elongate support means. Such means may be defined or located between the anchoring means and panel support frame and may, for example, be an adjustable arm. Thus, the system defines a secondary approximately vertical axis for adjusting the angle of the horizontal axis or elongate support means relative to the horizontal (a mounted surface), which need to be adjusted only seasonally. Seasonal adjustment is typically done once a month or less frequently. Seasonal adjustment may be accomplished by manual or mechanical means.

Conveniently, the system comprises at least one panel securing means for releasably locking the panel support frame into position about the elongate support means. In one embodiment, the jack is operable as the panel securing means.

Conveniently, the system comprises a counterweight to counter the moment exerted by the panel support frame and the attached panels about the elongate support means.

The system may further comprise a gauge positioned, e.g., in close proximity to an end of the solar panel assembly, the gauge in use secured to a fixed part of the structure, such as the elongate support means or the anchoring means, to indicate the relative position of the solar panel(s) with relation to the gauge. The gauge is used in conjunction with a clock and a lookup table (either published or calculated directly by a computer) to allow an operator to adjust the panel support rack to the correct alignment position for the time of day. Thus, the gauge provides an indication of the preferred rotation of the solar panels about the elongate support means and thus, the orientation to the sun, to effect maximum efficiency.

Alternatively, the solar panel or support rack may define an aperture through which the sun shines onto a predefined part of the fixed part of the structure, thereby to indicate the solar panel's orientation to the sun. By adjusting the panel support rack such that the sunlight through the aperture shines on a specific point on the structure, immediate feedback of the sun's position can be achieved. According to another aspect of the invention there is provided a method of generating electrical power comprising the steps of utilising a system which comprises manually adjustable photovoltaic panels, the system comprising a solar panel assembly secured or connected to anchoring means for mounting the system, wherein the panel support frame defines a horizontal axis of the system, wherein the method comprises the step of: an operator manually adjusting the panels daily about the horizontal axis of the system. Typically, this step may include adjusting the solar panel assembly about the elongate support means with reference to a gauge secured to the system.

The gauge may be used by the operator in conjunction with a clock and/or lookup table.

The method may further include the operator adjusting rotation means in order to rotate the panels about the horizontal axis of the system. A number of discreet adjustments, e.g., three or more adjustments per day, may be provided for by the rotation means and/or the gauge. The operator may lock the panel support frame into position about the elongate support means with panel securing means.

The method may further include the operator manually adjusting panels on a seasonal basis by elevating the horizontal axis of the system.

Conveniently the method of generating electrical power further comprises a system having varying integers as described above.

For purposes of the invention, the vertical axis is defined as being substantially vertical and in particular, substantially perpendicular relative to the horizontal axis. The inclination of the vertical axis is adjustable. The horizontal axis is similarly substantially horizontal and its inclination relative to the horizontal is adjustable. Further features, variants and/or advantages of the invention will emerge from the following non-limiting description of examples of the invention made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a perspective top view of an example embodiment of a photovoltaic panel assembly in accordance with the invention;

Figure 2 shows a side view of a photovoltaic panel assembly of

Figure 1 ;

Figure 3 shows a perspective view of another example embodiment of a photovoltaic panel assembly in accordance with the invention which includes a gauge to assist with the daily adjustments of the panel assembly; and

Figure 4 shows a graph plotting the comparison of power output of a photovoltaic panel assembly in accordance with a system of the present invention with that of a prior art fixed panel assembly over time.

DETAILED DESCRIPTION OF THE INVENTION

Figures 1 and 2 show a manually adjustable photovoltaic panel assembly 10 of the invention. The assembly comprises an elongate tube 12 about which a photovoltaic panel support frame 14 is secured along the longitudinal axis of the tube 12. The tube 12 is hollow to enable a reduced diameter rod 16 to be received therethrough. The tube 12 is adjustable or rotatable about the longitudinal axis of the rod 16, thereby together forming rotation means, which rod 16 consequently provides a fixed axis about which the panel support frame 14 is rotatable. This fixed axis defines the horizontal axis of the assembly.

