Description

Photovoltaic cells are solid-state semiconductor device that converts sunlight directly into electricity.

 

Usually made ​​of silicon (the second most abundant element in the earth's crust which is obtained from the sand) with traces of other elements and are first cousins ​​of transistors, light emitting diodes (LED) and other electronic devices.

 

Photovoltaic device (solar cell) is made up of layers of semiconductor materials with different electronic properties. In an average solar crystalline silicon cell, the majority of the cell would be made of silicon, with just a small amount of boron to give it a positive character. Then it is coated in a thin layer of phosphorous on the front of the cell, with a non-reflective glass layer to create the negative character. This ultimately creates an electric field between the two layers, which is called the junction.

 

The photons (particles from light), hit the solar cell and some are absorbed in the area of the junction, freeing the electrons in the silicon crystal. If the photons contain enough energy, the electrons will converge the electric field at the junction and will move freely through the silicon atoms in the cell and move into an external circuit as energy. As they move through the external circuit they release their energy as electricity to either 'Off Grid', for all your daily household needs and charging batteries for use in the evening. or 'On Grid' which can be sold back to the electricity utility company at an agreed price.

 

The photovoltaic process is an entirely self contained cycle with no moving parts and no materials being consumed or emitted, and with regular maintenance i.e. just keeping clean of dust and debris in many cases, can be up to 80-90% efficient for well over 40 years.

 

On a sunny day, an array of solar cells one square meter, exposed to the sun at noon will receive approximately 1 kilowatt (Kw) of power. Solar Innova monocrystalline cells convert roughly 17.8% of this into electricity, meaning one square meter of cells will generate 178 electric watts in full sunshine.

 

Different solar cell technologies create varying conversion rates with amorphous silicon thin film creating around 6%-8%, cadmium telluride thin film 8%-10%, polycrystalline also referred to as multicrystalline silicon 12%-15% and monocrystalline 14%-19%. These efficiency rates are being pushed higher almost every year with new technologies and more efficient silicon’s.

 

Solar Innova only produce monocrystalline and polycrystalline cells. The most significant differences are:

 Monocrystalline

Are created from a single crystal and are cut from a block of crystal which has only grown in one direction (one plane). Single crystalline is more difficult to manufacturer, making a more expensive option with greater efficiency than the multicrystalline (polycrystalline cells).

 Polycrystalline (Multicrystalline)

Are created from a multifaceted crystal which is cut from a block of crystal grown in multiple directions, making them slightly less efficient for the same size cells monocristalline, meaning having a larger surface area for the same output power.

 

 Production

Solar power generation technology is founded upon silicon, a common element that comprises approximately 25 % of the earth’s crust by mass.

 

Solar cells are produced from raw silicon materials in a multistage process. Firstly raw quartzite sand is processed to produce metallurgical-grade silicon. This material is further purified to semiconductor-grade or solar-grade polysilicon feedstock. Reclaimable silicon raw materials, which include tops and tails of discarded portions of silicon ingots, pot scraps and broken silicon wafers acquired from the semiconductor and solar power industries may also be used as feedstock. The use of reclaimable silicon raw materials to manufacture ingots can result in a lower overall cost of raw materials. However, the use of reclaimable silicon raw materials increases the difficulty of producing ingots of similar quality to those made only from polysilicon.

 

In the most widely used crystalline silicon-based solar manufacturing process, feedstock is melted in high temperature furnaces and then formed into ingots through a crystallization process.

 

The ingots are cut and sliced to produce wafers which form the basis of a solar cell. In the manufacturing process are added electrodes in the wafer for electrical connectivity. The wafers are then cleaned and treated prior to their introduction into the manufacturing process.

 

With the appropriate treatment, various layers are created that produce an electric field, which separates positive and negative charges as soon as light falls on the solar cells. The charges remain available for use at the two poles of the solar cell, as in the case of a battery. When light falls on high purity silicon, the PV (photovoltaic) effect causes the release of electrons from the silicon atoms. When silicon is fashioned into a solar cell with collection electrodes, the photovoltaic effect generates an electrical current.

 

Brief overview of the most important steps in the solar cell manufacturing process:

 

1.- Texturing and Cleaning

As a rule, the wafers in the manufacture chain for silicon solar cells also undergo wet chemical procedures. The wafers are cleaned in an etching bath, saw damage is eliminated and they are textured. Another treatment removes the phosphorus silicate glass, which is formed as a by-product of the diffusion process. These process steps can be carried out as inline or batch process. For this the wafers undergo wet chemical processes in a synthetic basin.

2.- Diffusion

Next, through a thermal process, a negatively charged coating is applied to the positively charged raw wafers in a diffusion furnace. At furnace temperatures of approx. 800-900 °C, applies phosphoric gas and phosphorus atoms are diffused into the waver’s surface, the phosphorous atoms diffuse into the wafer surface. Doping occurs and creates a negatively charged surface layer. As a result, the wafer now has two separate layers: a negatively charged layer on the surface and a positively charged layer below it.

3.- Isolation

To achieve a clean separation of the positive and negative layers, the edges of the wafers are isolated through etching, a process that removes a very thin layer of silicon around the edges of the solar cell resulting from the diffusion process.

4.- Anti-Reflection Coating

In this process step the future solar cells in the inline or batch process are coated with silicon nitride, which gives it its typical blue colour. The passivation of the surfaces and volumes of the silicon wafers means the performance of the solar cell is significantly increased.

5.- Printing

In a screen-printing process, silver paste is printed and aluminum is pasted to the front and back surfaces of the solar cell to act as contacts, with the front contact in a grid pattern to allow sunlight to be absorbed.

6.- Co-Firing

Subsequently, contacts are connected through an electrode firing process in a conveyor belt furnace at high temperature. The high temperature causes the silver paste to become embedded in the surface of the silicon layer forming a reliable electrical contact. The aluminum paste on the back of the cell serves as a mirror for particles which further enhances the efficiency level.

7.- Testing and Sorting

Finally, completes the manufacturing of solar cells by testing and sorting. The finished cells are sorted according to efficiency levels and optical criteria. Each cell is tested and assigned to a performance and quality class depending on the testing results.

 

Measurements:

  • Control of the front and the rear side.

  • Hot spot, IV curve, electroluminiscence.

  • Imprint, colour, geometry, contamination, holes.

  • Photoluminicence.

  • Bow.

  • Micro-crack.

8.- Interconnection

The solar modules are then assembled by interconnecting multiple solar cells through taping and stringing into a desired electrical configuration. The interconnected cells are laid out, laminated in a vacuum, cured by heating and then packaged in a protective lightweight anodized aluminum frame. The solar modules are sealed and weatherproofed and are able to withstand high levels of ultraviolet radiation, moisture and extreme temperatures.

 Downloads

Catalog

Catalog (pdf)