WO2014126472A2

WO2014126472A2 - Device for simultaneous harvesting of solar heat and generation of cold by means of emitted radiation

Info

Publication number: WO2014126472A2
Application number: PCT/NL2014/050096
Authority: WO
Inventors: Evert DU MARCHIE VAN VOORTHUYSEN; Ronald Roes
Original assignee: Solaq B.V.
Priority date: 2013-02-17
Filing date: 2014-02-17
Publication date: 2014-08-21
Also published as: WO2014126472A3

Abstract

A device for harvesting solar energy and radiation cooling, comprises a solar collector which for instance is composed from mirrors, solar collectors and/or photo- voltaic solar panels, and a collector for infra-red radiation with a long wavelength configured for generating cooling by means of outward radiation from a radiating surface. The solar collector is configured to bring about, that a selection of the infra¬ red radiation incident on the radiating surface, wherein the selection is performed such, that mainly infra-red radiation from the coldest parts of the sky is incident on the radiating surface, or that the solar collector itself functions as radiating surface.

Description

Device for simultaneous harvesting of solar heat and generation of cold by means of emitted radiation.

Field of t e invention

In general the invention relates to a combined device for the harvesting of solar energy including photosynthesis and for the generation of cold.

Background of the invention

Concentrating solar power is mainly applied in countries with a dry, sunny climate. One distinguishes here the harvesting of energy by means of mirror fields, in particular parabolic trough mirrors, in large solar thermal power plants, and harvesting of energy in smaller installations, wherein in most cases only heat or photo-voltaic electricity is harvested. The first technology is called Concentrating Solar Power (CSP), the second is called Concentrating Photo-Voltaics (CPV).

With concentrating solar energy systems, it applies in general that always at least one degree of freedom of movement is necessary in order to concentrate the reflected and/or refracted solar rays during the whole day on one line, respectively on solar cells. In case of floating parabolic trough mirrors this is achieved by mounting the mirror field on a floating member, which is floating on a liquid medium, for instance a sea, a lake or a basin and by rotating this floating member in the course of the day as a whole.

In the American patent specifications US 4,148,301 and US 4,296,731 floating, rotating fields with concentrating mirrors or lenses are described. Other descriptions of floating, rotating systems with concentrating mirrors can amongst others be found in US 4,350,143, US 4,786,795, US 5,445,177, WO 2009/001225, US 2010/059046, WO 2008/015064, US 2009/314926, US 4,786,795, and WO

2009/090538.

Apart from coastal locations in most countries where solar energy is employed it is a problem to obtain sufficient water for the cooling towers that are needed for cooling the condenser in a CSP-plant and for the discharge of heat in solar driven absorption and adsorption processes. As an alternative air cooling is applied, having a higher cooling temperature as most important disadvantage, resulting in a lower efficiency of the processes that are cooled, and higher investment and exploitation costs.

In countries with a dry, sunny climate cooling installations are of great importance, for air conditioning as well as for the conservation of food. There is also an increasing need to limit below certain maximum values the temperature in greenhouses for growing plants. The electrical energy for the required heat pumps is a substantial fraction of the total consumption of electricity. The efficiency of heat pumps increases when the temperature step decreases, and therefore when the temperature during the disposal of the heat to the environment decreases.

Radiation cooling, that is cooling by means of radiation of infra-red from a relatively warm surface towards the cold air layers in the atmosphere, stratosphere and troposphere, is a well-known phenomenon, which amongst others is described in the tripartite reference book "De Natuurkunde van het Vrije Veld" (The Physics of the Open Field) written by Prof. Dr. M. Minnaert (1937). The radiation cooling of a certain surface, measured in Watt per m², is equal to the difference between the outgoing radiation from the surface and radiation from the environment towards the surface. The outgoing radiation intensity depends on the absolute temperature of the surface to the power four according to Stefan-Boltzmann's law. The intensity of the radiation from the environment depends on the temperatures of the emitting surfaces, also according to Stefan-Boltzmann's law. The intensity of the radiation cooling is equal to the outgoing radiation minus the radiation incident on the surface. When the temperature of the bodies which emit the radiation incident on the surface decreases, the radiation cooling increases.

T.S.H. van Lieshout and R.J.J, de Jeu describe in the article "Energie uit onverwachte hoeK' (Energy from an unexpected corner), Nederlands Tijdschrift voor Natuurkunde 78, (2012) 192-193 that the radiation cooling increases if it is brought about by means of mirrors that the radiation incident on the surface is mainly originating from the sky and preferably from directions with a small zenith angle. This effect is theoretically demonstrated by G.B. Smith in the article "Amplified radiative cooling via optimised combinations of aperture geometry and spectral emittance profiles of surfaces and the atmosphere", Solar Energy Materials & Solar Cells 93 (2009) 1696-1701.

The effect of the mirrors is experimentally demonstrated by the inventors of the current patent application, see the first two figures. From a large number of measurements they conclude that in the absence of clouds the mirror-amplified radiation cooling is about 100 Watt/m².

The invention has for objective is to give solar-energy systems, for example parabolic trough mirrors, a second function, namely the generation of cooling by means of radiation, resulting in an increase of the efficiency of the entire system.

Summary of the invention

According to the invention it was recently found by surprise, that a radiating surface which cools down because of the outgoing radiation towards the cloudless sky acquires a larger cooling power if by means of mirrors a selection of the infra-red rays which are incident on the radiating surface is performed, a selection which brings about that these rays are mainly originating from the coldest regions of the sky.

In a first aspect of the invention, a device for harvesting solar energy is provided, suitable for driving one or more processes, which device comprises a first system having parabolic trough mirrors, parabolic dish mirrors, flat mirrors, spectral- selective mirrors, solar collectors or photo-voltaic solar panels, wherein the device at the same time comprises a second system for the generation of cooling by means of outgoing radiation.

The second system comprises an emitting surface for emitting infrared radiation, wherein this surface preferably has an emission coefficient of at least 90%, preferably at least 93% and more preferably at least 97%

Preferably, this emitting surface is arranged on plane or bent plates, which plates may, advantageously be covered with infrared absorbing material, e.g. titanium dioxide, polyvinylchloride or silicon oxide on metal.

The first system comprises a means of selection for reflecting infra-red radiation, wherein the means of selection is arranged such that mainly infra-red radiation originating from the coldest parts of the sky is incident on the radiating plates of the second system, and that solar rays and heat radiation from the surroundings of the device are blocked by the means of selection.

Preferably, the solar energy and the radiation cooling in the device according to the invention is harvested and generated, respectively, preferably simultaneously during the day and radiation cooling is generated during the night as well.

The cooling which is generated in the radiating surface can for instance be applied to cool a heat engine, such as the condenser of the Rankine process, the condenser of heat pumps including air conditioners that are fed by electricity or heat, a photo-voltaic solar panel, a chemical production process, growing vegetation, harvesting water by means of the deposition of dew, or the conservation of food. The cooling which is generated in the radiating surface can also be directly applied for air conditioning by connecting the radiating surface with ceilings by heat pipes, and for delivering of cooling to air conditioners which apply siccatives.

According to an embodiment of the invention, cooling produced in the radiating plates is removed by means of a heat pipe. The radiating plates are preferably mounted parallel to the optical plane of a parabolic trough mirror. In the case of parabolic trough mirrors which move in order to follow the sun during the day the radiating plates are on the optical plane.

In another embodiment the parabolic trough mirrors of the first system are mounted in a fixed position with respect to each other and collectively they form a floating member, which floats on a liquid medium during its operation. Preferably this liquid medium is water, which at the same time functions as medium for the storage of cooling. The parabolic trough mirrors may also be mounted stationary on the ground or on a flat roof.

According to another aspect of the invention a plane at, or near to, the optical plane of a stationary parabolic trough mirror is covered with strips, for instance made out of aluminium, which are thermally isolated with respect to each other, which are parallel with the focal line of the parabolic trough mirror, and which alternately can function as receiver of concentrated solar rays and as radiating surface, wherein every strip is connected by a heat pipe to a higher situated reservoir having a temperature at least some tens of degrees Kelvin higher than the temperature of the surroundings, and by another heat pipe to a lower situated reservoir having a temperature, which is lower than the temperature of the higher reservoir. When at a certain position of the sun a strip is irradiated by concentrated solar rays heat is delivered to the reservoir above. At the same time the other strips function as radiating surface, and deliver cooling to the reservoir below.

In another embodiment of the invention the strips are covered with photovoltaic solar cells, wherein the radiating surface can coincide with a photo-voltaic collector for producing electricity.

In yet another embodiment the radiating surface coincides also with a photo-voltaic collector for producing electricity, and the intensity of the solar radiation incident on the collector becomes amplified by a mirror. During the night the same mirror functions as means of selection for the reflection and blockade of infra-red radiation.

According to yet another embodiment the first system of the device is incorporated in a greenhouse for growing plants, wherein the roof of the greenhouse comprises a spectral selective window, which is transfers visible light in behalf of the photo-synthesis in the plants, and which reflects infra-red radiation to a radiating plate which delivers cooling to the greenhouse by a heat pipe.

The radiating surface can also be behind the optical plane of the parabolic trough mirror and if desired be covered with a porous material, which is hydrophilic at low temperatures and hydrophobic at high temperatures. During the night dew condenses on the porous material, which becomes soaked up by this material. During the morning the porous material is shone upon by concentrated sunlight and by this it becomes hydrophobic, such that the water is expelled and can be collected for useful application. These and other aspects of the invention will after this be discussed in more detail, also with reference to the appended drawings.

