CN104456980A - Secondary concentrated reflection-transmission type parabolic-trough type solar heat collector - Google Patents

Abstract

The invention discloses a secondary concentrating reflection-transmission type parabolic trough solar heat collector, which comprises a line-focusing Fresnel lens, a collimating Fresnel lens, a vacuum heat collecting tube and a parabolic trough reflector , with single-axis ray tracing capability. Among them, the real focus of the line-focusing Fresnel lens coincides with the virtual focus of the collimating Fresnel lens; the vacuum heat collector is located at the focal line of the parabolic trough reflector; the parallel sunlight passes through the line-focusing Fresnel lens to complete a concentration The light is re-diffused into parallel light through the collimated Fresnel lens; the parabolic trough reflector reflects the parallel sunlight after the primary concentration to the wall of the vacuum heat collection tube to complete the secondary concentration; the heat transfer medium in the vacuum heat collection tube Absorb concentrated solar energy to complete the heating process. The solar collector can be used in the field of solar thermal energy, and it solves the problem that the heat collection efficiency of traditional trough collectors is greatly reduced in winter and other periods when the solar radiation decreases and the incident angle increases, and the cost is low.

Description

A secondary concentrating reflective-transmissive parabolic trough solar collector

technical field

The invention relates to the technical field of solar thermal power generation, in particular to a secondary concentrating reflection-transmission parabolic trough solar heat collector.

Background technique

As an inexhaustible, inexhaustible, clean and pollution-free new energy source, solar energy has attracted more and more attention from people. There are mainly three types of solar thermal power generation: trough type, tower type and dish type according to the heat collection form. Among them, the trough type solar thermal power generation technology is the most mature and has been commercialized in foreign countries. It is the recent development of solar thermal power generation technology in the world. focus direction.

In summer with good irradiation conditions, for the trough collectors arranged on the north-south axis and tracked by the east-west axis, the peak heat collection efficiency can reach more than 65%, and the heat collection efficiency does not fluctuate much throughout the day. The trough thermal power generation system shows good thermal performance. performance. However, as the intensity of solar radiation decreases in winter and the angle of incidence of the sun increases, the heat collection efficiency of the trough collector decreases significantly. The solar heat collection efficiency in a typical day in winter is only about 30%. The decline in heat collection efficiency will bring solar thermal power generation. The reduced load operation of the steam turbine in the system makes it difficult to increase the average annual power generation efficiency of the trough thermal power generation system, or the addition of energy storage equipment to maintain stable operation of the steam turbine will further increase the investment cost and power generation cost.

The above-mentioned problem that the decline in heat collection performance makes it difficult to improve the technical economy is the key problem encountered by the current trough thermal power generation technology, which directly restricts its large-scale commercial promotion and application. Therefore, improving the heat collection performance of the trough collector when the solar radiation decreases and the incident angle increases is an important technical problem to be solved in this field.

Contents of the invention

(1) Technical problems to be solved

In view of this, the main purpose of the present invention is to provide a secondary concentrating transmission-reflection parabolic trough solar collector, by arranging linear Fresnel lenses and collimating Fresnel lenses to realize primary concentration of solar energy Light, and then through the parabolic trough reflector to realize the secondary concentration of solar energy, so as to solve the technical problem of the decline of the heat collection performance of the trough collector under the current working conditions of the declining solar radiation.

(2) Technical solutions

To achieve the above object, the present invention provides a secondary concentrating reflective-transmissive parabolic trough solar collector, which includes a line-focusing Fresnel lens 1, a collimating Fresnel lens 2. The vacuum heat collecting tube 3 and the parabolic trough reflector 4, the sunlight sequentially passes through the line-focusing Fresnel lens 1 and the collimating Fresnel lens 2 to irradiate the parabolic trough reflector 4, and is irradiated by the parabolic trough reflector 4 The reflection converges to the wall surface of the vacuum heat collection tube 3, thereby improving the heat collection efficiency of the trough heat collector.

In the above solution, the real focus of the line-focus Fresnel lens 1 coincides with the virtual focus of the collimating Fresnel lens 2 .

In the above solution, the sunlight passes through the line-focusing Fresnel lens 1 to complete one-time concentration, and irradiates to the collimating Fresnel lens 2 .

In the above solution, the sunlight that has completed primary concentration is re-diffused into parallel light through the collimating Fresnel lens 2 .

