Method for adjusting the inclination of their opening planes and the orientation of their axes for a cylindrical-parabolic sensor system with a general East-West orientation of the heat transfer tubes

Abstract

For a system of cylindrical parabolic sensors with a general East-West orientation of the heat transfer tubes, a method to determine the variation in orientation of the axis of the sensors to be made with respect to the East West direction, as well as the variation in angle of the opening plane of the sensors with respect to the plane of the structure which will allow optimal operation of the system.

Description

Title of the invention: Method for adjusting the inclination of their opening planes and the orientation of their axes for a system of cylindroparabolic collectors with a general East-West orientation of the heat transfer tubes

[0001] Context: The sensors are arranged in parallel rows on a disc-shaped structure located on a south-facing inclined plane, this plane being normal to the direction of the sun's rays at noon solar time on the day of the summer solstice. (The inclination of the plane depends on the latitude of the location.) Two types of movements are possible for the sensors: A rotation of the entire disk forming the structure around its center on the plane of the structure (rotation No. 1). The unison rotation of each parabolic trough sensor around its focal axis (rotation No. 2). We call [3 the angle between the horizontal plane and that of the structure. (See [Fig.l] on which P is the horizontal plane, P' the plane of the structure, the lines inside the disc representing the axes of the sensors, rotation No. 1 being a rotation with center O in the plane P'). We call a the angle formed between the opening plane of a sensor and the plane on which the structure is arranged, each sensor a having its opening plane which forms the same angle a with the plane of the structure. In [Fig.2] two parallel cylindroparabolic sensors are represented, the rotation movement No. 2 around the axes of these sensors being illustrated by the arrows.

[0002] Benefits provided: The combination of the two rotational movements, their angles being correctly adjusted, makes it possible to obtain, at any time of the day and in any season, an orientation of the plane of symmetry of the sensor passing through its axis such that it contains the direction of the sun's rays, and this for each sensor. This produces a reverberation of the sun's rays incident on the focal axes of the sensors. In addition, every day at noon solar time, the sun's rays have a direction normal to that of the opening plane of the sensors. The total surface area corresponding to the opening planes of the mirrors represents two-thirds of the surface area of ​​the structure's disk. Correct adjustment of the angles of each rotation ensures solar tracking without shadow effect between neighboring sensors.

[0003] Principle: The Earth rotates on its axis around a North-South axis passing through its center. At the same time, it completes a revolution around the Sun with a period of one year. For sensor angle adjustments during the day, this second movement will not be taken into account. For a given day, we then consider that the Earth has a fixed position around the Sun (the position retained being that at noon solar time). The only movement taken into account is the rotation of the Earth around its axis. During a given day, an observer O on Earth rotates around the axis (d): a straight line directed North-South passing through the center of the Earth, the Sun remaining fixed. From the point of view of observer O, the apparent movement of the Sun is therefore a rotation around the axis (d). The diameter of the Earth can be neglected compared to the Earth-Sun distance. Let S be the center of the Sun, the distance OS can be considered constant over the course of a day. A model assimilates the trajectory of the Sun to a circle located on the edge of a cone of revolution with an axis directed North South for a given day. At any time of the day, a solar ray [OS] constitutes a generator of this cone. In [Fig.3], the trajectory of the Sun is represented on the edge of a cone with vertex O (observer), and axis of revolution (d): straight line passing through O oriented North South. On equinox days, the cone in [Fig.3] is flattened, its half-angle at the center is 90°. The apparent trajectory of the Sun is therefore a circle with center O. The focal axis of the mirrors is oriented East-West and the angle a between the aperture plane of the sensors and the plane of the structure is set at 23.45°. This setting is fixed for the day. For other days, adjustment is necessary throughout the day, in order to vary the angle a and the direction of the focal axis of the sensors. In [Fig.4], K is the cone with center O grouping all the solar rays during the day, C is the circle of the apparent trajectory of the Sun on the day considered. H is the position of the Sun at time h, [OH] is the radius of the Sun at this time h, P' is the plane on which the disk of the structure is arranged. Let P(h) be the tangent plane along (OH) to the cone C. This plane intersects the plane P' along a line A(h) passing through O. The line A(h) is chosen as the direction of the sensor axis at time h. Thus, during a day, the axis of the sensors will be directed towards the rising sun (direction A(L) in the figure) at the beginning of the morning, then is gradually modified to reach the East West direction at midday, then reaches at the end of the day the direction of the setting sun (A(C) in the figure), the adjustment of the direction being controlled by the rotation of the structure around its center in the plane P'. After adjusting the orientation of the sensors' axes, at time h, the solar ray belongs to the plane P(h) which contains the focal axis of the parabolic trough sensor. In order for the solar rays to be reflected on the focal tube, the angle a must be varied in order to rotate the sensor around its axis A(h) until the orientation of the sensor's opening plane is perpendicular to the plane P(h). (See [Fig.5])