Brief description of the drawings

Figure 1 displays a measuring-instrument for demonstrating that a tube of infra-red mirrors is able to bring about cooling.

Figure 2 displays a graph with measured results obtained from the instrument of Figure 1.

Figure 3 displays the equilibrium of radiation of a horizontal surface in the open field.

Figure 4 displays an installation for concentrating solar energy with a wide positive lens.

Figure 5 displays the cooling effect on a surface next to the focal point brought about by the lens of Figure 4.

Figure 6 displays a parabolic trough mirror which concentrates the solar rays on tube-shaped receiver.

Figure 7 displays the cooling effect of the trough mirror of Figure 6 on vertical planes above and below the receiver, which function as radiating surfaces.

Figure 8 displays a floating field of parabolic trough mirrors, wherein the heat is used to drive an adsorption cooling machine. The adsorption cooling machine is cooled with water from the basin in which the trough mirrors are floating. The water in the basin is cooled by vertical radiating surfaces below the receiver.

Figure 9 displays a roof with stationary East-West oriented parabolic trough mirrors, with which water is heated.

Figure 10 displays the same roof with radiating surfaces, wherein the parabolic trough mirrors of Figure 9 form part of a system of mirrors which make the optical contact with the sky, such that the radiating surfaces cool down and in turn can cool down an air-conditioning.

Figure 11 displays a roof with stationary East-West oriented solar collectors for heating water. Figure 12 displays the same roof with radiating surfaces by wherein the solar collectors of Figure 11 form a system of mirrors, which bring about the optical contact with the sky, such that the radiating surfaces cool down and in their turn can cool down an air-conditioning installation.

Figure 13 displays a solar cooker for boiling water or preparing meals.

Figure 14 displays how the solar cooker of Figure 13 is used at night to generate cooling for a refrigerator.

Figure 15 displays rows of photo-voltaic solar panels and rows of mirrors, which reflect additional solar radiation towards the solar panels, wherein the solar panels are thermally connected with water reservoirs.

Figure 16 displays the same rows of solar panels, which function as radiating surfaces during the night, wherein the mirrors of Figure 15 bring about the optical contact with the sky, such that the radiating surfaces cool down and in turn can cool the water in the reservoirs.

Figure 17 displays a greenhouse for growing plants with a roof which transmits visible light and which reflects most of the infra-red radiation.

Figure 18 displays the same roof with radiating surfaces, wherein the roof elements of Figure 17 form a system of mirrors, which bring about the optical contact with the sky, such that radiation surfaces cool down and in turn can transport cooling to the plants in the greenhouse.

Figure 19 displays a field of stationary North-South directed parabolic trough mirrors with in the radiating plane a porous hydrophilic surface for harvesting water from dew. The mirrors bring about the optical contact with the sky, such that the hydrophilic surfaces cool down during the night.

Figure 20 displays the same field during the day, wherein the water from the porous surface is expelled because of the transition from the hydrophilic state to the hydrophobic state resulting from the heating by the concentrated solar radiation.

Figure 21 displays a floating field of parabolic trough mirrors during the day.

Figure 22 displays the same field during the night wherein the trough mirrors function as radiating surfaces and the heat of the water from the pond is transferred to the mirrors by evaporation and condensation.

Figure 23 displays a roof system of cooled photo-voltaic solar panels and mirrors during the day.

Figure 24 displays the same system during the night wherein the solar panels and the mirrors both operate as radiating surfaces and the heat from a stock of water is transferred to the mirrors by evaporation and condensation.

Figure 25 displays a field system of solar collectors and mirrors for

desalination of seawater. Detailed description of the invention

The invention is based in essence on the finding that the mirrors or solar collectors, which are applied for the harvesting of energy from solar heat, can be used at the same time in an efficient way to realise radiation cooling. Also roofs of greenhouses and photo-voltaic solar panels can be used to realise radiation cooling.

A radiation surface which cools down because of the outgoing radiation towards the unclouded sky obtains an increased cooling power, if by mirrors a selection is carried out of the infra-red rays which are incident on the radiating surface, wherein rays are selected which mainly originate from the coldest parts of the sky.

A device according to the invention may during the day simultaneously produce heat at one location, and generate cold by means of outgoing radiation at another location. During the night only cold is generated. Such device comprises preferably rotating, floating or stationary parabolic mirrors, solar collectors, photovoltaic solar panels, or a greenhouse with a spectral-selective roof, to which is added a radiating surface in such a way that this surface is not illuminated by the sun during the day, and that the mirrors, solar collectors etc. bring about that the infra-red radiation which is incident on the radiating surface is mainly originating from the coldest parts of the sky, being the parts having a small zenith angle.

A floating parabolic trough mirror according to two of the embodiments of the invention, which will be described hereafter, has two functions. The first function is the concentration of the solar rays on the receiver. For this purpose the floating trough mirror field is continuously kept in a position in which the plane formed by the receiver and the sun has a vertical position. Thus, the radiating plane, which is parallel with the optical plane of the parabolic trough mirror, is never shone upon by the sun. The second function of the parabolic trough mirror is selection of the infra-red radiation which is incident on the radiating plane. Because of the presence of the parabolic trough mirror the following radiation is blocked: (1) the largest part of the radiation originating from relative warm buildings and trees, and (2) the largest part of the radiation originating from layers of air with a large zenith angle. Because of the presence of the parabolic trough mirror infra-red radiation originating from air layers from directions with a small zenith angle are preferably reflected to the radiating plane.

Most radiation that reaches the radiating plate is therefore originating from the air layers from directions with a small zenith angle, therefore originating from the parts in the sky which are present more or less right above the device. The temperature of these air layers is very low, so that the intensity of the infra-red radiation selected by the parabolic trough mirror which is incident on the radiating plate is very low. The net cooling power of the radiating plate is equal to the outgoing radiation minus the incident radiation. Because of the selecting effect of the parabolic trough mirror the net cooling power of the radiating plate has increased. If, by a water circuit heat with a higher temperature is supplied, the radiating surface will be able to absorb a certain amount of heat power without a change of temperature, or be able to deliver a same amount of cold power. An important condition for proper functioning of the device according to the invention is, that the parabolic trough mirrors reflect and do not absorb the infra-red radiation with long wavelength that is emitted by the radiating surface. Therefore the mirrors are preferably realised as aluminium mirrors, which fulfil this condition. Glass mirrors, which are mostly applied in CSP-installations, do not satisfy in general.

Hereafter 12 different embodiments of the invention are described.

Embodiment 1

According to a first embodiment of the invention a solar thermal power plant is applied, which consists of rows of parabolic trough mirrors in the North-South direction, which rotate in the course of the day along a horizontal axis in order to follow the sun. The trough mirrors reflect solar rays as well as infra-red rays with a wavelength of 3 to 30 micrometers. In the receiver the heat coming from the concentrated solar radiation is transferred to a transporting liquid, for instance oil. The heat of the transporting liquid is used to drive a Rankine process. The condenser of the Rankine process is cooled with water from a storage reservoir.

In the optical plane of the parabolic trough mirror below and above the receiver are radiating surfaces. Water from the storage reservoir gets cooled since it flows both day and night through a tube below the radiating surfaces. The tube has contact with the radiating surfaces through heat pipes.

The cooling of the radiating surfaces arises by radiation from the radiating surfaces. The radiating surfaces are covered with a coating with a high emission coefficient for infra-red radiation with a long wavelength, for instance a layer of titanium dioxide. The cooling is partially hindered by infra-red radiation incident on the radiating planes from the surroundings.

During the night the parabolic trough mirrors are pointed to the zenith. The mirrors block all infra-red radiation that otherwise would be incident on the radiating surfaces from relative warm buildings and air layers. The parabolic trough mirrors also bring about that practically all infra-red radiation which is incident on the radiating surfaces originates from very cold layers of the sky. Because of these effects the intensity of the radiation which is incident on the radiating surfaces is low and the net cooling power of the radiating surfaces is high.

During the day the parabolic trough mirrors bring about that the radiating surfaces are never shone upon by the sun. The upper side of the radiating surface is shielded from the infra-red radiation originating from relatively warm buildings and warm layers of air by the trough mirror. The mirror also brings about that practically all infra-red radiation which is incident on this side of the radiating surface originates from very cold parts of the sky, where the sun is absent. Because of these effects the intensity of the radiation which his incident on the upper side of the radiating surface is low and the net cooling power is high.

The lower side is shone upon too by infra-red radiation arising from the heated soil and the heated back side of the neighbouring row of parabolic trough mirrors. This side will not, or only a little, contribute to the net cooling power.

When the temperature of the radiating surfaces is higher than the air temperature the cooling power becomes increased by the passing, cooler air.

The cooling occurs during the day as well as during the night.

Embodiment 2

According to a second embodiment of the invention a solar thermal power plant is applied consisting of rows of parabolic trough mirrors which are stationary with respect to each other and collectively form a field which floats in the water of a pond. The trough mirrors reflect solar rays as well as infra-red rays with a wavelength of 3 to 30 micrometers. In the course of the day the field rotates around a vertical axis, in order to direct the optical plane of the parabolic trough mirrors to the sun, resulting in the concentration of all reflected solar rays on the focal lines of the trough mirrors. In the receiver heat from the concentrated solar radiation is transferred to a transporting liquid, for instance oil. The heat of the transporting liquid is used to drive a Rankine process. The condenser of the Rankine process is cooled with water from the pond.

