DE10323157A1 - Solar heat collection system use for generating electricity, includes thermal exchanger which is arranged in return circuit and used for obtaining collected heat - Google Patents

Abstract

The solar heat collection system includes a thermal exchanger (6) which is arranged in a return circuit and used for obtaining collected heat. The return circuit is provided with a valve (8) operated by a piston (9) arranged in a cylinder. The piston is biased by a spring (11) via a guiding rod (10). The system also includes a transparent thermal insulator (2) covered with fiber glass of silica gel.

Description

Generally

at Flat plate collectors always escape with increasing usable temperature bigger part the one on the absorber surface generated heat through the cover plate of the collector. Through a selective acting Coating the absorber surface and transparent thermal insulation can this effect can be reduced.

The The aim of the present invention is the total incident solar energy to be exploited by the heat spreading to the cover plate Evaporation of a liquid mixture is recorded.

To for this purpose the collector is equipped with transparent thermal insulation, the one with a liquid adsorbent layer is coated. There is a mixture of more or less in this layer easily evaporable liquids. Partial evaporation of the mixture turns it into a cover plate spreading heat absorbed. The steam generated is removed behind the absorber surface.

The Steam becomes advantageous after a longer period of rest in a relatively short time Time drained and immediately afterwards, after partial heat release in an external one Heat exchanger, as well quickly returned to the collector room and the transparent thermal insulation.

By the evaporation of parts of the liquid becomes transparent Thermal insulation and the absorber surface Deprived of heat. The repatriation and Steam condensation occurs at a slightly lower temperature, so overall cooling entry.

The Collector can periodically even without evaporating liquid flowing in and out Gas operated. However, more heat can be absorbed with an evaporating liquid become.

While the usual Flat-plate collectors no longer heat at standstill temperature can give up can use this collector to absorb all of the solar energy in height the standstill temperature and even beyond.

A increase the temperature above the standstill temperature is also possible because part of the thermal energy taken from the collector is used to open the absorber surface with the help of a heat pump a higher one Bring temperature.

On this way the Carnot efficiency of a connected engine increase and it can higher Temperatures e.g. achieved for process heat become.

The Collector is also suitable for efficient generation of electrical energy.

In detail

construction

In the schematic drawings of 1 and 3 a section through a flat plate collector can be seen.

2 shows a section of the transparent thermal insulation in elevation.

To 1 is under the cover plate ( 1 ) transparent thermal insulation ( 2 ) appropriate. It advantageously consists of rows of wider ( 2 . 14 ) and flatter ( 2 . 15 ) Cells and can be made of polycarbonate or glass. If the collector after 1 is operated with a filling of steam, then a transparent thermal insulation is used, the surface of which is coated with a liquid-adsorbing layer, for example made of silica gel, or with a layer of fine fibers. The adsorbent layer can be produced by immersing the entire transparent thermal insulation in an appropriate bath.

In the adsorbent layer is a mixture of liquids adsorbed with different boiling points.

The transparent thermal insulation closes on one side with the cover panel ( 1 ). Small spacers or fine serrations are expediently attached to the upper edge of the cell walls, so that the coating of the transparent thermal insulation with the adsorbent layer is not interrupted by contact with the cover plate, but can continuously pass from one side to the other.

In the adsorbent layer is a mixture of liquids adsorbed with different boiling points.

The relatively large cells ( 2 . 14 ) of the transparent thermal insulation are on the opposite side of the cover panel by a vapor permeable absorber layer ( 16 ) covered. The incident solar radiation is absorbed in it. The absorber layer can expediently ig consist of metal wool, which is treated selectively acting.

Under In this cover, the wide cells are in one direction with each other connected so that a passage is formed through which steam is discharged can.

The flat cells ( 2 . 15 ) of the transparent thermal insulation open into a flat cavity under the transparent thermal insulation.

The wide cells of the transparent thermal insulation are connected to each other at their lateral edges by a manifold. This manifold runs through a pipe ( 13 ) and via a valve ( 12 ), which opens only in the direction shown, to the cylinder ( 8th ). In the cylinder ( 8th ) is a piston ( 9 ) with a guide rod ( 10 ) versatile. The guide rod is equipped with a firmly anchored mechanical or pneumatic suspension ( 11 ) connected. From the cylinder ( 8th ) carries another valve ( 7 ), which opens in the direction shown, via a heat exchanger ( 6 ) and the pipeline ( 5 ) back to the flat cavity under the transparent thermal insulation.

