WO2008107875A2

WO2008107875A2 - Solar energy convertor

Info

Publication number: WO2008107875A2
Application number: PCT/IL2008/000275
Authority: WO
Inventors: Tomer Valach
Original assignee: Convertpower Ltd.
Priority date: 2007-03-08
Filing date: 2008-03-04
Publication date: 2008-09-12
Also published as: IL181798A0; WO2008107875A3

Abstract

The invention is a system for collecting solar energy and converting it to heat. The system comprises a primary mirror on which the solar energy falls, an absorber to which the solar energy is directed by the primary mirror and a lens located between them. The primary mirror directs the solar energy through the lens, which distributes the solar evenly and without loss on the surface of said absorber. The collected solar energy can be utilized directly by concentrating the solar energy on the high temperature side of a delta T converter mounted at or near the focal point of the optical system and/or can be stored in the form of heat in a thermal fluid that can be transported to a location where it is needed and used immediately or stored for later use. Also described are various systems for utilizing the collected solar energy.

Description

SOLAR ENERGY CONVERTOR

Field of the Invention

The invention is related to the field of energy conversion. Specifically the invention relates to an apparatus for collecting solar energy and converting it to heat.

Background of the Invention

Many different types of solar to thermal energy collector/converters are known. These include: collection systems based on parabolic troughs, in which long parabolic reflectors are used to concentrate the sun's energy on a tube filled with thermal fluid; systems in which an array of movable mirrors are used to focus the energy of the sun at a central point in order to heat a working fluid; and parabolic solar collectors, in which large parabolic or spherical mirrors are used to concentrate the solar energy and heat the working fluid. In all cases, the working fluid is then used to drive turbines or a heat engine such as a Stirling engine to produce electricity. In order to produce electricity at night or during periods of low solar radiation, either supplementary heat sources such as gas burners or a way of storing the thermal energy until it is needed must be provided. The relatively few solar thermal electric power plants that are operating on a commercial basis around the world are generally relatively large plants designed to supply electricity to the power grid.

Since the technology of generating electricity from solar thermal energy is relatively new and the construction of commercially viable plants is very expensive, there is a great deal of interest in developing ways to increase the efficiency and reduce the costs. In particular it would be advantageous to develop a system that could be scaled either down or up to be able to economically provide the energy needs of small, medium, and large sized consumers. It is therefore a purpose of the present invention to provide a system for collecting solar energy, storing it in the form of heat, and converting the stored heat into other useful forms of energy such as electricity that could be scaled down or up to be able to economically provide the energy needs of small, medium, and large sized consumers.

Further purposes and advantages of this invention will appear as the description proceeds.

Summary of the Invention

The invention is a system for collecting solar energy and converting the solar energy to heat. The system comprises a lens located between a primary mirror and an absorber. The primary mirror directs the solar energy through the lens and the lens distributes the solar energy, which was reflected by the primary mirror evenly and without loss on the surface of the absorber.

In an embodiment the absorber is the high temperature input to a heat engine or a thermoelectric generator, in which case the heat is converted directly into electricity. In another embodiment the absorber is a hermetically sealed compartment containing thermal fluid and the heat is used to raise the temperature of the thermal fluid. In another embodiment an absorber that is the high temperature input to a heat engine or a thermoelectric generator and an absorber that is a hermetically sealed compartment containing thermal fluid are attached together and the heat is simultaneously converted directly into electricity and used to raise the temperature of the thermal fluid.

The primary mirror can be comprised of a single large reflecting surface, an array of smaller mirrors, or a mosaic of small segments. The lens can be comprised of an array of small lenses. The absorber may have any two or three- dimensional shape, e.g. rectangular, circular, cylindrical, elliptical, or spherical, depending on the application.

In preferred embodiments of the system of the invention all components of the collector are mounted on a platform. Sensors are provided to determine the position of the sun and a dual-axis tracking system operated automatically by a suitable control system is used to track the sun and move the platform as necessary to keep optical axis of the collector always pointed at the center of the sun whenever it is visible. Also a mechanism which causes translational motion of the lens and/or the absorber along optical axis can be provided.

The collector system can also comprise a convex or concave secondary mirror, in which case the primary mirror directs the solar energy towards the secondary mirror, the secondary mirror reflects the solar energy through the lens, and the lens distributes the solar energy reflected from the secondary mirror evenly and without loss on the surface of the absorber. In some embodiments of the collector system the primary mirror comprises a small hole at its center and the absorber is located on the side of the primary mirror opposite to that on which the lens and the secondary mirror are located.

The heat obtained by the system of the invention can be used directly to heat liquid for domestic or industrial purposes. In an embodiment the liquid can be non-potable water, which is heated above its boiling point to create steam and then the steam is cooled thereby providing distilled or desalinated water. The system of the invention can also comprise an accumulator subsystem in which the thermal energy contained in the thermal fluid is stored until it is utilized. The accumulator subsystem comprises: a) a tank filled with the thermal fluid; b) tubing to conduct the thermal fluid in a closed loop out of the tank, through the absorber, and back into the tank, c) one or more pumps activated by motors to push the thermal fluid through the tubing around the closed loop; and d) means for extracting the stored thermal energy from the tank when it is needed.