In the optical plane of the parabolic trough mirror there are vertical radiating surfaces below and above the receiver. Water from the pond gets cooled, as it stays in contact with the radiating surfaces by heat pipes, during the day as well as during the night.

The cooling of the radiating surfaces comes about by outgoing radiation from the radiating surfaces. The radiating surfaces are covered with a coating with a high emission coefficient for infra-red radiation with a long wavelength, for instance a layer of titanium dioxide. The cooling is partially hindered by infra-red radiation which is incident from the surroundings. The parabolic trough mirrors block the infra-red radiation from relative warm buildings and air layers that would be incident on the radiating surfaces. The parabolic trough mirrors also bring about that practically all infra-red radiation which is incident on the radiating surfaces originates from very cold layers of the sky, where the sun is absent.

Due to these effects the intensity of the radiation which is incident on the radiating surfaces is low and the net cooling power of the radiating surfaces is high. When the temperature of the radiating surfaces is higher than the air temperature the cooling power becomes increased by the passing, cooler air.

The cooling occurs during the day as well as during the night.

Embodiment 3

According to a third embodiment an installation is applied which generates electricity and cooling at the same time. The installation consists of rows of parabolic trough mirrors, which are stationary with respect to each other and collectively form a field which floats in the water of a pond.

The trough mirrors reflect solar rays as well as infra-red rays with a

wavelength of 3 to 30 micrometers. In the course of the day the field rotates around a vertical axis, in order to direct the optical plane of the parabolic trough mirrors to the sun, such that all reflected solar rays coincide on the focal lines of the trough mirrors.

The receiver is covered with photo-voltaic solar cells with a low internal resistance having an efficiency of about 15%. Through the receiver water is flowing which removes the remaining 85% of the concentrated solar energy in the form of heat. The heat of the transporting liquid is utilised to drive an adsorption cooling machine or a desalination installation. The water from the pond is utilised to cool the adsorption cooling machine or the desalination installation.

In the optical plane of the parabolic trough mirror vertical radiating surfaces are present below and above the receiver. Water from the pond is cooled because it is in contact with the radiating surfaces by heat pipes during the day as well as during the night.

The cooling of the radiating surfaces is effected by radiation from these surfaces. The radiating surfaces are provided with a coating with a high emission coefficient for infra-red radiation with a long wavelength, for instance a layer of titanium dioxide. The cooling is partially hindered by infra-red radiation incident on the radiating surfaces from the surroundings. The parabolic trough mirrors block the infrared radiation from relative warm buildings and air layers that would be incident on the radiating surfaces. The parabolic trough mirrors also bring about that practically all infra-red radiation which is incident on the radiating surfaces originates from very cold parts of the sky, where the sun is absent.

Due to these effects the intensity of the radiation which is incident on the radiating surfaces is low and the net cooling power of the radiating surfaces is high. In the case that the temperature of the radiating surfaces is higher than the air temperature the cooling power becomes increased by the passing, cooler air.

The cooling occurs during the day as well as during the night.

Embodiment 4

According to a fourth embodiment a device according to the invention is applied on flat roofs of offices, super markets and factories. During the day electricity, heat and cold are produced simultaneously. During the night only cold is produced. This description concerns an installation in the sub-tropics and the moderate zone of the Northern hemisphere.

On a flat roof rows of half, stationary parabolic trough mirrors are situated in the East-West direction. The trough mirrors reflect solar rays as well as infra-red rays with a wavelength of 3 to 30 micrometers. The optical plane is at the South side of a half parabolic trough mirror. The optical plane makes an angle of about 45 degrees with respect to the vertical. In or near to the optical plane is a receiver plane, having a width which is about equal to the width of the parabolic trough mirror. Each moment of the day a narrow region of the receiver plane is irradiated with concentrated solar radiation. The other part of the receiver plane is shielded by the parabolic trough mirror from infra-red radiation coming from warm buildings and warm layers of air. The parabolic trough mirrors also bring about that practically all infra-red radiation which is incident on that part of the receiver plane originates from very cold parts of the sky, where the sun is absent. Due to these effects the intensity of the radiation which is incident on that part of the receiver plane is low and the net cooling power of that part is high.

The receiver is split in a large number of horizontal strips which are thermally isolated from each other. The strips are completely or partly covered with photo-voltaic solar cells with a low internal resistance. Every strip is connected by a number of heat pipes to a water tube above the receiver plane through which water of 70°C is flowing, and by a number of other heat pipes to a water tube below the receiver plane through which water is flowing with a temperature which is equal to the air temperature, for instance 30°C. A heat pipe transports heat in one direction, from below to above. The water tubes are parallel to the focal line of the parabolic trough mirror.

Every strip is in one of the following four states:

1. The strip is shone upon by concentrated solar rays and functions as receiver. About 15% of the energy of the concentrated solar rays is transformed into electricity by the solar cells and the remaining 85% is transformed into heat. The temperature will rise fast. As soon as the temperature is higher than 70°C all heat is carried off to the water tube above the strip by the heat pipes, and from there to the device where this heat of 70°C is utilised.

2. The strip is not irradiated by concentrated solar rays and functions as radiating surface. As soon as the temperature is dropped below 30°C heat from the water tube below the strip is supplied to the strip by the heat pipes, with other words, cold is supplied to the water in the tube and from there to the device where this cold of 30°C is utilised.

This device is for instance a heat exchanger, with which the waste heat of a heat pump for cooling a building is disposed of to the environment. In that case the condenser of the heat pump will be identical with the water tube below the strip. The solar cells on the strip are shone upon with diffuse light from a part of the blue sky, where the sun is absent. With this electricity is produced, although in a rather small amount.

3. The strip is not irradiated by concentrated solar rays, but it is irradiated by direct solar rays. Because of the heating of the strip the strip cannot function as radiating surface. The solar cells will produce electricity.

4. The strip is in the transition from state (1) to state (2) or the other way around. The temperature is lying between 30°C en 70°C. There is no transport of heat between the strip and the upper lying and lower lying water tubes.

The heat of the water tube at the top of the receiver plane is utilised for the supply of hot water of the building or for driving an adsorption cooling machine. The cooling is utilised to increase the efficiency of the adsorption cooling machine or the efficiency of another heat pump for cooling the air conditioning, cold stores, and deep freezing installations.

At night only cold is produced. The heat as well as the cold can be stored in water reservoirs and the like, such that the thermal energy becomes available to be applied throughout the full 24 hours' day.

Embodiment 5.

According to a fifth embodiment a device according to the invention is applied in regions with a desert climate. In this embodiment water is produced by means of cooling resulting from outgoing radiation and heating resulting from concentrated solar radiation. In both processes stationary parabolic trough mirrors are utilised, which are standing in a fixed position in the North-South direction.

The optical plane of a trough mirror makes an angle of 45° with the horizon.

Behind the optical plane is a receiver plane, which is hollow most of the time. Due to the presence of the parabolic trough mirror practically every point of the receiver plane is exclusively hit by infra-red radiation which originated from the bright night sky. By this the receiver plane cools down during the night to 5 to 10 degrees below the air temperature and to below the dew point. In that case water from the air will condense on the receiver plane. The receiver plane is covered with a porous material, which is hydrophilic below a certain critical temperature and hydrophobic above that critical temperature. An example of such material is cotton that is impregnated with poly(N- isopropyl acryl amid), abbreviated as PNIPAAm.

The critical temperature of this material is 32°C. See further: H. Yang e.a., "Temperature-Triggered Collection and Release of Water from Fogs by a Sponge-Like Cotton Fabric", that will be published in 2013 in Advanced Materials. During the night and the early morning the hydrophilic, porous material soaks itself with water from the dew, which is deposited on the receiver plane cooled down by radiation cooling.

The next morning, after the sun has reached a certain height above the horizon, the receiver plane is irradiated by a rather wide band with concentrated solar light. The distance between the receiver plane and the optical plane is such, that on one hand the intensity of the radiation is sufficient to cause a rise of temperature well above the critical temperature, but that on the other hand it is prevented that dry material burns or is spoiled in another way.

As soon as the porous material has become warmer than the critical temperature the material becomes hydrophobic. The water is pressed out from it and will appear at the surface in the form of thick drops of water and flow downwards to a tube, through which it flows further to a storage reservoir. During the morning the band with concentrated sunlight moves over the receiver plane from above to below and most water is pressed out of all porous material. The next night the process is repeated again.

This installation has no moving parts and requires little maintenance, apart from cleaning the mirrors.

Embodiment 6

According to a sixth embodiment a device according to the invention is applied as following on flat roofs of offices, super markets and factories. This description concerns an installation in the moderate zone of the Northern hemisphere.

The roof is partially covered with East-West directed panels which are in the shadow of solar collectors for harvesting warm water out of solar rays. The panels have thermal contact with tubes with running water. A large fraction of the day the panels are in the shadow and in that case they function as radiating surface. The solar collector opposite to the panel blocks infra-red radiation from surrounding buildings and from parts of the sky with a large zenith angle. The solar collector is made reflective for infra-red radiation with wavelength between 3 and 30 micrometers. Thus, infra-red radiation coming from the warm solar collector which would be incident on the radiating surface is replaced by infra-red radiation originating from the cold parts of the sky. The radiating surface then cools down and is able to absorb day and night heat from the water that is flowing at the backside.

This cooling is utilised to increase the efficiency of a heat pump for producing cooling. The device can also be carried out such that the condenser of the heat pump is in the tubes that are directly behind the radiating panels.

