SOLAR THERMAL INTERCONNECTION SYSTEM WITH A LINEAR FRESNEL MIRROR COLLECTOR, USE OF THE SOLAR THERMAL INTERCONNECTION SYSTEM AND SOLAR THERMAL POWER PLANT WITH THE SOLAR THERMAL INTERCONNECTION SYSTEM

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a solar thermal interconnection system; the use of the solar thermal interconnection system and a power plant with the solar thermal interconnection system.

2. Description of the Related Art

A sun energy collecting unit of a sun field power plant based on the concentrated solar power technique is for instance a linear Fresnel mirror collector with linear Fresnel mirrors and a heat receiver tube. The heat receiver tube is arranged in a focal line of the mirrors. By sunlight reflecting sur ^¬ faces of the mirrors the sunlight is focused to the heat re ^¬ ceiver tube, which is filled with a heat transfer fluid, e.g. a thermo-oil. Via the heat receiver tube the energy of the sunlight is coupled into the heat transfer fluid. Solar en ^¬ ergy is converted to thermal energy.

A heat receiver tube with a heat transfer fluid (HTF) flowing there through is positioned in a focal line of the reflecting surfaces of the mirror facets of the Fresnel mirror for solar radiation collection. With some systems, an additional secondary mirror behind the focal plane directs the rays onto the heat receiver tube. In this way, the HTF collects heat of so ^¬ lar radiation which impinges on the receiver surface and transfers it to a power generation block (for example, a steam-electric power plant) of a solar thermal power plant. The elevation of the solar ecliptic over the solar field lo ^¬ cation on the surface of earth is dependant on the latitude of the location, and changes over the course of the year. This effect causes a reduction in the receiver's efficiency due to the incident angle between the sun's beam and the plane defined by east-west axis and the normal to the earth surface. This reduction is called Incident Angle Modifier (IAM) .

SUMMARY OF THE INVENTION

It is an object of the invention to provide a solar thermal interconnection system with which sun energy can be collected with more efficiency compared to the efficiency of the state of the art.

It is another object of the invention to provide an efficient solar thermal power plant for transferring solar energy into electrical energy.

These objects are achieved by the inventions specified in the claims . A solar thermal interconnection system is provided with at least one solar thermal interconnection system with at least one Fresnel mirror collector with at least one Fresnel mirror for concentrating sunlight in a focal line of the Fresnel mirror; at least one heat pipe with at least one heat pipe working fluid for absorbing solar energy, wherein the heat pipe is located in the focal line of the; at least one heat absorber system with a heat absorber medium; wherein the heat pipe and the heat absorber system are thermally coupled such, that a heat transfer from the heat pipe working fluid to the absorber medium can occur. For instance the heat absorber system comprises a heat receiver tube. The absorber medium is a heat transfer fluid. Additionally a use of a solar thermal interconnection system is disclosed to provide thermal energy. This use includes a use for transferring solar energy into electrical energy. Moreover the use includes a use in a plant for manufacturing goods by the aid of the thermal energy. For instance, these goods are goods of the chemical industry.

Additionally a solar thermal power plant for transferring so ^¬ lar energy into electrical energy with at least one solar thermal interconnection system is disclosed, wherein the linear Fresnel mirror collector is oriented with its longitudi ^¬ nal alignment in north-south direction. A Fresnel mirror comprises several mirrors. These mirrors are flat or slightly bended in order to reduce a reflected line width.

Preferably a plurality of solar thermal interconnection sys ^¬ tems is set up. In addition a tracking system is set up. For instance the tracking system is configured for tilting the heat pipe to lie in a plane substantially perpendicular to a path of incident solar radiation and/or for tilting said parabolic mirror to maintain its focal line and vertex aligned along a line parallel the path of incident solar ra ^¬ diation . In a preferred embodiment the heat pipe working fluid com ^¬ prises at least one material selected from the group existing of nitrogen, ammonia, methanol, water, mercury, potassium, sodium, lithium and silver. Other materials or mixtures thereof with the materials of the group are possible, too.

Preferably the solar the heat absorber medium comprises a heat transfer fluid. For instance the heat transfer fluid is a thermo-oil. A thermo-salt or a mixture of different thermo- salts is possible, too.

In a further preferred embodiment the absorber medium comprises a power block working fluid of a power generating block for generating electrical energy. For instance, such a heat absorber medium comprises water. By this direct steam generation is implemented. But alternative materials to water for generating a power block working fluid are possible. For instance the power block working fluid is based on Sulfur.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention are produced from the description of exemplary embodiments with reference to the drawing. The drawings are schematic.

Figure 1 shows a heat pipe.

Figure 2 shows a cross section of the heat pipe of figure 1 along the line II-II.

Figure 3 shows a detail of the solar thermal interconnection system. Figure 4 shows a sun field of a solar power thermal power plant with the solar thermal interconnection system.

Figure 5 shows a perspective view of the sun field. DETAILED DESCRIPTION OF THE INVENTION

In the suggested solar interconnection system 1, the heat absorber system 20 comprises a heat receiver tube 10 which is filled with a heat transfer fluid (HTF) 21. The heat transfer fluid is the absorber medium of the absorber system.

