Technical Papers

The photovoltaic industry was once, and for quite some time, the unappreciated renewable technology. Perceived as too expensive without subsidies to reduce the price of ownership, and sometimes as an energy choice primarily for environmental zealots, the industry has continued, nonetheless, to grow at a compound annual rate of 34% over the past 30 years. Growth at this rate would be envied by any industry, and certainly deserves recognition, particularly as it has come with significant problems and has been extremely difficult to achieve. Now, with worldwide consensus on global warming along with sufficient evidence that fossil fuels are rapidly depleting, solar electricity is finally earning some respect - but the industry still has perception problems to solve.

Si etch processes are vital steps in Si solar cell manufacturing. They are used for saw damage removal, surface texturing and parasitic junction removal. The next generation of Si solar cells, featuring thinner wafers and passivated rear surface, will pose more stringent demands on those steps. Surface decoupling (achieving different surface treatments on the front and the rear) has to be achieved while minimizing Si consumption. Plasma texturing is an emerging technique that appears very promising in that respect, as efficiencies as high as 17.4 % have been achieved on screenprinted multicrystalline Si solar cells incorporating this process.

Every day, mankind consumes as much energy as it took the earth 1,370 years to store. The International Energy Agency estimates that by the year 2030, worldwide electricity consumption will have increased annually by approximately 2.4%. City Solar AG is seeking to increase renewable energy stocks through grid-connected solar power utilities. As one of the leading producers of large-scale photovoltaic plants, City Solar is uniquely placed to give us a better understanding of how these plants are put together.

The next two years will be crucial in determining the market viability and future of what many see as the most promising thin-film photovoltaics technology: copper indium gallium (di)selenide (CIGS) and its gallium-free cousin, CIS. With potential conversion efficiencies just below that of crystalline silicon PV, low-cost manufacturing strategies offering a chance to reach sub-dollar-per-watt manufacturing costs on both glass and flexible modules, and applications ranging from utility- and industrial-scale farms to building-integrated commercial and residential uses, the quaternary compound has a large grid-parity upside - if the very real challenges of scaling production to commercial volume can be met.

Today’s PV industry is growing at a rapid rate, but the industry would grow even faster if costs could be reduced for both the final products and the capital investment required for scale-up. One strategy for reducing module cost is to reduce the amount of semiconductor material needed (the cost of the silicon solar cells typically comprises more than half of the module cost). Many companies are thinning the silicon wafers to reduce costs incrementally; others use thin-film coatings on low-cost substrates (such as amorphous/microcrystalline silicon, cadmium telluride, or copper indium gallium (di)selenide on glass or other substrates). Concentrating photovoltaics (CPV) follows a complementary approach and uses concentrating optics, which may be designed for low or high concentration, to focus the light onto small cells. Low-concentration concepts use silicon or other low-cost cells; high-concentration optics may use more expensive, higher-efficiency cells. The higher-efficiency cells can reduce the cost-per-watt if the cost of the small cells is minimal.

Solar enterprises will each be faced with the occasional surplus or lack of solar modules in their lifetimes. In these instances, it is useful to adjust these stock levels at short notice, thus creating a spot market. Spot markets serve the short-term trade of different products, where the seller is able to permanently or temporarily off-set surplus, while buyers are able to access attractive offers on surplus stocks and supplement existing supply arrangements as a last resort.

Standardized requirements for the quality of PV modules, solar cells and wafers are given in the according IEC norms (e.g., IEC 61215, 61646, and IEC 61730 for modules). However, the manufacturers of cells purchasing wafers and the module manufacturers purchasing cells want information beyond the final check of the product and to monitor each step during the production process to identify harsh handling and/or machine faults at the earliest stage possible. With consequential improvements of the process enabled, continuous improvements in throughput and yield improvement of the factory are likely, also allowing an early feedback on quality issues to the raw material supplier. Furthermore, by knowing all characteristics and factors of the cell and the module, prediction of electrical energy yield during the life cycle of a PV power plant is becoming more accurate and more reliable.

The importance of rapid and accurate measurement of the electrical power output and related characteristics of photovoltaic (PV) modules or panels concluding the manufacturing process cannot be overemphasized. Even though these modules will likely be deployed under a variety of outdoor solar illumination conditions, they must be tested under a set of standard conditions to assure consistency of results demanded by both the manufacturer and the customer. The ability to provide a measurement tool for this critical manufacturing step that possesses the proper specifications and qualities, ranging from spectral accuracy to ease-of-use, is imperative.

Increasing the efficiency and yield of production line processes forms an integral part of PV manufacturers’ technology roadmaps. For their next generation production lines, non-contact processing equipment is considered essential. This prioritizes laser-based processing, already established at several steps in c-Si and Thin-Film cell manufacturing. This paper summarizes the key issues when using lasers within PV production lines.

Thin-film solar cell manufacturing is poised to make a giant leap in scale with the birth of the gigawatt fab. Commercial thin-film plants are typically sized based on the capacity of the production line from the chosen equipment supplier. In most cases, initial investments have been for a single line, typically with an output capacity of no more than 60MWp. This period of initial development has allowed the industry to prove the robustness of the technology and capabilities of the equipment, as well as to understand the significance for the cost-per-watt of key cost drivers such as materials reduction, cell efficiency increases, and productivity. While large-scale manufacturing will positively impact costs, it presents a unique set of challenges for equipment and material suppliers, as well as the engineering and contracting companies tasked with designing, building, equipping and running a facility on this scale. In this paper, we present the insights of two specialty companies in the solar industry. Turner and Townsend, a design and project management consultancy, and Linde, glass manufacturer and gas and chemical company - share their views of the challenges of the gigawatt fab in three dedicated sections.