SunPower Corporation is an American energy company that designs and manufactures crystalline silicon photovoltaic cells and solar panels based on an all-back-contact solar cell invented at Stanford University. The company is majority owned by Total, the fourth largest publicly-listed energy company in the world and is publicly traded on the NASDAQ as SPWR.
History
SunPower was started when Richard Swanson, a professor of electrical engineering at Stanford University, was awarded grants to support his solar power explorations. With the help of these funds â€" as well as financial support from two venture capital firms â€" SunPower was officially incorporated on April 24, 1985. The original plan was to develop and market solar concentrator systems.
In 1990 the company received a research and development contract from EPRI and the US Dept. of Energy. Two years later, SunPower began shipping concentrator cells to customers. In 1995 SunPower's all-back contact solar cells powered Honda's solar car to victory in the annual Darwin to Adelaide race across Australia beating the second place winner by one full day. In 1997, the company's solar cells were used in the NASA Pathfinder high altitude aircraft.
in 2002, Cypress Semiconductor invested $8 million in SunPower. The following year Tom Werner joined as CEO. In 2004, SunPower opened manufacturing facilities in the Philippines and Bavaria. The company held an IPO in 2005.
In January 2007, SunPower acquired PowerLight Corporation, a large-scale solar power systems company. In February 2010, it acquired Europe's SunRay Renewable Energy for $277 million.
In April 2011, Total S.A. agreed to buy 60% of SunPower for US$1.38Â billion. In December 2011, the company announced an agreement to acquire Tenesol SA. In 2013 SunPower acquired Greenbotics, Inc., maker of robotic solar panel cleaning products and services for large-scale solar power plants.
Cells
The company's main product is a high-efficiency solar cell, trademarked "Maxeon", the same size and shape as conventional 6-inch/160Â mm single-crystal silicon cells, packaged into conventional 60-cell solar panels. The cells have a conversion efficiency of 21.5%, and each panel produces up to 345Â W; typical conventional panels produce up to 250 to 270Â W.
Silicon solar cells typically consist of a thin layer of silicon chemically treated to produce an electrically active layer near the front that produces electricity when the sun shines on it. Collecting that energy is normally handled via a series of very fine wires embedded on the front. There is an inherent paradox in the wiring design; larger wires lower electrical resistance and improve energy collection but reflect light that would otherwise reach the cell and improve energy creation. The wires are normally made of silver for a variety of reasons, although less expensive copper and aluminum wiring has been attempted with no great market success. The circuit is completed by a thin layer of aluminum that is deposited on the back of the cell.
The Maxeon design starts with the same basic silicon cell, but changes the electrical connections. The silver wiring on the front is eliminated and replaced by a transparent electrode material, similar to the materials used in LCD televisions and similar devices. These electrodes have poorer electrical characteristics than silver, but by covering the entire face of the cell they improve overall performance, while eliminating light blockage. The back of the cell replaces the thin aluminum layer with a thicker copper one, which both improves electrical performance as well as offering a much more physically robust platform while eliminating corrosion that occurs in the aluminum over time. On June 23, 2010, The company announced that it has produced a full-scale solar cell with a sunlight to electricity conversion efficiency of 24.2 percent, a world record confirmed by the U.S. Department of Energy's National Renewable Energy Lab (NREL).
After the cells are constructed, conventional assembly system uses a robot to place the cells into a grid of 6 columns of 10 cells - other arrangements are used, but rare outside commercial settings. As they are placed, wiring consisting of a strip of silver is woven between the cells and soldered to the connectors on the front and back. A small amount of space is required between the cells to allow the strips to pass over and under the cells. The layout takes place on top of a plastic sheet known as the backsheet, and the cells and wiring are glued to the sheet as the assembly advances. When the glue dries, the resulting laminate is ready for assembly into a panel, which consists of gluing the cell side of the laminate to a glass sheet, adding a junction box for electrical connections, and adding an aluminum frame around the outside for mechanical robustness. Different assembly systems may use different steps, but the end result is a glass sheet on top, cells and wiring in the middle, and the backsheet on the back.
The company's panels are similar in concept and layout, but include a number of additional changes to further improve the system. Instead of using silver strips to connect the cells together, which is no longer needed due to the lack of silver on the cells, its panels use a robust edge-connector that includes a built-in strain relief to reduce mechanical stress. According to the company, these changes eliminate 85% of the failures in conventional designs, which is due primarily to corrosion and electrical breaks. Only 14% of failures are due to cell or component failures.
The downside to these design changes is cost, both the materials and construction methods are more expensive and drive up the price of the panels. However, the price of the panel is not the only input to a solar power system's total cost, and in recent years it accounts for much less than half of the total. In this case, using a more expensive panel can actually produce a lower overall system cost if savings can be found in installation time or there are artificial limits on system size. These are both true in the case of residential installs, where the roof defines the total size of the system that can be installed, and the cost of labor is the largest single cost of the system. Simply replacing conventional panels with SunPower panels will increase the total power of the system as much as 25% without having any effect on install times, in which case the total install cost in terms of price per watt can improve in spite of higher prices on the panels.
Development in stock exchange
The company's shares have been listed on the Photovoltaik Global 30 Index since the beginning of this stock index in 2009.
See also
- Solar Impulse
- Helios Prototype
- Serpa solar power plant in Portugal
- Subsidiaries and affiliates of Total S. A.
References
External links
- Company website
