The massive solar build - equivalent to roughly double the entire global capacity additions seen in 2017 - will cost $200bn, SoftBank CEO Masayoshi Son told reporters in NY, where he unveiled the plans.
Mr Son said he envisions the project, which runs the gamut from power generation to panel and equipment manufacturing, will create as many as 100,000 jobs and shave US$40 billion off power costs.
Masayoshi Son said the project would create 100,000 jobs and reduce the cost of producing by 40 billion United States dollars. SoftBank's Vision Fund will give $1 billion for the first phase.
Speaking about the possibilities offered by Saudi Arabia, Masayoshi said at the briefing, "The kingdom has great sunshine, great size of available land and great engineers, great labour, but most importantly, the best and greatest vision".
Virtually all of Saudi Arabia's power comes from oil or natural gas.
Saudi's entire installed power capacity is now around 60 GW.
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The 200 gigawatts of capacity announced Tuesday will be spread throughout the kingdom.
Industry estimates say around 300,000 to 800,000 barrels per day of crude oil are burnt for Saudi power generation.
The deal is a step towards achieving the Crown Prince's ambition to diversify Saudi Arabia's economy.
The project was projected to cost $200 billion through 2030.
Saudi Arabia's Public Investment Fund is the largest investor in Softbank's $100 billion Vision Fund. The fund has already invested in companies in the U.S., India and Europe. "Saudi Arabia is targeting 9.5 GW of renewable energy by 2023, to be achieved through projects created to localize the renewable energy value chain".
The planned capacity of the enterprise is several times greater than that of any existing solar power plant.