Crystal growing and casting are metallurgical processes which are relatively energy intensive since they are processing molten silicon at around 1600°C.  They consist of a large number of units of process equipment operating in parallel. This modular nature makes for relatively easy expansion of plant throughput.

The starting material is lumps of chemically pure polycrystalline silicon, of a quality close to semiconductor-grade, produced by the Siemens process.  The solar industry has historically taken off-specification material that is rejected by the semiconductor industry.  However, as growth of the PV industry is overtaking that for semiconductors, this scrap is in short supply and an increasing proportion of more expensive prime-grade Si is having to be used as meltstock. 

A small number of companies, either integrated PV companies or independent wafer production operations, use one of two main methods of manufacture.  The traditional route for monocrystalline wafers is the Czochralski process in which a single crystal of up to about 150mm diameter is pulled from molten Si held in a large heated quartz crucible.  In the more recently developed method, Si is cast in a re-useable graphite mould to produce blocks of multicrystalline silicon (cubes of over 0.5m dimensions).  When sawn into bars and then wafers (just bigger than a compact disc) using a wire saw, the cleaned product is ready for cell manufacturing.  Multicrystalline wafers from the latter process are cheaper than monocrystalline wafers, but make slightly less efficient solar cells.  Click here for more details on crystalline Si solar cell technology.

Crystal growing and casting plants are best sited where there is an abundant source of reliable, cheap energy to power the high temperature operations.  They do not need to be sited close to solar cell plants because wafer transportation is cheap, but most are because the investment has been by PV manufacturers to secure wafer supply to their cell plants.

Thin film plants do not utilize crystalline Si wafers, so this whole piece of the manufacturing chain is avoided.  Instead, as a starting point for manufacture, they generally use large area glass sheet coated with a transparent conducting oxide layer (of the type used for special low emissivity glass products).  This is manufactured either on-line in a float glass factory, or off-line in large scale chemical vapor deposition (CVD) plants.  Some thin film plants are based around the use of roll-to-roll stainless steel sheet as the substrate for the cell, rather than glass. 

The capital cost of translating the solar cell into a laminated solar module is low, so the economics of smaller capacity plants can be justified. The main economies of scale can be captured in module assembly plants with an  annual capacity of 5 MW or greater. The capital cost for equipment will be around US$0.5M for this scale of plant, but the all up cost will be up to $5M. The number of jobs created in such a plant is very dependent on the level of automation utilized, but typically would be in the 30-100 range. From the point that the decision is made to proceed, and the site location has been acquired, module assembly plants can be operational within six to nine months. If a new building structure is required, these plants can be operational in twelve to eighteen months.

Solar module assembly usually involves soldering cells together to produce a 36 cell string (or longer) and laminating it between toughened glass on the top and a polymeric backing sheet on the rear. Frames are usually applied to allow for mounting in the field, or the laminates may be separately integrated into a mounting system for a specific application such as building integration.

The final part of the overall manufacturing process is the solar system assembly and installation. This has two aspects.

Firstly, the mechanical integration of the solar module into its chosen array structure. This array structure will depend on the final location, which could involve retrofitting on to a roof, integration into building materials for roofs or vertical walls, pole-mounting, ground-mounting or attachment to an industrial structure.

Secondly, the electrical integration of the solar module  with the other parts of the solar energy system. This will include connection of such elements as Inverters, Batteries, Wiring, Disconnects, and Regulators (Charge Controllers). This part also requires matching the equipment to the electrical load required by the customer. The Sales Company will usually utilize computer software, known as a sizing program, to make this calculation.

This part of the manufacturing process is the least capital intensive and can be located on small premises, or even be undertaken at the customers site. Sales companies (known as "Integrators", "Dealers" or "Installers") perform this task.  However, it is relatively labor intensive and this is an important component of job creation within the overall industry.