Product category:
Bearings
News Release from: SKF UK | Subject: Needle roller bearings
Edited by the Engineeringtalk Editorial
Team on 25 March 2004
Mechanics have a bearing on solar cell
efficiency
Mechanical engineering developments from SKF contribute to a new grinding machine that aids the quest for ever-increasing efficiencies from solar cells.
Increasing the efficiency of photovoltaic power plants is a continuous research process for the leading manufacturers of solar cells One recent advance has seen mechanical engineering developments from SKF contribute to a new grinding machine that aids this quest
A new grinding machine, developed in Germany by the Fraunhofer-Institut fur Produktionstechnologie (Institute for Production Technology - IPT) at Aachen, in co-operation with the University of Konstanz, endows the surfaces of the silicon wafers with V-shaped grooves approximately 160um wide.
This enlarges the active surface of the cell and, on the other surface, allows less sunlight to be reflected and lost.
Although it sounds simple, the development of the machine was highly complex.
From the outset, SKF's linear engineering experts co-operated closely with the machine manufacturer to meet the high technical demands.
The design brief made no hint of the solution, but only specified the targets to be achieved.
At first sight, the machine looks like a conventional grinder, however, closer inspection reveals the large number of precision components that play a decisive part in the performance of the new machine.
With the accuracy of the cells measured in microns, the typical structural geometries must be worked into the entire wafer surface with the utmost precision.
This, coupled with the fine structure of the silicon wafer, required an unconventional machine concept.
The machine has to grind brittle material without damaging the cells and prevent wafer fragments from impairing the process.
For economical reasons four cells, each measuring 125 x 125mm, have to be ground in one operation and the throughput rate needed to be up to 12m2 of cell surface per hour.
Heavy-duty SKF profile rail guides shift the vacuum work piece support under the grinding roll on an x-y cross-table on a base of rigid granite.
These extremely accurate guides achieve surface deviations of less than 4um over a stroke of +/-100mm.
A clearance-free SKF ball screw drives this slide on the x-axis (the oscillating stroke).
Thanks to the integral needle roller guides and the direct linear measuring system, the z-axis (for workpiece feed), driven by a linear motor, has an even higher accuracy than the x-axis.
The z-axis is mounted directly onto the x-axis.
Because cooling and rinsing fluid is used in the grinding process, the linear motor slide is completely sealed.
Furthermore, all visible components and surfaces are nickel coated.
The high-precision motorised grinding spindle, driven by a 33kW AC servomotor, enables the structuring tool to "nibble" into the silicon at a speed of 10,000rev/min.
Guidance is provided by ultraprecise SKF needle roller bearings.
The drive uses a planetary roller screw and a CNC system controls the entire machine.
Thanks to optimised process parameters, the grinding machine, working with form tools, achieves the required surface topography at high throughput rates.
The user gains an enhanced product, since the solar cells have higher efficiency and are homogeneous, even though they are, in part, multicrystalline in structure.
IPT scientists also intend to introduce the new grinding technology to the fuel cells market; the primary target being the power cells used in mobile equipment.
Because of their research, IPT's experts have proven that the mechanical structuring of silicon is the fastest method for the cost-effective application of a texture to silicon solar cells.
Moreover, the method can be integrated into fully automatic production lines without problems. Request a free brochure from SKF UK ...
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