How did we revolutionize the solar industry?

Transcription

1 How did we revolutionize the solar industry? White Paper March 2012

2 How did we revolutionize the solar industry? March 2012 Silicor Materials is a company founded to create inexpensive silicon to be used for solar cell production. Silicon is the largest component of the solar photovoltaic (PV) cells and modules that are becoming a critical part of the world s energy supply. Over 80% of installed solar PV in 2011 used silicon as their largest material input. 1 Any opportunity to reduce the cost of silicon will thus reduce the cost of an enormous part of the solar PV market. Simply put, we enable our customers to bring down the cost of solar energy. PHOTON magazine described our process to produce solar silicon as pure and simple 2. Our basic process philosophy starts with dissolving impurities into aluminum. Historically, the impurity levels of solar grade silicon have been too high for legitimate replacement of semiconductor grade silicon. We have solved this with our unique silicon and aluminum technology. This approach allows silicon to be produced at a much lower temperature and with less energy consumption when compared to traditional production techniques. Furthermore, this allows us to sell aluminum by-products that are generated in the manufacture of solar silicon. In this white paper, we will discuss how our process has revolutionized the solar industry. What is special about our solar silicon? Dressed to the nines Our silicon can be used with conventional ingot, cell, and wafer processing lines. Historically, the feedstock used for all these processing lines has been electronic-grade silicon (EG-Si), also called polysilicon. This is predominately manufactured through the socalled Siemens method after the company that commercialized the production process in the 1960s 3. Any line capable of processing EG- Si can process Silicor Materials solar silicon. Raw silicon for any industrial application is produced by carbothermic reduction of quartzite rocks in a submerged arc furnace (SAF). This results in metallurgical grade silicon (MG-Si), also called raw silicon or silicon metal, with a purity of 98 to 99%. MG-Si cannot alone be used by the photovoltaic industry as further purification is needed 4.

3 We require less energy It is estimated that over 90% of polysilicon production uses the Siemens process 5. It starts with MG-Si. This raw silicon is reacted with hydrochloric acid to produce trichlorosilane gas. These silanes are then purified by distillation until the desired purity is attained. These toxic gases are then introduced to a chemical vapor deposition reactor where the gas is decomposed leaving high purity silicon in solid form behind. The Siemens process was originally developed to produce EG-Si which has a silicon purity of at least %, or 9N ( nine nines ). This is a purity level needed in the microelectronics industry. Since a solar cell is much simpler than a microchip and does not have its level of miniaturization, the purity requirements in the solar PV industry are less stringent. Solar grade silicon requires % to % (6N to 7N) purity. Simplifications of the Siemens process are under development to produce silicon with these purity levels. However, two characteristics of the Siemens process have inherent disadvantages not shared by our process: 1. It requires chemical processing that converts the raw silicon into silanes and then back to high-purity silicon 2. It will continue to handle silane gases which are extremely hazardous Electricity is traditionally one of the largest costs of polysilicon production. Our process uses a fraction of the electricity of the Siemens process. Silicor Materials takes a different approach. Like the Siemens process, we start with MG-Si. We produce our solar grade silicon via metallurgical processes for purification. The Siemens method uses chemical processes and features four phase changes (solid to liquid, liquid to gas, gas to liquid, liquid to solid). Solar silicon from Silicor Materials only goes through two phase changes: solid to liquid, and liquid to solid. This by itself confers immense advantages in energy savings, which have traditionally been one of the largest costs of polysilicon production. Our process is easy to manage The general challenge of a metallurgical route from MG-Si to solar silicon is impurity control. A company must be able to tweak the metallurgical processes and measure the corresponding impact on PV cells made from that silicon. Silicor Materials, as a company that has historically had integrated silicon and cell operations, was able to quickly master these feedback loops.