The thermal fluid can be any liquid or gas that will remain stable over the range of temperatures that are achieved in different parts of the system.

Thermal mass can be added to the tank to increase its heat capacity. The tank can comprise an arrangement of distributed inlets, outlets, or both. The inlets can be nozzles that spray the returning thermal fluid onto the thermal mass.

In preferred embodiments of the accumulator subsystem, the pump is an internal pump placed inside the tank and the motor is located outside the tank. A magnetic coupling can be used to transfer the rotational motion of the shaft of the motor to the shaft of pump.

The accumulator subsystem can comprise an expansion tank or a cylinder comprising a piston and optionally a spring can be connected to the interior of the tank by means of tube.

The stored thermal energy can be extracted from the tank by means of thermal valves. In preferred embodiments, the means for extracting the stored thermal energy from the tank comprise one or more internal pumps inside the tank. The pumps are activated by means of external motors to which they are magnetically coupled. When activated, the pumps pump hot thermal fluid in a closed cycle out of the tank through tubes to subsystems that utilize the thermal energy and back to the tank.

The system of the invention can comprise a supplemental heater, which can be a gas heater. The system can also comprise one or more heat exchangers located in the closed loop. Each of the heat exchangers comprises a radiator that is connected to the closed loop. The radiator is located inside a tank filled with thermal fluid. In an embodiment the tank is connected in series in the closed loop of an additional accumulator subsystem.

In addition to an accumulator subsystem the system of the invention can comprise a heat-to-electricity subsystem in which electricity is produced. The heat-to-electricity subsystem can operate on the basis of a difference of temperature between a high temperature input supplied with hot thermal fluid from the accumulator and a cold temperature input supplied with a cold thermal fluid. The heat-to-electricity subsystem can comprise a heat engine, e.g. a Sterling engine that turns an electricity generator, thermoelectric generator or any similar device. The cold thermal fluid can be provided from a subsystem comprising a tank filled with a thermal fluid, a filter, a pump, a radiator, and a fan; wherein all of the components except the fan are connected by tubing in series to the inlet and outlet of the converter that produces the electricity to form a closed loop through which the thermal fluid circulates. In an embodiment the thermal fluid is water. In an embodiment, the thermal energy that is absorbed by the cold thermal fluid as it passes through the converter that produces the electricity is removed from the thermal fluid by heating an air stream created by the fan as it blows through the radiator. The heated air stream is directed by baffles through an absorber where the heat is transferred to thermal fluid flowing through tubing passing through the absorber. An array of mirrors can be provided between the radiator and the absorber. The mirrors are set up at an angle so as not to impede the air flow, while at the same time reflecting the heat reflected or radiated from the absorber back onto itself. The heat absorbed by the thermal fluid flowing through the absorber can be utilized to supply the hot water needs of the location at which the system is installed. The tubing passing through the heat absorber can be connected to an accumulator, which stores the thermal energy removed from the air stream for later use to another thermal energy to electricity converter.

In another embodiment the heat-to-electricity subsystem comprises a steam turbine, which is connected to an electricity generator. The steam used to operate the turbine is produced in a subsystem comprising: a) a heat exchanger located inside a tank filled with water which is heated to very high temperatures by hot thermal fluid from the accumulator that is pumped through the heat exchanger causing the water to boil and creating superheated steam; b) tubing that conducts the superheated steam through the steam turbine; c) tubing that conducts the steam that has passed through the steam turbine to a radiator that is cooled by a fan; d) tubing which conducts the steam that condenses to liquid water in the radiator to a water tank; and e) tubing that conducts the water from the tank to a pump which pumps the water through a one-way valve back into the tank containing the heat exchanger. The steam that has passed through the steam turbine can be utilized to distill water. The steam that has been utilized to distill water can then be passed through a heat exchanger to heat water for domestic or industrial use.

All the above and other characteristics and advantages of the invention will be further understood through the following illustrative and non-limitative description of preferred embodiments thereof, with reference to the appended drawings.

Brief Description of the Drawings

— Fig. 1 is a general schematic outline of the major components of the system of the invention; — Fig. 2 schematically shows the basic design of collector;

— Fig. 3 to Fig. 5 schematically show different embodiments of the optical design of collector;

— Fig. 6 schematically shows the structure of the accumulator and its connections to the collector; — Fig. 7 schematically shows another embodiment of the part of the system of the invention shown in Fig. 6;

— Fig. 8 schematically shows an embodiment of the system that uses differences in temperature to produce electricity and relative heat for electricity and or heating purposes. — Fig. 9 and Fig. 10 schematically show embodiments of the system in which a steam turbine is used to produce electricity.