The elongate tube 12 and rod 16 form an elongate support means for the panel support frame 14. The rod 16 is secured at either end by a pivotable joint 18. The rotation of the panel support frame 14 about the longitudinal axis is governed by a panel securing means, shown as lever 20. The lever is movable between a panel rotational position 24 and a panel-locked position 22 as indicated by perforated line 21. The lever comprises a quick release mechanism, which ensures that the tube 12 cannot rotate about the rod 16 when in a panel-locked position. This is achieved by the. lever engaging and pressing a friction pad against a friction surface on the rod 16 thereby creating a high level of friction. Upon releasing the lever 20 to the panel rotational position, the friction between the lever 20 and the tube 12 is relaxed thereby enabling an operator to rotate the panel support frame 14 about the rod 16.

The rotational adjustment of the panel support frame 14 is made in order that the normal of the photovoltaic panels 26 (as best shown in Figure 2) substantially tracks the movement (orientation) of the sun over the course of a day. This is achieved by providing an operator with pre-determined positions where the panel support frame should be locked during the course of the day. The positions are indicated by a schematic (not shown) indicating which position the panel support frame 14 should be locked relative the position of the sun in the sky. The schematic may comprise a disk or gauge with a central aperture through which the rod 16 is received. The schematic is fixed to the rod 16 thereby allowing the panel support frame 14 to move relative to the schematic. The schematic indicates the required angle of the panel support frame 14 relative to the position of the sun on the schematic, thereby managing the orientation of the panels with the sun. As such, the operator simply has to rotate the panel support frame 14 to a position in line with the appropriate schematic that is predetermined based on the position of the sun and the time of day. The operator thereby adjusts the inclination of the panel support frame in accordance with set times during the course of the day, in use.

The position of the sun can be calculated using well established and relatively simple computer algorithms, as can the optimal position of the panel support frame. This enables operators with limited education to easily rotate the panel support frame 14 throughout the course of the day to obtain an almost maximum yield of solar energy relative to fully automated solar tracking systems. This is due to the electrical generation rate of the panels being dependant on the cosine of the angle between the normal of the panel and the sun. As such, an eight degree misalignment only gives a one percent reduction in generation rate. Therefore, by manually tracking the sun with as little as seven re-alignments over the course of a day, the manual system can get within two percent, or better, of the performance gain of a full tracking system.

The rotational movement of the panel support frame is facilitated by a counterweight 28 which is suspended from the underside of the centre of the elongate tube 12. The counterweight comprises a spacing bar 29 about which the counterweight is securably movable to provide for the suitable positioning of the counterweight. The position of the counterweight is calculated so that its distance from the axis of rotation at the centre of the tube 12 creates a zero net moment between the combined structure of the system and the counterweight. This provides for the stability of the panel system when the operator is adjusting the panel support frame, in use.

The panel support frame 14 may be further secured in position by a tube securing pin 30. This securing pin 30 operates on a similar principle to the lever 20 in that screwing it inwards pushes a friction pad (not shown) attached to tube 12 firmly against rod 16. This is ideal for high wind conditions where the lever may be inadequate to secure the rotational position of the panel housing.

To further optimize the energy generation rate, a seasonal adjustment of the angle between the inclined horizontal axis of the assembly and the horizontal can be made. This is typically done once every one or two months through means to adjust the elevation of the horizontal axis. The adjustments are made by raising or lowering a fixed rod 32 inside a vertical support tube 34 (i.e. acting as such means). The rod has a plurality of apertures (not shown) through which a vertical axis securing pin 36 is secured to maintain the position of the fixed rod 32 in the vertical support tube 34. The vertical movement of the rod causes the panel support frame which is attached to the pivotable joints 18 via the rod 16 to adjust its angle relative to the horizontal. Again this is done with the assistance of a seasonal schematic. It will be appreciated that the schematic will vary for different latitudes. The vertical axis support tube along with a second set of rigid vertical support tubes 38 are anchored in concrete blocks 40 and together form mounting means of the system.

