I purchased these panels over a period of 8 years as finances and sales opportunities permitted. This accounts for the variety in size, power, and age of the panels I am using. The first panels were purchased in 1991 and are the gold colored ones. They were purchased used from the Carrizo Plains demonstration plant in southern California. The demonstration plant was dismantled and sold. The panels have performed flawlessly. The newest set of panels is a set of 14 BP275 panels purchased in 1998. When this photo was taken they were lying down on the roof awaiting a vertical mount. These brought the total system wattage up to 2.2KW and made it complete. Many times, systems are installed at one time with purchases being made of a single type of panel. There are many advantages to creating a system this way. Today, the state of Illinois will reimburse the purchaser of a system up to 60% of the cost. It becomes more feasable to purchase the entire thing at once with such a generous program in place. Indeed, this is one of the most generous reimbursement programs in the country.