Detailed Description of Preferred Embodiments

The motivation behind the present invention is to build a relatively compact and economical energy system that efficiently collects solar energy and converts it to heat. The collected solar energy can be utilized directly by concentrating the solar energy on the high temperature side of a delta T converter mounted at or near the focal point of the optical system used to collect the solar energy, e.g. the heat can be converted directly to electricity in a heat-to-electricity subsystem (300 in Fig. 1) by concentrating the solar energy on the high temperature side of a heat engine, e.g. a Sterling engine, which turns the rotor of an electric generator to produce AC/DC electricity, or of a thermoelectric generator (TEG), which produces DC electricity,. Alternatively the thermal energy can be stored in the form of heat in a thermal fluid that can be transported to a location where it is needed and used immediately or stored for later use. Both processes can be carried out simultaneously, i.e. the heat can be converted directly into alternative forms of energy and at the same time the heat can be stored for backing up changes in the level of solar radiation during daylight hours, at night, or weather changes. From the stored energy it is possible to produce all the energy needs of the location at which the system is installed. These energy needs can include electricity, purified or desalinated water, hot water and/or a heat source for various household and industrial purposes. The various embodiments of the systems are intended to be able to supply most of the energy needs for individual houses, factories, campsites, ships, etc.; however the systems can be scaled up and/or a plurality of small systems can be connected together to supply the energy needs of much larger consumers, e.g. large apartment or office buildings, power stations for cities, etc.

The general schematic outline of the major subsystems that comprise the energy systems based on the solar energy collector of the invention is shown in Fig. 1. Radiation from the sun 10 is collected and concentrated in collector

100, where the solar radiation is converted to heat. The collected heat can be used directly to heat a liquid for domestic or industrial purposes. The system is capable of heating water to a temperature greater than its boiling point. The subsystem shown schematically as block 400 can comprise a systeni to cool the steam and condense it to liquid water at lower temperatures. Thus non-potable water can be distilled or desalinated.

The collected heat can be converted directly to electricity in heat-to- electricity subsystem 300 or it can be used to heat a thermal fluid. Both methods can be used simultaneously by attaching the absorber 106 of collector subsystem 100 (to be described hereinbelow) to the high temperature input to the heat engine, TEG, or similar device and assuring good thermal contact between them. Sufficient heat energy will be transferred to the heat-to-electricity subsystem to produce electricity at the same time as the thermal fluid is being heated. Alternatively, the optical components can be adjusted such that the solar energy is distributed on the surface of both absorber 106 and the high temperature input. Thus thermal energy can be stored to operate the heat-to-electricity subsystem during the night without the necessity of relying on low efficiency rechargeable battery systems or alternative energy sources.

In the case in which the heat is used to raise the temperature of a thermal fluid, the thermal energy is transported by means of the of hot fluid to accumulator 200 where it is stored in accumulator 200 until it is needed, for example in a thermal energy to electricity converter 300 to produce electricity or in heat exchanger 400 to heat water for various purposes. The arrows show the general direction of energy flow in the system. As will be understood as the description continues hereinbelow, the situation is not as simple as it is shown in Fig. 1. The energy system can be assembled in many different configurations each of which comprises many different combinations of embodiments of the subsystems to be described hereinbelow.

Fig. 2 schematically shows the basic design of the subsystem known as collector 100 whose function is to collect solar radiation and convert it to a useable form of heat. The energy of the sun falls on a primary mirror 102 and is focused onto an absorber 106 in a manner similar to that of many prior art systems. The novel feature of the collector 100 of the present invention is the addition of a lens 104 on the optical axis 108 of the collector. Lens 104 is located between primary mirror 102 and absorber 106. The function of lens 104 is to distribute the solar energy collected by mirror 102 evenly and without loss on the surface of absorber 106. Use of lens 104 allows collector 100 to be much more compact than prior art collectors of similar energy absorbing capacity. Herein the word "lens" when used to refer to lens 104 is to be understood to be either a single lens or an array of lenses. Mirror 102 is a spherical or parabolic mirror. For the embodiments envisaged at this stage in the development of the invention is on the order of the size of a household satellite antenna, e.g. about one to two meters in diameter, although the system can be either scaled down or up depending on the amount of energy that the system must supply. Mirror 102 can be comprised of a single large reflecting surface or an array of smaller spherical, parabolic, plane mirrors, or comprised of a mosaic of small segments. For example a parabolic shaped mirror can be approximated by fitting together a plurality of small plane mirrors in an appropriately shaped frame.

Lens 104 must be made of a material that is both transparent to the heat- producing rays of the sun and robust enough to cope with the thermal stress caused by the energy reflected by mirror 102. Lens 104 is located between mirror 102 and its focal point. In conventional systems in which the diameter of the parabolic dish collector has a diameter on the order of several meters, it would not be practical to try to supply a large enough lens such as shown in Fig. 2.

Absorber 106 may have any convenient two or three- dimensional shape, e.g. rectangular, circular, cylindrical, elliptical, or spherical, depending - li on the application. For systems in which the solar energy is converted directly to electricity, absorber 106 can comprise part of the energy generating device, for example a blackened area on the surface of a TEG. A conventional arrangement for storing the electricity produced in batteries for use when the available solar energy is too low to operate electric power converter 300, e.g. at night can also be provided.