The heat of the solar collectors can be utilised for the hot water supply of the building or for driving an adsorption cooling machine. The cooling is utilised to increase the efficiency of the adsorption cooling machine or the efficiency of another heat pump for cooling the air conditioning, cold stores, and deep freezing installations.

At night only cold is produced. The heat as well as the cold can be stored in water reservoirs, such that the thermal energy becomes available to be applied during the complete 24 hours' day.

Embodiment 7

A seventh embodiment of the invention is an extension of the solar cooker, which is applied in tropical and subtropical regions. A parabolic dish mirror, which reflects solar rays as well as infra-red rays with a wavelength of 3 to 30 micrometers, is utilised to boil water and to prepare meals at daytime. In order to do this a pan is placed in the focal point and the dish is directed to the sun by hand or with a device to follow the sun. At night de dish is directed upwards and in the focal point cartridges are placed with a material which has a phase-change at for instance 15°C. In the morning these cartridges are placed in a thermally isolated box, in which food is lying that must be kept cool.

Embodiment 8

An eighth embodiment of the invention is applied in tropical and subtropical regions. This description applies to an installation in the subtropics on the Northern hemisphere.

Rows of stationary photo-voltaic solar panels for the production of electricity are arranged in the East-West direction. At the South side of the solar panels are mirrors, which reflect solar radiation as well as infra-red radiation. At day time the mirrors bring about an increase of the intensity of the solar rays that are incident on the solar panels. At night the solar panels function as radiating surface.

At night the mirror opposite to the solar panel blocks infra-red radiation from surrounding mountains and buildings and from the parts of the sky with a large zenith angle. By this practically all infra-red radiation that is incident on the solar panel is originating from the cold parts of the sky. By this the solar panel cools down.

The solar panels are mounted on reservoirs with water and have a good thermal contact with the water. By this the cooling which occurs in the solar panels at night due to the large net outgoing radiation is transported to the water. This cooled water brings about that at day time the solar panels are much colder, resulting in a considerable increase of the efficiency of the solar cells.

Embodiment 9

According to a ninth embodiment a greenhouse for growing plants is applied. This description regards a greenhouse at the Northern hemisphere. The greenhouse is covered with spectral-selective roof plates, which have the shape of a parabolic trough mirror. The spectral selectivity implies that visible light which is needed for the photosynthesis is generally transmitted and that the short-waved infra-red radiation with wavelength smaller than 3 micrometers is mainly absorbed or reflected. By this it is brought about that the temperature in the greenhouse does not increase too much at day time, which is of importance in the plant-breeding in the subtropics. An example of a suitable material for spectral-selective roof plates is IR3 glass or SIR glass.

In the East-West direction rows of spectral-selective roof plates are

positioned, which have the shape of a parabolic trough mirror with the focal line at the South side, such that they are optimally irradiated by the sun. Neighbouring roof plates are connected with plates which are approximately standing vertically on the roof plates. These plates are equipped with a coating with a high emission coefficient for infra-red radiation with a long wavelength, for instance a layer of titanium dioxide, and function as radiating planes.

The focal line of the parabolic spectral-selective roof plate at the North side of the radiating plate is just above the radiating plate. With this it is brought about that the solar rays that are reflected against the parabolic spectral-selective roof plate most of the time will not be incident on the radiating plane and therefore will not cause undesired warming up of the radiating plate. These radiating plates are mainly in the shadow. The spectral-selective roof plate reflect the infra-red radiation with long wavelength with a wavelength of 3 to 30 micrometers, which is brought about by the deposition of a metal mesh on top of the roof plates.

The parabolic spectral-selective roof plates block the infra-red radiation coming from relatively warm buildings and air layers that would be incident on the radiating plates. At the same time the parabolic trough mirrors bring about that practically all infra-red radiation that is incident on the radiating planes originates from very cold parts of the sky, where the sun is absent. Because of these effects the intensity of the radiation which is incident on the radiating planes is low and the net cooling power of the radiating planes is high. In the case that the temperature of the radiating planes is higher than the air temperature the cooling power is increased by the flowing, cooler air. The cooling occurs during the day as well as during the night.

The radiating planes are connected by heat pipes with panels or radiators on the ground of the greenhouse. The heat pipes transport heat from these panels or radiators towards the radiating planes on the roof, such that cooling is brought to the greenhouse. By this the desired cooling in the greenhouse is amplified and the intensity of the photosynthesis process also amplified. Thus, expensive water, that otherwise would be consumed to generate cooling, can be saved at the same time.

Embodiment 10

According to a tenth embodiment a solar thermal power station is applied which consists of rows of parabolic trough mirrors which are stationary with respect to each other and collectively form a field which floats in the water of a pond or a lake. The trough mirrors reflect the solar rays and absorb infra-red rays with a wavelength of 3 to 30 micrometers. The mirrors which are applied for concentrating solar power generally fulfil this condition, examples of this are glass mirrors, of aluminium which is covered with a thick transparent protection layer, and reflecting PMMA foil with a thin silver layer. The field rotates in the course of the day around a vertical axis, with the aim to direct the optical plane of the parabolic trough mirrors to the sun, such that all reflected solar rays coincide on the focal lines of the trough mirrors. In the receiver heat originating from the concentrated solar radiation is transferred to a transporting liquid, for instance oil. The heat of the transporting liquid is applied to drive a Rankine process. The condenser of the Rankine process is cooled with water from the pond.

The parabolic trough mirrors function as radiating surfaces at night. They are made out of glass plate, or out of a structure of aluminium. Because of this the thermal resistance between the upper surface and the lower surface of a mirror is sufficiently small that the temperature difference between upper surface and the lower surface is generally smaller than 1 Kelvin. The space between the lower surface of the mirror and the water surface is at the sides closed off from the wind. As soon as the mirror temperature is lower than the water temperature water vapour will condense on the mirror and water will evaporate from the water surface. This way heat becomes transported from the water to the mirror, and from the mirror towards the cold air layers above the mirror. In fact the space between the mirror and the water functions as a heat pipe with water as working medium. By this the water in the pond cools down and with the pond water the condenser of the Rankine process can be cooled. The depth of the water in the pond is sufficient to limit the daily temperature variation of the water to less than 5 Kelvin.

Also in day time the parabolic trough mirrors function as radiating surfaces. At the same time heating occurs caused by the part of the solar radiation which is not reflected by the mirrors. When the mirror temperature is lower than the water temperature water vapour will condense on the mirror and water will evaporate from the water surface, and the pond water is cooled. When the mirror temperature is higher than the water temperature the pond water will be heated op to only a small extent because of the isolating effect of the stagnant air between the mirrors and the water surface.

In the case that the temperature of the radiating surfaces is higher than the air temperature the cooling power is increased by convection cooling, that is cooling caused by passing cooler air.

Embodiment 11

An eleventh embodiment concerns the application of photo-voltaic solar panels in the field or on flat roofs, wherein mirrors are applied to increase the intensity in the solar panels, and radiation cooling is applied to cool the solar panels. This description concerns an installation on a roof on the Northern hemisphere.

In the East-West direction rows of stationary photo-voltaic solar panels for the production of electricity are standing which are directed to the South. The space between the solar panels is for the most part filled with mirrors which reflect solar radiation and absorb infra-red rays with a wavelength of 3 to 30 micrometers. At day time the mirrors bring about an increase of the intensity of the solar rays incident on the solar panels. At night the solar panels and the mirrors function as radiating surface.

Below the solar panels and the mirrors is a reservoir with a shallow layer of water, which by means of a pump is continuously circulating with a large storage reservoir of water at a lower level. This storage reservoir may coincide with the storage reservoir of water for fire-fighting, if present. At the backside of the solar panels is a mesh or sponge. At day time water is pumped to the top of the mesh or sponge. This water flows slowly down and absorbs heat from the solar panels. At the end of the day the temperature in the stock of water has increased with 1 to 5 degrees. At night the temperature of the mirrors and the solar panels drops to below the temperature of the water, because of radiation cooling and in certain cases convection cooling. The water starts to evaporate and the water vapour starts to condense against the lower side of the mirrors and the solar panels, after which the water drips back again to the reservoir. Because of this process the temperature of the stock of water drops in the course of the night with 1 to 5 degrees.

Because of the cooling of the solar panels their efficiency increases considerably.

Embodiment 12

A twelfth embodiment concerns a desalination installation or water purification installation by repeated distillation with heat from solar collectors as heat source. Mirrors are applied to increase the intensity on the solar collectors and radiation cooling is applied to deliver the required cooling. This description concerns an installation on a field on the Northern hemisphere, in a surroundings where no or little electricity is available and where qualified personal is scarce. In contrast to existing desalination methods this installation requires little maintenance. At day time solar collectors that are directed to the South deliver heat by means of a heat exchanger to a large reservoir with salt water or polluted water, which in the following will be called brine. The transporting liquid is pumped with a geyser pump which does not need electricity for pumping and for the control, see patent nr. WO2010/042171.

The space between the solar collectors is filled with mirrors which reflect extra sunlight towards the solar collectors, and which deliver the necessary cooling for the distillation process by means of radiation cooling and, if there is wind, convection cooling. Below the mirrors there are a number of to this parallel screens consisting of thin aluminium plates, or stretched polymer foils. The polymer is made out of a hydrophilic material. At the top side of the screens a thin layer of brine is flowing. Because of the large difference in temperature between the reservoir with the hot brine and the mirror the screens set themselves on an equilibrium temperature, wherein every screen always has a lower temperature than the screen below. By this in every space between the screens there occurs evaporation of brine, and

condensation against the lower side of the screen above. The condensation drops slide down along the bottom of the screen, and all the condensed water is collected in a drain. Because there are several screens, evaporation and condensation occurs many times during the heat transport from the hot brine reservoir to the cold radiating surface (the mirror). The Gain Output Ratio (GOR) of the desalination process, that is the efficiency of the process, is much higher than 1. At the same time condensation occurs against the bottom of the solar collector. The heat capacity of the brine is sufficient to keep the evaporation and condensation process going day and night.

