WO2019058148A2 - High- efficiency apparatus and process to utilize solar power, particularly for water withdrawal - Google Patents

Abstract

The present invention relates to a solar energy utilizing apparatus to utilize radiation in the solar radiation spectrum available at the earth-surface, that is, in portions of the solar spectrum in the visible (VIS) and ultraviolet (UV) frequency domains, by means of converting radiation in said solar radiation spectrum into infrared radiation (IR), as well as a use of the apparatus. The solar energy utilizing apparatus comprises a sunlight collector means to collect energy of the radiation in the solar radiation spectrum into substantially a single point, and a heating block in the form of a sunlight converter means comprising sunlight conversion material to receive and absorb the collected solar energy in the solar radiation spectrum, thereby converting said solar energy into infrared radiation, wherein at least a region of said sunlight converter means is arranged to contain said single point. Furthermore, in said solar energy utilizing apparatus, the sunlight conversion material exhibits absorption characteristics corresponding substantially to Planck's black-body radiation within the solar radiation spectrum for the sunlight incident thereon, and the sunlight conversion material exhibits emission characteristics corresponding to emission exclusively at a colour temperature that corresponds to a heating of said sunlight conversion material by the solar energy absorbed.

Description

HIGH- EFFICIENCY APPARATUS AND PROCESS TO UTILIZE SOLAR POWER, PARTICULARLY

FOR WATER WITHDRAWAL

The present invention relates to a high-efficiency solar energy utilizing apparatus and method, primarily for water withdrawal. The present invention also relates to a novel heating block applied in the apparatus for directly converting solar energy into thermal energy.

In the present age of climate changes and associated catastrophes, the demand for producing clean energy (primarily without carbon dioxide generation) is getting higher and higher. As the majority of energy sources available nowadays, as well as the life on Earth are attributed to light (electromagnetic) emission of our central celestial body, the Sun, it is highly understandable that to meet the vast majority of energy requirements of mankind, as clean energy source, the radiation emitted by the Sun is exploited.

Solar plants made use of today can essentially be divided into two groups, wherein

- the first group includes those solar plants that collect sunlight and thereby increase the internal energy (typically, the temperature and the pressure) of a working fluid of a steam turbine to produce electric energy by means of the thus obtained energy surplus of the working fluid; and

- the second group includes semiconducting photovoltaic panel systems, wherein the electricity is generated in the p-n junctions of semiconducting units.

The solar plant of Ivanpakh (Solar Electric) built in the Mojave Desert, California, is a representative example of the so-called solar plants with solar mirrors, which operates continuously since February 2014. In this solar plant, light coming from the Sun is projected onto three towers of about 137 meters in height each by means of about 3000 mirrors, each of which is 2 meters in height and 3 meters in width, formed traditionally as curved plane mirrors and controlled by an appropriate computer system, wherein heating-up of the working fluid of the turbine(s) takes place.

Generally, in case of solar plants used nowadays, and thus in case of the above discussed Ivanpakh solar plant as well, at least 55% of the light energy of the collected solar radiation gets lost due to reflection, transmission, radiation and absorption losses. Then, a water steam turbine converts the heat energy generated by the remaining sunlight energy at a conversion efficiency of 28.72% (here, the delivery of electricity to the electric distribution mains takes place at further losses and is reasonably expensive). Thus, the overall efficiency of such solar plants can be considered low and, hence, is to be improved. As a further technical problem in such solar plants, turbine systems getting cooled during night shall be started at operation temperature in the morning, which requires additional external heating before sunrise for a given amount of time; in particular, this takes place with natural gas in the Ivanpakh solar plant. Heating up to the operation temperature and/or compensating the lower energy production on cloudy days represent significant sources of costs.

The most frequently applied solution to the above-discussed difficulties is to heat salt either within the working fluid boiler units or directly by means of the obtained hot water to store thermal energy or alternatively to compensate for the lower energy generation during overcast days. According to this, at nightfall or when the energy production of the solar plant reduces on cloudy days, further pieces of equipment start to operate that make use of the thermal energy stored earlier. Furthermore, there is also a need for such auxiliary energy sources that make use of possibly renewable energy sources, which are capable of compensating for the temperature variations in a solar energy system. It is also of great risk of accidents that the mirror systems with large surface extension might e.g. dazzle the pilots who fly over such systems. From the point of view of environment protection, a further problem is that the birds flying above the solar plant get simply burned, while the still remaining biosphere is getting devastated on the land under the mirrors installed (particularly, here the protected desert tortoises should be mentioned).

Hence, when developing solar plants, it is an aim to eliminate situations that create risk of accidents (e.g. the possibility of dazzling pilots) and alleviate problems related to environmental protection, as well as to also decrease preferably the operating costs.

The solar plant built under the German project "Andrasol" in Andalucia, Spain, at a location within about 50 kilometres from Granada, that contains 600,000 solar mirrors arranged over about 1400 hectare and turning automatically towards the Sun tries to provide a solution for the above problems. The plant has got an advantageous geological location as it is built, on the one hand, in a desert area with clear air, high above the sea level and, on the other hand, there is water under the plant that provides the working fluid of its steam turbines. The solar mirrors of this Andalucian solar plant reflect the energy of the sunlight onto a column, where the thus collected thermal energy is then stored in about 30,000 tons of molten salt having the temperature of even 900°C. Then, to operate the steam turbines the working fluid in said steam turbines is heated, according to needs, by the molten salt through a heat exchanger. In this way, the length of the period of the continuous power generation is increased by about 7.5 hours relative to that of the sunny hours of the day. Thus, a more balanced power production can be achieved.

Unfortunately, the installation and operating costs of the above discussed type solar plants are really high, and the pay-out period is long. The operating time and the need for maintenance of and the solar plants with solar mirrors, as well as the protection against wind-borne sand consisting of hard quartz crystals represent further problems and challenges.

Moreover, nowadays there is an increasing demand for power turbines operating on high temperature (i.e. 900-1200°C) working fluids/steams due to their higher thermal efficiency (since e.g. in such turbines the Rankine cycle can be used very efficiently).

However, achieving high thermal efficiency is of relevance only in that case if power plants of not only experimental nature but capable of power production on the industrial scale are constructed. It is also apparent, that the amount of power produced by the above-referred solar plants is mainly determined by the amount of solar energy collected by the solar mirrors and then transferred to a boiler of the working fluid or a heating head.

Accordingly, the object of the present invention is to provide a means for collecting and utilizing a proportion as high as possible of the electromagnetic radiation per unit area arriving from the Sun to the Earth and reaching the earth-surface (typically, in the wavelength range of 250 to 3000 nm, i.e. sunlight in the solar spectrum in the visible and ultraviolet frequency domains), that is, for converting said proportion of sunlight into electric or thermal energy at conversion efficiencies as high as achievable; here, and from now on, the term conversion efficiency refers to a ratio of the amount of energy usable as electric or thermal energy to the amount of energy of the incoming sunlight over the unit area of a sunlight collecting surface. Or putting this other way, the object of the present invention is to maximize the efficiency of sunlight utilization at given geographical and climate conditions. In particular, the present invention aims at constructing a solar energy utilizing apparatus with high efficiency, wherein the individual units of the apparatus are capable of utilizing the energy of solar radiation arriving to the Earth in high proportions in a wide spectral range, practically over the complete solar spectrum range, i.e. said unit's efficiency of sunlight utilization is high.