The whole thing in one housing ( 4 ) be housed with normal thermal insulation.

If the collector with a gas filling is operated, then omitted coating with an adsorbent layer. For that are on upper end of the transparent thermal insulation every second cell wall, which leads from the wide to the flat cells, small Indentations attached through which a gas exchange takes place can.

3 shows the same structure as 1 , In addition to building 1 is on the cylinder ( 20 ) a valve ( 18 ) attached via a pipe to a throttle valve ( 17 ) leads, which in turn is connected to the pipeline leading to the wide cells of the collector with the absorber layer. The valve ( 18 ) on the cylinder by a mechanical connection with the guide rod ( 19 ) to be controlled.

function

When the collector is exposed to solar radiation, the absorber layer heats up ( 3 ). Gradually the heat penetrates through transparent and convection into the transparent thermal insulation. If the transparent thermal insulation is provided with an adsorbent layer in which a liquid mixture, for example various hydrocarbons, is bound, then depending on the temperatures which decrease towards the cover plate, correspondingly higher or lower boiling fractions of the liquid mixture evaporate. The composition of the liquid mixture changes accordingly after some time. A steady state occurs, with an appropriate mixture of the vapor and the liquid being established at each point of the collector depending on the temperature. Evaporation increases the pressure of the vapor trapped inside the collector.

After a certain period of heating and a certain increase in pressure, the pressure-dependent valve opens ( 12 ) towards the cylinder ( 8th ). Some of the steam flows out of the cells of the transparent thermal insulation through the absorber layer ( 3 ) in the passage behind. The absorber layer should have a sufficiently large flow resistance so that the steam flows out of all cells as evenly as possible. When flowing through the absorber layer, the steam has warmed up further, so that it is now in a dry, overheated state.

Through the pipeline ( 13 ) and the pressure-dependent opening valve ( 12 ) the steam now flows into the cylinder ( 8th ) and moves the piston ( 9 ) against the external air pressure and against the spring pressure of the spring ( 11 ). The vapor pressure can be higher or lower than the atmospheric pressure. After pressure equalization, the valve closes ( 12 ). The piston has received a certain amount of kinetic energy with which it now moves back. When moving back, the valve opens ( 7 ), which only opens in the direction shown, and lets the steam through the heat exchanger ( 6 ) and the pipeline ( 5 ) flow back into the collector.

Due to the heat given off in the heat exchanger ( 6 ) the pressure of the returning steam and the pistons decreases ( 9 ) experiences an acceleration, the force of which in the spring ( 11 ) is saved and is available for the next movement. Then the valve closes ( 7 ) in front of the heat exchanger ( 6 ) is attached.

If, as is assumed, not much heat is removed from the returning steam during a piston stroke, the returning steam is in an approximately saturated state. It now gets into the cavity under the transparent thermal insulation and from there back into the narrow cells. There the steam condenses according to its composition in the warmer and colder areas of the transparent thermal insulation and thus in areas that are closer or further to the cover plate. The condensed liquid gradually migrates to the other side of the cell walls due to capillary forces. The condensed liquid rises first on one side of the cell walls and then on the seeping down the other side. This ensures that the higher-boiling parts of the liquid mixture do not accumulate in the upper regions of the transparent thermal insulation close to the cover plate. Because of the heat given off in the heat exchanger vessel ( 6 ) the steam flowing back has a lower heat content. In addition, the transparent thermal insulation has been cooled to a somewhat lower temperature by the evaporation that took place just before, so that it can absorb the heat of condensation.

To the repatriation of the Steam in the collector expediently enters a rest phase which is the collector heat through the sun's rays. Then the one shown begins Process again.

When the steam is removed and returned, the transparent thermal insulation is cooled because more heat is removed than is returned. With maximum use of the achievable temperature, the cooling is just as great as the heat spread in the transparent thermal insulation in the direction of the cover pane. The in the heat exchanger ( 6 ) dissipated useful energy is then slightly below the standstill temperature, at which heat could no longer be dissipated in conventional flat collectors.

If the cooling is bigger there is heat absorption via the Cover plate, which is used in some useful applications, e.g. with room heating or hot water heating be desirable can.

at one filled with gas Collector is running in principle the same process except that the evaporation and the condensation is eliminated.

A Temperature increase over the Standstill temperature can also be achieved by when moving back part of the vapor is compressed and thus to a higher temperature brought. The mechanical energy for this compression can be achieved by the temperature difference between the incoming and outgoing steam is generated. But an additional one is better External drive, by mechanical energy e.g. taken from a heat engine that is due to the heat removal is driven from the collector.