The transporting liquid of the solar collectors flows partially through flexible tubes, such that is possible to rotate the solar collectors to a vertical position. Thus space is created for the maintenance personnel to lift out the screens and to clean them. The brine in the reservoir gets gradually a larger salt concentration, and has to be replenished with new brine, and after a few replenishments the concentrated brine has to be removed and replaced.

Hereafter the invention is elucidated further with reference to the Figures, which however are not intended to restrict the scope of the invention in any way. Figure 1 displays a simple instrument with which the phenomenon of radiation cooling can be demonstrated. A thin horizontal aluminium plate 1 is arranged on a thick isolating layer 2 and is covered with an infra-red absorbing paint. The

temperature of the plate 1 is measured with a thermocouple 3 and an infra-red thermometer (not drawn). Above the radiating plate 1 a thin polypropylene foil 4 is stretched in order to stop loss of heat to the air. The radiating plate 1 is covered at intervals by a case 5 of aluminium plates, which function as infra-red mirrors. By the case 5 it is brought about, that all infra-red rays that are incident on the radiating plate 1 are originating from the part of the sky where the zenith angle is smaller than 45°, where the temperatures are low.

When the case 5 is removed, the radiating plate 1 is also hit by radiation from the warmer parts of the atmospheric layer above the horizon and from buildings, trees, etc. By the presence of the case 5 the temperature of the radiating plate 1 will decrease and by the removal of the case 5 the temperature will increase. Figure 2 displays the result of a measurement with the instrument that is described in Figure 1. The measurement is performed in Groningen, The Netherlands, on August 27, 2012 from 1 PM to 3 PM (13 h to15 h) on a flat roof in the shadow of a building. About 25% of the sky was covered with cumulus clouds and 75% was blue sky. De wind was light.

5 The graph displays measured temperatures in degrees Celsius as a function of time in minutes after noon (12:00 h). The solid curve gives the temperature of the radiating plate 1 , displayed is the average value of the thermocouple 3 and the infrared thermometer. The dashed line gives the temperature of the air, displayed is the average of a mercury thermometer and an alcohol thermometer.

10 The case 5 was present in the periods 99-120 minutes and 132-152 minutes.

In the graph this is indicated by a thick horizontal line above the X-axis. There is a clear correlation between the presence of the case and a decrease of the temperature of the radiating plate 1 , and between the removal of the case and an increase of the temperature. With this the effect, which is predicted by G.B. Smith and which forms

15 the basis of the invention, is experimentally proven. The rise in temperature in the period 112-120 is probably caused by increased wind.

In Figure 3 the principle of radiation cooling is displayed. The figure shows the situation after sunset. The surfaces 10 and 11 lose heat by means of outgoing infra-

20 red radiation 12. This cooling process is substantially hindered by incoming radiation 13 originating from buildings or trees 14, from air layers low above the horizon 15, and from air layers near to the zenith 16. When the surfaces are thermally isolated an equilibrium temperature will set itself, the so-called stagnation temperature, which can be about 5°C lower than the temperature of the surroundings. When heat is supplied

25 at a temperature of for instance 2°C below the temperature of the surroundings, a certain amount of power is consumed and radiated out. Thus there is a production of cold.

In Figure 4 the principle of concentrated solar energy is displayed. The rays 30 20 from the sun 21 are concentrated by a concentrating element 22 (generally a parabolic mirror, but for clarity reasons here displayed as a positive lens) on a small area 10. By this the intensity of the solar radiation which hits area 10 is substantially increased. In that case the temperature of area 10 can become sufficiently high to drive a Rankine process. With the high intensity it also become economically viable to mount high efficient solar cells (not drawn) at position 10. These solar cells must be cooled, the heat of this cooling water can be utilized.

In Figure 5 the principle of the invention is displayed, namely the combination of radiation cooling and concentrated solar energy. A surface element 30 from the surface 1 1 loses heat by radiating out infra-red radiation. Heat is supplied by the capture of radiation 31. In the figure only the radiation is depicted which is absorbed by surface element 30. The concentrating element 22 has next to the main function, which is the concentration of solar rays to area 10, two other functions. The first function is shielding of radiation directed to the surface element 30 coming from relative warm sources, such as buildings 14, radiation from the sun 21 , and a substantial part of the radiation from air layers. The second function is the

concentration onto the surface element 30 of the radiation from a small region 32 in the sky with a rather small zenith angle 33.

Because the zenith angle 33 is small, this infra-red radiation originates from the high air layers, where the temperature is low. The concentrating element 22 brings about a selection of infra-red radiation, with as result that the major part of the infrared radiation which is incident on the surface element 30 originates from parts of the atmosphere where temperatures are low, resulting in a decrease of the intensity of the incoming radiation, and a lower stagnation temperature of the surface element 30 than in the situation of Figure 3. In other words, at constant temperature the net amount of heat that is radiated out by the surface element 30 is increased. The effect occurs both day and night. The effect is considerably magnified by the fact that the atmosphere is transparent in an important wavelength region, namely between 8 and 14 pm, especially at a small zenith angle 33. By this the concentrating element 22 brings about at the same time a partial optical coupling with the universe, where the temperature is very low, namely 3°K.

The essence of the invention is the combination of solar energy with radiation cooling. The addition of radiation cooling to certain embodiments of concentrated or non-concentrated solar energy demands a small extra investment en yields a substantially more viable economic process.

Figure 6 displays a concrete form of Figure 4 for the case of parabolic trough mirrors. A cross section is given of two half parabolic trough mirrors 40 and 41. The half trough mirror 40 is displaced with respect to the half trough mirror 41. By this the focal line 42 of the half trough mirror 40 is not at the same position as the focal line 43 of the half trough mirror 41. The width of a half trough mirror is equal to 4 times the focal distance f 44. The height of a half trough mirror is equal to the width. Both trough mirrors 40, 41 are positioned with their optical planes directed towards the sun, resulting in the solar rays being parallel to the optical plane. In this figure, as in the following figures, the projections of the solar rays 45 are drawn. It can be proven mathematically that the law of reflection (angle of incidence = angle of reflection) is also valid for the projected rays in the two-dimensional drawing plane. The rays 46 which are coming from the half trough mirror 46 are incident on receiver 47 at the focal line 42. The rays 48 which are coming from the half trough mirror 41 are incident on receiver 47 at the focal line 43. Because of the concentration of the reflected solar rays 46 and 48 heat is generated in the receiver, which can be utilised. The receiver may also be covered by photo-voltaic solar cells (not drawn).

Figure 7 displays the realisation of Figure 5 for the case of parabolic trough mirrors. Above and below the receiver 47 vertical radiating surfaces 50 are positioned in the area between the mirrors and a line at twice the focal distance f away from the mirrors. In the figure only the rays are drawn which are transporting heat to two different points on the radiating surfaces 50. The radiating surfaces 50 are covered with a coating with a high emission coefficient for infra-red radiation with a large wavelength, for instance a layer of titanium dioxide. At the top side of the radiating surfaces 50 a horizontal screen 51 is positioned, which takes care that the radiating surfaces 50 never will be hit by solar rays. The radiating surfaces 50 are hit by infrared radiation 52 and 53 coming from the higher layers of air, which have had one or more reflections from the trough mirrors 40 and 41. The radiating surfaces are hit too by rays 54, which originate from the higher layers of air without any reflection. The essence of the chosen dimensions is, that practically all infra-red radiation that is incident on the radiating surfaces 50 is coming from a more or less vertical direction, where the zenith angle of most rays is smaller than 45°. In the layers of air which emit these rays low temperatures are prevalent. By this the intensity of the radiation with is incident on the radiating surfaces 50 is low and the net cooling power of the radiating surfaces (intensity emitted radiation minus intensity absorbed radiation) is high.

An alternative formulation of the effect is the following. The half parabolic trough mirrors 40 and 41 bring about an optical coupling between the radiating surfaces 50 and an area in the atmosphere where low temperatures are present, with as a result that the intensity of the incoming radiation is decreased, and the stagnation temperature of the radiating surfaces 50 becomes lower than the temperature of the environment. With other words, at constant temperature the amount of net heat that is radiated out by the radiating surfaces 50 is increased. This effect occurs both day and night. The effect becomes substantially larger by the fact that the atmosphere is transparent in an important wavelength region, namely between 8 en 14 pm, especially at a small zenith angle 33. At the same time the trough mirrors 40 and 41 bring about a partial optical coupling with the universe, where the temperature is extremely low, namely 3°K. Figure 8 displays an embodiment for the production of electricity, heat, and cooling. It consists of a floating field of parabolic trough mirrors, drawn in the figure in a stereo-metric way, and an adsorption cooling machine, drawn in the figure in a cross section. The basin with water 9, in which the trough mirror field is floating, is located inland away from the coast at a dry, sunny location. The trough mirrors 40 and 41 concentrate the solar rays on the receiver 47. For this purpose the whole trough mirror field rotates along a vertical rotation axis 69 during the day. The receiver 47 is covered with solar cells (not drawn). The solar cells are cooled with water, which is pumped through the receivers 47 and the thermally isolated water vessel 71 by means of the pump 70. While flowing through the receivers 47 the water heats up from about 65°C to about 75°C. All mentioning of temperatures in this description are qualitative and mentioned only to give a better clarification of the invention.