To this end an object of the present invention is, on the one hand, to achieve the best reflection coefficient for the sunlight collecting surfaces applied in the solar energy utilizing apparatus for every wavelength of sunlight striking the earth-surface. On the other hand, a further object of the invention is to perform focusing of sunlight onto a sunlight converting heating block with an efficiency as high as possible.

In light of the above, the present invention relates to an apparatus for utilizing radiation in the solar radiation spectrum present at the earth-surface in accordance with the solar energy utilizing apparatus of claim 1. Further preferred embodiments of the solar energy utilizing apparatus according to the invention are defined by dependent claims 2 to 22. The present invention, in its further aspect, also relates to a use of the solar energy utilizing apparatus to operate a power machine and thereby to withdraw water from a stationary well in accordance with claims 23 and 24, respectively. Possible further objects to be achieved by and advantages of the present invention will be apparent in light of and discussed in detail in the following description. In the drawings, Figure 1 shows schematically a preferred arrangement to collect and then direct solar energy to the place of utilizing it; Figure 2 illustrates schematically a spinel sintering process performed under pressure; Figure 3 is a cross-sectional schematic view of an exemplary embodiment of a sunlight conversion means applied in the solar energy utilizing apparatus according to the invention; Figure 4 illustrates schematically a possible embodiment of a Stirling engine direct drive water withdrawal system, wherein the Stirling engine is in fluid communication by its working fluid with a tungsten heating block according to the invention; Figure 5 is a schematic representation of a preferred embodiment of a water withdrawal system capable of tracking the Sun's movement in the day-time; and Figure 6 is a schematic representation of a yet further preferred embodiment of a water withdrawal system capable of also producing electricity with photovoltaic means and comprising a double water-cooling mechanism to ensure optimal operating conditions for the photovoltaic means.

Basically, the sunlight reflector elements, i.e. the solar mirrors of the solar energy utilizing apparatus according to the invention are preferably formed as isotropic concave (that is, spherical) mirrors and/or mirrors with the shape of a paraboloid of revolution (that is, parabolic mirror).

As far as the sunlight reflecting material of said sunlight reflector elements is concerned, gold (Au) and silver (Ag) can preferentially be used, however, their reflectivity of about 100% gets significantly impaired at about 500 nm, and in the wavelength range of about 500 to 350 nm or below for gold and silver, respectively. As is apparent, the sunlight reflector elements will transmit all the solar components that are not reflected thereby. Hence, an additional aluminium (Al) layer is also arranged behind said reflecting layers made of Au or Ag in the sunlight reflector elements of the apparatus according to the invention. In this way, although the Au or Ag layer transmits light with wavelengths of less than about 500 nm, the Al layer arranged behind (in the travelling direction of the incoming light) the reflection layer of said sunlight reflector elements will reflect light in the wavelength range of 200 to 500 nm (that is, light in the ultraviolet and visible domains) with very high efficiencies, thereby improving reflection efficiency of the reflector elements.

The sunlight reflector elements are formed by applying solar reflecting materials onto a surface of an appropriate shape, in the case of e.g. a parabolic mirror, onto a body with a shape of a paraboloid of revolution. Figure 7 (see below) illustrates such a solar mirror with the shape of a paraboloid of revolution, or rather a portion thereof, in cross-sectional view. Here, the Au/Ag reflection layer 2.2 is applied to a substrate 2.1 made of spinel, in particular, on a surface of the substrate 2.1 that faces in a direction opposite to the Sun when the mirror is in use, to this Au/Ag reflection layer 2.2 a further Al layer 2.3 is applied. Said reflecting metal layers are deposited by e.g. vacuum evaporation (and by means of further technological processes well- known in the field of e.g. lamp production). To the Al layer 2.3, a protective layer 2.4 is applied, said protective layer is a customary used protective layer well-known by a skilled person in the art. The protective layer 2.4 provides the mechanical protection (against e.g. abrasion, scratching) of the reflecting layers arranged underlying. The thus obtained reflective surfaces are used then to collect solar energy.

To this end, said surface of paraboloid of revolution made of reflective is oriented directly towards the Sun and thus it becomes also exposed to all environmental influences. When it gets aged and its reflection capability deteriorates, the sunlight reflector element is simply replaced. Another possibility is to alloy the metallic reflective surface with other metals so as to improve its wear resistance. Nevertheless, in practice, this kind of modification induces a decrease in the selective spectral reflectivity and thus results in a further decrease in the efficiency of solar energy utilization.

It is also an option to arrange a protective glass surface element above (in front of) the reflecting surface of the sunlight reflector element and this piece of glass element is replaced when needed.

U.S. Pat. Nos. 4,543,346 and 4,584, 151 disclose a sintered body made of a given mixture (spinel) of A1203 and MgO, as well as a process to produce said sintered body. The light transmission of a polycrystalline profile body obtained by the process, which is transparent in the visible domain, is about 77% at the wavelength of 600 nm and the thickness of 1 mm.

Nowadays, synthetic opto-ceramic spinel materials with better optical and mechanical properties can be produced; in particular, see e.g. the products by Surmet Corporation (31 B Street, Burlington MA 01803, USA) that have the light transmission of about 90% even for a material thickness of 2 mm.

Thus, the reflecting surfaces of the sunlight collector elements made use of in the solar energy utilizing apparatus according to the present invention are formed as concave (spherical, paraboloid of revolution) surfaces with focal points that are made of synthetic opto-ceramic glass (or putting other way, spinel), wherein the reflection coating (preferably, made of gold or silver, which is cheaper) is applied to the rear side of the spinel glass, said rear side facing in a direction opposite to the direction of the Sun. On top of said reflection coating, an Al layer is applied as the coating that reflects the light in the wavelength range below 500 nm. The synthetic spinel opto-ceramic "glass" used in the apparatus according to the invention is an MgA1204 poly crystalline material obtained by alloying aluminium-oxide, A1203, with magnesium oxide, MgO. Said spinel is the second hardest material after diamond, it is much harder than quartz, and thus than wind-borne quartz-sand (in particular, diamond, spinel and quartz have got Mohs hardness numbers of 10, 9 and only 7, respectively).

Said synthetic spinel has got an excellent light transmission over the whole solar radiation spectrum, hence almost no reflection or solar energy absorption arises when it is used as the substrate for the sunlight reflector elements. Its hardness (1600 kp/mm²), bending strength (170 MPa), melting temperature of 2135°C and specific gravity (3.58 g/cm³) makes the spinel suitable for accomplishing the objects of the invention. Furthermore, its expansion by heat is also negligible (its cubic thermal expansion coefficient is 6.97 x 10^~6 m.K/m³). Moreover, as its hardness is much higher than that of the abrasive particles present in the clouds of a desert sand storm, and it is also a relatively cheap material, said spinel is an ideal candidate for the construction of the sunlight reflector elements of the solar energy utilizing apparatus according to the invention.

In particular, the sunlight reflector elements, or the solar mirrors, are constructed through preparing a profile body with the shape of a paraboloid of revolution, then applying a coating of gold or silver to the surface of said body facing opposite to the Sun (later on, when in operation), and then applying a further layer of aluminium to the gold/silver-coated surface, thereby preparing the complete reflecting layer structure of the mirrors. Then, the surface of the thus obtained structure facing opposite to the Sun is provided by a customary protective means. Finally, the thus obtained solar mirror is arranged within an appropriate frame by means of a substance ensuring proper fixation to the frame and/or fitting elements.