If the solar energy is to be stored in the form of heat, then absorber 106 comprises some form of hermetically sealed compartment containing thermal fluid. The sealed compartment has an input and an output that are connected to external tubes that connect it in a closed circuit to the accumulator 200 as will be discussed hereinbelow and shown in the figures, e.g. in Fig. 6. The sealed compartment can be in the form of a tube that is either straight or bent into a coil or some other shape through which the thermal fluid flows. Alternatively the absorber can have any other form known in the art, e.g. a hollow block or a block with internal channels created inside of it. The energy that is concentrated on the surface of absorber 106 by lens 104 heats the walls of absorber 106. The heat from the walls is transferred to the thermal fluid, which circulates through the tubes, thereby raising its temperature. In order to increase the efficiency of heat absorption by the walls of absorber 104, methods such as painting or coating the absorber 106 black are employed in preferred embodiments.

In preferred embodiments of the invention, all components of the collector are mounted on a platform. Sensors are provided to determine the position of the sun and a dual-axis tracking system operated automatically by a processor/computer is used to track the sun, and move the platform as necessary to keep optical axis 108 of collector 100 always pointed at the center of the sun, whenever the sun is visible. Additionally a mechanism is provided to cause translational motion of the lens 104 and/or the absorber

106 along optical axis 108. In this way the elements are moved relatively to each other and to mirror 102 to adjust the focus and therefore the temperature of the circulating thermal fluid. Preferably, this mechanism is also controlled by the processor/computer using information supplied to it by appropriate sensors strategically placed in the closed loop system. These mechanisms are well known in the art and therefore are not further described or shown in the figures herein.

It is to be noted that in general only the main elements of the subsystems are shown in the figures. For purposes of clarity and to simplify the description elements such as mounting platforms and supports, baffles to direct the flow of energy, casings and covers to provide thermal insulation and protection from environmental disturbances, etc. are not shown. All of these are design features that skilled persons would recognize as either necessary or advantageous and would also know how to design and build. In addition sensors and one or more processing units or other known type of control systems such as analog/digital closed loop systems are normally provided to allow automatic control of the components of the various subsystems in order to allow optimal conditions of temperature, pressure, flow rate, etc. to be maintained throughout the system.

The apparatus of the invention for collecting solar energy and converting it to heat can have many different designs. Fig. 3, Fig. 4, and Fig. 5 schematically show examples of different embodiments of the optical design of collector 100. The embodiment shown in Fig. 3 has a Cassegrain reflector design. Radiation from the sun 10 is reflected by concave primary mirror 102 towards convex secondary mirror 110, which reflects the radiation through lens 104 onto the absorber 106. The embodiment shown in Fig. 4 is similar to that shown in Fig. 3 with the exception that secondary mirror 110 is concave in this embodiment. As in the case of primary mirror 102, secondary mirror 110 can be comprised of a single reflecting surface or an array of smaller spherical, parabolic, or plane mirrors or an array of small segments. For example a parabolic shaped mirror can be approximated by fitting together a plurality of small plane mirrors in an appropriately shaped frame.

In both the embodiments shown in Fig. 3 and Fig. 4, a small hole can be created at the center of primary mirror 102. This will allow the absorber 106 to be placed behind mirror 102. This configuration is particularly advantageous since the electric power converter 300 and/or absorber 106 will not block the solar radiation falling on primary mirror 102 and can be mounted directly on the platform and vibrationally isolated from the optical components of collector 100.

In the embodiment shown in Fig. 5, absorber 106 has a spherical shape. An array of small lenses 104 is held by crescent shaped holder 112 so that each lens will concentrate a part of the energy reflected from primary mirror 102 onto a different part of the surface of the sphere. The radius of curvature of the imaginary line passing through the center of each of the lenses 104 together with the number and size of the lenses are chosen such that as much as possible of the surface of absorber 104 is uniformly "illuminated" with the solar radiation

In order to be able to supply energy on demand and particularly during periods of darkness or on cloudy days, the energy collected by subsystem 100 must be stored. This is the function of subsystem 200, known herein as the accumulator. Fig. 6 schematically shows the structure of accumulator 200 and the connections between the accumulator 200 and collector 100. The accumulator 200 comprises a tank 202, which is filled with thermal fluid to level 204. The thermal fluid can be any liquid or gas that will remain stable over the range of temperatures that are achieved in different parts of the system. A preferred thermal fluid is one of the many known types of synthetic thermal fluid because of their high heat capacity and the high operating temperatures at low operation pressures that can be obtained by using them. The exterior walls of tank 202 are lined with thermal insulating material to reduce as much as possible transfer of heat from inside the tank to the surroundings. In order to increase the heat capacity of the tank, thermal rαass, for example stones or lumps of metal or ceramic material, can be added either distributed within the interior or attached to the inner walls of the tank. The dimensions of tank 202 depend on the quantity of thermal energy it is desired to store.

The thermal fluid is pumped out of tank 202 through insulated tubing 216 into absorber 106 where the thermal fluid absorbs the heat collected by the optical components of collector 100. The heated thermal fluid continues to flow through insulated tubing 218 until it reenters tank 202. The term "tubing" is used to refer to any type of closed tube, pipe, or conduit through which a fluid can flow from one point to another in the system. Typically, the tubing is surrounded by thermal insulation to preserve the temperature of the thermal fluid flowing through it. As the thermal fluid circulates around the closed loop the temperature of the thermal fluid in tank 202 steadily rises. The thermal fluid circulates through the absorber 106 until the temperature in the tank reaches its maximum value. Schematically shown within tank 202 are arrangements of distributed inlets 220 and of distributed outlets 214. The purpose of these arrangements being to more evenly distribute the heat within the tank and prevent cold pockets which could occur if the thermal fluid was only pumped out of the tank from a single location. If the tank contains thermal mass 206, the inlets 220 can advantageously be nozzles that spray the returning thermal fluid onto the surface of the thermal mass.