In the hollow rotation axle 69 there are two sliding seal couplings (not drawn), so-called swivels, enabling the transport of water between the moving receivers 47 and the stationary water vessel 71 during the daily rotation of the mirror field over more than 180 degrees. At the end of the day the mirror field rotates back to the regular position at sunrise. The water vessel 71 is continuously completely filled and functions as a heat storage vessel according to the thermocline principle. The water at the top of water vessel 71 has a temperature of 75°C and the water at the bottom 65°C. The boundary layer between the hot water at the top of the water vessel 71 and the colder water at the bottom moves downward at day and upward at night.

The hot water from the water vessel 71 is used to drive a refrigerator 72, such as a silica gel adsorption refrigerator. Although these machines are already

commercially available, a short description will be given here because of the big synergetic advantage of the coupling of the refrigerators to a floating trough mirror field. The consumer of the cooling is for instance the central air conditioning of a hotel, where the water is heated up from 10°C to 15°C. In the evaporation vessel 73 of the silica gel adsorption refrigerator 72 water is evaporating because of the very low partial pressure of the water vapour, which is the result is the silica gel 74 in vessel 75, which is held at a rather low (<25°C) temperature. The necessary evaporation heat is delivered by the water which cools down in the vessel 73 from 15°C to 10°C. At the same time the silica gel 74 in vessel 76, which brought about dryness in vessel 73 at an earlier stage, is baked at a temperature of 65-75°C.

The necessary heat is delivered by the water vessel 71 by means of the pump

77.

The originated water vapour condenses in the condenser vessel 78 at a temperature of 20-25°C. The condensed water runs back through the conduit 79 to the evaporation vessel 73. When the silica gel 74 in vessel 75 is saturated, the valves between the vessels 73, 75, 76, and 78 are reversed, the hot water of 75°C is directed through vessel 75, and the cooling water of about 20-25°C is directed through vessel 76, etc. (the necessary pipes and valves are not drawn).

The necessary cooling water for the silica gel adsorption process is delivered by the water 9 in the basin at a temperature of 20°C. After the heating up in the condenser vessel 78 and the vessels 75 and 76 the cooling water has obtained a temperature of 25°C and it flows back to the water stock 9, upon which the mirror field is floating.

Below the receivers 47 there are vertical radiating surfaces 50 at both sides of the poles (not drawn) upon which the receivers 47 are mounted. The radiating surfaces 50 are equipped with a coating with a high emission coefficient for infra-red radiation with a long wavelength, for instance a layer of titanium dioxide. The trough mirrors 40 and 41 bring about that the radiation which is incident on the vertical radiating surfaces 50 is mainly originating from the very cold high lying air layers, but not from the part of the sky where the sun is present.

As very low temperatures are present in these parts of the atmosphere the radiating surfaces 50 cool down. The radiating surfaces 50 have a thermal contact with the water 9 of the basin by means of vertical heat tubes 80. With them heat is transported upwards to the radiating surfaces 50, which deposit this heat to the high lying air layers by means of outgoing radiation. With this, cold is delivered to the water 9, resulting in a lowering of the average temperature of the water 9 from 25°C to 20°C. This cooling process occurs both at day and at night. In order to limit unwanted heating of the water 9 by hot air at day the open parts of the basin are covered with an isolating layer (not drawn). The cooling process occurs day and night.

The mounting of the radiating surfaces 50 and the heat pipes 80 enables a more efficient operation of the silica gel adsorption refrigerator, more precise, each kilowatt hour heat of 75°C results in a larger amount of kilowatt hours of cold of 10°C. Figure 9 displays an embodiment, in which cooling is delivered to the air- conditioning of a building with a flat roof, and at the same time hot water is produced by means of concentrated solar radiation. Long parabolic trough mirrors 60 are mounted in a fixed position on a flat roof 61 in an approximate East-West direction. At the Northern hemisphere the focal lines 62 are at the South side of the parabolic trough mirrors 60. Above and below the focal lines 62 are receiver planes 63. In the receiver planes 63 there are narrow, metal strips (not drawn) which are parallel to the focal lines 62. Every strip has a good thermal contact with a water tube 35 just above the receiver plane 63. The water tube 35 is parallel to the focal line 62. The thermal contact is realised by means of a heat pipe (not drawn), with which heat can be transported exclusively from below to above. As soon as a strip is hit by concentrated solar rays the strip functions as receiver and heat is transported to the water tube 35 by means of the heat pipes, from where the heat is transported by the water towards a useful application.

Every strip has as well a good thermal contact with a water tube 36 or with a condenser 36 of a heat pump which is positioned below the receiver plane 63. The water tube 36 or condenser 36 is parallel with the focal line 62. The thermal contact is realised by means of a heat pipe (not drawn), with which heat can be transported exclusively from below to above. As soon as a strip is not hit by concentrated solar light, and also not by direct solar light, the strip functions as radiating surface. Heat is absorbed from the water tube 36 or the condenser 36 and radiated out by the strip. The strips are covered with a layer which absorbs the radiation from the sun as well as infra-red radiation from bodies at room temperature. Instead of this the strips can be covered with photo-voltaic solar cells (not drawn). Next to the production of electricity the solar cells function as, and often at the same time, as radiating surface.

Figure 9 displays the projection of the incoming solar rays and reflected solar rays on a plane which is perpendicular to the focal lines 62 of the trough mirrors 60. Three situations are given. The left hand trough mirror is shone upon at a high projected solar position A. The receiver plane 63 is shone upon by the sun, by concentrated solar rays in the region 68, and by non-concentrated solar rays on the remaining part of the receiver plane 63. Therefore the receiver plane 63 cannot function as radiating surface. The middle trough mirror in Figure 9 displays the situation in which the incoming solar rays are parallel to the optical plane of the parabolic trough mirror 60. The reflected rays cross each other on a sharp line, the focal line 62. Only one of the strips is shone upon by concentrated solar light. All other strips are available as radiating surface. The right hand trough mirror in Figure 9 displays the situation at a low projected solar position C.

Figure 10 displays the same embodiment, but now infra-red rays are shown which run from the part in the sky where the sun is absent to a few strips 75, 76, and 77 of the receiver plane 63. The strip 75 is hit by infra-red rays originating from a high part of the sky. When the sun is not in this part, as is displayed in Figure 9 by the solar directions B and C, the strip 75 will cool down because of the outgoing radiation. The strip 76 is hit by infra-red rays originating from another part of the sky. When the sun is not in this part, like displayed in Figure 9 with solar direction C, the strip 76 will cool down because of the outgoing radiation.

The strip 77 is hit by infra-red rays originating from a lower part of the sky. When the sun is not in this part, like displayed in Figure 9 with solar direction B, the strip 77 will cool down because of the outgoing radiation. The ray 73 is not coming from the cold sky, but from one of the other strips. Such rays therefore do not contribute to the radiation cooling. However, only a small fraction of the surface of the strips is shone upon by these rays, so the harmful effect of these rays is limited.

Figure 11 displays an embodiment in which cooling is delivered to the air conditioning of a building with a flat roof and at the same time hot water is produced by means of flat solar collectors. Long, nearly vertical radiating surfaces 60 are mounted on a flat roof 62 in an East-West direction. The radiating surfaces 60 are thermally coupled to water tubes 63, with which heat from a liquid containing circuit is transported to the radiating surfaces 60. At the North side (at the Southern

hemisphere the South side) flat solar collectors 100 are present, which are covered with a spectral-selective layer which absorbs the solar rays having a short wavelength and reflects the infra-red rays having a long wavelength.

The figure shows two situations, at the right hand side when the position of the sun is not too high, wherein the radiating surfaces 60 are completely in the shadow. In that situation the radiating surfaces 60 are able to deliver cooling during the day too. At the left hand side the situation is drawn which occurs in summer time around 6 hours and 18 hours solar time. During these periods the radiating surfaces 60 are not only shone upon from the cold, blue sky, but also directly by the sun, which is then mostly at a position near to the horizon. The cooling power of the plates will most of the time be undone by the heating from the sun, so during these periods there is no radiation cooling available. After sunset cooling is produced in all cases. At day time the heat which is produced in the solar collector 100 by the absorption of the solar rays is carried off by water which flows through the tubes 104. Figure 12 displays the same embodiment, but now the infra-red rays are shown which are incident on two different points on the radiating surfaces 60. The radiating surfaces 60 are equipped with a coating with a high emission coefficient for infra-red radiation with a long wavelength, for instance a layer of titanium dioxide. Because all infra-red rays are coming from above an optical coupling arises with the cold air layers right above the radiating surface 60, causing its cooling down. Through the tubes 63 a liquid is flowing coming from the hot side of the heat pump of the air- conditioning installation in the building. Because of the outgoing radiation the waste heat of the heat pump is removed in an efficient way and at a low temperature, causing a considerable increase of the efficiency of the heat pump and at a

considerable decrease of the electric power consumption at the same cooling power. This effect occurs during the day as well as during the night, as long as the radiating surfaces 60 are not heavily hit by the solar rays.

