|In the background: Capitol Police Headquarters|
and Union Station
I couldn't find anything on Google, so I contacted the communications team at the Architect of the Capitol (AOC)--the agency that manages the 553 acres of Capitol land and 17.4 million square feet of Capitol buildings. Here's what I found.
The solar installation is small--it powers 18 lamps (2 lamps/pole). In a 2008 testimony before the Senate Committee on Rules and Administration, then-acting AOC Stephen Ayers said that the “[...] New lights will save 1,825 kilowatt hours per year.” That's not a lot. Heck, according to the U.S. Energy Information Administration, the average annual electricity consumption for an American house in 2012 was 10,837 kilowatt hours.
This is a great symbolic project and I expect to see a few more installations in the next five years. The AOC "...is required to meet annual reductions in energy consumption and report annual progress (AOC Accountability and Transparency Page)". However, it's PEPCO that supplies electricity to the grounds. The AOC's focus is on conserving water and energy, not generating it. PEPCO, step up your game.