Google today is launching a fascinating experiment in clean-tech investing in the form of a worldwide search for products, services, and technologies that can advance the market for plug-in electric vehicles. And it plans to invest a total of $10 million in the ones it likes.

The request for proposal just issued by Google.org, the company's philanthropic arm, invites "entrepreneurs and companies to show us their best ideas" with the aim of making "catalytic investments to support technologies, products and services that are critical to accelerating plug-in vehicle commercialization." Google.org says it will invest between $500,000 and $2 million in the companies it believes stand the best chance of advancing plug-in technology.

Think of it as "The Apprentice" meets "An Inconvenient Truth."

As the company explains in a "Googlegram" it distributed this morning:

We realize that this type of open call for proposals is not the usual model for investment, but we wanted to use a process that was open to new ideas and new entrants. Part of our goal is to get as many people as possible to work on solutions to our vehicle emissions challenges. We welcome and expect to receive submissions from a wide variety of companies -- from cutting edge battery technologies to innovative service businesses - and from companies of all sizes. We also encourage participants from all over the world to submit proposals. This is a global challenge, and it will take all of us to solve it.

Entrants are asked to submit a five-page proposal by October 15. Those entries selected will be asked to submit a more complete business plan, which will then go through the usual vetting and due diligence processes. (Read an FAQ doc here.)

Why the open RFP? "It is, admittedly, an unusual approach, but we felt as though we wanted to reach the largest number of people with potentially interesting products, services, or technologies that could advance plug-in vehicles," Dan Reicher, Director of Climate Change and Energy Initiatives at Google.org, told me earlier this week. "We felt these technologies, services, products need to be developed sooner rather than later given the climate challenge that we've got. We thought this would be an interesting way to get maximum response."

A worldwide competition for the chance to have Google invest two million bucks in your fledgling firm? "Interesting way," indeed.

As the Googlegram puts it:

This open RFP process is a new approach to mission-focused investing, and we're interested to see what we can learn from it, both in terms of opportunities and gaps that exist in this space today, as well as ways that we can improve on this solicitation process for future investments. Our focus on learning is the primary reason we decided to narrow this first RFP to investments in private companies, rather than a combination of grants and investments.

The RFP is the latest in a string of efforts by Google to advance electric vehicles. Earlier this year, Google.org launched the RechargeIT Initiative that aims to "reduce CO2 emissions, cut oil use, and stabilize the electrical grid by accelerating the adoption of plug-in hybrid electric vehicles and vehicle-to-grid technology." RechargeIT to date has focused on philanthropy, committing $1 million in donations to nonprofits, and has created a small demonstration project that, the company says, will eventually lead to 100 or more plug-in hybrids in Google's corporate fleet. In addition, the foundation is putting its money toward advocacy and policy matters related to growing the plug-in hybrid market.

So, how will Google vet what could be a tsunami of investment proposals? "We're going to take advantage of the talent we have here at Google," explains Kirsten Olsen, Project Manager for RechargeIT initiative. "We have a lot of people here who have experience either screening business plans or have worked for electric vehicle companies." Eventually, she says, they'll whittle down the initial pool and use Google.org's management team, along with outside advisers, to choose the company that will comprise Google's investment portfolio.

I suggested to Reicher the potential for Google.org to receive countless business plans from small, struggling players with little to offer beyond a promising idea -- the kinds of things that many of us working in this space see on a daily basis. "We're not looking to fund research," he replied. "We're looking for commercially viable products, services, and technologies." On the other hand, he said, "some of these may look like earlier-stage ventures."

In the end, Reicher emphasized, these are investments, not grants. "We're going to put money to work in an equity-like way and expect to make something on it." But it's clear that making the most bang for the buck is not Google.org's mission. And, in Google's typically quirky way, there's a significant fudge factor here: Google.org isn't committed to how much it will actually invest -- "we could invest less than $10 million, we could invest more," says Reicher. It doesn't have any goals to actually make money, though it could easily do so if any of the investments take off. Instead of setting out internal rates of return, he says, "We have a specific problem we're trying to solve."

It will be interesting to watch, both to see what products and services eventually come out of this quirky experiment, but also how much the RFP investment approach itself is replicated by others. On the one hand, it seems obvious to invite the best and the brightest to compete for a relatively small but meaningful pool of money. On the other hand, like so many of Google's other innovative initiatives, no one has done this kind of thing before -- or at least done it well.