Figure 13 displays an embodiment, consisting of a solar cooker for boiling water or preparing meals, which also is used as a refrigerator. In the figure the parabolic mirror 85, consisting of a parabola of revolution about the axis 86, is directed to the sun, which means that the sun is present on the axis 86, the axis also being the optical axis. The diameter of the outer edge of the revolutionary parabola 85 is 2 meters. In the focal point 87 a kettle 88 is positioned where upon the reflected solar rays 89 are concentrated, by this the kettle can reach temperatures higher than 100°C. The parabolic mirror 85 is on a frame with two rotational axes (not drawn) and several times per hour its position is adjusted by hand in order to follow the movement of the sun along the sky. Figure 14 displays the same embodiment after sunset. The axis 86 of the parabolic mirror 85 is directed to the zenith. In the region between the focal point 87 and the bottom of the mirror 85 a closed cylinder 90 is placed on a thick thermally isolating layer 91. The cylinder 90 is filled with cartridges or small bags filled with a material with a melting point in the region between 5 en 15°C. The cylinder 90 is equipped with a coating with a high emission coefficient for infra-red radiation with a long wavelength, for instance a layer of titanium dioxide.

The cylinder 90 is standing in optical contact with the thin layers of air in the atmosphere by means of the parabolic mirror 85, this contact is demonstrated by a few rays 93 which were reflected against the mirror 85 once, and rays 94 which connect the cylinder and the sky directly. Because of this optical contact the cylinder 90 cools down strongly, and the cold is absorbed by the cartridges or bags.

Before the installation is applied as solar cooker the bags or cartridges containing the cold are stored in a case with isolating walls containing food which must be kept fresh.

Figure 15 displays an embodiment in which electricity is produced by means of photo-voltaic solar panels, which are cooled by means of radiation. Thanks to the cooling the efficiency of the solar panels becomes increased. Long rows of solar panels 110 are mounted on a field 114 in an East-Westerly direction. At the opposite side of the solar panels there are flat mirrors 113. Solar rays which are incident on the mirrors 113 are reflected towards the solar panels 110. The solar panels 110 are thermally coupled to vessels 111 filled with water 112. At day the temperature of the water 112 is mostly lower than the temperature of the air. Because of the good conductance between the vessels 111 and the solar panels 110 the temperature of the solar panels 110 remains low during the day too and consequently the electrical efficiency is high.

The figure displays the projection of solar rays 115 onto the drawing plane for an installation located north of the tropic of Cancer. At the right hand side the situation is given at the middle of the day at a not to high solar position. At the left hand side the situation is given which occurs during the summer around 6 hours and 18 hours solar time. During this period the intensities of the rays 115 incident on the mirrors 113 and the solar panels 110 are approximately equally high, and the total intensity on the solar panels is doubled. By this the decrease of yield caused by the large zenith angle is partially compensated.

Figure 16 displays the same embodiment, but now the infra-red rays are shown which are running to two different points on the solar panels 110. The solar panels are such that they have a high emission coefficient for infra-red radiation with a large wavelength. The rays 116 are running directly from the sky towards the solar panels 1 10. The rays 117 originate from the sky and are incident on the solar panels 110 after one reflection against the mirror 113. After sunset all rays which are incident on the solar panels 110 are originating from the cold sky.

Figure 17 displays the roof of a greenhouse in a subtropical climate. The purpose of the greenhouse is protecting the plants against a too high temperature, and the reduction of the water consumption of the plants. The roof is covered with East-West directed trough mirrors 121 , which are spectrally selective. The visible part 122 of the solar rays 120 is passed to the plants by the spectral selective trough mirrors 121. The infra-red part 123 of the solar rays 120 is mainly reflected or absorbed by the spectral selective trough mirrors 121. Below the focal line 124 of the spectral selective trough mirror 121 is a radiating surface 125.

The figure gives the projection of the direct and the reflected solar rays on a drawing plane which is perpendicular to the focal lines 124. The projected solar position A occurs in the summer around 6 hours and 18 hours. The radiating surface 5 125 is shone upon directly by the sun as well as by concentrated infra-red rays 123 and is therefore not able to produce cold. The situations B and C occur much more often. The radiating surface 125 is not hit by concentrated infra-red rays 123 and also not shone upon by the sun. The radiating surface 125 is now able to produce cold. A part of the rays which are admitted by the spectrally selective roof reflect against the 10 mirrors 126, which are present at the inner side of the radiating surfaces 125.

Figure 18 displays the same embodiment, but now the infra-red rays 130 with a long wavelength originating from the sky are given, which are incident on the points 126, 127, and 128 of the radiating surface 125, after being reflected against the

15 spectral selective trough mirrors 121 or not.

Figure 19 displays a field of North-South directed stationary parabolic trough mirrors 140. The optical plane 141 of the parabolic trough mirror 140 has an angle of 45° with respect to the horizon. Behind and below the optical plane 141 there is a

20 receiver plane 142. The receiver plane 142 is hollow, which means that the shape looks like a reflection of the shape of the trough mirror 140. The receiver plane 142 is covered with cotton 143 which is impregnated with PNIPAAm. Figure 19 shows the projection on the East-West directed drawing plane of a random selection of rays which are incident on five different points 144-148 on the cotton surface 143. Most

25 rays originate from the sky, and especially from directions which make a rather large angle with the horizon, after being reflected by the trough mirror 140, or not. These rays are coming from matter with a very low temperature and therefore contribute considerably to a strong net cooling of the cotton 143. Some rays 149, which are incident on the points 144-148, are originating from other parts of the cotton surface

30 143. These rays do not contribute to the cooling, but they form a minority. Because of the cooling down of the cotton surface 143 dew is depositing on the surface. Because of the fact that the porous structure of the cotton 143 is hydrophilic, all water is absorbed in the rather thick layer 143 of PNIPAAm-impregnated cotton. Figure 20 displays the same embodiment, but now at five different points of time in the morning after sunrise. The point of time is indicated in the beam of solar rays which are incident on the parabolic trough mirrors 140 and the receiver planes 142. The right most trough mirror 140 is hit by solar rays at 7:30 hours solar time, when in the projection the sun is standing about 20° above the horizon. The area 150 on the cotton surface 143 is hit by concentrated solar rays. This area 150 is heating up. As soon as the temperature has crossed the critical temperature of 32°C the state of the PNIPAAm, with which the cotton 143 is impregnated, switches from hydrophilic to hydrophobic. The water that was absorbed during the night before appears at the surface, flows downwards along the surface 143, and is collected in the tube 151.

At 8:30 the radiated area 152 on the cotton surface 143 is shifted downwards, and now water is driven out of the cotton 143 at that spot. As the morning passes by the area which is heated by the concentrated is moving from the top to the bottom. At about noon all the water that was absorbed by the cotton 143 the night before is pushed out by the transition from the hydrophilic state to the hydrophobic state of the PNIPAAm with which the cotton 143 is impregnated. The water is drained away by means of the tubes 151 to a container (not drawn).

Figure 21 displays the cross section of a field of parabolic trough mirrors 40 which float on the water 9 of a pond or a lake during the day. The plane of symmetry of each parabolic trough mirror is vertical. At any moment the position of the mirrors is such that the sun is present in this plane of symmetry. In that case the mirrors concentrate the solar rays 45 on the receivers 47. Through the receivers 47 a liquid (oil, water, liquid salt, etc.) is flowing which is heated inside of the receivers. The heat is utilised in a Rankine process, for driving an absorption cooling process or an adsorption cooling process, for seawater desalination, dehydration of gypsum, or a chemical process. The receivers can be covered with photo-voltaic solar cells (not drawn). Most processes that are driven by the heat from the receivers also need cooling. This cooling is delivered by the water in the pond. In order to prevent that the temperature gradually becomes too high the following measures are taken:

1. The surface of the trough mirrors 40 is absorbing and emitting for infrared radiation with a wavelength between 3 and 30 micrometers. By this the mirrors are able to dissipate heat by means of radiation towards the blue sky during the day and black sky during the night.

2. The thermal resistance between the top side and the bottom side of the trough mirrors is small

3. The space 160 between the mirrors 40 and the water surface 9 is closed from the wind.

During a part of the day the temperature of the bottom side of the mirrors 40 will be lower than the temperature of the water 9. A net stream of water vapour will arise through the space 160 from the bottom to the top, wherein evaporation heat is consumed at the water surface 9 and condensation heat is deposited against the bottom of the mirrors 40. This heat flows through the mirrors 40 to the top surface of them. From there the heat is removed by means of outgoing radiation to the blue sky and in certain cases by convection.

Because of the condensation against the bottom of the mirrors 40 water drops

161 are formed. They fall back in the water 9, preventing loss of water through the evaporation. If there is a need for pure water, for potable water, process water, or for irrigation water, the drops 161 will be collected in the drains 162 in order to drain away the distilled water.

Figure 22 displays the same embodiment as Figure 21 , but now during the night. The top surfaces of the parabolic trough mirrors 40 have a high (>95%) emission coefficient for infra-red radiation with a wavelength of 3 to 30 micrometers. The surface elements 163 and 164 loose heat by means of radiation, and receive heat by means of incoming infra-red radiation. Most infra-red radiation 165 is originating from very cold air layers high above the horizon. A smaller part 166 is originating from less cold air layers lower above the horizon. A rather small fraction 167 of the infra-red radiation which is incident on the surface elements 163 and 164 is coming from the mirror 40 and the receiver 47. This fraction does not contribute to the radiation cooling. During the night the bottom side of the mirrors 40 is colder than the water 9 in the pond. In the closed space 160 between the mirrors 40 and the water 9 upwards transport of water vapour occurs, and with this the transport of cooling towards the water 9, as described by Figure 21. The condensed water 161 falls back in the pond 9, or can be carried off in the drains 162 for a useful application.

