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SiGen vFinal DR 2/9/09 11:15 Page 34
MANUFACTURINGISSUES
Built in cost savings Analysis and Impact
Figure 4 shows a factory layout concept with the The Cost Reduction Analysis used an assumed
implant and cleave modules in a more simplified cost for poly-silicon at $90/Kg. It is quite evident
wafering environment. Also shown in the layout is the cost reduction in the upstream value chain and
a brick station, with functions to load/unload bricks even at lower prices of poly the cost savings are
for inspection, refilling the tray and reconditioning still indispensable to reach <$1/Wp module cost.
the bricks. The annual estimated silicon feedstock material
usage for 373MW wafers for a wire saw factory and
The following methodology was used to compare cleaving factory is shown in Table I.
the cost reduction benefits provided by the SiGen
Issue IV 2009
cleaving process: Baseline cost assumptions were For the above metrics, the upstream cost is
used for the fully integrated factory on an annual substantially reduced ranging from 53% to 70%
basis A realistic and validated model has been depending upon the wafer thickness considered
generated for the cost of wafering for both, the and the price of poly-Si. Even at lower prices of
Wire Saw (WS) and the SiGen PolyMax system poly-Si, the savings are extremely important to
(PM) for integrated PV manufacturing. On the basis achieve the module cost target in the market. The
of this model a cost savings is quantified in $/Wp downstream processes, cell and module, will
-pv-management.com for mono-c-Si wafers by comparing the higher benefit with a lower starting cost per wafer and
higher quality material from the cleaving process.
.solar
Wafer Wafer thickness 180 (WS); 150um and 50um (PM)
www
Kerf loss 50.7% (WS); 0% (PM)
At about $2/Wp module prices, solar cells are said
to be competitive to grid electricity and for that to
34
Size 156mm x 156mm
happen the referred analysis shows that the cost of
poly needs to be reduced to $0.24/Wp level. The
Solar Cell Efficiency 15.8%
Cost Reduction Analysis shows that the cleaving
approach would be between $0.22/Wp and
overall cost of WS to PM for wafers 180um, 150um $0.07/Wp which in either case is well below the cost
and 50um thick respectively, using validated target. In general, multi-crystalline wafers offered
production assumptions for yield, throughput, fixed some advantages over mono-crystalline wafers. The
and variable costs. This $/Wp cost is combined process cost of multi-crystalline wafers was
with the cost assumptions provided by the industry considered lower with the existing manufacturing
for cell and module manufacturing costs to practices. But the cost reduction analysis showed
determine the total module cost in $/Wp. that the wafering cost reduction achieved with the
cleaving process overturns this manufacturing cost
Note that in all cases, the parameters utilized for difference with the additional benefit of higher
the WS case are based on industry benchmarks conversion efficiency for mono-crystalline wafers.
and inputs from industry representatives.
Knowledgeable choice
The numbers include an average value of 3.85 The Cost/Watt advantages achieved by the
Watts per wafer as a benchmark. The results show cleaving process is likely to allow companies to
that the wafering step is a key cost component in better withstand the competitive market dynamics
both the upstream and in the downstream of the with a higher likelihood to take the leadership
PV value chain as it determines the amount of position in the PV industry with lower
feedstock material necessary to meet the projected manufacturing costs and improved conversion
capacity for the cell and module production. The efficiencies. With the steep price decline, the
entire cost analysis will be presented at the 24th cleaving approach is not merely a manufacturing
Table I: Poly-Si European Photovoltaic Solar Energy Conference in tool but a financial tool providing a competitive and
Material Usage Hamburg, September 2009. sustainable cost-per-watt advantage. The
per Year economic impact and applicability of the cleaving
process for wafering is substantial. The detailed
Wire Saw Cleaving
cost analysis demonstrates that the cleaving
process using the SiGen proprietary PolyMax
180um 150um 50um
technology is fundamental for the crystalline-silicon
Poly-Si usage (MT/year) 2,500 924 308 based PV solar cells to win the race to <$1/Wp
Poly Ratio 1 0.36 0.12
and yet provide substantial gross margin
protection to the manufacturers.
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