One or more pumps, depending on the size of the system, are needed to cause the thermal fluid to circulate. In all cases it is possible to use in external pumps; however, in preferred embodiments of the invention, an internal circulation pump 208, placed inside the tank 202 is used. This is because internal pumps are typically less expensive than external pumps of the same capacity and also there is no problem of leaking thermal fluid associated with internal pumps. Internal pump 208 must be designed to operate in the conditions, especially over the temperature range, which exist inside tank 102 and also must have a pumping capacity large enough to insure continuous circulation of the thermal fluid at the optimal flow rate.

A motor 210 must be supplied to activate pump 208. Since motor 210 is located outside of tank 202 and pump 208 inside, a way to provide the mechanical coupling between the two must be provided. This can be done by simply making a straight connection through the top of tank 202. However, the seals around the rotating shaft have a tendency to leak both thermal fluid and more importantly heat. Since the purpose of the tank 202 is to store as much heat for as long as possible it is desirable to have as few openings, no matter how well sealed/insulated, between the hot interior and colder exterior. Therefore in the preferred embodiments of the invention a magnetic coupling 212 is used to transfer the rotational motion of the shaft of motor 210 to the shaft of pump 208.

As the temperature of the thermal fluid rises its volume also increases, therefore tank 202 can not be filled with thermal fluid unless a second expansion tank can be provided connected to tank 202. As the volume of the thermal fluid in tank 202 expands, the overflow will enter the expansion tank. This type of arrangement, which is typically found in accumulators similar to accumulator 200 is not favored in preferred embodiments of the invention because of the potential heat losses involved and the necessity of providing means to return thermal fluid to the tank 102 from the overflow tank when the volume of thermal fluid in tank 102 is reduced. According to the invention, the maximum level 204 of the thermal fluid in tank 202 is determined such that a volume of air at room temperature at least as great as the maximum increase of the volume of the thermal fluid at the maximum temperature is trapped inside the top of tank 202. A cylinder 222 comprising a piston 224 and optionally a spring 226 is connected to the interior of tank 202 by means of tube 228. As the temperature inside tank 202 rises, the pressure of the air increases as its temperature increases and also as it is compressed by the expanding thermal fluid. When the pressure becomes great enough to overcome the force of piston/spring 226 and piston 224 is pushed upwards, thereby allowing air to flow into cylinder 222 and reducing the pressure inside tank 202. When the temperature inside tank 202 is reduced the air is pushed by the spring 226 and piston 224 out of the cylinder 222 back into the tank. If spring is present or not a small hole can be created through the piston allowing the pressure to be equalized on both sides of the piston. In this case, as the pressure in tank 202 is reduced below that of the air behind the piston, the air will be pulled out of cylinder 222 and back into the tank. Other mechanisms, such as creating a back pressure on the side of the piston opposite the tank 202 can also be used to return the air to the tank. To reduce the temperature of the air entering cylinder 222, tube 228 can be bent into the shape of a spiral coil as shown in Fig. 6 or some other type of radiator or air/ liquid cooler (not shown) can be used.

In order to extract the stored thermal energy from accumulator 200, conventional solar energy systems use thermal valves. These valves are expensive and also not always reliable; therefore, although thermal valves can be used, the preferred embodiments of the present invention make use of a different approach. According to the invention a second internal pump 208' is provided inside tank 202. When pump 208' is activated by means of motor 210' to which it is magnetically coupled, then hot thermal fluid is pumped in a closed cycle out of tank 202 through tubes to heat-to-electricity converter 300 or heat exchanger 400 (see Fig. 1) and back to tank 202. The connections to the tubing carrying the heated thermal fluid away from and returning the cool thermal fluid to tank 202 are shown as A and B respectively in the figures. Motor 210' and pump 208' are not activated continuously but only on demand in order for the system of the invention to be able to supply electricity or energy for some other purpose and to preserve heat.

Fig. 7 schematically shows another embodiment of the part of the system of the invention shown in Fig. 6. In this embodiment a supplementary heater 20 fueled by another heat source is added to the system to heat the thermal fluid during periods when the sun does not supply enough radiation to meet the demands on the system. Preferably supplementary heater 20 is a gas heater for reasons of economy, ease of operation and maintenance, and minimal pollution. Supplementary heater 20 can be inserted at any convenient location in the system. One such location is shown in Fig. 7, i.e. supplementary heater 20 is inserted in series in the tubing 216,218 that comprises the closed circuit through which the thermal fluid is pumped by pump 208. Alternatively, an additional circulation pump can be provided to pump thermal liquid directly from tank 202, to supplementary heater 20, and back into tank 202. For the reasons given above, this additional pump is preferably located inside tank 202.

