Absorber, device for manufacturing an absorber and method for manufacturing an absorber

p0001The invention relates to an absorber according to the preamble of patent claim 1, an apparatus for manufacturing an absorber according to the preamble of claim 9 and a method of production of an absorber according to the preamble of patent claim 11.

p0002An absorber of the type mentioned is intended in particular for installation in a solar collector. This consists of a provided with an optically selective coating carrier element, wherein a specific layer thickness containing coating is formed of a metallic component and a portion of at least one low molecular weight element (oxygen, nitrogen) or a small molecule (eg, hydrocarbon), wherein the concentration ratio of the two components varies with each other to adjust the optical refractive index in the course of the layer thickness (so-called gradient - is then reviewed in detail). Such absorber serves to absorb sunlight and deliver the energy which results from the amount of a fluid heat transfer medium.

p0003Regarding the performance of such an absorber are especially two physical concepts of importance:<ol><li>a) The so-called absorption coefficient α: This indicates how well the absorber is able to absorb the incident sunlight. The aim, of course, high levels of absorption, which nowadays absorption rates of up to 92% will be achieved.</li><li>b) The so-called emissivity E: This describes how much thermal radiation is emitted from the absorber. The lower the emissivity, the more energy can be delivered to the fluid heat transfer medium. Typical values ​​of the emissivity be about 5% today.</li></ol>

p0004In order to achieve the highest possible degree of absorption α and the lowest possible emissivity ε, in particular two types of absorbers are known. Here, the first absorber is in both cases of a metal carrier element having an optically selective coating. The support element is usually formed from copper sheet. The difference between these two types is substantially in the coating. During a so-called gradient layer is provided in a type, the other type of a so-called index layer.

p0005The mechanically very stable gradient layer is essentially a single layer over the layer thickness continuously varying refractive index n. The variation of refractive index is defined on the composition of the gradient layer, which usually metal from a portion, such. As chromium, and a proportion of of a lighter element or a low molecular compound, for., hydrocarbon, in amorphous or fluorinated form, is. Regularly the metallic portion is carrier element side quite high, while the surface side of the insulating acting hydrocarbon fraction (or oxygen or nitrogen content) is more significant.

p0006The mechanically less robust, with respect to their optical characteristics per se but better index coating consists in principle of a number of different individual layers, each with defined fixed refractive index, wherein the shift-related refractive indices from the carrier element (z. B. copper sheet with n = 3.5), starting with the outer surface of the coating towards ever smaller.

p0007In the prior art forming <patcit id="pcit0001" dnum="EP0736612B1"><text>EP 736 612 B1 0</text></patcit> is described, it is assumed that the below the gradient layer.

p0008The invention is based on this prior art based on the object, firstly, an absorber having a higher absorption coefficient α and lower emissivity ε to provide, secondly, to provide an apparatus for the production of such an absorber, and thirdly to provide a method for producing such absorber.

p0009This object is solved objectively with an absorber according to the characterizing features of claim 1. The apparatus, solve the characterizing features of claim 9, the object. The characterizing features of patent claim 11 achieve the object finally procedurally.

p0010According to the invention is therefore provided that the coating carrier element away with an additional, a refractive index of 1 &lt;n &lt;1.6 containing surface layer is provided.

p0011In other words, according to the invention is applied, an additional surface layer to the gradient, the air similar refractive index (air is about the refractive index n = 1), so that optical losses at the surface of the absorber can be kept as low as possible. This approximation of the refractive index of the surface layer leads to the refractive index of the surrounding area, as experiments revealed to an absorption rate of about 94% and an emissivity of about 3%, in other words a significant increase compared to the prior art.

p0012It is essential that the surface layer is made of materials that are not included in the gradient, so that ultimately results in a combination of a gradient and an index layer. As the material for the surface or index layer is preferably silicon oxide (SiO₂) Having a refractive index of n ~ 1.46 provided. In consideration but are also materials such as cerium fluoride (CeF) or Magnesiumdifluorid (MgF₂). It is crucial that the surface layer is not "contaminated" by elements such as carbon, as such materials to an increase in the refractive index and thus to an undesired increase in the reflection lead at the interface between the ambient air and surface of the coating.

p0013Other advantageous further developments result from the dependent claims.

p0014The absorber according to the invention, the apparatus for producing the absorber and the method for its preparation are described in greater detail with reference to the drawings of a preferred embodiment.