The fixed rod 32 and vertical support tube 34 is instrumental in defining a vertical axis which is substantially perpendicular with the horizontal axis of the assembly. The inclination of the vertical axis is adjustable by adjusting the fixed rod 32 in the vertical support tube 34. The horizontal axis is similarly substantially horizontal and its inclination relative to the horizontal is thus also adjustable through the fixed rod and vertical support tube.

The inclined photovoltaic panel system of this example embodiment of the invention offers greater stability relative to vertical axis mounted systems of the prior art, as it is anchored at both ends. This can be significant in situations of high wind, when the wind can generate a large moment about the central point of attachment.

As solar panels as such and their manufacturing are well known, no further description insofar as the panels were deemed necessary. Suffice to say that the panels are usually manufactured from wafer-based crystalline silicon cells or thin-film cells based on cadmium telluride or silicon.

Turning now to Figure 3, a second embodiment of the invention is shown in which reference numeral 110 generally indicates another manually adjustable photovoltaic panel assembly. The assembly 110 comprises an elongate frame member or support means 112 which is pivotally connected along its longitudinal axis to a panel support frame 114. Similar to the previous embodiment, this fixed longitudinal axis defines a horizontal axis of the assembly 110. The elongate frame member 112 defines multiple pivot points (representatively shown by reference numeral 116) to which the panel support frame 114 is connected thereby allowing the panel support frame 114 to be adjustable about this horizontal axis, i.e. the elongate frame member 112.

Adjustment about the horizontal axis is accomplished through rotation means, shown as a jack 118, which is connected between an anchoring means 120 and an intermediate point 124 on the panel support frame 114. The anchoring means 120 extends from the elongate frame member 112 to a foundation 122. It is important for the anchoring means 120 to provide sufficient structural support in order to carry the support frame and solar panels during any expected weather conditions. For example, the anchoring means 120 typically has an extensive foundation to provide the assembly with structural support in windy conditions.

The intermediate point 124 on the panel support frame (which is the other securing point) is between the elongate frame member 112 and a side 126 of the panel support frame 114. On turning an actuator 128 of the tracking jack 118, the jack telescopically expands or retracts thereby increasing or decreasing the distance between the two securing points and allowing the support frame 114 to rotate or be adjusted about the horizontal axis. As previously described in detail, this rotation is a primary adjustment made several times a day in order to ensure that the normal of the panel substantially tracks the movement or orientation of the sun over the course of a day.

In order to provide for the inclination of the horizontal axis of the assembly to be adjusted relative to the horizontal, i.e. ground level or mounted surface, means in the form of an elevation adjustment link 130 or adjustable arm is provided. This link 130 is securable on one end to the elongate frame member 112 and on its other end to the anchoring means 120. In this example embodiment, the elevation adjustment link 130 is pivotally secured to the anchoring means 120 and adjustably connected to the elongate frame member 112 thereby enabling the change in elevation or inclination. A person skilled in the art will however appreciate that the other end may be adjustably connected to the anchoring means 120. Conveniently, the distance between an end of the elongate support means and the anchoring means defines a secondary vertical axis for adjusting the angle of the horizontal axis relative to a mounted surface, which need be adjusted only seasonally. Seasonal adjustment is typically done once a month or less frequently. Seasonal adjustment may be accomplished by manual or mechanical means.

In order to show the efficiency and benefits of the system of the present invention against priori art fixed panel assemblies, a prototype was set up in the Southern hemisphere during the winter month of June. For both the fixed panel assemblies and the prototype panel assemblies of the present invention Tenesol ® photovoltaic modules (TE2200 : 210-240 Wp) were used during the testing.