4 The primary impurities in solar silicon are boron and phosphorus. Not every impurity is harmful in silicon and some of them are even useful. For instance, a certain amount of boron needs to be added to silicon to obtain the necessary p-type conductivity and assure resistivity control. For n-type materials, the addition of phosphorus is necessary. Solar silicon produced through the route of metallurgical refinement like ours naturally contains both of these essential impurities. Hence, silicon quality is not determined by the number of nines, but rather the relative mix of essential impurities. Silicon containing both boron and phosphorus is considered compensated silicon because boron and phosphorus practically cancel each other electrically. The only difference in relative levels of impurities contributes to conductivity type and resistivity. The particularities of our silicon will save our client time and money by reducing process complexity and increasing yield. We produce high-quality PV products Silicor Materials produces silicon that can be used in high-performance PV products. We have proven our silicon technology by producing over 500 MT of silicon for sale and internal use. This, in turn, has produced over 15 million solar cells demonstrating over 16.6% conversion efficiency on average. Champion cells are over 17% in a standard solar manufacturing technique. Continuous testing of our material allows us to improve product quality and work with customers to meet their specifications While these efficiencies are comparable to efficiencies produced from EG-Si, our product has additional electrical properties that are advantageous. One such advantage of our solar silicon is a narrow resistivity range. This is achieved through carefully monitoring and tweaking of the relative mix of boron and phosphorous in our solar silicon. Narrowing the resistivity range has positive consequences for the manufacture of high-quality PV products: ingot yields can be better optimized and ever advancing cell processes can be better adopted. It is important to note that the doping of solar silicon with boron and phosphorous occurs naturally with our process. EG-Si can utilize chemical methods to intentionally dope, though this will require an additional cost.

5 The Silicor Materials process Why 13 and 14 are our favorite numbers We have proven that our patented production process leads to solar silicon which our customers turn into high performing solar cells and modules. Our process is designed to optimize the industry s need for fast growth, low cost and high quality. Our process has identical inputs and outputs to those production facilities employing the Siemens method. Both start with MG- Si and end with silicon capable of being turned into high-efficiency PV cells. For our process, we smelt solar silicon from the combination of MG-Si and aluminum. The MG-Si is dissolved in molten aluminum at temperatures significantly lower than those required to melt pure silicon. The dissolution process dilutes and binds impurities in the aluminum. The mixture is then allowed to cool, thereby precipitating the silicon into purified crystals. These crystals contain trace amounts of the dopants of silicon, namely boron and phosphorus. It is the use of aluminum (the 13 th number on the periodic table of the elements) as a solvent and purifying media that gives the We are more than just a solar silicon company. All raw materials entering our process are converted to saleable by-products such as aluminum-based alloys and polyaluminum chloride. Silicor Materials process the unique ability to attain high purity levels for our silicon (the 14 th number on the periodic table of the elements). Once the silicon has precipitated from the mixture, the aluminum portion is simply poured off. This leaves the purified silicon, in crystal form, to be mechanically harvested. The resulting co-product of aluminum-silicon alloy is highly valuable in the aluminum industry and is sold as a master alloy. Once collected, these silicon crystals are processed in an acid cleaning step designed to wash the inherent aluminum coating off the silicon crystals. This removes the bulk of the remaining contaminate aluminum. The resulting co-product, polyaluminum chloride, is sold to the wastewater treating industry. The process is then concluded by melting the silicon crystals, firstly to form a solid product, and secondly to remove remaining traces of metallic impurities via directional solidification. In this final step, the silicon is directionally frozen from the bottom up, pushing any contaminate to the very top surface layer of the resulting ingot with its bulk of purified silicon.