Figure 23 displays the North-South cross section of an embodiment with East- West directed photo-voltaic solar panels 110 on a flat roof 170, wherein mirrors 171 are applied to increase the intensity on the solar panels 110, and radiation cooling is applied to cool the solar panels 110. The solar panels 110 and mirrors 171 are standing above a shallow layer of water 172. This water is connected with a large vessel (not drawn) elsewhere in the building and circulated by means of a pump (not drawn). At the backside of the solar panels 110 a metal mesh 173 is glued .

Figure 23 displays the situation during the day with the projection on the drawing plane of the solar rays 174 at a high solar position and solar rays 175 at a low solar position. In both cases the mirrors 71 are hit by solar rays, and the reflected rays are completely or partially absorbed by the solar cells 1 10, resulting in an increase of the annual yield of the solar cells 110 with some tens of percents. The pumps 176 pump up water, after which this water flows back to the water surface 172 through the metal mesh 173. This way the solar cells on the solar panels 110 are cooled, resulting in an increase of the efficiency with 10 to 20% as compared to solar cells in the same position, but then in a frame in the open air.

Figure 24 displays the same embodiment as Figure 23 but now during the night. The solar panels 110 and the mirrors 171 cool down because of outgoing radiation to the cold night air. The net cooling power is big, because most incoming infra-red rays are originating from the very cold air layers high above the horizon, as described in more detail at Figure 22. At night and in the late afternoon the

temperature of the mirrors 171 is lower than the temperature of the water 172. The space 160 is closed off from the open air. In this space 160 evaporation occurs at the water surface 172 and condensation occurs against the bottom of the mirrors 171 and the metal mesh 173 at the back side of the solar panels 110. The condensed water falls back to the water 172 in the form of droplets 161. The water 172, which forms a part of a large stock of water, cools down at night, enabling it to be able to deliver a sufficient amount of cooling to the solar panels 110 next day.

Figure 25 displays an embodiment in which seawater 200 is desalinated by means of distillation, or polluted water is purified. The necessary heat is delivered by solar collectors 202 and the necessary cooling by mirrors 203. The solar collectors 202 are covered with window panes 204 in order to prevent loss of heat by outgoing radiation and convection. The heat from the solar collector 202 is transported to a heat exchanger 205 in the reservoir 201 by means of a transporting liquid, for instance a mixture of water and glycol. A part of this circuit extends through hoses (not drawn). This enables the possibility to rotate the solar collectors around a horizontal axis 206 to a vertical position. By this working space is created enabling maintenance personal to reach every part of the installation.

After a few sunny days the brine 200 in the reservoir 201 is heated to a high temperature, 60°C or more. An equilibrium arises in which the daily averaged supply of heat to the reservoir 201 is equal to the loss of heat because of evaporation of water from the brine 200. The space below the solar collectors 202 and the mirrors 203 is closed off from the open air in a wind-tight way. All water vapour from the reservoir 201 condenses against the lowest screen 216 and during the night also against the back side of the solar collector 202. The condensed droplets 208 slide or roll downwards, and the distilled water is collected and drained off with the drain 209.

The screens 207 are parallel to each other. The highest screen 207 is covered with weather-resistant reflecting aluminium 203 or a reflecting foil 203. With this the annual yield of the solar collectors is increased with some tens of percents. The mirror material absorbs and emits infra-red radiation with wavelength larger than 3

micrometers. By this the highest screen 207 is able to remove a lot of heat by means of outgoing radiation. The screens 207 are made out of sea water resistant aluminium, or are a stretched hydrophilic polymer foil.

Brine is transported to the screens 207 by means of the pump 210. The pump is supplied with power from a battery which is charged by a photo-voltaic solar panel at day. The whole surface of the screens 207 becomes covered with a thin layer of brine. The brine is stopped by the strips 211 and flows back to the reservoir 201 through the pipes 212. Because of the large difference in temperature between the brine 200 in the reservoir 201 and the mirror 203 the temperatures of the screens 207 will stabilise on equilibrium values, wherein temperature of a higher screen 207 always is lower than the temperature of a lower screen 207. In every interspace 213 between the screens 207 evaporation occurs at the brine "on the floor" of the interspace 213, and condensation "against the ceiling". The condensation droplets 214 slide or roll downwards and finally end in the drain 209. The valves 215 are adjusted such that about half of the brine on the screens 207 evaporates, and the other half flows back to the reservoir 201. The major part of the heat flow from the reservoir 201 crosses the screens 207 and is removed from the mirrors 203 by means of radiation cooling and convection cooling. Most heat is transported by means of evaporation and

condensation. In the case of 5 screens 207, as given in Figure 28, in the ideal case the Gain Output Ratio is equal to 5.

During the operation the volume of the brine 200 decreases gradually, and the liquid must be replenished with new seawater or new polluted water every few days. After one or two weeks the concentration of the remaining brine 200 in the reservoir 201 is increased to such extent that the brine has to be drained away and the reservoir has to be replenished completely with fresh seawater or new polluted water. The necessary tubes, hoses, and pumps for this are not drawn in the figure. Filtering is hardly needed, because dirt in the reservoir 201 has sufficient time to settle down. When the solar collectors 202 are turned in the vertical position the screens 207 can be easily dismounted and cleaned by two persons.

It will be apparent for the skilled person that the present invention is not limited to the embodiments, which here are described and shown in the figures as examples. The device according to the invention may be realized in different shapes and sizes and with different modifications, without departing from the essence of the invention. Such modifications and amendments are also encompassed in this invention. The scope of the invention is solely determined by the appended claims.

Claims

1. Device for harvesting solar energy and radiation cooling, comprising a solar collector which for instance is composed from mirrors, solar collectors and/or photo- voltaic solar panels, and a collector for infra-red radiation with a long wavelength configured for generating cooling by means of outward radiation from a radiating surface characterised in that the solar collector is configured to bring about a selection of the infra-red radiation incident on the radiating surface, wherein the selection is performed such, that mainly infra-red radiation from the coldest parts of the sky is incident on the radiating surface, or that the solar collector itself functions as radiating surface .

2. Device according to claim 1 , characterised in that the radiating surface surface has an emission coefficient of at least 90%.

3. Device according to claim 1 or 2, characterised in that the surface of the radiating surfaces plates is covered with an infra-red-absorbing layer, comprising for instance titanium dioxide, polyvinylchloride or silicon monoxide on metal.

4. Device according to any one of the claims 1-3, characterised in that the solar collector comprises a means of selecting reflecting infra-red radiation, wherein the means of selection is configured such, that mainly infra-red radiation from the coldest parts of the sky is incident on the radiating plates of the second system.

5. Device according to claim 4, characterised in that the means of selection blocks solar rays and infra-red radiation from the surroundings of the device.

6. Device according to one of the preceding claims, characterised in that the solar energy and the radiation cooling are harvested and generated, respectively, simultaneously.

7. Device according to one of the preceding claims, characterised in that the cooling which is generated in the radiating surface is utilised as cooling of a heat engine such as the Rankine process, the condenser of heat pumps including electricity- or heat-driven air conditioners , a photo-voltaic solar panel, a chemical production process, growing vegetation, harvesting water by means of the deposition of dew, the desalination of water, the conservation of food, and direct cooling of buildings.

8. Device according to one of the preceding claims, characterised in that the cooling which is generated in the radiating surfaces is transported by means of a heat pipe.

9. Device according to one of the preceding claims, characterised in that the parabolic trough mirrors of the first system are stationary with respect to each other and together form a floating member, which during its operation is floating on a liquid, preferably water.

10. Device according to one of the preceding claims, characterised in that the radiating surfaces are parallel with the optical plane of the parabolic trough mirror.

11. Device according to claim 10, characterised in that a plane at or near to the optical plane of the parabolic trough mirror is covered with strips which are thermally isolated from each other, which are parallel to the focal line of the parabolic trough mirror, which can function as receiver of concentrated solar rays, and which can function as radiating plate, wherein every strip is connected by means of a heat pipe to a higher situated reservoir having a temperature which is at least some tens of degrees Kelvin higher than the temperature of the surroundings, and connected by means of another heat pipe to a lower situated reservoir having a lower temperature than the higher situated reservoir.

12. Device according to claim 1 1 , characterised in that the strips are covered with photo-voltaic solar cells.

13. Device according to one of the preceding claims, characterised in that the radiating surface coincides with a photo-voltaic collector for producing electricity.

14. Device according to one of the preceding claims, characterised in that the solar collector is integrated in a greenhouse for growing plants, wherein the roof comprises a spectral selective window, which transmits visible light and reflects infra- red radiation.

15. Device according to one of the preceding claims, characterised in that the radiating surface is situated behind the optical plane of the parabolic trough mirror and the radiating surface is covered with a porous material which is hydrophilic at low temperature and hydrophobic at high temperature

16. Device according to the claims 1 , 2, 6, 7, and 13, characterised in that the mirrors at the same time function as radiating surface for the emission of infra-red radiation.

17. Device according to the claims 8 and 16, characterised in that the heat pipe consists of a closed space with air under atmospheric pressure, in which water is evaporating and condensing. 8. Device according to claim 7, characterised in that the condensed water is drained and utilized.

19. Device according to the claim 17 and 18, characterised in that the heat pipes are connected in series such that the solar heat is repeatedly utilised for evaporating seawater or polluted water.