Both AES Solar and NRG Energy Corp. are selling off some of their solar farms. AES Solar, a joint venture of AES Corp. (NYSE: AES) and Riverstone Holdings LLC, will sell roughly 117 megawatts of its European solar thermal plants. And NRG (NYSE: NRG) will sell off $350 million in some of its solar plants in the U.S. The news comes as both companies are poised to build gigantic new solar thermal plants in the Southwest U.S.

The sale was announced by Morgan Stanley Managing Director Ray Spitzley at a Beijing renewable energy conference, according to Dow Jones Newswires. Morgan Stanley is helping to coordinate the sales, but declined to comment on the sales.

“They tend to buy and sell projects on a regular basis,” said Standard & Poor’s equity analyst Christopher Muir. “They probably see a good price for those plants based on the current market.”

AES Solar will sell off roughly 117 megawatts of solar plants in Italy, Spain and elsewhere in Europe. And NRG will sell roughly $350 million of solar projects in the U.S.

“For them [i.e., NRG], that’s a fairly small amount. Their market cap is $3.5 billion. Their solar portfolio is quite small compared to the rest of their energy portfolio,” Muir said. AES’ market cap is even higher, at $10 billion, according to Muir.

Both power producing companies are always working to optimize their generating capacity, Muir said. These sales are a small percentage of their overall energy portfolio. For instance, NRG has about 25 gigawatts of overall power-producing capacity in its portfolio. Of that, 0.1 percent of its generating capacity is solar power, according to Muir.

Both companies are still interested in expanding their renewable energy portfolios, Muir said. AES recently reached an agreement with a Chinese investment company to expand its wind generation there, for example.

“Renewables are being built out, but it’s so small right now,” Muir said. “Eventually they’ll see them as revenue drivers.”

The interest is likely to continue as long as the credits are available and states continue to have renewable energy standards, he said.

Both companies are also still developing massive new solar projects in the Southwest, however. AES Solar recently agreed to purchase and develop the 709-megawatt Imperial Valley Solar Project in California. And NRG is developing a 392 megawatt solar thermal plant in California and purchased the 250-megawatt Agua Caliente Solar Farm that’s being developed in Arizona.

Image courtesy of NRG Energy Corp.