To 3 is on the cylinder ( 19 ) a valve ( 18 ) attached, which only opens in the direction shown. The valve is via a throttle valve ( 17 ) connected to the pipeline leading to the wide cells of the collector and the absorber layer. A control system, which is operated by the guide rod ( 21 ) is controlled, the valve ( 22 ) in front of the heat exchanger ( 23 ) is closed after a certain time of the return movement of the piston. At the same time, the valve, which opens depending on the pressure ( 18 ) to the throttle valve ( 17 ) leads, opened. The steam trapped in the piston is compressed and heated by the action of the throttle valve.

The Compression of part of the steam can also be done in a separate Cylinder or by a second stroke of the piston.

To flowing through of the throttle valve, the steam is released, but retains its heat content. The steam flows into the pipe, which leads to the wider cells and is heated by the heat content obtained the absorber layer.

The Repatriation of the heated Steam in the wide cells occurs after the somewhat cooled steam is returned into the narrow cells.

On in this way additional heat is supplied to the absorber layer.

In the subsequent period, in which there is no exchange of steam, the incident solar radiation brings the absorber surface to a higher temperature level than would have been the case without additional heating. The energy for this heat pumping process is generated by the heat given off in the heat exchanger ( 23 ) reached. For example, it is possible to dissipate half of the thermal energy collected in the collector as useful energy and to use the other half for a heat pumping process.

The heat flowing into the transparent thermal insulation not lost but becomes permanent to something higher Temperature level raised. Raising to a higher temperature level happens through the energetically high quality solar energy that is on this way is better used thermodynamically.

It is advantageous here that the heat emission required for such a heat pumping process takes place at a high temperature level according to the Carnot law. The higher working temperature increases the Carnot efficiency of an engine that works with the heat from the heat exchanger ( 23 ) is operated or allows use as process heat, which requires higher temperatures.

In particular could with this type of collector electrical energy with a good efficiency be generated.

Claims (3)

Solar collector with transparent thermal insulation ( 2 ) in a heat-insulated housing ( 4 ) is housed, characterized in that the transparent thermal insulation ( 2 ) is covered with a thin layer of a liquid-adsorbing, e.g. fibrous or fine-pored material, such as glass fibers or silica gel, that in this layer or in the material of the thermal insulation a mixture of liquids of different boiling points is bound by adsorption, that at the lower end transparent thermal insulation every second cell with an absorber layer ( 3 ) it is provided for the incident solar radiation that the absorber layer is permeable to gas and steam, that the cells in which an absorber layer is located can be larger than the adjacent cells, that the cells under the absorber layer are connected to a passage that is in A manifold at the edge of the transparent thermal insulation opens so that the other cells can be connected to each other by a cavity under the transparent thermal insulation, so that the steam that arises in the collector during solar radiation and heat propagation is removed from the collector at certain time intervals and immediately after the withdrawal, it is returned that the collector can collect heat for some time between the withdrawal of the steam and the return thereof, that the withdrawal of the steam from the collector by a valve ( 12 ) is controlled by the level of pressure and / or by another signal such as, for example, by a temperature sensor on the cover plate of the collector or by the guide rod ( 10 ) of the piston is actuated so that the extracted steam is a piston ( 9 ) in a cylinder ( 8th ) or a diaphragm moves that the piston with a spring ( 11 ) (mechanically or pneumatically) is connected that a valve ( 7 ) is opened in the return line, that a heat exchanger ( 6 ) is attached, through which heat can be extracted, Device and method according to claim 1, characterized in that during the return movement of the piston ( 20 ) in the cylinder ( 19 ) the piston ( 20 ) a force is supplied by which a part of the steam is compressed, so that additional heat is added to the collector and the working temperature is increased, so that the force for this compression from the heat removal by the heat exchanger ( 23 ) by means of which the heat collected in the collector is dissipated or by supplying energy from outside that part of the steam enclosed in the cylinder can be compressed, in a final phase of the return movement of the piston, the return of the steam via the heat exchanger is blocked that the valve ( 22 ) can take place in front of the heat exchanger ( 23 ) that the vapor compressed in the cylinder is attached via a valve ( 18 ) and a throttle valve ( 17 ) is fed back into the supply line of the wide cells with the absorber surface. Apparatus and method according to claim 2, characterized characterized that the compression of the steam in its own Cylinder happens or in another stroke of the piston.