JPS58124159A - Reflecting plate for solar heat collector - Google Patents

Abstract

PURPOSE:To obtain a heat collector excellent in reflecting properties, durability and reliability, by coating a galvanized steel plate or the like with a coating material comprising metallic particulates having favorable reflecting properties for solar rays. CONSTITUTION:The reflecting plate 1 for the solar heat collector is produced by using an inexpensive material such as an aluminum-treated steel plate or a plastic plate as the galvanized steel plate or the like and coating the plate with a coating material comprising particulates of at least one metal (e.g., aluminum, copper, brass) having favorable reflecting properties for the solar rays and a binder. Accordingly, a heat collector excellent in reflecting properties and ensuring durability and reliability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reflecting plate for a solar heat collector that improves the amount of heat collected by the solar heat collector.

Since the oil crisis, research has been active in the use of various natural energy sources as an alternative to oil, and solar energy has attracted attention as a reliable and accessible alternative energy source, and water heaters are now common in ordinary households. It is being done.

In various solar heat utilization systems, solar heat collectors are
It is a device that collects and heats the solar energy that falls on the earth's surface and makes it effective, and it can be said to be the heart of the system. Improving the efficiency of solar heat collectors is an extremely important issue, and research is actively focused on technologies such as selective permeation membranes for transmission plates, convection prevention methods, and selective absorption membranes for heat collection plates.

However, as the fate of alternative energy and new energy technologies, the performance will always be that of conventional ones, such as gas and oil.

Since it is difficult to evaluate the economic efficiency of the system in terms of electric energy prices, it is difficult to pursue it from the perspective of effectiveness versus cost.

In other words, even if a comparable technology (cost) is invested in a solar heat collector that is well-balanced to some extent, it becomes increasingly difficult to achieve commensurate efficiency improvements. In this sense, the application of a reflector that produces the effect of enlarging the heat collection area of a solar heat collector is commonplace, but it is a development in a different direction from the technology described above.

The annual amount of solar heat collected is maximum when the installation angle of the solar collector is adjusted to the latitude of the installation location.

However, in this case, in winter when the amount of solar radiation is low, the sun shines in from a low position, so the amount of energy that enters the solar collector decreases.

In order to improve the amount of heat collected in the winter, natural circulation solar water heaters and the like have been put into practical use that are equipped with stainless steel reflectors. The reason why stainless steel is used here is that it is highly durable and reliable, including good corrosion resistance. However, when looking at the sunlight reflection characteristics that are originally intended, even if the stainless steel surface has a mirror finish, the reflectance for sunlight is about 0.67.

Furthermore, a reflective film based on a plastic film has been proposed as a low-cost film having high sunlight reflectance. This is a metal vapor-deposited layer formed on a plastic film. For example, a thin film of aluminum or copper is formed on a polyethylene terephthalate film with a smooth surface using a vacuum vapor deposition method or a sputtering method, and then A protective film made of acrylic resin or the like is formed on the surface. However, in the case of this reflective film, it is just a film, so if it is used on a flat surface and there are four pages, it is necessary to stretch it properly.

In this case, even if the tensioning method is devised using a spring or the like, it is difficult to properly arrange the tensioner because it may crack or sag due to temperature changes.

The present invention uses low-cost materials such as zinc-treated steel plates, aluminium-treated steel plates, and plastic plates. The purpose of this project is to provide a reflector for solar heat collectors that has a coating film formed with a paint consisting of the above and a binder.Compared to conventional reflectors made of stainless steel, etc., the reflector is made of a material that has excellent reflective properties and is cheaper. Therefore, it has the effect of reducing costs and further guaranteeing durability and reliability.

FIG. 1 shows a perspective view of a natural circulation solar water heater. Reference numeral 1 denotes a reflector according to the present invention, and this reflector 1 is placed in front of a hot water storage tank 2. As shown in FIG. 3 is a heat collecting plate, 4 is a transmission plate, and 5 is a water supply pipe. Figure 2a.

b is a cross-sectional view showing the incident angle of sunlight of 6 degrees in summer and winter when the water heater shown in FIG. 1 is placed on the roof 6, and the effect of the reflector on this; As shown in Figure 2a, sunlight 7 is transmitted to the heat collecting plate 3.
On the other hand, the beam is incident at an angle of approximately 90°. However,
In winter, as shown in Figure 2, the sunlight 7 enters from a low position, so the amount of heat collected is reduced compared to when the incident angle is 90°. At this time, sunlight 7 is incident on the reflecting plate 1 placed in front of the hot water storage tank 2 and is reflected on the heat collecting plate 3. This reflective effect is intended to improve the amount of heat collected in winter.