In use, the frame with the solar mirror is moved, i.e. oriented towards the Sun by means of a customary mechanical construction known by a skilled person in the art, which is program- controlled as to the movements in this case. The thus obtained sunlight reflector elements, in particular parabolic solar mirrors, focus the light beams striking thereon into a single point, that is, the focal point of said paraboloids in revolution. (Here, due to the large distance between the Sun and the Earth, the sunbeams striking on the parabolic mirrors can be treated as parallel beams.)

It is also well-known from geometrical optics that a convex lens also focuses the light beams passing there through into a focal point. Moreover, it is also known that a light source positioned in the focal point of a convex lens results in parallel light beams on the opposite side of the lens. Consequently, in a geometrical arrangement wherein the focal point of the sunlight reflector element, i.e. specifically the parabolic solar mirror corresponds to that of a convex lens, which means that said lens functions as a condenser lens, the energy of the sunbeams collected by said parabolic mirror can be transported as a narrow and well-shaped beam. Moreover, based on the concept of the Galilean telescopes, the collected sunbeams may be focused and narrowed further that allows 'to aim' the head of a sunlight collecting column in a more precise manner

(compared to the case wherein a plane mirror simply bent to the shape of a parabola is applied for the same purpose).

In accordance with the present invention, the luminous energy carried by the sunbeams is projected with high precision onto e.g. a centrally located solar energy utilizing apparatus through a system of lenses optically coupled with the sunlight reflector element(s), specifically the one or more parabolic solar mirrors. This also results in an increase in the efficiency of solar energy utilization.

Figure 1 schematically shows a preferred arrangement to collect solar energy by means of an individual solar parabolic mirror and then direct the thus obtained solar energy in the form of a focused narrow beam to the place of making use of the solar energy. Here,

reference numeral 1 denotes sunlight striking on a parabolic mirror;

reference numeral 2 refers to the parabolic mirror itself that collects said sunlight;

reference numeral 3 refers to a focal point of said parabolic mirror;

reference numeral 4 denotes a condenser lens, a focal point of which coincides with that of said parabolic mirror, for producing a parallel beam leaving the parabolic mirror;

reference numeral 5 refers to a beam narrowing means comprising a system of appropriate lenses (in particular, e.g. a Galilean telescope);

reference numerals 6 denote beam directing elements, preferably prisms and/or plane mirrors; reference numeral 7 refers to a beam collected, collimated, narrowed and directed to the place of utilization, wherein

reference numeral 8 denotes the working fluid heating tungsten (W) heating block of the solar energy utilizing apparatus according to the invention.

The illustrated optical system, that is, the parabolic mirror and the system of lenses coupled with the mirror, is mounted with high precision to a parabolic mirror supporting and moving means through a bracing system having a very small expansion by heat in such a way that the optical axis of said parabolic mirror always coincides with the optical axis of the condenser lens (and thus of the a beam narrowing means as well). In this way, a required portion of the sunlight collector tower, even a point thereof, can be aimed by means of clockwork programmed prisms and/or mirrors that are moved as desired. Here, the prisms may be replaced by plane mirrors having appropriate reflectivity. As the prisms spectrally resolve the transported light beam and make it also divergent, plane mirrors deem to be more preferred if the beam of light has to be directed over a longer distance.

Thus, said parabolic sunlight collectors can always be oriented towards the Sun to the full extent, since by means of a collective synchronized movement of the system of prisms (and/or plane mirrors), it can be ensured that the beams of light collected by the parabolic mirrors and concentrated by the system of lenses always strike at right angle on the solar energy utilizing block (see Figure 1) that makes use of the beams as heat source to heat the working fluid of the solar plant to the required temperature. Hence, in this way there is no need for the "solar towers"; the solar energy produced by the parabolic mirrors can be directed from anywhere to the solar energy utilizing blocks (or apparatus) arranged even stationary on the ground. It is also apparent that there is no need to cover huge, biologically connected areas with solar farms and thus to ruin such areas; the rocky elevations around a planned solar plant, as well as the useless hillocks, etc. form ideal installation places for the above-discussed sunlight collector elements and the matched optical ancillary pieces of equipment.

As discussed above, the optical units of the solar energy utilizing apparatus according to the invention comprises the spinel instead of ordinary glass, as a result of which the efficiency of sunlight utilization becomes the highest compared to that of existing similar constructions in such a way that the wear resistance of said optical units exposed to environmental influences increases significantly relative to that of the substances used previously.

Due to its extreme hardness, spinel is produced on the industrial scale from molten aluminium oxide and magnesium oxide as abrasive material since 1920. This abrasive material comprises powdery microcrystals. Since it is a crystalline substance, one could try to produce synthetic spinel by sintering. At appearance, synthetic spinel is water-clear as glass is, however, its transmissivity (over the whole optical electromagnetic wavelength range) and structural strength are much higher than those of glass. Moreover, synthetic spinel can be used under pressure, too. As synthetic spinel is prepared by sintering, which process ensures that spinel crystallites (crystalline powders) get agglomerated and are fused into uniform homogeneous blocks in a cheap and bulky manner, synthetic spinel is highly preferred as the starting material for the profile bodies of the substrates used in the sunlight collector element.

Sintering (dense sintering) is a well-known powder metallurgical process, a heat treatment procedure. It includes a couple of different technologies, the best result can be achieved if during heat treatment pressing is applied simultaneously ("hot pressing"). The process temperature is always below the melting point of the workpiece, however, it approaches a value at about 90% thereof. To hinder chemical influences, the sintering process is generally performed in a protective gas atmosphere, thus a lateral evaporation of any incidental impurities is also allowed. When sintered, the workpiece undergoes a significant amount of change in size, it gets shrinked. The change arises due to the interdiffusion of the crystallites of the powder to be sintered at high temperatures, said crystallites fill the space available and form a uniform polycrystalline solid block after the sintering procedure, i.e. the crystallites will no longer form and behave as powder. Said hot pressing results in a better and more homogeneous sintered workpiece containing less pores. Consequently, it is a preferred powder metallurgical process to produce the profile bodies of the sunlight collector elements. In light of this, the solar mirrors and their auxiliary optical means are produced by means of a spinel sintering process performed under pressure, as is shown schematically in Figure 2, wherein

reference numeral 1 denotes a pressure-tight and heat-resistant power cylinder;

reference numeral 2 refers to pressure-tight and heat-resistant (pressing) upper and lower plungers arranged in the power cylinder at a temperature T and a pressure P of the sintering process; and

reference numeral 3 denotes the crystalline spinel MgA1204 powder to be sintered (i.e.

shrinked) in the system of said cylinder and plungers in a manner known to a skilled person in the art.

In practice, it is extremely difficult, if not impossible, to produce the profile bodies with a shape of paraboloid of revolution having larger dimensions, with a surface area of typically e.g. about 50 m². Nowadays, the demand for an accurate paraboloid design is getting higher and higher, and it is a clear tendency that even the profile bodies of the smaller-sized "domestic" parabolic solar mirrors are manufactured as planar sections and then the obtained sections are assembled to accomplish the profile body of the solar mirror with the shape of a more or less (i.e., approximating the) paraboloid of revolution.

In light of this, according to the present invention, the sunlight collector elements, in particular, the parabolic solar mirrors are manufactured, as discussed above, in the form of sections, wherein said sections are assembled to the profile body with the shape of a paraboloid of revolution at a later time. Nevertheless, according to the invention, instead of planar sections, said sections are manufactured in the form of sections with the shape of a paraboloid of revolution, thereby creating parabolic mirrors with much higher geometrical precision.

