There is a very very large dam in the middle of a desert; it operates similarly to the Qattara Depression Project, and was constructed both to power the areas south of it, but primarily for political reasons.
The dam has recently finished construction & operation has been handed off to a private company to operate.
However it is generating an incredibly immense amount of excess energy, even after so many things that need a lot of energy were built. This private company now wants to find a way to sell this excess energy. Unfortunately, there's nothing more to power further nearby, and environmental conditions prevent power-lines from being built to further away areas.
So, this newly formed company is faced with a problem, how does move this energy to where it can be sold & used without too much cost getting there?
Density & weight are not problems due to broad gauge & very high loading gauge railway line access to major ways being built to move materials for the construction of the dam. Salt water is abundant & can be assumed to be effectively free.
Technologies that would be available up until our own roughly early 1970s are available. The goal is to move large volumes of electricity without power lines at the lowest cost possible. What is the best way to achieve this?
EDIT: I probably should have described the geography better initially, to the south is the area where things are being powered, there isn't much of anything to the east further inland, west to the coast can be done easily but there isn't much of anything there, while to there north there's a lot but there's a large impassable area between the dam & the things that can be powered that can't be easily crossed by anything. The rail lines go to the south & to the coast.