Adjustment of the panels or modules about the horizontal axis of the system was accomplished through rotation means as set out above, in accordance with the adjustment table below which was provided to an operator. Only six daily adjustments were made by the operator at time intervals of typically one and a half hour. It is to be noted that the angle provided in the second column, in the example of the prototype, is the angle between the horizontal and the actual angle the panel frame is to be rotated. It should be borne in mind that the whole rotational axis also undergoes seasonal adjustment, thus the "horizontal" is actually an inclined axis.

Figure 4 shows a graph that shows the comparison of power output (in Watts) over the time of day on June 18th 2011 of the prototype panel assembly of the invention with that of a prior art fixed panel assembly. It has to be mentioned that the test site of the prototype suffered from shading from trees on the East side, so only the afternoon data was useful. However, the data should typically be symmetric around noon. If the output of the fixed panels versus the adjustable panel assembly of the present invention is integrated, a 35% gain from the invention is evident on this particular day.

It will be appreciated that many factors may influence the total tracking gain over a year, e.g., day length is a crucial factor. In the Southern hemisphere June is accordingly not when a maximum tracking gain is expected. Rather, the maximum is expected during the summer months due to the longer days. Irrespective, the June data can be compared with existing models and indicates an average tracking gain in June of 33%. Extrapolating this data and comparing it with the Photovoltaic Geographical Information System (PVGIS) model, the applicant expects a yearly tracking gain of about 35%. The horizontal inclined tracking system of the invention which relies on only adjustment of one axis on a daily basis (e.g., three or more adjustments per day), also has an improved energy generation efficiency compared to the vertical system of the prior art. The inclined system of the invention, with a monthly or more seasonal adjustment, is approximately five percent more efficient than the vertical system with a similar monthly adjustment. It should be noted that for utility power this represents a clear increase in turnover and hence revenue for no extra cost, and can therefore considerably impact the bottom line of such a utility. The only way the vertical system can approach the inclined system in efficiency is for both axes to be effectively adjusted each time the system moves. In such a case, if two axes are adjusted rather than one, then the adjustment process becomes a lengthier one with a consequent impact on running costs. Further the dual axis mechanisms have an increased mechanical complexity and manufacture cost relative to the invention. These dual systems would also result in additional maintenance requirements due to the added working components required. The secondary and seasonal vertical axis adjustment of the invention therefore mitigates the disadvantages associated with a vertical system in that the adjustment of the second axis only takes place about once a month. The adjustment is simple as no daily adjustment is required, rather an adjustment between fixed points about the vertical axis support tube. As such no dual axis rotational mechanism is required.

Further advantages of the horizontally inclined system of the invention is that it catches more early morning and later afternoon sun than vertically inclined systems. Such added energy generation is significant for utility generated power, as these are commonly times of peak electricity demand.

The invention is not limited to the precise details described above and shown in the drawings. Modifications may be made and other embodiments developed without departing from the spirit of the invention. For example the vertical axis securing pin of the first embodiment may be a nut and bolt assembly. Further the photovoltaic panels may be independently movable about the panel housing about either the vertical, alternately the horizontal axis of the system. Further, the supports anchoring the system to the concrete blocks may include flexible wire supports. These supports would enable the system to be additionally secured to another suitable item such a tree trunk about a different axis relative to the rigid supports. The supports anchoring the system could also be piles driven into the ground to which the vertical supports are attached The number of supports on each side of the assembly may be varied in accordance with user requirements, for example the front mount of the assembly may have three supports, while the rear has a single support.

Claims

CLAIMS:

1. A system for manually adjusting photovoltaic panels comprising a solar panel assembly secured to a panel support frame, the support frame being secured or connected to anchoring means for mounting the system, wherein the panel support frame defines a horizontal axis of the system and the photovoltaic panels are primarily adjustable about the horizontal axis, with the primary adjustment being defined as adjustment of the panel (or frame) in order that the normal of the panel substantially tracks the movement of the sun over the course of a day and the daily adjustment occurs only about the horizontal axis.

