Warren Buffett’s MidAmerican Energy Holdings agreed to buy a 49 percent stake in NRG Energy Inc. (NRG)’s $1.8 billion Agua Caliente solar project, the billionaire’s second investment in solar this month. The 290-megawatt power plant is being built in Arizona by First Solar Inc. (FSLR), which expects to complete the installation of its panels by 2014, Princeton, New Jersey-based NRG said today in a statement. Terms of MidAmerican’s purchase weren’t disclosed. Buffett’s foray into solar shows that utility-scale power plants offer good returns with little downside risk, said Paul Clegg, an analyst at Mizuho Securities USA in New York. Power from the plant, which won a $967 million loan guarantee from the U.S. Energy Department this year, will be sold to a PG&E Corp. utility under a 25-year contract at undisclosed prices. “The utility contracts are favorable and solid,” Clegg said today in an interview. “Plus, they offer tax credits that may be useful to large, profitable companies.” NRG Solar Power Plant - Bloomberg