Claims:CLAIMS

1. A Solar Glass Mirror comprising:
a glass substrate,
a reflective layer of metal deposited on the rear side of glass substrate,
a coating of paint over the reflective layer and
a protective coat such that the protective coat is in contact with the entire coat of paint on the reflective layer of metal deposited on the glass substrate as and the exposed edges of the glass substrate wherein the protective coat is a lacquer comprising of silicon.
2. The solar glass mirror of claim 1, wherein the solar glass mirror is prepared in customized size.
3. The solar glass mirror of claim 1, wherein the solar glass mirror is used in concentrating solar power/thermal apparatus.
4. The solar glass mirror of any preceding claims wherein the glass has a solar reflectance greater than 85%.
5. A process for preparing a solar glass mirror with customized size comprising of:
obtaining a glass substrate,
depositing a reflective layer of metal on the glass substrate,
coating the reflective layer of metal on the glass substrate with a paint to obtain glass mirror,
cutting the above glass mirror to obtain the customized size of the glass mirror having exposed edges and
applying the protective coat on the entire coat of paint on the reflective layer of the glass mirror and sealing the exposed edges of the glass mirror wherein the protective coat is a lacquer comprising of silicon.
6. A process for preparing a solar glass mirror with customized size comprising of:
cutting the glass substrate to obtain glass substrate of customized size,
depositing a reflective layer of metal on the rear side of glass substrate,
coating the reflective layer of metal on the glass substrate with a paint to obtain glass mirror and
applying the protective coat on the entire coat of paint on the reflective layer of the glass mirror as well as sealing the edges of the glass mirror wherein the protective coat is a lacquer comprising of silicon.
7. The process for preparing a solar glass mirror of claim 5 and 6, wherein said reflective layer of metal comprises one or more layers of a metal selected from the group comprising of silver and copper.
8. The process for preparing solar glass mirror of claim 5 and 6, wherein said coating with paint comprises of one or more layer of the paint.
9. The process for preparing a solar glass mirror of claim 5 and 6, wherein protective coat comprises of lacquer comprising of silicon.

Dated this the 5th day of November, 2015

Signature: _____________________
Name: (Meghana Damani)
of Nanavati Associates
Applicant’s Agent , Description:FIELD OF THE INVENTION
The present invention relates to a Solar Glass Mirror that may be prepared in desired customized size and has high durability and solar reflectance. The Solar Glass Mirror of the present invention is useful for concentrating solar thermal/power apparatus.

BACKGROUND OF THE INVENTION
Solar Energy is one of the important sources of energy with tremendous application in domestic, industrial and commercial verticals. The solar industry is primarily based on two technologies namely photovoltaic (PV) and concentrating solar thermal/power (CST/CSP). In photovoltaic technology the sunlight is directly converted to electricity by use of photovoltaic cell. The CST/CSP technology uses multiple mirrors to concentrate the energy from to sun onto a small area. The concentrated energy is used to heat up water which gives steam that is used for the generation of electricity and thermal heat. The CST/CSP technology is widely used in India for purposes of mass cooking in pilgrims like Shirdi, Tirupati, Bramhakumaris Mount Abu, etc.

The glass mirror is a primary component of the concentrating solar thermal/power apparatus. Glass mirrors that are available commercially are manufactured by applying a reflective coating to a glass substrate. In general the reflective coating comprises of a layer of silver deposited on the surface of glass which is covered by protective coating of copper layer to prevent oxidation of silver metal. The metal layers are further protected by two or more layers of waterproof paint. The silvered glass mirrors are widely used indoors in furniture, bathrooms or decorative purposes.

Application of glass mirrors in solar power apparatus’ is known since several decades. Installation of such outdoor units tends to expose glass mirror to external harsh environment conditions that leads to weathering of mirror, reducing its life to just couple of years! This in fact makes the installation of concentrating solar thermal/power apparatus expensive and cumbersome.

