FACILITYMANAGEMENT
3. Improvement of the quality of interactions between equipment supplier and producers (after sales, transfer of expertise, training, ramp up assistance, maintenance).
4. And the underpinning of improvement measures with data and facts (PQMS-System)
Technology development
The process chain to bring a solar module with its energy yield onto the grid is made up of many technologically different steps. The potentials that can be used even today are described.
Diamond wire
The use of diamond wire represents a disruptive innovation in wafer manufacturing. Roughly double the output is achieved with the same number of saws because the diamond cutting process belongs to a direct cutting mechanism and the standard slurry process is based on a lapping mechanism. The diamond wire process produces fewer microcracks and of top of that the depth of microcracks is lower. The high durability of the wire, plus being able to avoid the slurry, reduces the TCO by 12%. Although the diamond wire is more expensive than other wire, the entire process is affordable.
Automated gluing and brick manufacture Although this process seems to be unspectacular, the effects on the TCO are enormous. The loading of the wire saw can be raised typically from 85% to 95% by almost the same cutting time. To reach this goal, the optimum block choice for loading the saw can be calculated from an algorithm based on an operation research programme. This leads to a 10% saving of sawing machines.
Automatic gluing process
Automatic gluing has two superb advantages that further reduce the TCO. As detailed DOE (Design of Experiments) show, the amount of special adhesive can be reduced by 50%. The costs of the saved adhesive alone result in a payback of less than 12 months for the Gluemaster machine. The number of usable wafers is increased by 1 to 3% - compared to the manual adhesive application - in the subsequent steps: sawing and deglueing. On the one hand, the wafers have a secure connection to the workpiece carrier (beam) and, on the other, can be detached from the beam in a smooth defined manner. This provides a higher wafer yield, resulting in a reduction of about 1% on the entire LCOE. The pay back of the Gluemaster over the whole wafering process is less than 1 month.
New Solar Cell Designs Selective emitter
The largest market share of solar cells used to consist of a standard solar cell technology with a uniformly doped emitter on the sunny side and
whole-surface metallization of the back. So far, this design has proved to be ideal in the overall costs. Newer designs make it possible to have local doping in the area of the contacts, which reduces the recombination losses between the contacts.
Galvanic processes could replace the expensive silkscreen pastes for a simultaneously higher conductivity. The pastes create up about 40% of the current cell manufacturing costs. With one to three additional production steps – depending on the architecture of the selective emitter – the cell efficiency can be increased by 0.3 to 0.8% absolute. This is a result mainly of the higher UV sensitivity of the IQE curve of the cell. But this economic advantage can be used in the module only in certain conditions. The encapsulation material must be characterised by high transmission in the short-wave range. It can be seen from this example that even at first sight non- adjacent processes (like cell and module manufacturing) are dependent on one another.
Thinner wafers
There is an optimum ratio of wafer surface and wafer volumes for every cell technology. If the wafer becomes thinner, the surface has a greater influence. For example, the technology of the selective emitter, with the lower recombination losses in the surface, enables a reduction in the cell thickness. At the same time this has the advantage that the requirements of the diffusion length can be slightly lower and so the durability of the minority carrier can be smaller, which of course has a double effect on the material costs.
Hetero junction cells
The hetero junction design is not new but still very promising. Sanyo had been one of the first movers who pushed into mass production with about 20% cell efficiency. The design is, related to other high efficiency designs, simpler and fabrication is done with no more steps than a standard solar cell. Because efficiency is one of the main drivers to
Chart 1
A symbolic overview of optimisation of the entire value chain and the three folded approach of thinking in the box, between the box and outside the box
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www.solar-pv-management.com Issue II 2011
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