Well the best solution is probably nuclear meeting the base load while solar helps with daytime peaks.
But otherwise pumped storage has promise. Have 2 reservoirs at different elevations connected by a turbine and pumps. When there is excess power durning the day, pump water to the upper reservoir. At night, let the water flow by gravity to the lower reservoir through a turbine and make power.
Transoceanic power transmission is just too expensive.
What are some promising solutions to solar power's lack of night time availability? Is "transoceanic power transportation" on the list?
EDIT: Submarine power transportation is indeed on the list...