Further, depending on outlay and design of certain concentrating solar thermal/power apparatus the mirror size needs to customize in order to obtain the maximum output from the apparatus. It is also useful for safe and easy supply and logistics purposes to prevent from breakage and easy handling and installations.

It was observed by the inventors of the present invention that the commercially available glass mirrors are offered only in large sizes say approximately in range of 6 feet by 8 feet. When such a mirror is cut in order to make customized size mirrors for concentrated solar thermal/power apparatus like the Linear Fresnel Reflector, Parabolic Trough or Dish Stirling, or any CST/CSP thermal design apparatus, it results in exposed edges of the custom size mirror. Here, the bonding of paint with glass substrate and reflective coating is destroyed. This directly leads to penetration of rain water and other atmospheric elements into the layer of metal coated on the glass substrate. Due to such seepage the metal coating on the glass substrate gets oxidized resulting in degradation of glass mirrors and reducing the life of reflecting mirrors to less than couple of years. Longer life of the glass mirror say up to twenty years is an important factor for making economical concentrating solar power/thermal apparatus’.

Therefore, there is a need to develop glass mirrors that are specifically adaptive for use in solar energy devices particularly for concentrated solar thermal/power technology (CST/CSP). In other words there is a need to develop ‘Solar Glass Mirrors’ which can be made in customized size to suit the requirement of the concentrated solar power apparatus. Further, such Solar Glass Mirrors should have a prolonged life such that it renders the installation of concentrating solar thermal/power apparatus’ commercially viable.

The inventors of the present invention have developed unique Solar Glass Mirrors that involves a technology wherein the exposed edge as well as the reflective layer of metal deposited on the glass substrate of the custom sized glass mirrors are sealed thereby preventing it from substantial degradation due to environmental factors. The aforesaid technology does not involve any expensive material or procedure thereby making the resulting product substantially cheap and to be used efficiently in the concentrating solar thermal/power apparatus.

SUMMARY OF THE INVNETION
Taking into consideration the practical problems encountered during the development of CST technologies in India, it is therefore an object of the present invention to provide Solar Glass Mirrors that can be used economically an efficiently in concentrating solar thermal/power apparatus.

It is also an object of the present invention to prepare Solar Glass Mirrors in customized sizes that have a longer life and are not prone to degradation in extreme harsh environmental conditions.

In accordance with the objects of the present invention, the present invention provides a Solar Glass Mirror comprising a glass substrate, a reflective layer of Silver metal deposited on the rear side of glass substrate, a coating of paint over the reflective layer and a protective top coat such that the protective top coat is in contact with the entire coat of paint on the reflective layer of metal deposited on the glass substrate as well as the exposed edges of the glass substrate wherein the protective coat is a lacquer comprising of silicon.

The present invention provides a Solar Glass Mirror that can be prepared in customized sizes. The present invention further provided a Solar Glass Mirror that has a solar reflectance greater than 85%.

An embodiment of the present invention provides a process for preparing a Solar Glass Mirror in customized size comprising of obtaining a glass substrate, depositing reflective layer of metal on the glass substrate, coating the reflective layer of metal on the glass substrate with a paint to obtain glass mirror, cutting the above glass mirror to obtain customized size of the glass mirror with exposed edges and applying the protective coat on the entire coat of paint on the reflective layer of the glass mirror as well as sealing the exposed edges of the glass mirror wherein the protective coat is a lacquer comprising of silicon.

Another embodiment of the present invention provides a process for preparing a Solar Glass mirror comprising of obtaining the a glass substrate of customized size, depositing reflective layer of metal on the rear side of glass substrate, coating the reflective layer of metal on the glass substrate with a paint to obtain glass mirror and applying the protective coat on the entire coat of paint on the reflective layer of the glass mirror as well as sealing the exposed edges of the glass mirror wherein the protective coat is a lacquer comprising of silicon.

