The two transmission system companies have formed a joint venture to pursue the Sued:Link project.
This direct-current extra high-voltage line is intended to transport renewable energy from Schleswig-Holstein, where a great deal of Germany's wind farms are located, into the the high-consumption regions of Bavaria and Baden-Württemberg.
"With this power line we will be building the main artery of the energy transition, which will bring wind power from the north to the south of Germany," said Rainer Joswig, chief executive of TransnetBW.
"It will secure the energy supply to the region in times when an increasing amount of convetional power generation from coal or nuclear power plants will be decommissioned."
The project consists of two links, a connection between Wilster near Hamburg and Grafenrheinfeld near Schweinfurt, and a connection between Brunsbüttel and Großgartach in Baden-Württemberg.
Both are being proposed as part of the government's plan to expand the national grid.
Before a formal application is made to the Federal Network Agency, Tennet and TransnetBW will consult the public on possible routes for the cables.