In the above solution, the parabolic trough reflector 4 reflects and converges the sunlight that is once concentrated and re-diffused into parallel light to the wall surface of the vacuum heat collecting tube 3 to complete the secondary concentration.

In the above scheme, the vacuum heat collecting tube 3 is located at the focal line position of the parabolic trough reflector 4, so as to ensure that after the sunlight is focused by the parabolic trough reflector 4, the focused light spot falls on the vacuum heat collecting tube 3 accurately, and the vacuum heat collecting tube 3. The internal heat transfer medium absorbs concentrated solar energy to complete the heating process.

In the above solution, the parabolic trough solar collector has a single-axis ray tracing capability.

(3) Beneficial effects

As can be seen from the foregoing technical solutions, the present invention has the following beneficial effects:

1. Using the present invention, through the Fresnel lens and the parabolic trough reflector, the secondary concentration of solar radiation can be realized, thereby increasing the solar energy flux density received by the vacuum heat collecting tube, and greatly improving the trough collector. heat collection efficiency.

2. Utilizing the present invention, the Fresnel lens is mostly a thin sheet made of polyolefin material, and the lens body is light and thin. Using a Fresnel lens as a secondary light concentrating device can relatively increase the opening area of the traditional trough collector to collect more solar radiation, which can reduce the strength requirements of the solar collector for the supporting structure and save steel for the support The amount used, thereby saving costs and improving the economy of trough solar thermal power generation.

3. Utilizing the present invention, the Fresnel lens has the advantages of convenient processing, mass production, and low price, and has been widely used in modern industry. Using a Fresnel lens as a secondary light concentrating device can reduce the cost of the high concentration ratio solar collector and improve the economical efficiency of trough solar thermal power generation.

4. With the present invention, according to the change of actual heat collection requirements, the structural design of the linear Fresnel lens and the collimation Fresnel lens can be redesigned, so that the light concentration ratio of the heat collector can be adjusted by only replacing the Fresnel lens , easy to transform the collector.

Description of drawings

Fig. 1 is the schematic diagram of traditional parabolic trough solar collector;

Wherein the reference signs are: 1 - vacuum heat collecting tube; 2 - parabolic groove reflector.

2 is a schematic diagram of a secondary concentrating transmission-reflection parabolic trough solar collector according to an embodiment of the present invention;

The reference signs are: 1-line focusing Fresnel lens; 2-collimating Fresnel lens; 3-vacuum heat collecting tube; 4-parabolic groove mirror.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

As shown in Figure 2, the transmissive-reflective parabolic trough solar collector provided by the present invention includes a line-focusing Fresnel lens 1, a collimating Fresnel lens 2, a vacuum heat collecting tube 3 and a parabolic trough reflector 4 , the sunlight passes through the line-focusing Fresnel lens 1 and the collimating Fresnel lens 2 to irradiate to the parabolic trough reflector 4, and is reflected by the parabolic trough reflector 4 to the wall of the vacuum heat collecting tube 3, thereby improving the trough heat collection efficiency of the collector.

The real focal point of the line focusing Fresnel lens 1 coincides with the virtual focal point of the collimating Fresnel lens 2. The line-focusing Fresnel lens 1 condenses the parallel sunlight once and irradiates it to the collimating Fresnel lens 2; the collimating Fresnel lens 2 re-diffuses the once-condensed sunlight into parallel sunlight, and The parabolic trough reflector 4 is irradiated; the parabolic trough reflector 4 reflects and converges the parallel sunlight after the primary concentration to the wall surface of the vacuum heat collecting tube 3 to realize secondary concentration. The vacuum heat collecting tube 3 is located at the focal line position of the parabolic trough reflector 4 to ensure that after the approximately parallel solar rays are focused, the focused spot can accurately fall on the vacuum heat collecting tube 3, and the heat transfer medium inside the vacuum heat collecting tube 3 absorbs and focuses Solar energy completes the heating process.

In the traditional trough collector, as shown in Figure 1, the parabolic trough reflector can only receive sunlight in the opening surface. Decrease, the heat collection performance of the mirror field decreases significantly, resulting in a decrease in the average annual efficiency.

In the present invention, as shown in Figure 2, by arranging a linear Fresnel lens and a collimating Fresnel lens in the direction of the opening of the parabolic trough reflector, more sunlight can be concentrated on the parabolic trough reflector, This solves the problem that the heat collection efficiency decreases due to the decline in the effective incident solar radiation received by the collector after the solar radiation decreases in winter and the solar incident angle increases, and effectively improves the heat collection performance of the mirror field under low radiation.

