DE19630201C1 - Self-tracking heliostat for solar power plant tower - Google Patents

Abstract

The heliostat has a photodetector (1) receiving the reflected sunlight directed onto the absorber by the heliostat mirror (3), to provide signals representing the alignment error for controlling the heliostat electric setting motor (6). The photodetector is secured to the support structure (2) of the heliostat in a fixed position, e.g. via a vertical support (8) projecting through an opening at the centre of the heliostat mirror.

Description

The invention relates to a self-aligning heliostat for a solar Tower power plant.

In addition to the use of solar heat by collectors and direct generation of electricity with photovoltaic components has long been the principle of solar thermal power plant, mostly realized in training as a solar Tower power plant, known.

In a solar tower power plant, which is shown schematically in FIG. 2, the radiation coming from the sun ( 10 ) is focused on an absorber ( 12 ) by a field of mirrors, called heliostats ( 11 ), which is located on a tower ( 13 ). Whose radiation-induced strong warming can be used, among other things, by the thermal energy is transported through a coolant via a line ( 14 ) to a conventional thermal power plant ( 15 ) that generates electricity with a typical efficiency via heat exchanger / evaporator, turbine and generator . There is also waste heat, which can also be used.

For the operation of a solar tower power plant, direct sunshine is mandatory radiation is required because it is not possible to focus diffuse light. This means that only extremely sunny regions of the world can be used. A working on this principle power plant is, for. B. in California Mojave Desert operated successfully under the name "Solar Two". The The facility is a joint project involving the US Department of Energy, the Califormia Energy Commission, the Electric Power Research Institute, the utility company PacifiCorp and others are involved.

Because the angle of incidence of the sun changes due to the earth's rotation and the Earth movement around the sun is constantly changing, is a constant tracking of the Heliostats required so that the reflected light focuses on the absorber remains.

A key aspect for the prospects of success of an alternative energy source is their economy. As with all concepts for electricity, this is the case today generation from solar energy also for the solar tower power plant due to the high investment costs not yet achievable.

A major contribution to these costs is made up of the heliostats, their tracking So far, it has only been possible to move towards the sun with great technical effort z. B. the direction of irradiation of the sun is measured in short time intervals or calculated in advance and then every single heliostat with the help of a computer Controlled via a digital data connection and with the help of electric motors aligned. Because this alignment control and mechanics is very expensive, one tends towards relatively few, large heliostats.  

However, this requires a curvature of each individual mirror to be one to get a sufficiently small focus, which in turn is very expensive. Furthermore this approach is opposed to making the heliostats cheaper by the masses production.

From US 39 06 927 solar tower power plants are also known in front of each heliostat a photodetector to control the sun tracking exhibit. It is disadvantageous that the photodetectors are separate from the Heliostats are set up, thus additional space, additional foundations and require long connecting lines. The main disadvantage is that relatively large distance of the photodetector from the heliostat mirror, which according to the direct sunlight is no longer available (e.g. by passing Clouds) can cause the reflected light to move on Sun no longer hits the detector and the detector is therefore not correct Tracking signal can generate more.

The invention is therefore based on the object of a more compact structure Heliostats, better adjustability of the detectors and a larger Unemp Sensitivity of the control loop against temporary loss of direct suns to achieve irradiation.

This object is solved by the features of claim 1.

The invention has the advantage that only one supply is left for the heliostats with a low DC voltage of low power required for the servomotors is. This supply can be done by simply connecting many heliostats in parallel in groups. By simply turning this utility off groups of heliostats can be taken out of operation, which enables control of the irradiation power at the absorber. On Polarity reversal of this supply voltage z. B. at night the Helio with the help of a simple circuit in the starting position for the next Run back tomorrow.

The self-control allows you to operate the entire system individual heliostats are repaired or exchanged or additional heliostats to be added. The placement of the heliostats can also be done according to Inbe system start-up can be optimized, reducing the cost of advance calculations and planning drastically reduced and an application z. B. in climatically Developing countries simplified and suggested.

Finally, the technical simplicity of execution according to the in Claim 3 formulated features in combination with a manufacture e.g. B. a cheap mass production in injection molding technology.

Fig. 1 shows a possible embodiment of the heliostat using the ball joint described in claim 3. A second servomotor for tracking in the direction perpendicular to that shown has been omitted for reasons of clarity.

Before starting up each heliostat, its detector ( 1 ) must be aligned once with the absorber. For this purpose, it is provided with the adjustable fastening ( 2 ) shown in FIG. 1. A commercially available laser pointer can be useful for alignment, which is placed on the detector parallel to the axis for the duration of the alignment process and points away from the inlet opening of the detector to the absorber.

The detector consists, as is common practice, of two pairs of photosensitizers Components such as phototransistors, each through a shading device are separated. When the light falls at an angle, one of the phototransistors is located more in the shade than his counterpart. Now with the help of a simple electronic circuit for each pair the difference between the two individual signals formed, which becomes zero if and only if the light hits both components equally strongly, thus occurs in parallel.

If this is not the case, the differential signal of each pair of transistors is increasingly used to control the associated servomotor ( 6 ) and thereby to adjust the mirror ( 3 ) until the condition of parallel light input is met again. If the detector is correctly adjusted, this also means that the reflected light also hits the absorber.

Claims (3)

1. Self-aligning heliostat for a solar tower power plant with a photo detector ( 1 ) which, aligned along a connecting line to the receiver (absorber) of the power plant, receives the (sun) light which was reflected by the heliostat mirror ( 3 ) and generates two signals, which correspond to the magnitude and polarity of the deviation of the incident light from the axis parallel in two directions perpendicular to each other and the axis of symmetry and which are used to control the servo motors ( 6 ) of the heliostat, which means that the light is constantly reflected on the receiver (absorber) Power plant is reached, characterized in that the photodetector ( 1 ) is fixed in place and direction on the support structure ( 2 ) of the heliostat. 2. Heliostat according to claim 1, characterized in that the attachment ( 2 ) for the detector ( 1 ) through a central opening in the heliostat mirror ( 3 ) and is connected to the standpipe ( 8 ). 3. Heliostat according to claim 2, characterized in that the ball joint for pivoting the heliostat consists of a support ring ( 4 ) which slides on a hemispherical bearing piece ( 5 ) and carries the heliostat mirror ( 3 ), with the center of gravity at the center of the Ball cap falls together.