In general, a solar cell module is formed by interconnecting individual solar cells and laminating the interconnected cells into an integral solar cell module. More specifically, the module usually includes a stiff transparent cover layer made of a polymer or glass material, a transparent front encapsulant which adheres to the cover material and to a plurality of interconnected solar cells, a rear encapsulant which can be transparent or any other color, a stiff backskin for protecting the rear surface of the module, a protective seal which covers the edges of the module, and a perimeter frame made of aluminum which covers the seal. The frame protects the edges of the module when the front cover is made of glass.
Before the frame is mounted, the module is laminated under heat and pressure. These conditions cause the layers of encapsulant material to melt, bond to adjacent surfaces, and to literally "encapsulate" the solar cells. Since crystalline silicon solar cells are usually brittle, the encapsulant serves to protect the solar cells and reduce breakage when the module is subject to mechanical stress during field usage. After the lamination process, the frame is attached to the module. The frame includes mounting holes which are used to mount the framed module to an object in the field. The mounting process requires screws, bolts, and nuts and can be accomplished in a variety of ways.
Because existing methods for manufacturing solar cell modules tend to be too high, solar electricity is generally not cost-competitive for grid connected applications. For example, three areas in which manufacturing costs need to be reduced include: (i) the materials from which the modules are made; (ii) the labor required to deploy these materials; and (iii) the materials and labor associated with mounting the modules in the field. In particular, the cost of known backskin materials, the cost of the aluminum frame, and the cost of labor required for field mountings in remote areas are known to be too high.
One known method aimed at reducing solar cell module manufacturing costs includes eliminating the aluminum frame and using a polymeric material as both the backskin and the edging. For amorphous silicon solar cell modules, polymeric frames of a molded thermoplastic material are widely practiced. Reaction injection molding may be used to mold a polyurethane frame around an amorphous silicon module. Reaction injection molding is done in situ (i.e., on the module), and this is a significant cost savings advantage. However, this molding process has several disadvantages. For example, this process includes the use of a chemical precursor (e.g., isocyanate) which poses environmental hazards. This process also requires a mold, further adding to the overall manufacturing cost. In addition, modules made this way tend to be small (e.g., 5-10 Watt size), not the 50-80 Watt size more generally deployed using aluminum frames. The modules tend to be smaller because of the higher cost of the mold and the limited strength of the resulting polymeric frame with its integral mounting holes. As a result, reaction injection molding is marginally successful in reducing manufacturing costs for amorphous silicon solar cell modules.
For crystalline silicon modules, the backskin material is generally quite costly. There are two widely used backskin materials, both of which tend to be expensive. The most popular material used is a Tedlar.RTM./polyester/ethylene vinyl acetate laminate, and the other widely used backskin material is glass. Two additional layers of material are often deployed between the solar cells in the module and the backskin, further adding to the manufacturing costs. A rear sheet of the same material as the transparent encapsulant, (e.g., Ethylene Vinyl Acetate) and a sheet of"scrim," which allows for efficient air removal during vacuum lamination, must be applied over the cells before the backskin material is deployed.
Both amorphous and crystalline silicon modules also include a junction box which is mounted onto the backskin material and from which all external electrical connections are made. Further labor is required to make connections to the junction box.
A frame, along with an elastomeric edging material, is often used when the front support for the module is formed of tempered glass. This construction protects the edges, as the tempered glass is vulnerable to breakage if an edge is damaged. While the use of a frame adds durability to the solar cell module, it also adds significantly to the manufacturing costs.
The labor intensive process of mounting the module can add significantly to the overall cost of solar electricity. Modules are mounted by assembling screws, nuts, and bolts to the appropriate mounting holes on the aluminum frame. However, solar cell modules are often located in remote areas which have no other source of electricity. As such, the mounting process often involves attaching the hardware in difficult, awkward and not readily accessible locations such as on rugged terrain, or roof tops. Therefore a need exists for a low-cost solar cell module that can be used as a roof tile.
The foregoing discussion demonstrates that the manufacture of solar cell modules tends to be too costly and involves too much labor to allow for the realization of the goal of cost-competitive solar electricity for wide-scale global use.