The power company sells electricity to 2.4 million customers in the U.S., and is the largest supplier in Iowa, Wyoming and Utah, according to Buffett's most recent annual letter to Berkshire shareholders. Buffett is chairman and chief executive officer of Omaha, Nebraska-based Berkshire.
The unit transports 8 percent of the country's gas through its pipelines and is among the largest producers of wind energy.
First Solar has agreed to build and operate the plant in San Luis Obispo County for MidAmerican. Construction began in November and is set to finish by early 2015, the companies said.
"Selling such a project before you build it makes your life so much easier," Reid said about First Solar. Photovoltaic energy is also a "much safer" bet than wind because there's less maintenance and weather risk, he said.
Buffett, 81, has said that businesses like utilities have earnings power even under adverse economic conditions and can provide fair returns on capital as long as they make investments in infrastructure to meet customer needs. Owning utilities is "not a way to get rich," he said at a meeting of U.S. state regulators in 2006. "It's a way to stay rich."
Berkshire's earnings from the utilities and energy business were $888 million in the nine months ended Sept. 30, an increase of 13 percent from the same period last year.