The initiative will be backed by Softbank's Vision Fund technology investment vehicle, with a first 7.2GW phase costing $5bn, Son said.
The plants are expected to have a total capacity of 200 gigawatts - equivalent to that of about 200 nuclear reactors. The project is also set to more than quadruple Saudi Arabia's solar capacity, which is now around 60GW.
The SoftBank founder Masayoshi Son, who is known for his ardent support for ambitious endeavors, presented the project at a ceremony in NY with the crowned Prince Mohammad Bin Salman Al Saud. The solar project is part of such efforts.
"The kingdom has great sunshine, great size of available land, great engineers, great laborers", he said.
The cost of the two parks will be about $5 billion, with $1 billion coming from Softbank's Vision Fund and $4 billion from project financing.
The deal is a step towards achieving the Crown Prince's ambition to diversify Saudi Arabia's economy.
The solar project is expected to generate at capacity 200 gigawatts of energy, which is far more than any solar project in existence produces. Electricity demand in the country has risen by as much as 9 per cent a year since 2000, according to BNEF. The project is so huge that it will support the manufacturing kingdom, said SoftBank CEO Masayoshi Son. The Prince has arrived in the United States with a three-week official visit, the channel said. Although the kingdom has been endeavoring to enter the clean energy sector for years, it started working on the first projects only in 2017, gathering offers for a 300-megawatt plant in October.
Earlier on Tuesday, the Saudi-U.S. CEO Forum gathered American and Saudi business leaders in NY, where the kingdom announced about three dozen memorandums of understanding with U.S. firms, which are often the first step in establishing business ventures. He established the Vision Fund, which, in conjunction with the Delta Fund set up to invest in Chinese ride-sharing firm Didi Chuxing, has funneled $27.5 billion into 20 tech firms as at the end of December. The fund is now closed.