p0015It shows<dl id="dl0001" compact="compact"><dt>figure 1</dt><dd>schematically in section the structure of a solar panel;</dd><dt>figure 2</dt><dd>schematically in section the layer structure of the inventive absorber; and</dd><dt>figure 3</dt><dd>side view of a coil coating line for the production of the absorber according to the invention.</dd></dl>

p00161 shows the general, known per se construction of a solar collector schematically (not to scale) is shown first. From top to bottom the following components are provided: a low-iron glass plate 6, the absorber itself, including a pipeline 7 for a heat transfer fluid (regularly treated with an antifreeze) and finally an insulation. 8

p0017The in figure 2 absorber (not to scale) illustrated consists of a provided with an optically selective coating 2 carrier element 1, wherein a specific layer thickness d exhibiting coating 2 consists of a metallic fraction and a proportion of at least one low molecular weight element or a low molecular compound wherein the concentration ratio of the two components n varies d over the layer thickness to each other for adjusting the optical refractive index.

p0018In the illustrated, preferred embodiment, the support member 1 is formed of copper plate and has a thickness of 0.2 mm. The metallic portion of the applied coating 2, which typically has a layer thickness d of about 80 nm to 140 nm, preferably 120 nm, is formed of chromium; as low molecular weight compound is hydrocarbon used so that the coating 2 is formed in a broader sense as a metal-ceramic gradient. The solar selective properties of the coating 2 are obtained by varying the ratio of these two components on the layer thickness d. In a preferred embodiment, the chromium content is for example between 15% and 50%, which refractive indices n from 3.5 to 2.1 over the course of the layer thickness d with the result.

p0019Alternatively, metal parts made of molybdenum or titanium in combination can be provided with low molecular weight elements such as oxygen or nitrogen.

p0020Essential to the inventive absorber is now with again, reference to Figure 2 that in order to reduce optical losses at the surface of the absorber coating is 2 carrier element away with an additional, a refractive index of 1 &lt;n &lt;1.6 containing surface layer 3 is provided.

p0021In the illustrated, preferred embodiment, this surface layer 3 is made of silicon oxide having a refractive index n of about 1.5 is formed. The thickness of this surface layer is about 50 nm to 70nm, preferably 60nm. Alternatively come cerium fluoride, Magnesiumdifluorid or other suitable materials of low refractive index into consideration.

p0022In Figure 3, finally, the device for the production of the absorber according to the invention is shown. This consists firstly in a known manner from at least one so-called coil coating portion 4 for applying an optically selective coating 2 having a d varies over the layer thickness refractive index n on a carrier element first

p0023The support member 1 (as mentioned, preferably a copper sheet) is in this case (see the right in Figure 3) unwound from a coil and passes through the first bridge-like portion of the coil coating plant in a conventional manner, first a cleaning station 9, a cooling station 10 and then an activation station 11th

p0024In the middle part of the coil coating line is then provided with respect to the direction of passage of the carrier element 1 Next, the above-mentioned coil-coating portion 4 for application of the coating the second The application of this gradient occurs in the illustrated embodiment consolidated in a per se known physical vapor deposition.

p0025The apparatus, it is now essential that the Bandbeschichtungserabschnitt 4 a further web coating portion 5 for applying a downstream surface layer 3 having a refractive index of 1 &lt;n &lt;1.6, the coating on the second In this case, so that there will be no mixing of the gradient and index layer, the two coating band portions 4, 5 are arranged in mutually hermetically separated chambers.

p0026At the coil coating section 5 according to the invention then includes in a known per se manner, inter alia, a further cooling station 12 and the winding mechanism for the inventively constructed absorber sheet.

p0027considered the method, an optically selective coating is applied with 2 over the layer thickness d of varying refractive index n thus first in at least one stage of the procedure on a support member. 1 In one essential to the invention, the further subsequent stage of the procedure is then as described, is applied, an additional surface layer 3 having a refractive index of 1 &lt;n &lt;1.6 on the optically selective coating 2nd

LIST OF REFERENCE NUMBERS

p0028<dl id="dl0002" compact="compact"><dt>1</dt><dd>support member</dd><dt>2</dt><dd>coating</dd><dt>3</dt><dd>surface layer</dd><dt>4</dt><dd>Coil coating section for coating</dd><dt>5</dt><dd>Coil coating portion for the surface layer</dd><dt>6</dt><dd>glass plate</dd><dt>7</dt><dd>pipeline</dd><dt>8th</dt><dd>isolation</dd><dt>9</dt><dd>cleaning station</dd><dt>10</dt><dd>cooling station</dd><dt>11</dt><dd>activation station</dd><dt>12</dt><dd>cooling station</dd></dl><dl id="dl0003" compact="compact"><dt>d</dt><dd>Layer thickness of the coating</dd></dl>