WO2008041046A2

WO2008041046A2 - Vacuum tube solar collector with double parabola shell

Info

Publication number: WO2008041046A2
Application number: PCT/HU2007/000090
Authority: WO
Inventors: Zoltán TAKACS
Original assignee: Takacs Zoltan
Priority date: 2006-10-05
Filing date: 2007-10-04
Publication date: 2008-04-10
Also published as: WO2008041046A3; HUP0600764A2; HU0600764D0

Abstract

The subject of the invention is a vacuum tube solar collector with double parabola shell, making possible the concentration of sunshine on the heat-taking tube placed in the focal point, respectively on the heat-taking liquid in the tube acting as heat medium, or on the tube condenser doing the heat transfer, so substantially greater heat output can be achieved. The vacuum tube solar collector according to the invention with double parabola shell characterized by that, the solar collector element consists of an outer tube shell (1) with double parabola cross-section, as well as an inner tube (3) of circular section which are fixed to each other with permanent joint (6) and there is a vacuum space (5) between them.

Description

Vacuum tube solar collector with double parabola shell

The subject of the invention is a vacuum tube solar collector with double parabola shell, making possible the concentration of sunshine on the heat-taking tube placed in the focal point, respectively on the heat-taking liquid in the tube acting as heat medium, or on the tube condenser doing the heat transfer, so substantially greater heat output can be achieved.

Nowadays there are several methods for the energy supply of industry and households. One of the most common solutions is the conversion of sunshine into heat, or electric power. One of the state of the art medium of the conversion of sunshine is the so-called vacuum tube heat-conversion element. Various vacuum tubes have been developed in the solar industry.

One of the examples of these tubes is the glass vacuum tube sunshine/heat converter made by APRICUS. These vacuum tubes were originally developed at the Sydney University in Australia and it has been used in Germany, Canada, China and in the United Kingdom for years. There are several types of vacuum tube in the solar industry. Among those "Apricus" twin-glass tube solution is widely used due to its reliability, high output and low production cost. Here the high temperature (400 C⁰) for the steam production of generators necessary for the conversion of sunshine to electric power, namely the higher output is ensured by directing the sunshine to a heat-absorbing tube with the help of a parabolic mirror running in the focal point of the parabola trough.

In the state of the art there are various methods for the utilization of solar power. A generally known and applied solution is, when the heat-taking tube in the focus of the parabola is heated with the help of a cylindrical parabolic mirror, and the parabolic mirror is moved in step with the Sun. As heat-taking medium a. liquid is flown in the tube system or heat absorbing system, placed in the focus of the parabola, and the heat absorbing system is in a horizontal or sloping position. The patent description US 4 149 523 makes known a solar power collecting system built with moving mirrors. The essence of which is, that several cylindrical parabola mirrors are placed horizontally, in parallel. In the focal axis of the parabolic mirrors there are tubes for the flow of the heat exchange liquid, and the sunshine is projected on these by the parabolic mirrors. The parabolic mirrors are moved at the same time with the help of a structure built pole, so the mirrors always project the sunshine on the heat exchange poles.

The international application WO 02/09371 published on 5 December 2002 makes known equipment for solar power conversion. The sunshine collecting system of the equipment is an array of cylindrical parabolic mirrors moving on a horizontal, rotating stool facing continuously the Sun, so the cylindrical parabolic mirrors project the sunshine always in the best position to the heat-taking elements.

The JP 59150251 Japanese patent makes known a double vacuum tube solar collector. According to the solution vacuum is created between the smaller diameter glass tube and the outer glass tube, and a concave specular surface is placed in the vacuum between the two tubes on the opposite side of the sunshine. A heat conductor tube is placed in the focus of the concave specular surface in the inner tube.

The US 4 108 154 patent description makes known a solar collector system built with a cylindrical parabolic mirror of sloping axis, the heat exchange is placed in the focal line of the cylindrical parabola. The cylindrical parabolic mirror is rotated around a sloping axis with the help of a driving mechanism in step with the Sun's movement, so the sun radiation is always projected to the focal line of the parabola.

The GB 2 032 129 and the DE 195 17 471 German patent publication on 11 January 1996 make known a solar power utilization equipment with moving projecting elements, placed horizontally, respectively built with mirrors. The WO 99/20953 international patent application published on 29 April 1999 makes known a sunshine collecting system with specular elements in standing position placed around a cylindrical surface. The vertical specular elements project the sunshine on a heat- taking unit of standing position placed in the axis of the cylinder surface.

