Power plants – Utilizing natural heat – Solar
Reexamination Certificate
2001-02-21
2002-04-09
Nguyen, Hoang (Department: 3748)
Power plants
Utilizing natural heat
Solar
C060S641800, C060S641900
Reexamination Certificate
active
06367257
ABSTRACT:
The invention relates to an installation for producing solar thermal energy, having an absorber layer for conversion of sunlight into thermal energy and a transparent heat-carrying liquid for transporting the heat produced in said absorber layer for further use, said absorber layer being situated within said heat-carrying liquid.
Installations for producing solar thermal energy are known in various conformations. Examples include solar tower power plants or parabolic trough power plants, which make solar energy usable by thermal conversion on a commercial scale. However, such power plants have very large surface area requirements. In addition, the use of same is limited to latitudes where high direct solar radiation is assured, because they can make little use of the diffuse portion of the sunlight.
On a smaller scale, facilities for producing solar thermal energy are known in the form of solar collectors for residential water heating, said collectors preferably being installed on the roof. However, such a decentralized use of solar energy serves more to reduce residential energy costs than to replace fossil energy fuel as the primary energy source.
A floating solar power plant for the commercial-scale production of electricity is known from Patent DE 25 43 687 C2. The surfaces of said solar power plant are designed as absorbers and track the sun's path. Said absorbers are hereby mounted on a floating collector platform, designed as a circular plate of very large diameter, made from a flexible material designed to absorb tensile stress. Said floating collector platform is provided with devices that can turn the platform on the water.
Patent DE 28 19 946 A1 describes a thermal storage pond and an energy generating installation using same. Said thermal storage pond contains a thermal storage liquid that floats upon an insulating layer, said layer being thick enough to thermally insulate said thermal storage liquid. Said energy generating installation encompasses said thermal storage pond. In addition, a thermal engine is provided to extract heat from said thermal storage liquid.
A solar collector having an absorber situated within a transparent heat-carrying liquid is known from Utility Model DE 296 03 275 U1. This specialized arrangement of said absorber is intended to minimize heat loss from said absorber to said heat-carrying liquid during heat transfer, and in particular to avoid radiation loss from said absorber. However, the material costs for this known solar collector are relatively high, so that use is limited to residential water heating.
Proceeding from the prior art, the object of this invention is to provide an installation for producing solar thermal energy, using the aforementioned principle of the absorber arrangement, to make solar energy usable by thermal conversion on a commercial scale, without additional fuel firing. This objective is achieved by an installation having the features of accompanying claim
1
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Advantageous developments and further developments of the invention arise from claims
2
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19
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The main element of the installation according to the invention is at least one thermal storage water heater wherein hot water at a temperature typically around 100° C. is produced from solar radiation and simultaneously stored, using an absorber layer on the inside thereof. Said thermal storage water heater is situated to float beneath a water surface. The installation according to the invention is thus set up in a body of water, preferably in an ocean, so that no land area is consumed. Solar radiation is directly converted to heat in the energy storage unit, thus eliminating energy loss during heat transport. Use of integrated energy storage removes the need for fossil fuels during the time when solar radiation is absent.
The thermal storage water heater is provided with thermal insulation to reduce heat loss to the surroundings. Said thermal insulation is transparent on the upper side of said thermal storage water heater to allow solar radiation to penetrate to the absorber layer.
Hot water can be removed from the thermal storage water heater as a heat-carrying liquid, with which electricity or drinking water can be produced without additional fuel firing at middle to base load conditions. Heat decoupling for supplying district heating, for example, is also possible.
One advantage of the invention is that the installation may be operated for producing solar thermal energy outside daylight hours, because sufficient energy can be stored at night and in times of low solar radiation by appropriate sizing of the thermal storage water heater. Depending on the size of the installation and the climate zone of the installation site, economic operation at middle to base load conditions is possible.
In contrast to known parabolic trough power plants, the installation according to the invention can use not only parallel solar radiation but also the diffuse portion thereof. Thus, said installation may be used even in tropical and moderate climate zones, thereby greatly increasing the areas of use.
The concept according to the invention, to transfer the heat generated in the absorber directly to the contents of the thermal storage water heater and to remove the heat-carrying liquid from said thermal storage water heater for further use, is particularly usable on a commercial scale due to the floating design of said thermal storage water heater. Said thermal storage water heater may be simply constructed in sizes that assure efficient energy storage.
A variable-volume design of the thermal storage water heater offers further advantages: depending on the intensity of solar radiation, the storage capacity can be modified. When the incident energy radiation is high, said thermal storage water heater can be enlarged by addition of colder water, thus eventually heating the colder water to the storage temperature with no loss of excess energy. When the installation is operated in the absence of solar radiation (at night), hot water is removed from said storage unit, thus decreasing the storage volume. Thus, colder water must not flow back into said thermal storage water heater, so that the storage temperature can remain unchanged at its high level, even during nighttime operation of said installation.
It is advantageous to provide the thermal storage water heater with membrane-like, movable walls. This not only conserves materials, but also avoids static difficulties and stability problems with the storage unit wall. Finally, in this manner water movements may be intercepted to a certain degree without risking damage to the storage unit walls.
Since most processes using the heat removed from the thermal storage water heater do not cool the hot water to ambient temperature, it is advantageous to provide a warm water recirculation heater for the returning heat-carrying liquid, said warm water recirculation heater being installed adjoining said thermal storage water heater. If the interface between the two said heaters is sufficiently large, heat loss from said thermal storage water heater to the surroundings is significantly reduced. Heat is transferred from said thermal storage water heater to said warm water recirculation heater more slowly due to the smaller temperature gradient, so that the heat flowing into said warm water recirculation heater is still not lost for the utilization process.
Preferably, the thermal storage water heater and the warm water recirculation heater can be designed as a module with common outer walls, whereby a movable partition separates the storage contents from one another. The movable design of said partition, which can be composed of thermal insulation, allows the volume of said thermal storage water heater and of said warm water recirculation heater to be modified, thus offering advantages depending on the solar radiation and the operating situation.
Such a partition designed as thermal insulation is preferably produced in a module as a single unit with the absorber layer, wherein the density of the entire structure is adjusted to be sligh
Witt Ilse
Witt Janine
Witt Michael T.
Gardere Wynne & Sewell LLP
Nguyen Hoang
Witt Michael T.
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