The above summary is not intended to disclose objects, aspects and embodiments of the present invention entirely. The advantages and other features of the invention may be understood by the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1: Commercially available silver mirror.
Fig. 2: Concentrated Solar apparatus’ used in CSP/CST technology
Fig. 3: Solar Glass mirror of the present invention.
Fig. 4: Installation of Parabolic troughs using Solar Glass mirrors of the present invention.

DETAIL DESCRIPTION OF THE INVENTION
The commercially available silver mirror is shown in the Figure-1. It comprises of a glass substrate 1, with a layer of metal 2 deposited on the glass surface, by wet chemical process, wherein a thin layer of chemically reduced silver is precipitated onto a sensitized glass surface, which is then protected by a coat of paint 3. In general the layer of metal 2 is the reflective layer of the mirror. The reflective layer of metal 2 comprise of a silver metal coating. When there is a silver metal coating on rear side of glass substrate, optionally a second coating of metal like copper is applied in order to prevent oxidation of silver metal layer by climatic factors. Then the reflective layer of metal 2 is protected by coating of paint 3. Such a coat of paint can be of single layer or more than one layers. After drying the commercially available silver mirror described in Fig. 1 is ready. Such a process for preparing mirror for indoor applications is well known in the prior art.

When the commercially available mirror is cut to prepare customized size mirrors as per the requirement of the concentrated solar thermal/power apparatus’ for e.g. as shown in Figure-2, the edges of the customized size mirror 4 shown in Figure-1 and 3 gets exposed. As a result the coating of paint 3 protecting the reflective layer of metal 2 becomes loosely bound to the glass substrate 1. This allows the free passage of atmospheric elements like air, water and heat between the reflective metal layer 2 and the glass substrate 1 and also between the reflective metal layer 2 and the coat of paint 3 that leads to degradation from the exposed edges 4 of the glass mirror. Thereby, the glass substrate and the metal layer are damaged that reduces the overall solar reflectance of the mirror and also its life.

An embodiment of the present invention provides a Solar Glass Mirror comprising a glass substrate, a reflective layer of metal deposited on the glass substrate, a coating of paint over the reflective layer and a protective coat such that the protective coat is in contact with the entire coat of paint on the reflective layer of metal deposited on the glass substrate as well as the exposed edges of the glass substrate wherein the protective coat is a lacquer comprising of silicon.

Another embodiment of the present inventions provides a process for preparing Solar Glass Mirror in customized size comprising of obtaining a glass substrate, depositing reflective layer of metal on the glass substrate, coating the reflective layer of metal on the glass substrate with a paint to obtain glass mirror, cutting the above glass mirror to obtain customized size of the glass mirror with exposed edges, and applying the protective coat on the entire coat of paint on the reflective layer of the glass mirror as well as sealing the exposed edges of the glass mirror wherein the protective coat is a lacquer comprising of silicon.

The technology of the present invention is applicable to commercially available mirrors as well as mirrors prepared by methods knows per se.

A preferred embodiment of Solar Glass mirror of the present invention is shown in Figure-3. It includes the glass substrate 1, a reflective layer of metal deposited on the glass substrate 2, a coating of paint over the reflective layer 3 and a protective coat 5 such that the protective coat 5 is in contact with the entire coat of paint on the reflective layer of metal deposited on the glass substrate as well as the exposed edges 4 of the glass substrate 1.

The glass substrate 1 is generally float glass/sheet glass, which contains low iron glass or extra clear glass. The thickness of glass substrate may vary from 2 -12 mm. The size of such glass substrate may vary form 6 feet to 8 feet. The large sheet of such a glass is polished and then sensitized by conventional methods and then it is subjected to coating of reflective layer of metal 2.

The reflective layer of metal 2 comprises one or more layers of a metal selected from but not limited to the group comprising of silver and copper. The metal is coated on glass substrate 1 by methods known in prior art e.g. wet chemical process.

Further, the glass substrate 1 covered with reflective layer of metal 2 is coated with at least one layer of paint. The e.g. of paints which may be used herein include but are not limited to acrylic, epoxy, or alkyd-based, poly urethane or polyester. Thereby, a large sheet of glass mirror is obtained.