The disadvantages of the above described, as well as those of the commercially available solutions are, that in case of solar collectors with parabolic mirrors the mirrors are placed in the open space, and can not be protected from adverse weather conditions (wind, hail, ice layer on their surface etc.), respectively weather conditions greatly deteriorate reflectance of the mirrors, respectively resulting from this reduce their performance. Due to these causes parabolic mirrors can be used with limitations on temperate zone areas, requiring very expensive maintenance. In case of sunshine/heat converters with vacuum tubes only one side of the tube with heat absorbing coating is exposed to the sunshine, so the heat absorbing surface is smaller due to which only lower temperature can be produced with lower output than for example with parabola solar collectors.

When working out the solution according to the invention we aimed to produce a solar collector element, which can include the benefits of sunshine/heat converters with vacuum tubes and with parabolic mirrors, so a solar power utilizing element can be produced with easy realization and greater output.

When creating the solution according to the invention we realized, that in case a tube containing heat-taking liquid, provided with heat-absorbing surface is placed in the focus of a tube shell with double parabola cross section provided with specular surface, and vacuum is created between the two tubes, then the set aim can be achieved.

The invention is a vacuum tube solar collector with double parabola shell to be used in solar collectors for converting sunshine to thermal energy, which is characterized by that, the solar collector element consists of an outer tube shell with double parabola cross- section, as well as an inner tube of circular section which are fixed to each other with permanent joint and there is a vacuum space between them.

In one preferred embodiment of the solution according to the invention one of the inner or outer surfaces of the double parabola tube shell is provided with radiation reflecting coating, whereas the surface towards the parabola tube shell of the inner tube with circular section is provided with a radiation absorbing coating.

In another preferred embodiment of the solution according to the invention the focus of the parabola tube shell is in the center of the inner tube, and the co-ordinates of the cross- section of the parabola tube shell are described by the equation y=(X*X)/(4*p), where y means the height points of the parabola, X means the width points of the parabola, p means the focal point of the parabola.

In a further preferred embodiment of the solution according to the invention the parabola tube shell towards the sunshine is coated in one direction with such a translucent material, which lets light through from the direction of radiation, but in the other direction it creates a light reflecting mirror surface.

The solution according to the invention is furthermore set forth by the enclosed drawings: Fig 1 shows one of the possible advantageous realizations of the solution according to the invention in semi-view-semi-section.

Fig 2 shows the setup of the solution according to Fig 1 in B-B section showing the direction of sunshine as well.

Fig 1 shows one of the possible advantageous realizations of the solution according to the invention in semi-view-semi-section. The outer tube shell 1 of double parabola cross- section can be seen in the picture, where the inner surface of one of the parabola components of the tube shell 1 is coated with radiation-reflecting coating 2 preferably with mirror surface. The outer surface looking towards the parabola shell of the inner tube 3 with circular section is provided with radiation-absorbing coating 4. It can be very well seen in the picture, that the tube shell 1 as well as the inner tube 3 are closed in one of their ends by permanent joint 6 and that the tube shell 1 as well as the inner tube 3 are fixed to each other by permanent joint 6 (eg. welding, brazing, sticking) in such a way, that before the final closing of the permanent joint 6 the air is pumped out from the part between the two tubes, forming this way the vacuum space 5.

Fig 2 shows the setup of the solution according to Fig 1 in B-B section showing the direction of sunshine as well. The outer tube shell 1 with double parabola cross-section can be seen in the picture, where on the inner side of the tube shell 1 in opposite direction with the incoming sunshine there is a radiation-reflecting coating 2. The outer surface of the inner tube 3 of circular section is coated with radiation absorbing surface. It can be seen well in the picture that the inner tube 3 is placed in the focus of the tube shell 1 of double parabola cross-section ensuring this way that the incoming radiation through the parabola- like surface of the tube shell 1 of double parabola cross-section concentrates in the liquid placed in the focus inside the inner tube 3. The vacuum space 5 formed between the tube shell 1 and the inner tube 3 prevents, that the light coming into the tube shell 1, goes out of it.

In case of a preferable realization of the solution according to the invention the double parabola tube shell is formed in such a way, that the focal points of the parabola shells placed facing each other symmetrically are identical, namely they are formed in a parabola shape of identical focal points. The shape, geometry of the tube shell 1 of parabola form can be determined on basis of the known formula, by the equation y=(X*X)/(4*p) where y means the height points of the parabola, X means the width points of the parabola, p means the focal point of the parabola. Preferably the inner or outer parabola surface opposite the incoming sunshine of the tube shell 1 is coated with radiation reflecting coating 2 increasing the rate of the utilization of heat radiation in a great extent. The parabola surface towards the incoming sunshine of the tube shell 1 can be provided with such a special coating that gives way to sunshine, but prevents its going out in the opposite direction.