The secondary concentrating reflective-transmissive parabolic trough solar collector provided by the present invention has uniaxial ray tracing capability, and can determine the concentrating ratio of the solar collector according to the actual required heating amount or the actual required temperature, thereby Determine the tooth angle and pitch of the line-focusing Fresnel lens and collimating Fresnel lens, the opening shape and opening width of the parabolic reflector and other structural parameters.

Taking the trough collector LS3 with the north-south horizontal axis arranged east-west tracking as an example, the design and transformation of the second concentration is carried out. Assuming that the collector is installed in the Shizuishan area with abundant solar energy resources in China, its annual effective cumulative radiation (greater than 300W/m ² ) up to 1988kWh/m ² . Among them, the effective incident radiation at noon on the summer solstice is: DNI×cosθ=1022W/m ² ×0.96=981W/m ² ; however, on the winter solstice, the effective incident radiation at noon drops to: DNI×cosθ=900W/m ² ×0.46=414W/m ² . Among them, cosθ is the cosine of the sun's incident angle. It can be seen that even in a type of area with such abundant solar energy resources, the effective irradiance at noon in winter has dropped by at least half compared with summer, that is, the energy received by the mirror in winter is the same as the tracking method and the collector area is constant. Density dropped by about half.

In order to improve the energy density in winter, it can be considered to add linear Fresnel lens and collimating Fresnel lens to the trough collector in winter for secondary concentration. On the winter solstice, the energy density received by the opening surface of the parabolic trough is reduced by about half. ratio) is set to f ₂ /f ₁ =2. For the LS3 trough collector with an opening of 5.77m and a focal length of the parabolic trough mirror of 1.71m, it can be calculated that the focal length _f2 of the line focusing Fresnel lens is about 6m, and the distance between the two lenses is about 3m. It is estimated that after the second concentrating transformation, the annual average heat collection efficiency of the solar heat collection field will increase from the current annual average of 45% to 50% to 60% to 65%.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (7)

1. a secondary concentrating reflection-transmission type parabolic trough solar collector, is characterized in that, this parabolic trough solar collector comprises line focusing Fresnel lens (1), collimating Fresnel lens ( 2), the vacuum heat collector (3) and the parabolic trough reflector (4), the sunlight sequentially passes through the line focusing Fresnel lens (1) and the collimating Fresnel lens (2) to irradiate the parabolic trough reflector (4), reflected by the parabolic trough reflector (4) and converged to the wall surface of the vacuum heat collection tube (3), thereby improving the heat collection efficiency of the trough heat collector. 2. secondary concentrating reflection-transmission type parabolic trough solar collector according to claim 1, is characterized in that, the real focal point of described line focusing Fresnel lens (1) and collimating Fresnel lens The virtual focus of (2) coincides. 3. secondary concentrating reflection-transmission type parabolic trough solar heat collector according to claim 1, is characterized in that, described sunlight passes through line focusing Fresnel lens (1) to complete primary concentrating, and Irradiation hits the collimating Fresnel lens (2). 4. The secondary concentrating reflective-transmissive parabolic trough solar collector according to claim 3, characterized in that the sunlight that completes the primary concentrating is re-transmitted through the collimating Fresnel lens (2). Diffusion into parallel light. 5. The secondary concentrating reflection-transmission type parabolic trough solar heat collector according to claim 4, characterized in that, the parabolic trough reflector (4) will once concentrate and be re-diffused into parallel light The reflected sunlight converges to the wall surface of the vacuum heat collecting tube (3) to complete secondary light concentration. 6. The secondary concentrating reflection-transmission type parabolic trough solar collector according to claim 1, characterized in that, the vacuum heat collecting tube (3) is located at the focal line position of the parabolic trough reflector (4) , to ensure that after sunlight is focused by the parabolic trough reflector (4), the focused light spot falls on the vacuum heat collecting tube (3) accurately, and the heat transfer medium inside the vacuum heat collecting tube (3) absorbs the focused solar energy to complete the heating process. 7. The secondary concentrating reflective-transmissive parabolic trough solar collector according to claim 1, characterized in that the parabolic trough solar collector has a single-axis ray tracing capability.