The environmental college and the Internet search-engine company reached a loan agreement to transport the solar panel to highlight the importance of alternative-energy sources for the United States and the possibility of greater support for them under the Obama administration.

"It's an exciting journey for the panel. It's about the green economy," said Rob Constantine, the college's vice president for advancement. "We want to demonstrate that Maine is at the forefront of that as we talk of real-world, sustainable-energy solutions."

As part of his economic-stimulus plan, Obama proposes to double the output of alternative energy over the next three years. The Obama administration also has called for 10 percent of the country's electricity to come from renewable sources by 2012, and 25 percent by 2025.

Coinciding with the solar panel's arrival is a "green ball," to be hosted by former Vice President Al Gore on Monday and sponsored in part by Google, welcoming President Obama and his wife, Michelle, and other dignitaries. Mitchell Thomashow, president of Unity College, plans to attend the ball.

Google will tell the story of Unity College and the former White House solar panels, college officials said.

In June 1979, Carter proposed a "new solar strategy" to "move our nation toward true energy security and abundant, readily available energy supplies," according to the Jimmy Carter Library & Museum in Atlanta, Ga. To set an example -- and establish a prominent symbol -- for the country, Carter had solar panels installed on the roof of the White House West Wing to heat water for the staff mess and other areas.

At the time, Carter warned, "a generation from now, this solar heater can either be a curiosity, a museum piece, an example of a road not taken, or it can be a small part of one of the greatest and most exciting adventures ever undertaken by the American people; harnessing the power of the sun to enrich our lives as we move away from our crippling dependence on foreign oil."

President Ronald Reagan took the solar panels down in 1986 when the White House roof was repaired.

Flash forward 20 years, when Swiss directors Christina Hemaner and Roman Keller started making a documentary film about the panels as a lead-in to exploring American oil dependency and alternative-energy sources.

In the film, "A Road Not Taken," the two directors join two Unity College students -- Sara Trunzo and Jason Reynolds -- and load two panels into the back of the students' pickup truck (modified to run on vegetable-oil diesel) and deliver the panels to the Jimmy Carter Library & Museum in Atlanta, where they remain on display. The film debuted last July at the Maine International Film Festival in Waterville.

Trunzo, a 2008 graduate who is now the college's community-market coordinator, said the latest journey of a Carter solar panel is "really exciting and not that surprising."

"I feel like there's a lot of serendipitous occurrences around the solar panels. It's been a really great tool, because it gets you excited not just about alternative energy, but about American history as well," Trunzo said.

Recent news coverage of the documentary film caught the attention of many Internet blogs and, ultimately, of Google officials, who initiated contact with Unity College about the arrangement, Constantine said. Under their agreement, Google has been loaned the panel for one year.

Google sent a truck to load the panel -- it's 6 feet by 3 feet, 6 inches -- and it arrived at the D.C. headquarters on Friday, Constantine said.

"The panels are an important piece of American energy history and policy, and we want to be good stewards of the panels. We want to make sure whoever is using them represents what they represent," Constantine said.

Google spokesman Jamie Yood said his company has invested in alternative energy projects, such as spending $4.5 million to help companies develop renewable energy that costs less than coal and investing millions of dollars in developing plug-in electric vehicles that get 90 miles a gallon.

Yood said Google officials are thrilled to receive the solar panel to highlight the importance of future energy solutions -- and the history behind them.

"It's a fun way to talk about the story of the panels," Yood said. "We're excited about it."