JPH05280807A - Device for collecting solar heat - Google Patents

Abstract

PURPOSE:To permit a reflecting mirror to be cleaned at extended intervals of time by coating the outer surface of the glass, which is a component of the reflecting mirror, with a surface-active agent. CONSTITUTION:A reflecting mirror 3' comprises a glass plate 7 and a back plate 8. These glass plate and back plate 7, 8 adhere closely to each other with an evaporation film of aluminum or silver therebetween. By this evaporation film the solar rays falling on the glass plate 7 are reflected to a specific direction. The glass plate 7 is overlaid at its outer surface with a film 9 of a surface-active agent of a fluorine- based polymer. Applicable to this use is a film with a thickness of 10-odd dynes/cm and with a hydrophobic property of extremely low surface tension. When dust in the air descends as dust particle 6 together with steam 10 that condensates on the film 9 of the surfactant, the resultant film of water 10 makes a large contact angle thetato the surface of the glass plate. By virtue of this large contact angle theta the negative pressure which occurs in a space 10' formed inside the film of water 10 is small and the adhesion of the dust particle 6 is rendered extremely low so that it is possible for the dust particle 6 to fall off easily under its own weight or some external force from, for example, wind. Thus the intervals of time at which the reflecting mirror needs cleaning can be extended.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar heat collecting apparatus which improves a reflecting mirror and improves heat collecting efficiency.

[0002]

2. Description of the Related Art As shown in FIG. 4, a solar heat collector 1 has a structure in which a plurality of reflecting mirrors 3 are attached in a curved panel shape to a frame 2 having a mechanism for tracking the sun orbit. The solar thermal energy collected by the reflecting mirror 3 is used as a power source of the Stirling engine 4 supported by the frame 2.

In the conventional reflecting mirror 3, aluminum or silver is vapor-deposited on the back surface of a polyethylene film or glass to efficiently reflect solar heat. However, the conventional reflecting mirror 3 is liable to be dusty as described below. That is, since the dust 6 in the atmosphere serves as a condensation group of water vapor, it probably contains water. Raindrops can be mentioned as a typical example. Dust 6 containing such water (water film)
On the glass surface, the water forms a water film 5 due to its surface tension. The space 5 ′ inside the water film 5 has a negative pressure, and the water film 5 and the dust 6 are held on the glass surface and do not fall due to the force due to the pressure difference with the atmosphere. The force for holding the dust 6 (adhesive force) changes depending on the contact angle θ between the water film 5 and the glass surface.

The adhesion of the dust 6 on the outer surface of the reflecting mirror 3 causes a decrease in reflectance. As shown in FIG. 3, in the conventional example, the reflectance of the reflecting mirror decreases with the lapse of days due to the attached dust. The decrease in reflectance lowers the amount of heat collected and adversely affects the engine output. In fact, when the reflection amount decreases by 5%, the engine output decreases by 5-9%, so that the reduction of the reflection amount becomes a serious problem even if it is several%.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art.

[0006]

The present invention employs means for improving the outer surface of a reflecting mirror in order to solve the above-mentioned problems. That is, a means for adhering a surfactant to the outer surface of the glass forming the reflecting mirror is adopted.

More specifically, the present invention relates to a frame provided with a mechanism for tracking a solar orbit, a power engine supported by the frame, a reflector fixed to the frame and supplying thermal energy to the power engine. The solar heat collecting apparatus is characterized in that the reflecting mirror comprises glass, a back plate, a vapor deposition film between the glass and the back plate, and a film of a surfactant on the outer surface of the glass.

[0008]

The outer surface of the glass to which the surface-active agent is adhered has a large contact angle with the water droplets attached to the outer surface and has a very small adhesive force, so that it easily falls due to the external force such as the weight of dust or wind. When this state is described with reference to FIG. 4, the reflectance can be improved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention basically relates to a reflecting mirror 3'used in a device as shown in FIG. Therefore, the whole device is shown in FIG.
The reflecting mirror 3 will be described with reference to FIG. The reflecting mirror 3'has, for example, a glass plate 7 having a thickness of 0.2 mm and a back plate 8 made of a rigid body. The glass plate 7 and the back plate 8 are adhered to each other via an aluminum or silver vapor deposition film. The vapor deposition film reflects sunlight incident on the glass plate 7 in a predetermined direction.

A film 9 of a fluoropolymer surfactant is attached to the outer surface of the glass plate 7. The film thickness is 1 μm to several tens of μm
As the surfactant to be used, a hydrophobic one having an extremely low surface tension of 10 and a few dynes / cm is used.

The action of the surfactant film 9 will be described with reference to FIG. When the dust 6 in the atmosphere is condensed with the water vapor 10 on the surfactant film 9, the contact angle θ between the water film 10 and the glass surface becomes large. This large contact angle θ is due to the water film 10
The negative pressure generated in the space 10 'inside the container is small, and the adhesion force of the dust 6 is made extremely small, so that the dust 6 can be easily dropped by its own weight or external force such as wind.

Referring to FIG. In the example of the present invention using the surfactant, the reflectance can be maintained clearly higher than that of the conventional example after about one week.

[0013]

The film of the surfactant of the present invention can be applied on site by spraying or the like, and therefore the work of forming the film is simple. This film can increase the cleaning interval of the reflecting mirror.

[Brief description of drawings]

FIG. 1 is an exploded view of a reflecting mirror of an example of the present invention.

FIG. 2 is a diagram showing a relationship between a water film and dust.

FIG. 3 is a graph showing reflectance.

FIG. 4 is a perspective view of an example of a solar heat collector.

FIG. 5 is a diagram showing a relationship between conventional dust and a water film.

[Explanation of Codes] 2 Frame 3, 3'Reflector 4 Stirling Engine 6 Dust 7 Glass 8 Back Frame 9 Surfactant Film 10 Water Film

Claims (2)

[Claims] 1. A frame having a mechanism for tracking a solar orbit, a power engine supported by the frame, and a reflecting mirror fixed to the frame and supplying thermal energy to the power engine, the reflecting mirror comprising: A solar heat collecting apparatus comprising: glass, a back plate, a vapor deposition film between the glass and the back plate, and a film of a surfactant on the outer surface of the glass. 2. The surface tension of the surface active agent is 10 or more dynes /
The solar heat collector of claim 1 in cm and the power engine is a Stirling engine.