Saudi Arabia’s sovereign-wealth fund and Japan’s SoftBank GroupCorp. 9984 -3.75% announced plans to launch the world’s biggest solar-power-generation project, providing another ambitious goal for two of the world’s richest investors.  The development would start this year with a $1 billion investment from the joint Saudi-SoftBank Vision Fund, said Masayoshi Son, chief executive of SoftBank. It is expected to grow into a $200 billion behemoth that provides about 200 gigawatts of power by 2030, he added—more power than Saudi Arabia would need to light up the entire country by then.

“It’s by far the biggest solar project ever,” Mr. Son said at a news conference Tuesday night in New York, after signing a non-binding agreement for the project’s development with Saudi Crown Prince Mohammed bin Salman. The first stage of the project will cost around $5 billion and begin this year, Mr. Son said, with the installation of solar panels that will produce around 7.2 gigawatts of power in 2019. Most of it will be financed with debt.