In order to prepare the customized size Solar Glass Mirror, the large sheets of commercially available glass mirrors prepared by methods described above or prepared by procedure known per se, are cut in desired size. The large sheets may be cut into sizes for e.g. but not limited to dimensions as small as 40 mm by 102 mm. It is obvious to person skilled in the art that if desired the shape of the glass mirror can also be varied e.g. square, rectangle, circle, oval, triangle or it is also possible to apply knowledge of the present invention on glass mirrors that are curved in shape. The term ‘customized size’ as used herein the specification refers to all such variations in size, shape and thickness of the mirror.

Those skilled in the art will appreciate that wherein the Solar Glass Mirror is prepared by first cutting the glass substrate 1 into the customized size and shape and then deposition of reflective layer of metal 2, followed by coat of paint 3 and subsequent application of the protective coat 5, is well within the scope of the present disclosure.

When the large glass sheet is cut, the reflective metal layer 2 and coat of paint 3 is largely absent from the edge 4 of the glass substrate shown in Fig. 2. However, it would be apparent to those skilled in the art that presence of reflective metal layer 2 on one or more edge 4 is within the disclosure of the present invention. Similarly, presence of the coat of paint 3 on one or more of edge 4 is within the scope of the present disclosure.

The protective coating 5 of the present invention is to applied to entire coat of paint 3 on the reflective layer of metal 2 deposited on the rear side of the glass substrate 1 as well as the exposed edges of the glass substrate 4 as shown in Fig. 3.

The protective coat 5 comprises of lacquer comprising of silicon. The lacquer comprising of silicon has unique properties like water repulsion and water vapour permeability. The water repulsion property prevents penetration of moisture from outside and the property of water vapour permeability allows water vapour that is generated inside to escape. The silicon lacquers are resistant to acid rain and the ultraviolet components of sunlight making it extremely suitable for outdoor applications. Such lacquers comprising of silicon are commercially available however, their application in the field of Solar Glass Mirrors is not known till date.

The protective coat is applied by method of curtain coater where a controlled dry film thickness of paint insulates the entire rear side an edges of the glass substrate.

The corrosion/degradation of Solar Glass Mirrors of the present invention is tested using CASS (Copper Accelerated Acetic Acid Salt Spray) test. The procedure for conducting the said test is in accordance with that set out in International Standard ISO 9227:2012. The duration of the test was 400 hours.

Further, Solar Glass Mirrors of the present invention is tested using weather-o-meter chamber wherein the black panel temperature was maintained at 60°C for 400 hours.

The UV-resistance test was performed on the Solar Glass Mirrors of the present invention at 60°C with irradiance of 0.7w/m2 for 400 hours.

The finished Solar Glass Mirror has solar reflectance greater than 85% more preferably greater than 90%.

The advantages and the economic significance of the present invention are as follows:
1. The Solar Glass mirror is prepared in customized size.
2. The Solar Glass mirror has high durability and solar reflectance.
3. The process for the preparation is simple and easy to apply on a commercial scale.
4. The finished product can be made available at a reasonably affordable price.

Examples:
Example 1-4 are Solar Glass Mirrors prepared by cutting customized size mirrors from large sheet of mirror. These mirrors were subject to coating by protective coating comprising of lacquer comprising of silicone by curtain coater technique. The results are summarized in Table-1.

Ex. No. Dimensions of Mirror CASS 25 days average Weather-o-meter Test* UV-Resistance Test#
1 102 x 152.4 x 3 mm Passed 3~4 1-2
2 40 x 1605 x 3 mm Passed 3~4 1-2
3 250 x 152.4 x 3 mm Passed 3~4 1-2
4 102 x 76.2 x 3 mm Passed 3~4 1-2
* Grading for colour change given as per ISO grey scale, 1 is bad and 5 is good.
# GSR rating

Table-1

While the invention has been described with reference to various specific and preferred embodiments and examples, it should be however understood that variations and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.