1920s

• Pennsylvania Power & Light establishes a formal marketing presence and helped to pioneer the use of electric appliances and equipment.

• Hydroelectric development on the nation’s rivers and streams reaches its peak.

• Holtwood, operated by Pennsylvania Water & Power Co., becomes the only power plant in the world to combine a hydroelectric station and a fossil-fuel station on the same site.

• Wallenpaupack hydroelectric station is put into service, creating Lake Wallenpaupack, a 5,760-acre reservoir one mile wide, 16 miles long and 60 feet deep.

• The Pennsylvania-New Jersey Interconnection, the world’s first fully integrated power pool, is formed in 1928. The pool links Pennsylvania Power & Light, Philadelphia Electric Co., and Public Service Electric & Gas Co. together with a ring of 220,000-volt transmission lines.

• In July 1928, construction is completed on "The Tower," Pennsylvania Power & Light’s general headquarters building at the corner of Ninth and Hamilton streets in Allentown. Still an Allentown landmark, the 23-story skyscraper, at the time, is the tallest building from New York City to Pittsburgh. Built at a cost of $3.2 million, it becomes the prototype for art deco architecture in New York City. The 1930 edition of The Encyclopedia Britannica features the building because of its unique construction and design.

• Between 1928 and 1938, Pennsylvania Power & Light achieves a major expansion of its system by acquiring 62 companies, as well as purchasing stock in an additional 12 companies, from 1928 to 1930. The companies whose stock is acquired are integrated into the PP&L system by 1938.