Another optional addition to the basic system is heat exchanger 230, which is located in the circuit between absorber 106 and accumulator 200. Heat exchanger 230 is an insulated closed container 232 filled with thermal fluid. Thermal fluid flowing through conduits 216 and 218 flows through radiator 234 inside container 232 after it has absorbed heat in absorber 106. Some of this heat is then transferred to the thermal fluid inside container 232 as the thermal fluid in conduit 218 continues on its way back to tank 202. Radiator 234 can be a simple coil of metallic tubing or preferably of a more sophisticated design known in the art. A second accumulator comprising all of the features of accumulator 200 is attached to heat exchanger 230 by means of tubing 236 and 238. Inside the second accumulator pump 208 push.es thermal fluid through tubing 236 into the interior of container 232 forcing hotter thermal fluid back into the tank of the second accumulator gradually increasing the quantity of heat energy stored therein.

In a preferred embodiment accumulator 200 is relatively small to allow the thermal fluid therein to be heated to a sufficient temperature for operating the heat-to-electricity subsystem rapidly. The second accumulator is much larger, which provides sufficient heat capacity to allow operation of the system for extended periods of time when there is insufficient solar radiation but requires a long time to heat the large volume of thermal fluid. By the use of two accumulators, the system of the invention can provide the consumer with electricity from the small accumulator without having to wait a long time while the thermal fluid in the larger accumulator heats up to operating temperature.

A second option for using heat exchanger 230 is when the level of solar radiation is very high. Under these conditions, the thermal fluid inside the main tank 202 will reach the optimal operating temperature at which point, under ordinary operating conditions, steps must be taken to reduce the amount of energy collected. If however one or more heat exchangers 230 are provided in the system, then the second tank can be activated to store the extra heat, thereby reducing or avoiding the necessity of "throwing away" solar energy.

The essential elements of the thermal energy collection and storage subsystems and the connection between them have been shown in Fig. 6 and Fig.7. The thermal energy collected in accumulator 200 can be utilized in many different ways to generate electricity and supply other needs, such as hot water or a pure water supply to the site at which the system of the invention has been installed. All that is necessary is to connect outlet A and input B to an appropriate subsystem 300 and/or 400 (Fig. 1). Exemplary but not limiting examples of embodiments of such subsystems are shown in Fig. 8 and Fig. 9.

Fig. 8 schematically shows an embodiment of the system that uses differences in temperature to produce electricity. Many different types of heat engines 302, such as a Sterling engine can be used to turn an electricity generator 308. Alternatively a thermoelectric generator (TEG) based on the Seebeck effect can be used to produce direct current electricity. In any case, high temperature must be supplied at high temperature input 304 and a lower temperature at input 306. When it is desired to produce electricity, motor 210' is activated. As a result pump 208' pushes hot thermal fluid through outlet A causing it to flow through tubing (not shown) to the high temperature side 304 of the thermal energy to electricity generator and back to inlet B of tank 202.

As schematically shown in Fig. 8, a subsystem 400 provides the cold temperature at input 306. The components of subsystem 400 essential to the electricity production are: tank 310, filled with a thermal fluid, which in preferred embodiments of the invention is water; filter 312; pump 314; radiator 316; and fan 318. AU of these components, except the fan are connected by tubing in series to form a closed loop as shown in Fig. 8. The filtered water is pumped to cold side 306 of the thermal energy to electricity converter 302, e.g. a Sterling engine, and from there it flows through the radiator where it is cooled by the fan blowing through the radiator on its way back to the tank to complete the cycle.

Depending on the efficiency of the heat engine 302 used to convert the thermal to mechanical energy (or, in the case of a TEG, directly into electricity) a large quantity of heat is absorbed by the cold water passing through the cold side of the heat engine. This quantity of heat is removed by the air stream created by fan 318 as it blows through the radiator 320 and can be utilized to supply the energy needs of the location at which the system of the invention is installed. Referring to Fig. 8, heat absorber 320 comprises a continuous tube 322 through which a thermal fluid can be caused too flow. Absorber 320 is located directly in front of radiator 316 and suitable baffles 326 are supplied to insure that the entire hot air stream created by fan 318 passes through absorber 320. Tube 322 is configured and its outer surface is designed to maximize the transfer of heat from the air stream blowing past it to the thermal fluid inside it. As an additional method of insuring the maximum energy transfer to the fluid in tube 322, an array of mirrors 324 are provided between radiator 316 and absorber 320. The mirrors are set up at an angle as shown so as not to impede the flow, while at the same time reflecting heat from absorber 320 back in the direction of the absorber. This arrangement of mirrors increases the efficiency of heat absorption by the thermal fluid in tube 322 while preventing part of the heat that is radiated by the radiator from being radiated or reflected back upon itself, which would reduce the efficiency of the cooling of the thermal fluid flowing towards tank 310.

The thermal fluid entering tube 322 at C can be cold water from the mains supply or any other source. In this case the hot water exiting at D can be directed either to a storage tank for later use or directly to the hot water distribution network of the house or other installation. In another embodiment C and D can be connected to the high temperature side of an additional thermal energy to electricity converter 300 in a corresponding manner to connections A and B in the figure. In yet another embodiment, C and D represent the output and input to another accumulator in which the excess thermal energy produced in subsystem 400 is stored for later use.

