Space elevators. Robots. Submarine cables. Wi-fi. Cellphone software. Social networking. Artificial intelligence. Web-based business software.

Oh yeah, and search advertising.

What do they all have in common? They are areas that Google is working on. Add renewable energy to the list.

Tuesday's announcement that the search giant has taken it upon itself to generate enough renewable energy to power the time-traveling De Lorean from Back to the Future, has tech watchers wondering just how many disparate areas the company can get into without diluting its core business focus.

Are we ready for Google power plants?

RBC Capital Markets analyst Jordan Rohan told the New York Times' Brad Stone that when he first heard about Google's renewable energy initiative, called REC, his first reaction was, "Is this a joke?"

"I've written off Google's competition as a threat to Google's long-term market share gains," Rohan said. "But I haven't written off Google's own ability to stretch too far and try to do too much. Ultimately, that is the biggest risk in the Google story."

For years, Google watchers have been warning that the company risks overextending itself, with its ambitious array of initiatives across multiple fields and disciplines.

"I can't help but think Google is a company with too much cash on its hands and is spreading itself too thin," ZDNet blogger Larry Dignan wrote.

But despite the concerns, the company continues to plunge headfirst into areas that appear completely unrelated to search advertising.

During a conference call with reporters, Google co-founder Larry Page addressed the "distraction" issue.

"This doesn't count as search and advertising," Page said, "but we do want to give our business some latitude to look into new areas especially when they are strategic."

To hear Page tell it, renewable energy dovetails nicely with other Google initiatives.

"We have gained expertise in designing and building large-scale, energy-intensive facilities by building efficient data centers," Page said in a statement announcing the renewable energy plan. "We want to apply the same creativity and innovation to the challenge of generating renewable electricity at globally significant scale, and produce it cheaper than from coal."

In typical Google fashion, the company's ambitions are extreme.

"Our goal is to produce one gigawatt of renewable energy capacity that is cheaper than coal," said Page. "We are optimistic this can be done in years, not decades."

One gigawatt can power a city the size of San Francisco. But could there be another idea motivating Google's entry into the energy business?

As it turns out, 1.21 gigawatts powers the flux capacitor needed to run a De Lorean time machine.

Sam Gustin