Next, the structure of the sunlight reflecting plate of the present invention will be explained. First of all, regarding the support, since the reflection of sunlight depends on the fine metal powder of the coating film, there are no limitations on the material, and low-cost materials such as zinc-treated steel sheets, aluminum-treated steel sheets, steel sheets, etc.
Metal materials or various plastic materials such as polyethylene and polypropylene are applicable. The paint used to form a coating film on these supports is made of fine metal powder and a binder that have good sunlight reflecting properties. Examples of materials with good sunlight reflecting properties include metals such as gold, silver, nickel, copper, aluminum, and brass. As a binder, copper, brass, and aluminum are preferably used, and fine powders of these metals are used.As a binder, various organic resins such as acrylic resin, polyester resin, silicone resin, urethane resin, and epoxy resin are used. A paint is obtained by mixing these metal fine powders and a binder with a solvent using a dispersing machine such as a ball mill.

This paint is spray-painted onto a support and then dried and baked to obtain a coating film. At this time, the organic resin that is the binder impairs the transparency of sunlight to some extent, so it is desirable to make the film as thin as possible. Forming a film itself has a negative effect on corrosion resistance. Therefore, when the support is a metal material with poor corrosion resistance, it is desirable that the thickness of the coating film be 10 μm or more. In this case, since the transparency of the resin is impaired by the thick film, it is required that the fine metal powder that reflects sunlight floats on the surface of the coating film and is arranged in parallel. Such properties can be achieved by using flaky metal fine powder. This property is called leafing.

Hereinafter, the present invention will be described in detail focusing on examples.

(Example 1) A 70 x 150 x 1 m/m polypropylene plate was used as a support, and after activation treatment in a dichromic acid mixture, it was dried.
A paint consisting of three types of fine powders of brass and aluminum and Rhodosil Resin 9031, a polyester modified silicone resin manufactured by Dainippon Ink Co., Ltd., was spray-painted to a thickness of 15 μm and baked. At this time, three types of metal fine powders were Each has a content of 15 wt% based on the resin solid content,
These dispersion mixings were carried out in a ball mill for 10 hours.

The reflectance of this test piece to zero light is:
Shimadzu spectrophotometer MPS-5000 model wavelength 0.3
The spectral reflectance in the range of ~2.0 μm was measured, and the atmospheric mass 2
The reflectance for solar radiant energy was calculated. In addition, stainless steel (SUS-4308A finish)
The reflectance was also compared. The results are shown in Table 1.

(Example 2) A zinc-treated steel plate of 70 x 150 Regarding this test piece, the solar reflectance was calculated in the same manner as in Example 1. The results are shown in Table 2.

As is clear from the above Tables 1 and 2 on page 9, the reflector according to the present invention is 16 times stronger than the stainless steel shown in Table 1.
% higher reflectance.

Furthermore, in order to check the reliability of the coating film, the test piece prepared in Example 1-2 was subjected to a salt spray test (Bs-Z-2381
), after spraying for 1000 hours, washing with water and measuring the reflectance, the reflectance was only about 2% lower.
Further, even when the coating film was subjected to a cross-cut test, there were no abnormalities and it showed good characteristics.

Next, a weather meter test (J
I5-Z-0230) was carried out for 2000 hours, but there was almost no change in the adhesion and reflectance of the coating film.

As described above, the solar heat collector reflector of the present invention has extremely good reflection characteristics, high reliability, and durability. It exhibits superior properties compared to those that are less promising.

Note that when the content of the metal fine powder is 15 wt % or more based on the solid content of the binder, extremely good reflection characteristics are exhibited.

[Brief explanation of the drawing]

Figure 1 is a partially cutaway perspective view of a natural circulation solar water heater, and Figures 2 a and b are cross-sections showing the effect of the solar input plate in summer and winter when the water heater in Figure 1 is placed on the roof. It is a diagram. 1...Reflector. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 12

Claims (1)

[Claims] (1) A reflector plate for a solar heat collector, which has a coating film made of a paint made of fine metal powder and a binder on a support made of metal or plastic. 3. The reflective plate for a solar heat collector according to claim 1, wherein the metal fine powder is one or more selected from the group consisting of aluminum, copper, and brass.