[0004] Variations in the values ​​of the angle a during the day of the summer solstice. The maximum difference between the value of a at sunrise and at noon solar time is obtained at the time of the summer solstice. On that day, the tilt plane of the structure is normal to the direction of the Sun's rays at noon solar time. The opening planes of the sensors are then parallel to the plane P' of the structure. We then have a = 0° at noon solar time. For a site located at 42° North latitude, a calculation gives a = 36° at sunrise (angle a identical to that of sunset). The angle a will therefore decrease during the morning then increase again during the afternoon to return to a value identical to that of the morning in the evening. However, given the spacing chosen between two consecutive mirrors, for any angle a less than 47°, there is no shadow effect of the mirrors on their neighbors. During this solstice day, the values ​​of the inclination a remain in a range of 0° to 36°, we therefore respect the condition that we set ourselves concerning the absence of shadow effect.

[0005] Variations in the values ​​of the angle a during summer and autumn days (except equinox days). During these days, the values ​​of a are maximum at the time of sunrise (or sunset), and minimum at noon solar time. The variations of a are therefore the same as at the time of the summer solstice, the amplitude of the variations diminishes as we approach the equinox days. The values ​​of a also remain below 47° at all times of the days during this period. There is also no shadow effect between the sensors during this period.

[0006] Variations of the angle a on the day of the winter solstice. [Fig.6] represents the cone of revolution with an axis directed towards the North on the edge of which we find the trajectory of the Sun, at three periods of the year: Left in the spring summer period. In the center on equinox days. The half angle at the center of the cone is right, we obtain a flattened cone, that is to say a disc normal to the North South axis passing through O. On the right, in the autumn and winter periods; compared to the figure on the left, the cone has changed orientation (like an umbrella turning inside out in windy weather). The axis of revolution of the cone is then directed towards the South. The cone described above corresponding to the winter solstice and that corresponding to the summer solstice are symmetrical to each other with respect to the plane normal to the North-South axis passing through O. the variations of the angle a during the day of the winter solstice are therefore the opposite of those observed at the summer solstice. On the day of the winter solstice, the maximum value of a is obtained at noon solar time. (47° to the nearest 1°, this is the maximum value of a for the year) Throughout this day, the inclination of the sensors relative to P' therefore remains less than 47°. The criterion of absence of shadow is still satisfied.

[0007] Variations of the angle a on autumn and winter days. The maximum for a is also reached at noon solar time, and this maximum is less than or equal to 47°. The previous criterion is still satisfied.

Claims

Claims

1. Parabolic cylindro-sensor system comprising parabolic cylindro-sensors arranged in parallel rows, their assembly being inscribed in the surface of a disk located on an inclined plane (plane normal to the direction of the Sun's rays at noon solar time on the day of the summer solstice), the disk as well as all the sensors located therein can rotate around its center in the plane of the structure, and each of the sensors can pivot around its axis, this system being characterized in that it comprises two solar tracking modes.

2. : Method for adjusting the inclination of opening planes and the orientation of axes of the parabolic trough sensor system according to claim 1, characterized in that it comprises a step of calculating the angles which make it possible to adjust the solar tracking of said system from a model which assimilates the trajectory of the Sun to a circle located on the edge of a cone of revolution with an axis directed North South for a given day.

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