While most power in the US is AC (Alternating Current), another approach for transmission lines is to use High Voltage Direct Current (HVDC) technology. 

In fact, Dominion is already proposing HVDC for part of Virginia’s main power backbone: an underground direct-current line that would end in Loudoun. (Loudoun Now)

• HVDC has higher voltage and can carry more power. 
• It has fewer losses over longer distances and can be less complicated to bury underground (fewer cables). Direct current also performs better underwater than AC for lines longer than 30 miles. 
• HVDC above ground can be configured to carry significantly more power than is generally used underground, and above ground is preferred for extremely long HVDC lines because of improved electrical performance above ground.
• HVDC transmission lines are less expensive to build per mile than AC lines, 
• The endpoints of the line require expensive AC/DC converter stations (about $400 million for each end). Thus, HVDC is usually reserved for cases longer than about 200 miles, but there are exceptions for circumstances in which the DC characteristics are necessary, such as when interconnecting two AC grids that are not synchronized (e.g., the western and eastern grids or Texas in the United States.)