The inner tube 3 is placed in the common focal point of the tube shell 1 of double parabola cross-section, this way the incoming radiation coming from the parabola surface of the tube shell 1 is concentrated in the liquid placed inside the inner tube 3 in the focus, acting as medium for heat transfer. The tube shell 1 as well as one end of the inner tube 3 are closed at the ends by permanent joint 6 with the known method (eg. welding, brazing, sticking).

The assembly of the vacuum tube solar collector with double parabola shell element according to the invention takes place the following way: first the inner tube 3 is positioned properly in the focal point inside the tube shell 1. Following this, the tube shell 1 and the inner tube 3 are fixed to each other at the other end by a permanent joint 6 in such a way, that before the final closing of the permanent joint 6 the air is pumped out of the part between the two tubes, forming this way the vacuum space 5. Creating the vacuum space 5 is important, because the heat coming from the Sun absorbed by the solar collector element formed with vacuum space, can not leave, the incoming quantity of heat can not disappear, as vacuum prevents thermal conduction, so collectors with vacuum tube can operate in cold weather as well.

The inner tube 3 contains the liquid acting as heat medium, or the thermal conversion unit consisting of an evaporating tube of closed system and steam condenser. On the upper, open end of the solution according to the invention, the tube containing the liquid transferring heat, or the tube condenser doing the heat transfer, can be found. The vacuum tube solar collector elements according to the invention can be placed vertically joining a backbone guide in the required number, next to each other, or they can be placed in an angle of 40-45 grade.

In a definite realization of the vacuum tube solar collector element according to the invention the material of the outer tube shell 1 is transparent glass, or plastic, preferable strong, clear boron silicate glass, which can resist even a hail with hailstones of 25 mm diameter. The material of the inner tube 3 is glass, plastic, preferably also boron silicate glass. The inner tube 3 is preferably coated with radiation absorbing surface, which is preferably made with Al-N/Al coating, which is an excellent light and heat absorbing coating, respectively their ability of reflecting light and heat is minimal.

The advantage of the solution according to the invention is, that by applying it, vacuum tube collectors of greater output can be made, which are suitable for producing higher temperatures. This way the number of collectors necessary to produce a given quantity of heat can be reduced, so utilization of thermal power gained from sunshine can be more economical. By putting the reflecting parabolic mirror (radiation concentrator) into a closed enclosure, the damage of parabolic mirrors caused by adverse weather conditions can be greatly reduced, so the equipment can be used in temperate zone areas as well and the heat transfer medium (water, or oil) can be heated to higher temperature making possible the operation of steam turbines as well.

The solution according to the invention makes possible the elimination of the drawbacks of known solutions, because making use of the benefits of the inner absorbing tube, the double parabola shell collector is created by an outer shell, where parabolas have identical focal point, and on one parabola side a reflecting coating is formed. The air is pumped out of the space between the double parabola shell and heat absorbing tube creating vacuum, and with the help of the known methods eg. brazing, sticking or welding, the ends of the elements are fixed airtight to each other.

Claims

CLAIMS:

1. Vacuum tube solar collector with double parabola shell to be used in solar collectors for converting sunshine to thermal energy, characterized by that, the solar collector element consists of an outer tube shell (1) with double parabola cross-section, as well as an inner tube (3) of circular section which are fixed to each other with permanent joint (6) and there is a vacuum space (5) between them.

2. Solar collector element according to Claim 1 characterized by that, one of the inner or outer surfaces of the double parabola tube shell (1) is provided with radiation reflecting coating (2), whereas the surface towards the parabola tube shell (1) of the inner tube (3) with circular section is provided with a radiation absorbing coating (4).

3. Solar collector element according to Claim 1 or 2 characterized by that, the focus of the parabola tube shell (1) is in the center of the inner tube (3), and the co-ordinates of the cross-section of the parabola tube shell (1) are described by the equation y=(X*X)/(4*p), where y means the height points of the parabola, X means the width points of the parabola, p means the focal point of the parabola.

4. Solar collector element according to any of Claims 1-3 characterized by that, the parabola tube shell (1) towards the sunshine is coated in one direction with such a translucent material, which lets light through from the direction of radiation, but in the other direction it creates a light reflecting mirror surface.