In particular, by means of using the above referred spinel like optical ceramics that can be sintered, a perfect parabolic solar mirror can be obtained. Thus, the focal point of said mirror becomes well-defined with a point-like behaviour. This allows proper matching of the condenser lens, and hence, the solar radiation collected can be directed in the form of a concentrated beam to any desired location. That is, we have realized that

- optical ceramics based on corundum A1203 crystals can be easily sintered if provided in the form of a crystalline powder, and thus synthetic polycrystalline profile bodies can be produced therefrom which are suitable for the manufacturing of sunlight collector elements, i.e. parabolic solar mirrors and respective auxiliary optical elements, since the desired production precision can be achieved; and

- if the spinel MgA1204 with the composition of MgO x A1203 is sintered into the desired profile body, such a solid, wear-resistant body is obtained that is hard enough and

simultaneously exhibits the best possible optical properties.

However, the available technological possibilities and limitations, such as e.g. manufacturing the huge sintering power cylinders and respective upper and lower plungers from substances of excellent material quality, providing the pressure-tight power cylinders with adequately large hydraulic systems, heating the ceramics powder to be sintered to high temperatures by electric heating over the large cross-sections concerned, ensuring homogeneity in relatively large volume portions, etc. set limits for realization in practice.

Nevertheless, on the one hand, the spinel sintering technique illustrated in Figure 2 in combination with the light directing system used in the solar energy utilizing apparatus according to the invention allows the manufacturing and application of solar mirrors in the form of several sections with shapes matching to a paraboloid of revolution, each section having a smaller surface of about 1 to 2 m² in size but prepared with a geometry of extremely high precision (mounted then onto one or more supporting/moving frames formed expediently), since the solar energy collected by the solar mirrors can be directed from the location of the collection by means of the optical system discussed previously to any other location.

On the other hand, it is also possible to manufacture several smaller spinel profile bodies (modules) with the shape of an exact paraboloid of revolution for the sunlight collector elements, which allows to direct the energy collected by each of the smaller (and/or larger) parabolic solar mirrors, acting as individual modules, to a single solar energy utilizing heating block. This solves the above discussed major process engineering problems: the working fluids (and/or working fluids, etc.) of the energy producing apparatuses (turbines, Stirling engines, etc.) to be used for doing work are heated by concentrating the solar energy collected by each of said smaller parabolic solar mirrors.

As it is clear, a major task of the present invention is to generate thermal energy. Therefore, the energy of the collected sunlight should be converted to heat at the highest possible (thermal) efficiency and/or used to heat the working fluid of the above discussed apparatuses. To this end, in accordance with the present invention and as discussed below in detail, the main unit of the high-efficiency solar energy utilizing apparatus, that is, the heating block for heating the working fluid, is formed as a specific element comprising tungsten (W).

As far as the scope of heat is concerned, in gases and liquids it is proportional to the speed of thermal motion of molecules, while in solids it is proportional to the vibrational and/or rotational energy of atoms and/or molecules (the internal energy of the substance). If the spectral energy distribution of the sunlight reaching the earth-surface (i.e. the solar spectrum) is considered, one can realize that only about 52% of the solar energy obtained by the parabolic mirrors falls into the infrared (IR, or thermal radiation) domain inducing direct heating of the substances, while about a half of it (48% of the solar energy) gets simply lost (from the point of view of thermal excitations, i.e. heating). Through an increase in the vibrational, rotational, as well as other molecular and/or atomic motion, the absorption of the infrared radiation increases the internal energy of the target (here, the block for heating the working fluid), and hence, its temperature, too, as the internal energy and the temperature is connected to each other through the well-known U = 3/2 kT + U(0) relation, wherein k stands for the Boltzmann constant and U(0) represents the initial internal energy of said target; this means, that the (increase in the) temperature T is proportional to the increase in the internal energy, and thus, the amount of the energy carried by the absorbed IR radiation.

It is also known, that the absorption condition for the visible and ultra violet (etc.) light radiation is that the energy of light should be equal to the energy difference dE between two quantized electron levels, that is, dU = h.f = dE holds (wherein h is the Planck's constant, and f stands for the frequency of said light). For further details, see e.g. the university notes

'Experimental atomic and molecular physics' by Dr. Patko and Dr. Harangozo, made publicly available by the Department of Solid States Physics of Kossuth Lajos University (Debrecen, 1986, p. 35)

One can easily understand that substances of covalent or ionic binding cannot absorb significant amounts of energy from the visible and ultra violet radiation domains of the solar spectrum that make out 48% of the total solar energy. To enhance, thus, such absorption, a novel industrial technique has been developed.

This technique is based on the finding that the metallic substances are such specific

(metal)crystals, in which the (kernels of the) metal atoms form covalent bindings with each other by means of the inner electrons of the electronic shells (and this leads basically to a lattice structure of metals), while the electrons of the external electronic shells create an electronic cloud of free electrons, i.e. electrons with non-quantized energy, around said lattice of the metal atoms. As the electrons of said electronic cloud are not forced to occupy quantized orbits, they can be excited by light of practically any frequency. Hence, an electromagnetic radiation of any frequency will increase the internal energy of the crystalline, polycrystalline solid metals and metal alloys, and thus, in the present case, also the temperature of a heating block that absorbs light radiation in the solar spectrum.

In light of this, the collected sunlight in the solar spectrum is utilized by means of heating a member provided in the form of a metallic block, i.e. the heating block itself, and the working fluid (that will drive e.g. a turbine) is heated with the heat generated in said metallic block (similarly to what takes place in a furnace or a smelter). As the metal to be used to convert the energy of sunlight in the solar spectrum into thermal energy used to heat the working fluid flowing through the block made of the metal, metals with high melting point can be chosen. Evaluating certain other properties of such metals, such as their evaporation characteristics, expansion by heat, heat endurance, chemical properties, etc. tungsten is chosen for this purpose, since it has the possible highest melting point amongst the applicable metals. When choosing tungsten, it is also taken into account that a tungsten filament heated to the operation temperature of incandescent lamps, i.e. to about 2000 to 3000°C, will radiate only about 10% of the energy supplied into it electrically as visible light and emits the remaining amount of said energy in the IR domain as heat. Or putting this another way, in the inventive new technique, to convert solar energy, a sunlight conversion material exhibiting, on the one hand, absorption characteristics corresponding substantially to Planck's black-body radiation within the solar radiation spectrum for the sunlight incident thereon, and, on the other hand, emission characteristics corresponding to emission exclusively at a colour temperature that corresponds to a heating of said sunlight conversion material by the solar energy absorbed are made use of.

In particular, if a target made of tungsten (W) is used, the heating performed by the sunlight collected by means of the sunlight collector elements according to the invention, in particular, the parabolic solar mirrors, may result, and in practice preferably results, in temperatures that fall into the range of 900 to 1200°C, that is, a radiation in the infrared domain. That is, essentially 100% of the solar energy collected by means of said sunlight collector elements is utilized in the form of heating the tungsten block. To this end, the working fluid to be heated (i.e. the steam to be directed to the turbine, the working fluid of a Stirling engine, etc.) is led through cavities formed within the bulk of the tungsten block (in particular, through tungsten tubes also sintered into the tungsten block), wherein said working fluid gets heated and evaporates, or the gas used as the working fluid gets heated, even to extreme high temperatures. Thus, the energy supplied through the sunlight into the heating block made of tungsten is used to heat up at first the block itself and then the working fluid.

Here, the aim is to reach the possible highest temperature that can be used in power generation, since in that case the electric power generation efficiency (see e.g. the Carnot-cycle, the Rankine-cycle, etc.) of the turbines or Stirling engines (wherein, as is known by a skilled person in the art, said electric power generation efficiency is defined by the temperature difference of Th-Tc/Th) is increased.