6 The contaminant rich top layer is then removed and sent back into the process for recycling. The ability to recycle silicon material at various points along the value chain of the Silicor Materials process is another key strength. This ensures that virtually all of the MG-Si entering the plant leaves as purified product. What this means for our customers Can a mass spectrometer tell the difference? Silicor Materials solar silicon is able to be integrated to any standard ingot casting process, either as a blend with EG-Si or a standalone charge of 100% Silicor Materials content. Consider both the beginning and end of the value chain of our customers. At the beginning, our unique formulation gives a total wafers per ingot yield demonstrated to be equivalent to EG-Si. And at the end of the PV value chain, modules made from solar cells using 100% of our solar silicon have achieved both IEC and UL certifications conducted by the highly regarded listing bodies TÜV Rheinland and Underwriters Laboratories Inc. Compared to EG-Si, a tighter resistivity range is achievable by taking advantage of p-type and n-type dopants already present in our silicon. We tune this for maximum yield and target resistivity using a patented doping process. This process has been applied on hundreds of directionally solidified ingots, cast by Silicor Materials itself and by our customers. These ingots, in turn, have demonstrated to lead to solar cells with performance that is competitive with cells made from EG-Si. Cell efficiencies average well over 16.5% with many exceeding 17%. Lab results with 100% Silicor 17.00% Cells Manufactured (mil) Our silicon Electronic-grade silicon 25 Cell Efficiency 16.50% 16.00% 15.50% 15.00% 14.50% 14.00% May-10 Sep-10 Dec-10 Jun-11 Nov Cells Manufactured from Our Silicon (millions) Historic cell manufacturing quantities and efficiencies

7 Materials material have demonstrated cell efficiencies of 18.8%. >1MW systems and we have shipped over 50MW since inception. Furthermore, our product meets current requirements regarding light induced degradation (LID) with consistently less than 2% relative degradation. As we have learned how to get the most out of our solar silicon, we are eager to share this know-how with our clients. For example, we can support with solar cell processing know-how to optimize low light performance for maximizing the energy harvest of solar modules (kwh per year and installed kwp). The final validation of our technology is in our shipments to date. In total, Silicor Materials cells have been installed in large utility scale What does this mean for our employees and investors? Silicor Materials aims to bring down the cost of solar energy. We have a production process that, compared to the industry-standard Siemens process, has lower energy requirements, lower capital requirements, and a greener footprint. The pure and simple production process described earlier enables a nimble buildout of capacity where production volumes are easily scaled up or down depending on market conditions. Simply put, our investors are deploying capital that goes farther in manufacturing silicon than our competitors. 1,500 Mlelting Point (Degrees C) 1,300 1, Our process kwh/kg Liquid Solid Siemens process kwh/kg 300 0% 20% 40% 60% 80% 100% % of Silicon Contained in Aluminum-Silicon Mix Eutetctic diagram showing melting point of combinations of aluminum and silicon

8 A submerged arc furnace under construction by our partner SMS-Siemag Credit: SMS-Siemag An important nature of our process is such that it is environmentally safe, it can be located in light industrial parks and has no environmentally detrimental intermediates, byproducts or waste streams. This makes for a safe work place and a safer community. Where do we go from here? Our global footprint is expected to grow further. We operate a world-class R&D facility in Berlin, Germany. It continues to develop and deploy innovative material science to further reduce costs and assure competitiveness of our products. Its internal talent and relationships with premier German universities, place it among the best in the world for material science and electronic device innovation. We are currently expanding its manufacturing capacity with the construction of a 16,000 metric ton facility in the state of Mississippi. At full capacity, we expect to have one of the lowest cost structures in the industry. This factory will include a dedicated metallurgical silicon factory which feeds directly into the solar silicon factory. This combined approach optimizes all costs including logistics and process optimization by eliminating all unnecessary freezing and melting steps. The energy consumption will be a fraction of that needed for producing conventional

9 semiconductor grade polysilicon. We operate in a rapidly expanding but increasingly commoditized global solar energy market. Our significant cost advantage and high return on capital employed enables us to have a leadership position in accelerating the global availability of solar energy at grid parity. 1 PHOTON The Wall 2 Sollmann, Dominik. Pure and simple: Canada s 6N Silicon presents its innovative process for direct silicon purification PHOTON International Magazine, May 2009, pp Luque, Antonio et. al. Handbook of Photovoltaic Science and Engineering (2 nd edition) Wiley Komp, Richard. Practical Photovoltaics: Electricity from Solar Cells (3 rd edition). Aatec PHOTON The Wall