Fig. 9 and Fig. 10 schematically show embodiments of the thermal energy to electricity converter and heat exchanger subsystems in which the production of electricity is based on the use of a steam turbine. Fig. 9 shows the heat-to-electricity subsystem 300. Tubing connects outlet A and inlet B from accumulator 200 (Fig. 6 or Fig.7) to the ends of heat exchanger 354, which is located inside tank 350 that is filled with water to level 352. As the hot thermal fluid circulates through heat exchanger 354, it heats the water in tank 350 to very high temperatures causing the water to boil and creating superheated steam. The steam flows through steam turbine 356 connected to electricity generator 308, thereby producing the electricity. The steam that passes through turbine 356 continues around the closed circuit of tubing 360 until it passes through radiator 316. The steam in the radiator is cooled by fan 318 and condenses to liquid water which enters water tank 310. A radiator 316 is described here as an example, but a cooling tower or similar structure can be used in place of or in addition to cool the steam/water circulating around the system. The water in tank 310 is pumped by pump 312 through a one-way valve 358 back into tank 350 where it is again converted to steam to cause the turbine to rotate.

Fig. 10 shows several embodiments of a heat exchanger subsystem 400 that can be used in conjunction with the subsystem 300 shown in Fig. 9 in order to utilize the energy available in the steam that exits from turbine 356. As shown in Fig. 10, the steam that exits from turbine 356 enters heat exchanger 364. Heat exchanger 364 is immersed in a tank 362 full of water supplied from source 366. Source 366 is filtered non-potable water, for example seawater, or groundwater with a high salt content. The steam passing through heat exchanger 364 is hot enough to boil the water in tank 362. The steam passes via tubing 368 to radiator 316 cooled by fan 318 where the steam is condensed. The distilled water is collected in storage tank 370 and can be used for drinking and cooking.

The steam that entered heat exchanger 364 may exit as either steam at a lower temperature or as very hot water. In either case the heat energy it contains can be utilized by passing it through a second heat exchanger 372 in a tank 374 filled with cold water from source 376. The water in tank 374 is heated and transferred to hot water storage tank 378. The steam or hot water that entered heat exchanger 372 has now been cooled considerably and continues its journey around closed circuit 360 returning to water tank 310.

Skilled persons will recognize that the two uses of the steam that passes through turbine 356 are only given as examples. Other uses of the thermal energy contained in this steam are contemplated by the inventor, for example the steam can be directed through a system of pipes and radiators to heat a dwelling or to turn a turbine for electricity production.

Although embodiments of the invention have been described by way of illustration, it will be understood that the invention may be carried out with many variations, modifications, and adaptations, without exceeding the scope of the claims.

Claims

1. A system for collecting solar energy and converting said solar energy to heat, said system comprising a lens located between a primary mirror and an absorber, wherein said primary mirror directs said solar energy through said lens and said lens distributes the solar energy reflected from said primary mirror evenly and without loss on the surface of said absorber.

2. A system according to claim 1, wherein the absorber is the high temperature side of a delta T converter.

3. A system according to claim 1, wherein the absorber is a hermetically sealed compartment containing thermal fluid and the heat is used to raise the temperature of said thermal fluid.

4. A system according to claim 1, comprising both an absorber that is the high temperature side of a delta T converter and an absorber that is a hermetically sealed compartment containing thermal fluid that are attached to each other, wherein the heat is simultaneously converted directly into electricity and used to raise the temperature of said thermal fluid.

5. A system according to claim 1, wherein the primary mirror is comprised of one of the following: a) a single large reflecting surface; b) an array of smaller mirrors; or c) a mosaic of small segments.

6. A system according to claim 1, the shape of the absorber is selected from: a) rectangular; b) circular; c) cylindrical; d) elliptical; or e) spherical.

7. A system according to claim 1, wherein all components of the said system are mounted on a platform, sensors are provided to determine the position of the sun, and a dual-axis tracking system operated automatically by a control system is used to track the sun and move the platform as necessary to keep the optical axis of said system always pointed at the center of the sun, whenever the sun is visible.

8. A system according to claim 1, comprising a mechanism that is adapted to allow translational motion of the lens and/or the absorber along the optical axis.

9. A S3^stem according to claim 1, additionally comprising a convex or concave secondary mirror, wherein the primary mirror directs the solar energy towards said secondary mirror, said secondary mirror reflects said solar energy through the lens, and said lens distributes said solar energy reflected from said secondary mirror evenly and without loss on the surface of the absorber.

10. A system according to claim 8, wherein the secondary mirror is comprised of one of the following: a) a single reflecting surface; b) an array of smaller mirrors; or c) a mosaic of small segments.

11. A system according to claim 9, wherein the primary mirror comprises a small hole at its center and the absorber is located on the side of the primary mirror opposite to the side on which the lens and the secondary mirror are located.

12. A system according to claim 1, wherein the lens is comprised of an array of small lenses.

13. A system according to claim 1, wherein the heat is used directly to heat a liquid.

14. A system according to claim 13, wherein the liquid is water, which is heated above its boiling point to create steam and then said steam is cooled thereby providing distilled or desalinated water.