2. A system as claimed in claim 1 wherein the support frame is secured to an elongate support means which defines the horizontal axis of the system.

3. A system as claimed in claim 2 wherein the elongate support means is connected with the anchoring means at ends of the elongate support means or at some point towards its centre.

4. A system as claimed in claim 3 wherein the panels are rotatable about their horizontal axis independently of the panel support frame.

5. A system as claimed in claim 3 wherein the panel support frame is rotatable about the horizontal axis with the panels in a fixed mounted position.

6. A system as claimed in claim 5 wherein adjustment about the horizontal axis is accomplished through rotation means which is connected between the anchoring means and an intermediate point on the panel support frame between the horizontal axis and a side of the panel support frame.

7. A system as claimed in claim 6 wherein the rotation means is a jack which telescopically expands or retracts thereby increasing or decreasing the distance between its two securing points thereby allowing the support frame to rotate or be adjusted about the horizontal axis.

8. A system as claimed in claim 1 further comprising means to adjust the elevation of the horizontal axis thereby in effect adjusting the angle of the horizontal axis or elongate support means relative to the horizontal, to accommodate seasonal adjustments of the assembly.

9. A system as claimed in claim 8 wherein the means is an elongate support means defined or located between the anchoring means and the panel support frame.

10. A system as claimed in claim 9 wherein the elongate support means is an adjustable arm located between the anchoring means and the panel support frame.

11. A system as claimed in claim 1 further comprising at least one panel securing means for releasably locking the panel support frame into position about the horizontal axis.

12. A system as claimed in claim 7 wherein the jack is operable as a panel securing means for releasably locking the panel support frame into position about the horizontal axis.

13. A system as claimed in claim 2 further comprising a counterweight to counter the moment exerted by the panel support frame and the attached panels about the elongate support means.

14. A system as claimed in claim 1 further comprising a gauge secured to a fixed part of the structure, to indicate the relative position of the solar panel(s) with relation to the gauge, the gauge being used by an operator in conjunction with a clock and a lookup table to allow the operator to adjust the panel support rack to the correct alignment position for the time of day with the sun to effect maximum efficiency of the system.

15. A system as claimed in claim 14 wherein the gauge is positioned in close proximity to an end of the solar panel assembly.

16. A system as claimed in claim 14 wherein the solar panel or support rack defines an aperture through which the sun shines onto a predefined part of the fixed part of the structure, thereby to indicate the solar panel's orientation to the sun, in that, by adjusting the panel support rack such that the sunlight through the aperture shines on a specific point on the structure, immediate feedback of the sun's position is achieved.

17. A method of generating electrical power comprising the steps of utilising a system which comprises manually adjustable photovoltaic panels, the system comprising a solar panel assembly secured or connected to anchoring means for mounting the system, wherein the panel support frame defines a horizontal axis of the system, wherein the method comprises the step of: an operator manually adjusting the panels daily about the horizontal axis of the system.

18. A method as claimed in claim 17 wherein the step of manually adjusting the panels daily about the horizontal axis of the system includes adjusting the solar panel assembly about the elongate support means with reference to a gauge secured to the system.

19. A method as claimed in claim 18 wherein a gauge is used by the operator in conjunction with a clock and/or lookup table.

20. A method as claimed in claim 18 comprising the operator adjusting rotation means in order to rotate the panels about the horizontal axis of the system.

21. A method as claimed in claim 20 wherein the operator is provided with a number of discreet adjustments by the rotation means and/or the gauge.

22. A method as claimed in claim 21 wherein the support frame is secured to an elongate support means which defines the horizontal axis of the system and wherein the method includes the operator locking the panel support frame into position about the elongate support means with panel securing means.

23. A method as claimed in claim 18 further including the operator manually adjusting panels on a seasonal basis by elevating the horizontal axis of the system.