Since the sunlight collector element, i.e. the parabolic solar mirror (with the working fluid heating block) moves (that is, tracks the Sun along the path it travels during a day), the high pressure and high temperature working fluids can be led to the turbines in tubes that are extreme pressure-tight and resist to high temperatures, as well as are heat insulated and flexible. Such tubes are very specific and expensive, rarely used in everyday life, but available.

The solar energy utilizing apparatus according to the present invention comprises a sunlight conversion means formed as a stationary (working fluid heating) heating block being fixedly connected to a unit performing work, such as a turbine block or e.g. a Stirling -engine; the sunlight collected by means of the solar collector element(s), in particular the solar mirror(s), is directed onto the sunlight conversion means, wherein it is converted into thermal energy in an arrangement, a possible exemplary embodiment of which is illustrated in Figure 3. Here, reference numeral 1 stands for a tungsten metallic block manufactured by means of powder metallurgy;

reference numeral 2 denotes a tungsten tube that passes through the tungsten metallic block, the working fluid, in operation, flows in this tube;

reference numeral 3 represents synthetic spinel opto-ceramic "glass" elements;

reference numeral 4 stands for a heat insulation that encases the tungsten metallic block;

reference numeral 5 denotes a reinforcing support (steel) casing that encloses said insulated tungsten block;

reference numeral 6 denotes heat-insulating vacuum; and

reference numeral 7 stands for a layer of colloidal graphite, said graphite layer is arranged between the tungsten block and the spinel glass element covering the tungsten block and acts to improve the contact between the tungsten and spinel, and also deteriorates the albedo of the surface of the tungsten block.

A possible field of application for the solar energy utilizing apparatus according to the present invention, apart from the traditional electric power generation through steam power, is agricultural irrigation, wherein the unit performing work is preferably a Stirling engine that is in direct fluid communication with the heating block. In what follows, as a yet further aspect of the invention, one possible such application of the solar energy utilizing apparatus is discussed in detail. This exemplary application to be explained here, as is clear for a skilled person in the art, nevertheless, does not represent the only possible application of the solar energy utilizing apparatus according to the invention. For the time being, the most common means used to utilize solar energy are the solar mirror power plants with power generating turbines, however, today it is also an object to increase the efficiency of solar energy utilization by applying Stirling engines to generate electric power and then to operate the water withdrawal pumps e.g. on the obtained electric power.

Hence, in a further aspect, the present invention relates to an improved technique for water withdrawal by means of a Stirling engine fluidically coupled to the heating block of a solar energy utilizing apparatus according to the invention which is a cheap and stable solution and has enhanced efficiency. In what follows, the technical details are discussed.

The Stirling engine, or thermomotor, is an external-combustion heat engine which is constructed, in general, with a piston-crank mechanism. Contrary to internal -combustion engines, the heat source of the Stirling engine is not the fuel that is burnt in the cylinder, like in the case of the Otto- and diesel-engines, or (e.g. gas) turbines, but it locates outside of the engine. The heat exchange process applied in the Stirling engines allows to achieve the possible highest efficiency for the Stirling engine amongst the heat engines; its efficiency almost reaches the efficiency of such an ideal Carnot cycle that can be realized in practice by making use of available structural materials. The Stirling engine comprises a given mass of gas, generally, air, hydrogen or helium separated from the environment through sealings. The characteristic values (for example, pressure, temperature, specific volume) of this gas change in accordance with the gas laws. When the given volume of gas in in the engine is heated, its pressure increases and the gas performs mechanical work in the expansion period through acting on the surface of the piston. When the gas is cooled, its pressure decreases which means that the difference in the energy of the two states can be used to perform work. This difference in energy appears as useful work on the output of the engine. (Here, the gas circularly flows between the heating and cooling heat exchangers.)

The thermodynamical efficiency of the Stirling cycle is equal to that of the Carnot cycle which, in principle, is the highest. The efficiency of the Carnot cycle is

h = 1 - ( Tc / Th )

wherein

^• Th (T hot) is the temperature at the hot side, and

· Tc (T_cold) is the temperature at the cold side.

This means that the greater the difference in temperature between the "hot side" and the "cold side", the higher the theoretical thermodynamical efficiency is. In case of Stirling engines, an efficiency of as high as about 40 to 50% can be obtained. The existing solar mirror driven Stirling engines are constructed in such a way that the Sun's rays coming from the parabolic mirror heat the hot side of the engine, while to cool the working fluid of the engine, a cooling fan is installed at the cold side. Heating of the "hot side" changes from type to type of the Stirling engines, however, the commonly used solution according to which the working fluid of the Stirling engine passes, generally, in front of ordinary optical heating blocks, seems to be far from optimal. Neither it is advantageous to provide the "cold side" of the Stirling engines with cooling fans and cooling radiators (as is the present practice), since current drain of these additional means decreases the amount of useful energy produced.

A yet further difficulty of Stirling engines with parabolic mirrors is that the problem of how to prepare large-sized parabolic mirrors with the accurate shape of a paraboloid of revolution has not yet been solved. Nevertheless, sintering spinel like optical ceramics in accordance with the present invention, as discussed above, actually solves this problem. However, in everyday practice, only an approximate construction is used, that is, plane mirrors are mounted onto a parabolic-like (metallic) frame; such an approximate solar mirror construction has got no well- defined focal point.

If an accurate paraboloid mirror is used which has a unique focal point, the solar energy collected by said mirror can be led away by means of the above discussed optical arrangement as said unique focal point can be matched with the focal point of a condenser lens. However, in case of a mirror approximated by plane mirror segments mounted on a parabolic frame, one will immediately notice, by means of e.g. geometrical construction, that the paths of rays do not intercept each other at a single point (i.e. the focal point) but pass through an ellipsoid of revolution. It is also clear from such a construction that said ellipsoid of revolution defined by the paths of rays could be enclosed into a rectangular solid.

Hence, according to a further aspect of the present invention, said ellipsoid of revolution with the enclosing theoretical rectangular solid is formed as a tungsten block as discussed above, because physical properties of tungsten, in particular, its melting point of 3422°C, thermal expansion coefficient of 4.5 μπι/ιη.⁰€, heat conductivity of 173 W/m.°C and even its vapour pressure coefficient are extremely advantageous from the point of view of the aimed heating and heat producing objectives.

Thus, in harmony with the above discussed and in a yet further aspect of the present invention, the following construction is proposed for heating the "hot side" working fluid of Stirling engines:

- by means of the customary, long-standing and well-known powder metallurgical process by Tungsram Zrt. to be discussed below in more detail, a rectangular solid or block made of tungsten (W) is produced with such length and width dimensions that correspond to those of a rectangular solid enclosing the ellipsoid of revolution matching with the "focal point" of said parabolic(-like) solar mirrors; the height dimension of said tungsten rectangular solid is tailored to the volume of the working fluid to be heated. To allow to direct the working fluid of the Stirling engine in use through said tungsten rectangular solid (see e.g. Figure 3) obtained by powder metallurgy an appropriate passage is provided within the volume of the rectangular solid in the form of preferably e.g. a pipe or a continuous coiling made of tungsten (or any other chemically resistant metal that has a high melting point as well). Preferably said pipe/coiling is compressed into the tungsten rectangular solid when the powder metallurgical step is performed to prepare said rectangular solid. The design (e.g. length, diameter) of said passage, in particular, of pipe, continuous coiling, etc. is determined by the volume flow and the flow rate of the working fluid to be heated; thickness (height dimension) of the tungsten block prepared by powder metallurgical sintering is chosen to conform to these latter parameters;

- a surface of the thus prepared tungsten block facing towards the solar mirror is coated by optical ceramics that withstand to even strong abrasive impacts, but exhibit an excellent light transmission property. To this end, most preferentially, spinels or spinel like synthetic ceramics are made use of which are MgOxA1203 type optical ceramics (i.e. magnesium oxide combined with corundum). In this way, a protective coating - a material of which is also cheap - with a hardness being significantly greater than that of abrasive particles in desert quartz sand storms is achieved; hence, synthetic ceramics represent highly advantageous constructional substances for the inventive solutions.

