FACILITYMANAGEMENT
manufacturing of solar modules is based on $/Wp. This is regrettable as fundamental KPI (Key Performance Indicators) such as durability and performance ratio (PR) have a very high sensitivity compared to improvements for the reduction of the generated energy process in $/kWh, but are not considered along the manufacturing chain.
New standards not based on Wp but on kWh will enhance the technological road map of the wafer, cell and module manufacturing. As long as these standards are absent, technological developments focused on high potential reductions in terms of $/kWh are disregarded since the decisive factor widely found in the market is $/Wp and not $/kWh.
Part-optimised processes may well lead to the improvement of production characteristics, but negatively affect $/kWh costs. Optimization of the entire value added chain can be viewed as a three folded process. Thinking in the box, thinking between the boxes and thinking out of the box.
The following are examples for thinking in, between and out of the box.
Example 1: the cell manufacturer makes 2 bus bar cells, meaning higher cell efficiency because of less contact shading than with 3 bus bar cells. Module manufacturers prefer 3 bus bar cells, because of higher module efficiency due to less serial resistivity of the interconnection of all cells.
Example 2: an optimised coating of the cell leads to higher cell efficiency (in air a refractive index n=1.0) and hence to a good cell price, but, because of the encapsulation under glass and EVA (n=1.5), has a lower light injection as a result. Here again cell manufacturer and module manufacturer have different targets.
Example 3: partially shunted cells are not noticeable in the performance measurement of a module, but lead in the event of shadowing of this one shunted cell to a hotspot and to the destruction of the module and to a reduction of durability as a result. The cause of such shunts can be found already in the quality of the silicon casting process.
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Example 4: new encapsulation films are dearer than the existing ones, but hold longer, have a higher transmission and let dissipate the heat better. Such materials lower the costs for the $/kWh but they rise the $/Wp. It can be seen from the examples that only total investigation of all processes that are necessary to generate photovoltaic energy in kWh will reflect the actual cost picture. To reduce the $/kWh the entire process chain in terms of LCOE will need to be examined in principle.
Leverage effect and sensitivity As described, the LCOE are made up of two parts. Manufacturing/TCO and PV application/BOS. The entire value-added chain is depicted in table 1 and it shows which processes need to be adhered to in order to reduce the TCO and LCOE.
Table 1: Relative production costs by different views calculated for a standard module with 16.5% cell efficiency, 3% cell-to-module losses, 1000 kWh/m2, PR of 85%, temp. coeff. of -0.45%/°C by 53°C average module temperature and 20 years of used time. The italic lines showing bigger fractions of the overall costs
Example 1: Improvement of cell efficiency by 10% relative reduces the energy cost ($/kWh) by 9.5% = 95% x 10%.
Example 2: Improvement of durability by 10% relative reduces the energy cost ($/kWh) by 10%= 100% x 10% .
It appears clear that technological improvement must base on the following six sigma procedure. 1. The exact conformity with customer needs 2. The stability of the technical and logistical processes and the achievement of the product quality, where the variance determines the six- sigma level
www.solar-pv-management.com Issue II 2011
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