(Recasts throughout; adds details, comments from conference call)

By Nichola Groom

July 27 (Reuters) - First Solar Inc on Thursday raised its revenue and earnings outlook for the year, citing strong demand for solar panels and robust U.S. investor interest in infrastructure that has boosted pricing of the power plants it builds and sells.

Shares of the U.S. solar panel maker and project developer soared 11 percent in extended trading following the announcement.

The company now expects 2017 sales of between $3 billion and $3.1 billion, $150 million higher than a prior view of $2.85 billion to $2.95 billion. Earnings per share, before one-time items, are estimated to be between $2 and $2.50, sharply higher than the 25 cents to 75 cents First Solar had forecast previously.

On a conference call with analysts to discuss the company's second quarter results, First Solar executives said they expect to sell several major projects for higher prices than they had originally forecast.

"There's just a very robust market for U.S. asset sales today," Chief Financial Officer Alex Bradley said on the call.

The company is in the process of selling two California solar projects - the 40 megawatt Cuyama and 280 MW California Flats, and expects to complete those sales later this year.

Demand for First Solar's cadmium telluride solar modules is also strong due to a sharp decline in the cost of solar energy that has made the renewable power cost competitive with other forms of electricity, Widmar said. In addition, a trade petition filed by a bankrupt U.S. solar panel manufacturer that could result in tariffs on imported solar products is prompting some solar developers to procure supplies sooner than usual.

"They're trying to protect their projects," said Widmar, who added that with a modest tariff, the industry would "continue to thrive" and could end up with more U.S. manufacturing jobs.

First Solar posted a second-quarter net profit of $52 million, or 50 cents per share, compared with a net loss of $11.4 million, or 11 cents per share, a year ago.

Excluding one-time items, Tempe, Arizona-based First Solar earned 64 cents a share. On that basis, Wall Street analysts had been expecting a profit of 60 cents per share, on average, according to Thomson Reuters I/B/E/S.

First Solar shares closed at $44.81 on Thursday on the Nasdaq, soaring to $50 in extended trade. The company's stock has gained 75 percent since hitting a 52-week low of $25.56 in April. (Reporting by Nichola Groom; editing by Dan Grebler and Phil Berlowitz)