Via the transport politic, here, Bombardier introduced their PRIMOVE streetcar system. This system is catenary-free, meaning there are no overhead wires. There are systems currently in place - such as third rails, but that makes it impossible for them to be actual streetcars - due to dangers associated with that. Apparently Alstom, a Bombardier competitor, has a system with a buried-ish third rail that only supplies power when a train is directly overhead - which is the best technology in place for cities that don't want overhead wires.
Anyway ... to talk about PRIMOVE, it is basically a buried wire that has some kind of electromagnetic field running through it. The streetcar then has a device that converts the field into electricity which can run the car. Aka, no wires or visible third rail is necessary.
This is perfect for any city which does not want streetcars due to overhead wires, but especially good for DC. By an act of Congress (and for obvious historical reasons), overhead wires are prohibited throughout the District. Thank you Bombardier :)
The Bombardier press release is here.