HTF is heated by a heat pipe 12 instead of the by direct heating by focused solar radiation on the heat receiver tube 10. As illustrated in Fig. 1, each HTF pipe 10 is connected to a plurality of heat pipes 12, each protruding there from.

Each heat pipe 12 is associated with a linear Fresnel mirror 22 (figure 5) . As seen in Fig. 2, each heat pipe 12 comprises a transparent casing 14 with an evacuated interior 16, and a sealed thermal pipe 18 therein. The thermal pipe 18 carries a heat pipe working fluid, which occupies (when in liquid form) only a small percentage of the volume of the thermal pipe. The remainder of the interior volume of the thermal pipe 18 may be at least partially evacuated. One end of the thermal pipe 18 protrudes into the interior of the HTF pipe 10, where it is within the HTF By convention, the portion of the thermal pipe 18 within the casing 14 is referred to as a hot interface 18a, and the por ^¬ tion of the thermal pipe within the HTF pipe 10 (and in con ^¬ tact with the HTF) is referred to as the cold interface 18b. The cold interface 18b may be provided with a construction or other appropriate means for increasing the rate of heat transfer between the heat pipe working fluid of the thermal pipe 18 and the HTF thereby. For example, it maybe be pro ^¬ vided with fins (not illustrated) for this purpose. During operation, incident and reflected (by the parabolic reflector) solar radiation impinges on the heat pipe 12 and the hot interface 18a of the thermal pipe 18, thus heating the heat pipe working fluid therein. The heat pipe working fluid therein boils, thus absorbing latent heat. The heated and vaporized heat pipe working fluid enters the portion of the thermal pipe 18 which is adjacent the cold interface 18b, wherein it condenses. The condensation results in a release of the latent heat absorbed in the heat pipe working fluid, which is subsequently absorbed by the HTF. The condensed working fluid flows back to the portion of the thermal pipe 18 adjacent the hot interface 18a, for absorbing more solar thermal energy.

In this way the HTF is heated by incident and reflected solar radiation for providing thermal energy for driving the operation of the thermal power plant. In addition, by separating the HTF from the receiver tube, the system which collects heat directly from solar radiation is separated from that which transfers that heat to the power generation block. Thus, each may be positioned independently of one another. For example, in some applications, it is ad ^¬ vantageous to dispose the pipes carrying the HTF at a certain angle, for example to take advantage of heat gradients, dif ^¬ ferent phases of the HTF, etc. At the same time, a different set of considerations governs the angle at which the receiver tubes should be angled (either each receiver tube, or a plane which contains several receiver tubes), typically the inci ^¬ dence angle of solar radiation. Thus, by separating the physical systems in which the functions of solar radiation collection and heat transfer occur (i.e., heat pipe 12 and HTF pipe 10, respectively) the dispositions thereof may be provided and/or adjusted independently of one another.

The system described above may be designed according to any one or more of the following in combination, mutatis mutan- dis:

- The HTF may be thermal oil which is passed through a heat exchanger of the power block for heating working fluid of the power generation block. Alternatively, the HTF may be the working fluid of the power generation block, for example in a direct steam generation configuration of the solar thermal power plant.

- The thermal pipe 18 may be provided with a mechanism (not shown) for regulating the pressure therein. In this way, the temperature of the working fluid thereof, and thus of the HTF, can be regulated based on the requirements of the power plant. Non-limiting examples of mechanisms and/or configura ^¬ tions for providing the regulation include a gas load pipe, excess liquid, and vapor flow modulation.

- The working fluid may be any appropriate material, for ex ^¬ ample based on the desired temperature range of the HTF. Non- limiting examples of materials for use as working fluid in ^¬ clude water, mercury, magnesium, potassium, sodium, and lithium. - Although the examples presented in Figs. 1 and 2 provide a single heat pipe 12 at any given point along the length of the HTF pipe 10, a second heat pipe may be provided. Typi ^¬ cally, one heat pipe 12 would be extending upwardly from the HTF pipe 10, and a second downwardly there from. The heat pipe 12 which extends upwardly may be provided with any known technology for use thereof in such a configuration, includ ^¬ ing, but not limited to, a fine fiber bundled wick, thin grooves formed on the inner surface of the thermal pipe 18, a screen mesh, or a sintered powder.

- The system may be configured to tilt and/or rotate to track the sun. For example, rotation may be facilitated about the longitudinal axis of the HTF pipe 10 in order to track the sun as the height of the ecliptic (i.e., the solar elevation) changes throughout time (e.g. day) . In addition, rotation of each parabolic mirror about its focus (i.e., about the longi ^¬ tudinal axis of the heat pipe 12) may be facilitated in order to track the sun over the course of the day as it moves east- west along the ecliptic.

In comparison to a solar interconnection system based on trough technology there are following additional advantages:

- The efficient use of land associated with the Fresnel tech- nology is translated to shorter heat transfer tubes and hence to less pressure drop and heat losses.

- Sun tracking can be omitted. The heat pipe in the focal of the receiver is fixed. This is mandatory for a heat pipe ap- plication and much easier to implement in Fresnel technology.

- Less wind load in both direction results in less complexity of the whole system and hence in a cost reduction. - The low optical efficiency related to Fresnel technology is due to the incident angle which is less problematic in in ^¬ clined arrangement.