A yet further important characteristics of spinel is that the light transmissivity of a plate of 2 mm in thickness made of spinel is about 90% over the complete solar spectrum present on the earth- surface - to coat said tungsten block on its front surface in order to provide a proper mechanical protection of the block, however, a much thinner spinel layer is already adequate.

A yet further advantageous property of spinel materials, which is also of great technological importance, is that micro-crystallite powders of spinels used for preparing synthetic profile bodies can be easily sintered, that is, their sintering is simple and can be performed directly onto the novel tungsten heating blocks to be applied in Stirling engines according to the present invention. In particular, said sintering can be accomplished with perfect contact with tungsten surfaces, thereby protecting said tungsten surfaces from any chemical actions, mainly from oxidation, besides the already mentioned abrasive impacts. The obtained tungsten (W) heating blocks according to the invention which perform the heat-up of the working fluid of Stirling engines are then heat insulated on the remaining side faces thereof, and mounted in front of parabolic solar mirrors by means of stable support structures in a manner similar to what is shown in Figure 3. Nowadays, Stirling engines installed in front of parabolic mirrors are mostly used for electric power generation, moreover, a part of the thus produced electric power is used to energize the built-in cooling fan of the Stirling engine; although, in this way, the high mechanical efficiency of Stirling engines (which is proportional to the fraction of [T(h) - T(c)] / T(h) and, in principle, equals to it) is deteriorated by the low efficiency of the electric power generation. (Furthermore, as it was already discussed above, the amount of electric power that can be transported to a distant consumer is decreased by the fact that "cold side" cooling of present Stirling engines is performed by cooling fans which are energized by the electric power produced on the spot.)

As one of our present objects is to develop Stirling engine water withdrawal pumps to irrigate desertifying arable lands, and the irrigation of arid agricultural areas is aimed to accomplish chiefly with ground waters (of various origin) withdrawn from below earth on the spot, the irrigation techniques applied nowadays can be enhanced by means of synergistically combining some elements thereof. In particular, Stirling engines driven by parabolic mirrors according to the invention are used to do mechanical work at the excellent mechanical efficiency, instead of generating electric power. That is, a load transmission arm on the output side of the Stirling engine is used to drive a direct water withdrawal pump, i.e. the Stirling engine drives an arm that is coupled to a swivel arm of the pump arranged in a well to be used as water source by a customary articulated mechanism. At the same time, cooling of the "cold side" working cylinder of the Stirling engine is effected by the relatively cold water withdrawn from below earth, and thereby, a temperature difference which is reasonably large and almost constant over time arises between the temperature of the hot working fluid provided by a tungsten heating block according to the invention heated by a parabolic mirror and the "cold point" of said Stirling engine. In this way, both the stable operation conditions for and the high mechanical efficiency of the Stirling engine driven water pump according to the invention are ensured.

A schematic constructional diagram of such a water withdrawal system is shown in Figure 4, wherein

reference numeral 1 denotes striking sunlight;

reference numeral 2 stands for a parabolic solar mirror collecting said sunlight;

reference numeral 3 refers to a common focal point of the parabolic mirror and a condenser lens, from which concentrated solar energy is transported by means of a mirror and/or prism light guiding arrangement discussed above in detail onto a tungsten (W) heating block of a Stirling engine;

reference numeral 4 refers to a water pump having a Stirling engine combined with a heating block;

reference numeral 5 represents cooling of the Stirling engine by means of water pumped out from a stationary well; reference numeral 6 represents transportation of the pumped-out water for irrigation purposes or into a storage facility; and

reference number 7 refers to the drilled well suitable for water withdrawal.

Thus, the afore-discussed agricultural irrigation technique according to the invention based on local water withdrawal also provides a reliable and stable cooling of the "cold side" of the applied Stirling engine besides retaining the excellent mechanical efficiency of Stirling engines and the availability of a very hot working fluid heated by solar energy. Moreover, this technique is not a service-intensive technique.

It is also possible to further decrease the costs and increase the efficiency of the mechanical construction to accomplish the present inventive technique. Thus, a practical and simpler embodiment of the water withdrawal system can be obtained. In particular, nowadays, Stirling engines are installed into the approximate "focal point" of a mirroring configuration which is considered to be a parabolic mirror. Hence, both the engines and the supporting

elements/components therefor shadow the solar mirror to a great extent. Furthermore, it is also a reasonable technical/technological challenge to fix the Stirling engines to said mirrors in a sufficiently stable manner, balance the centre of gravity of the relatively heavy engines, as well as compensate for the effects of the occasional vibrating motion of the engines - each of these alone represents a yet solvable task.

Contrary to this, the working fluid of the Stirling engine flows through the tungsten heating block according to the invention and is heated to very high temperatures; said working fluid can be led anywhere in the vicinity of the parabolic(-like) mirror in heat insulated pipes and into the "hot side" working cylinder of the fixedly arranged Stirling engine. That is, it is sufficient to mount merely the tungsten (W) heating block which heats up the working fluid into the appropriate location of the parabolic mirror and direct the hot working fluid flowing through the heating block into a Stirling engine arranged at a different location. However, the aforementioned problem according to which the parabolic mirror tracks the Sun's movement, i.e. in the day-time, in operation, it moves both vertically and horizontally, also arises here. Hence, to track said path, in particular, heat-resistant and pressure-tight, as well as flexible pipes/pipings are applied for directing the hot working fluid.

In a yet further aspect, the present invention thus provides another simple, but highly practical water withdrawal system based on a Stirling engine with water-cooling on its cold side (the system is installed in a well), said water-cooling using water as the cooling medium won by the system itself from the well, wherein

- a tungsten heating block according to the present invention is arranged at the focus discussed above (or the "quasi focus") of the parabolic mirror in such a way that said heating block is attached to the support frame of the parabolic solar mirror construction that holds the mirrors (also tracking the Sun's motion) by means of at least one tube that withstands to heat and is suitable for the intended use from the chemical point of view, too (in particular, in case of a Stirling engine with the working fluid of e.g. gaseous krypton (Kr), strong, but relatively light- weight and heat-proof titanium (Ti) tube(s) will be excellent choice as said tube(s));

- the Stirling engine itself is arranged and fixed onto the side of a support grid of the parabolic mirror system, said side of the grid facing away the Sun and said grid being configured to be moved in a program -controlled manner, if possible, along a symmetry axis defined by the tungsten heating block and the parabolic mirror system so as to also decrease the torque that might act on the supporting structure of the mirrors (this provides an additional minor technical advantage);

- the working fluid (e.g. gaseous krypton) coming from the tungsten heating block according to the present invention is fed into the Stirling engine through said supporting tube(s) (made of e.g. titanium) attached to the hot side of the engine, while on the cold side of said engine, already the pumped-out (cooling) water circulates;

- in this way, on the one hand, the Stirling engine can be connected to the water withdrawal well-head by means of a flexible water-piping tube (made, particularly, of rubber, silicone, etc.) which has appropriate (water) volume flow rate through its cross section, is pressure-proof and adapted to ambient conditions (sunshine, variation in temperature, etc.), and, on the other hand, said cooling water pumped out from the well is directed through (partially or fully) the cooling part of the Stirling engine, and then can be transported to a spraying head for irrigation or into any other water storage tank (e.g. a pool) by means of similar flexible tubes.

