First Solar, based in Tempe, Ariz., is also likely to build a factory in China to make thin-film solar panels, said Mike Ahearn, the company’s chief executive. “It is significant that a non-Chinese company can land something like this in China,” Mr. Ahearn said in an interview.

Most proposed large-scale solar projects use solar thermal technology, which deploys mirrors to heat a liquid to create steam that drives an electricity-generating turbine. But as photovoltaic technology becomes more cost-competitive, utilities are turning to companies like First Solar for big solar power farms. Such projects generally have fewer environmental impacts and can be brought online faster than solar thermal plants.

“This is nuclear power-size scale,” Mr. Ahearn said of the China project. “A two-gigawatt solar project, if this is connected and is economical at the grid level, demonstrates that solar on a large scale really does work.”

Financial terms of the agreement have yet to be reached and will depend on China completing a feed-in tariff that pays a premium for electricity generated by renewable energy projects. First Solar said the 2,000-megawatt power plant would cost $5 billion to $6 billion if built in the United States today, but it said the cost to build such a project in China would probably be lower.

The Ordos agreement is the latest large-scale solar farm deal that First Solar has signed in recent months as it expands its business from manufacturing solar modules to building power plants. The company also has agreed to supply two California utilities with 1,100 megawatts of electricity from three big solar farms.