21 June 2010
The New England Patriots football team’s new 1.3-million square-foot stadium complex, Patriot Place, is shaping up to be a great showcase of the potential of sustainable solar energy. The photovoltaic (PV) system installation, which began in October 2009, will generate approximately 525 kilowatts of solar power or about one-third the electricity for the complex. The complex includes entertainment, retail and dining destinations adjacent to Gillette Stadium in Foxborough, Massachusetts.
A 525 kilowatt solar power system will be installed by Constellation Energy
on the rooftops of seven buildings of Patriot Place, including The Hall at
Patriot Place Presented by Raytheon, depicted in this artist's rendering.
(Photo: Business Wire)
The photovoltaic system includes 2800 crystalline silicon solar panels (205 W each) from Evergreen Solar. Evergreen solar panels are constructed using a “String Ribbon” process, which is a technology developed at MIT in Cambridge, Massachusetts in the 1980s by Professor Emanuel M. Sachs. His intention was to bring down the cost of manufacturing solar panels so they could compete with conventional power sources. He realized that a lot of waste or kerf was created in the traditional process of making silicon wafers. So, as a solution, developed the String Ribbon process, which makes long sheets of silicon in the thickness of a wafer, and no slicing is needed.
The way it’s made
Chunks of silicon are melted in a furnace, and two strings are unwound from spools and heated in a shallow crucible of molten silicon. As the strings, or filaments, rise out of the silicon, they bring with them a thin film of silicon sandwiched between them. The film turns solid, forming an 8-centimeter-wide silicon ribbon that’s 200 microns thick.
The silicon ribbon is cut into 2-meter lengths, and then each is cut with a laser into wafers. The process is continuous, with the wafers going directly onto conveyor belts to be turned into solar cells.
Evergreen Solar licensed this process and uses it in making crystalline silicon PV modules. Today in its plant in Marlborough, Massachusetts, 120 machines manufacture 15 MW of PV panels a year. Another plant in Thalheim, Germany makes another 30 MW a year.
One advantage to the String Ribbon process is that the wafers are made with a fraction of the emissions that result from making conventional silicon panels. Evergreen also uses lead-free solar cells, so they are non-toxic and more easily recycled at the end of their lifetime. They also use cardboard-free reusable packaging, which seems like a minor point until you consider that at this one construction site, nearly 2800 panels have been shipped in and unpacked, so the packaging is of some significance.
The panels have anti-reflective glass, which delivers 2 to 3 % more electricity compared to panels with standard glass. In addition, the panels maintain up to 4% higher output than most other crystalline silicon panels under hot conditions.
There are seven inverters – (1)30 kW, (3)75 kW & (3)100 kW from Advanced Energy Industries of Fort Collins, Colorado, which is integrating a performance monitoring solution from a third-party partner on the commercial inverters. The monitoring system enables Constellation Energy, the company that is overseeing the project, to verify that maximum energy is being delivered and track the returns on its investment. Data monitoring tools capture historic production data and manage revenue-grade data for production and/or renewable energy credit payments. Under a 20-year power purchase agreement, Constellation Energy's Projects & Services Group will own the energy assets and sell the electricity it generates on site to Patriot Place.
One of the buildings hosting the solar power system is The Hall at Patriot Place Presented by Raytheon, an award-winning sports and educational experience. The PV panels on the roof will be visible to visitors from inside Gillette Stadium and from Patriot Place's upper retail plaza.
The sustainable result
Constellation Energy's Projects & Services Group estimates that the PV system will generate more than 12 million kilowatt hours of electricity over 20 years. Furthermore, they estimate that it will prevent the release of more than 8,800 metric tons of carbon dioxide into the atmosphere, which is the equivalent of removing more than 1,600 passenger vehicles from the road for a year.
In addition to putting panels on the roofs of Patriot Place, sustainable design practices are used throughout the construction. These include low-emitting construction materials and white roofs to facilitate heat island reduction. An on-site wastewater re-use system saves millions of gallons of water annually, and solar-powered trash receptacles throughout the complex reduce waste volume and energy consumption.
Written by Anne Fischer, Solar Novus Today Managing Editor