15. A system according to claim 1, comprising an accumulator subsystem in which the thermal energy contained in the thermal fluid is stored until it is utilized, said accumulator subsystem comprising: a) a tank filled with the thermal fluid; b) tubing to conduct said thermal fluid in a closed loop out of said tank, through the absorber, and back into said tank, c) one or more pumps activated by motors to push said thermal fluid through said tubing around said closed loop; and d) means for extracting said stored thermal energy from said tank when it is needed.

16. A system according to claim 15, wherein thermal mass is added to the tank.

17. A system according to claim 15, wherein the tank comprises an arrangement of distributed inlets, outlets, or both.

18. A system according to claim 17, wherein the tank comprises thermal mass and the inlets are nozzles that spray the returning thermal fluid onto the thermal mass.

19. A system according to claim 15, wherein the pump is an internal pump placed inside the tank and the motor is located outside said tank.

20. A system according to claim 19, wherein a magnetic coupling is used to transfer the rotational motion of the shaft of the motor to the shaft of pump.

21. A system according to claim 15, comprising an expansion tank.

22. A system according to claim 15, comprising a piston and optionally a spring inside a cylinder that is connected to the interior of the tank by means of a tube.

23. A system according to claim 15, wherein the means for extracting the stored thermal energy from the tank are thermal valves.

24. A system according to claim 15, wherein the means for extracting the stored thermal energy from the tank comprise one or more internal pumps inside said tank, said pumps activated by means of external motors to which they are magnetically coupled; wherein, when activated, said pumps pump hot thermal fluid in a closed cycle out of said tank through tubes to subsystems that utilize said thermal energy and back to said tank.

25. A system according to claim 1, comprising a supplemental heater.

26. A system according to claim 25, wherein the supplemental heater is a gas heater.

27. A system according to claim 15 comprising one or more heat exchangers located in the closed loop, wherein each of said heat exchangers comprises a radiator that is connected to said closed loop and located inside a tank filled with thermal fluid.

28.A system according to claim 27, wherein the tank is connected in series in the closed loop of an additional accumulator subsystem.

29. A system according to claim 15, comprising a heat-to-electricity subsystem in which electricity is produced.

30. A system according to claim 29, wherein the heat-to-electricity subsystem operates on the basis of a difference of temperature between a high temperature input supplied with hot thermal fluid from the accumulator and a cold temperature input supplied with a cold thermal fluid.

31. A system according to claim 30, wherein the heat-to-electricity subsystem comprises a heat engine that turns an electricity generator.

32. A system according to claim 31, wherein the heat engine is a Sterling engine.

33. A system according to claim 30, wherein the heat-to-electricity subsystem comprises a thermoelectric generator.

34. A system according to claim 30, wherein the cold thermal fluid is provided from a subsystem comprising a tank filled with a thermal fluid, a filter, a pump, a radiator, and a fan; wherein all of the components except the fan are connected by tubing in series to the inlet and outlet of the converter that produces the electricity to form a closed loop through which said thermal fluid circulates.

35. A system according to claim 34, wherein the thermal fluid is water.

36. A system according to claim 34, wherein the thermal energy that is absorbed by the cold thermal fluid as it passes through the converter that produces the electricity is removed from said thermal fluid by heating the air stream created by the fan as it blows through the radiator; wherein said heated air stream is directed by baffles through an absorber where the heat is transferred to thermal fluid flowing through tubing passing through said absorber.

37. A system according to claim 36, comprising an array of mirrors between the radiator and the absorber; wherein said mirrors are set up at an angle so as not to impede the air flow, while at the same time reflecting heat that is reflected or radiated from said absorber back onto itself.

38. A system according to claim 36, wherein heat absorbed by the thermal fluid flowing through said absorber is utilized to supply the hot water needs of the location at which the system is installed.

39. A system according to claim 36, wherein the tubing passing through the heat absorber is connected to an accumulator, which stores the thermal energy removed from the air stream for later use.

40. A system according to claim 36, wherein the tubing passing through the heat absorber is connected to another thermal energy to electricity converter.

41. A system according to claim 29, wherein the converter that produces the electricity is a steam turbine, which is connected to an electricity generator.

42. A system according to claim 41, wherein the steam to operate the steam turbine is produced in a subsystem comprising: a) a heat exchanger located inside a tank filled with water which is heated to very high temperatures by hot thermal fluid from the accumulator that is pumped through said heat exchanger causing the water to boil and creating superheated steam; b) tubing that conducts said superheated steam through said steam turbine; c) tubing that conducts the steam that has passed through said steam turbine to a radiator that is cooled by a fan; d) tubing which conducts the steam that condenses to liquid water in the radiator to a water tank; and e) tubing that conducts the water from said tank to a pump which pumps the water through a one-way valve back into said tank containing said heat exchanger.

43. A system according to claim 42, wherein the steam that has passed through said steam turbine is utilized to distill water.

44. A system according to claim 43, wherein the steam that has been utilized to distill water is then passed through a heat exchanger to heat water for domestic or industrial use.