Such a water withdrawal system capable of tracking the Sun's movement in the day-time is shown schematically in Figure 5, wherein

reference numeral 1 represents striking sunlight;

reference numeral 2 stands for the reflecting surface and the frame structure of a parabolic solar mirror collecting sunlight;

reference numeral 3 refers to the projection of the reflected sunlight onto the tungsten (W) heating block according to the invention;

reference numeral 4 represents the heater used to heat up the working fluid of the Stirling engine;

reference numeral 5 represents an input pipe for the cold working fluid;

reference numeral 6 stands for an output pipe for the heated working fluid;

reference numeral 7 refers to a built-in Stirling engine;

reference numeral 8 denotes a pump (preferably a centrifugal pump); reference numeral 9 refers to a tilting mechanism of the parabolic solar mirror system (for tracking the Sun's movement vertically);

reference numeral 10 represents the firmly affixed pipeline for the hot working fluid;

reference numeral 11 stands for a trimming water tank;

reference numeral 12 represents a flexible water hose (or pipe/tube) tailored to technical needs; reference numeral 13 denotes the well-head;

reference numeral 14 represents a flexible water discharge pipe tailored to technical needs; reference numeral 15 refers to a rotating mechanism of the parabolic solar mirror system (for tracking the Sun's movement horizontally); and

reference numeral 16 denotes an output pipeline for discharging withdrawn fresh water, e.g. for irrigation.

It should be here also noted that a working fluid of extremely high temperature and pressure can be produced, if the heated working fluid is directed through more than one tungsten heating blocks connected in series. The thus obtained working fluid can be equally used as the working fluid of "traditional" power generators to drive them and thus to generate electric power in the traditional sense.

Furthermore, if the hot working fluids coming from more than one tungsten heating blocks according to the invention are integrated, by means of e.g. connecting said heating blocks in parallel, to drive a traditional power generator, practically, an arbitrary amount of hot working fluid can be produced. In this way, larger electric plants with turbines can also be operated with the hot working fluid obtained by the inventive tungsten heating blocks. Alternatively, instead of connecting the heating blocks in parallel, to heat up a larger amount of working fluid, the solar energy connected by a set of (smaller) solar mirrors with the precise shape of a paraboloid of revolution is directed onto the heating portion of a tungsten heating block of larger capacity. In a yet further embodiment, the high-capacity tungsten heating block is simply rotated out of its position at the centre of the solar mirror from time to time or the solar energy collected by the parabolic mirror is projected temporarily onto a photovoltaic panel by means of a reflecting surface arranged in front of the heating block in the path of the collected solar energy, and thus a suitably designed secondary battery is charged by the current generated, as is illustrated in Figure 6. In this way, amongst others, for example, an internet and/or mobile connection would also become available, e.g. in case of emergency, on farms located far away from inhabited areas.

In light of the afore-mentioned, in a yet further aspect of the invention, the advantages of photovoltaic current generation and those of a parabolic mirror/Stirling engine driven water withdrawal system are combined synergistically. In particular, the photovoltaic panel is driven by either a parabolic mirror, the solar energy of which is shared between the panel and the water withdrawal system, or an additional further parabolic mirror, as is illustrated in Figure 6. Here, synergy arises as (the semiconductor elements of) the photovoltaic panel (have) has an optimal working temperature below which (they) it (output) outputs very small currents, however, too high temperatures decrease the efficiency of the panel and, in extreme cases, may damage the panel itself (thermal degradation). To avoid this latter negative scenario, the water withdrawn by the Stirling engine driven water pump is used to cool the photovoltaic panel as well, besides cooling the working cylinder of said Stirling engine. That is, the temperature of the photovoltaic panel is adjusted to the optimal operation temperature by a part of the water withdrawn. Thus, a preferred embodiment of the water withdrawal system of the present invention comprises a double water-cooling mechanism, as is shown in Figure 6; here, the spent water or the surplus in withdrawn water is simply directed into a reservoir for further use, e.g. irrigation.

The water withdrawal system combined with a photovoltaic panel is shown schematically in Figure 6, wherein, in the right side of Figure 6, there is shown a Stirling engine water withdrawal system according to a preferred embodiment of the invention discussed in detail with reference to Figure 4, and wherein

reference numerals 1 represent striking sunlight;

reference numerals 2 denote parabolic solar mirrors;

reference numerals 3 denote the common focal point of each parabolic solar mirror and the respective condenser lens, from one of these points concentrated solar energy is directed onto the tungsten heating block of the Stirling engine by means of the mirror and/or prism light guiding arrangement discussed above (see the construction at the right side of the figure); reference numeral 4 denotes a Stirling engine water pump combined with a tungsten heating block;

reference numeral 5 represents a water-cooling of the Stirling engine effected by water withdrawn from a well;

reference numeral 6 represents the discharge of the pumped-out water for irrigation or into a reservoir (etc.);

reference numeral 7 represents a drilled stationary well suitable for water withdrawal.

Furthermore, a part of the solar energy collected by the parabolic solar mirror 2 or the solar energy collected by the additional parabolic solar mirror 2 (see the left side of the figure) is directed onto said photovoltaic panel, wherein, in Figure 6,

reference numeral 8 denotes said photovoltaic panel generating electric current;

reference numeral 9 refers to a water cooled radiator of the photovoltaic panel;

reference numeral 10 denotes a discharge pipe with a controlled water flow rate (to accomplish cooling of the photovoltaic panel through its heat-exchanging type cooling radiator); reference numeral 11 represents pipelines for discharging "spent" water;

reference numerals 12 and 13 stand for current conductors connected to a (secondary) battery unit;

reference numeral 14 denotes the battery unit that stores current and serves to prime electric units (e.g. a satellite telecommunication device) for the operation thereof.

Optionally, water reservoir 15 can be used to subsidiary fish breeding. As is clear for a skilled person in the art, further specific agricultural synergies can also be exploited by the solutions according to the present invention.

SUMMARY:

(a) By inserting tungsten (W) blocks into reflected and concentrated beams generated by parabolic solar mirrors, and thereby allowing to exploit for heating purposes both visible and ultraviolet sunlight reaching the earth-surface through the atmosphere, the present invention has increased the efficiency of solar energy utilization for heating by about 48%.

(b) The pipes made (typically) of tungsten for circulating the working fluid of a Stirling engine to be heated are arranged in said tungsten heating blocks of proper design, and hot working fluid is fed into a working cylinder of a Stirling engine. Thus, the heating block could be separated from the engine itself that allows to mount, instead of the whole Stirling engine, merely the smaller and more stable tungsten heating block in front of the parabolic solar mirror - the Stirling engine can thus be arranged at any other suitable place.

(c) As it is the mechanical efficiency of Stirling engines that is extraordinary high, Stirling engines are used primarily for water withdrawal from wells by pumps doing mechanical work directly, instead of generating electric power. Thus, in comparison to the case of producing at first electric power and then withdrawing water from wells by applying electric pumps operated on the electric power produced, a significant increase in efficiency has been achieved.

(d) To cool the working cylinder of a Stirling engine, it is common practice nowadays to apply one or more air-cooled radiators cooled by respective fans. On the contrary, the present invention applies water-cooling, wherein withdrawn water is used to perform cooling of the "cold side" working cylinder of the Stirling engine. In this way, not only energy can be saved - and thereby water withdrawal efficiency of the system can be increased - but, by creating a "cold point" that is stable over time, operation safety of the Stirling engine itself gets improved. Moreover, as the withdrawn water has got, in general, a smaller temperature than what can be achieved by means of fans/cooling radiators, the efficiency of the Stirling engine made use of has also been increased.

Claims

1. A solar energy utilizing apparatus to utilize radiation in the solar radiation spectrum available at the earth-surface, that is, in portions of the solar spectrum in the visible (VIS) and ultraviolet (UV) frequency domains, by means of converting radiation in said solar radiation spectrum into infrared radiation (IR), said solar energy utilizing apparatus comprising

~ a sunlight collector means to collect energy of the radiation in the solar radiation spectrum into substantially a single point, and

~ a heating block in the form of a sunlight converter means comprising sunlight conversion material to receive and absorb the collected solar energy in the solar radiation spectrum, thereby converting said solar energy into infrared radiation, wherein at least a region of said sunlight converter means is arranged to contain said single point, characterized in that

the sunlight conversion material exhibits absorption characteristics corresponding substantially to Planck's black-body radiation within the solar radiation spectrum for the sunlight incident thereon, and

the sunlight conversion material exhibits emission characteristics corresponding to emission exclusively at a colour temperature that corresponds to a heating of said sunlight conversion material by the solar energy absorbed.

2. The solar energy utilizing apparatus according to claim 1, characterized in that tungsten (W) is used as the sunlight conversion material.

3. The solar energy utilizing apparatus according to claim 2, characterized in that said sunlight conversion material is provided as tungsten metal powder sintered to a shaped metal block.

4. The solar energy utilizing apparatus according to any one of claims 1 to 3, characterized in that the apparatus further comprises a system of hollow passages formed in the bulk of the metal block constituting said sunlight conversion material to allow flowing of a working fluid therein, wherein the system of hollow passages is provided with at least one inlet for entry of the working fluid into the sunlight conversion material and at least one outlet for exit of said working fluid from the sunlight conversion material, and wherein said system of passages and said sunlight conversion material are arranged in heat transfer connection with each other.

5. The solar energy utilizing apparatus according to any one of claims 1 to 4, characterized in that the system of passages is provided as a tube or tubing made of a metal of high melting temperature.

6. The solar energy utilizing apparatus according to claim 5, characterized in that the tube or tubing is made of tungsten.

7. The solar energy utilizing apparatus according to any one of claims 1 to 6, characterized in that the sunlight conversion material in said sunlight converter means, except in a region of a certain area around the substantially single point, is enclosed by heat insulation, said heat insulation is enclosed by a casing made of a substance with high tensile strength, wherein the region of a certain area around the substantially single point is covered by at least two plates, said plates are located at a given distance apart from each other, arranged connected to the heat insulation and made of an opto-ceramic material being transparent substantially in the entire solar radiation spectrum, and wherein one of the at least two plates bears on said sunlight conversion material and there is provide vacuum between the at least two plates.

8. The solar energy utilizing apparatus according to claim 7, characterized in that a layer of colloidal graphite is arranged between the sunlight conversion material and the plate bearing on said sunlight conversion material.

9. The solar energy utilizing apparatus according to claim 7 or 8, characterized in that a synthetic spinel of the formula MgAhC with high hardness is used as the opto-ceramic material.

10. The solar energy utilizing apparatus according to any one of claims 1 to 9, characterized in that the apparatus further comprises a sunlight transferring means to perform optical imaging of a location of said substantially single point, the sunlight transferring means is arranged between the sunlight collector means and the sunlight converter means, wherein optical image of said single point is located in said region of the sunlight converter means.

11. The solar energy utilizing apparatus according to claim 10, characterized in that the sunlight transferring means is constructed as a combination of optical elements, wherein said optical elements are configured to direct the collected energy in the solar radiation spectrum along a pre-defined optical path.

12. The solar energy utilizing apparatus according to claim 11, characterized in that optical elements, in particular one or more convergent lenses or divergent lenses, prisms and mirrors with metallic reflection coating, made of synthetic spinel of the formula MgAhCH with high hardness are used as the optical elements.

13. The solar energy utilizing apparatus according to any one of claims 1 to 12, characterized in that the sunlight collector means has got a shape of a rotation paraboloid or a spherical shape bound by a front surface and a rear surface when viewed from a direction of incident light, wherein there is provided a reflection coating on the rear surface that reflects essentially over the entire solar spectrum, and wherein said sunlight collector means is made of a substance with high hardness, high melting temperature, low thermal expansion and large optical transmissivity over the solar spectrum.

14. The solar energy utilizing apparatus according to claim 13, characterized in that the sunlight collector means is fabricated as a single element or consists of several segments fitted together with high precision.

15. The solar energy utilizing apparatus according to claim 13 or 14, characterized in that the optical transmissivity of the substance of the sunlight collector means is at least 85% at any frequencies in the solar spectrum for a substance thickness of 2 mm.

16. The solar energy utilizing apparatus according to any one of claims 13 to 15, characterized in that the Mohs' hardness of the substance of the sunlight collector means is at least 8.

17. The solar energy utilizing apparatus according to any one of claims 13 to 16, characterized in that the melting temperature of the substance of the sunlight collector means is at least about 2000°C.

18. The solar energy utilizing apparatus according to any one of claims 13 to 17, characterized in that the coefficient of linear expansion of the substance of the sunlight collector means is at most 8xlO^"6 m/m.K.

19. The solar energy utilizing apparatus according to any one of claims 13 to 18, characterized in that optical ceramics or spinels obtained through sintering crystalline or poly-crystalline powdered MgAhCH is used as the substance of the sunlight collector means.

20. The solar energy utilizing apparatus according to any one of claims 13 to 19, characterized in that a first reflection coating is arranged on the rear surface of the sunlight collector means, and a second reflection coating is arranged on the first reflection coating, wherein said first reflection coating has got a reflectivity of about 100% for any wavelengths of the solar spectrum below a certain threshold wavelength, and wherein said second reflection coating has got a reflectivity of about 100% for any wavelengths of the solar spectrum above said certain threshold wavelength.

21. The solar energy utilizing apparatus according to claim 20, characterized in that said threshold wavelength is about 500 nm, and said first reflection coating is made of gold and/or silver, and said second reflection coating is made of aluminium.

22. The solar energy utilizing apparatus according to any one of claims 1 to 21, characterized in that the sunlight collector means is provided with a support frame and equipped with computer- controlled electro mechanics configured to track the Sun both horizontally and vertically.

23. Use of the solar energy utilizing apparatus according to any one of claims 1 to 22 to heat the working fluid of a power machine, said power machine being spatially separate from but in fluid communication with the solar energy utilizing apparatus, wherein the working fluid of the power machine is directed through the inlet, the system of passages and the outlet formed in the sunlight conversion material at a pre -set flow rate.

24. The use according to claim 23, wherein a Stirling engine is used as the power machine, said Stirling engine having a hot side, a cold side and a connecting rod, wherein the sunlight converter means is configured to form said hot side, the connecting rod is operatively connected with a swivel arm of a pump arranged within a stationary well, and heat exchange effected with a portion of the fluid withdrawn from the well by operating the pump provides said cold side.