Wal-Mart Stores, the world's largest retailer, is inviting the greentech community to help it wean itself from fossil fuels and generate zero waste from its operations.

At the Cleantech Forum in Toronto, the company launched a Web portal Thursday called the "Cleantech Accelerator."

Companies with new green technologies can register on the site to offer ways for Wal-Mart to decrease its environmental footprint and -- at the same time -- lower its operating costs.

In five years, Wal-Mart is aiming to make its existing stores 20 percent more energy-efficient and to reduce the energy consumption of new stores by 30 percent. It's also working to make its transportation fleet more efficient and to turn its trash into a revenue stream.

At the Cleantech Forum, Rand Waddoups, senior director of corporate strategy and sustainability at Wal-Mart, told investors the retailer wants to "incentivize innovation" by offering itself as a potential guinea pig for large-scale demonstration.

"It's a fantastic opportunity," he said, pointing out that something as simple as turning off the lights on staff vending machines can save millions of dollars a year. "We haven't even got to all the low-hanging fruit. We're picking thousand-dollar bills off the floor."

Wal-Mart is partnering with Cleantech Advisors, part of the Cleantech Group of companies behind the forum, on the new Web site. The group will operate the portal, assess public submissions on the site and ultimately select technologies for consideration by the retailer.

Michael Kleeman, managing director of Cleantech Advisors, said Wal-Mart isn't prescribing which technologies it wants. Rather, the company will define between five and 10 problem areas, then invite any company to submit a proposal to solve them.

"It's an organization that, once it decides to move, it moves decisively," said Kleeman, adding that the technologies that are selected will have the ultimate showcase. "We ask all of you to tell your companies, your contacts and your friends about it."

The site will launch next week at www.cleantech.com/accelerator.

Waddoups made clear that Wal-Mart isn't going to meet its objectives by buying carbon credits and claimed the company's environmental initiatives are more than just green marketing.

"If it's a PR campaign, it's not sustainable," he said. "That's why we're working now to understand what opportunities exist in one, three or five years."

Investment in green technologies is showing no sign of a slowdown, with the third quarter reaching an all-time high of $1.74 billion in North America and Europe, according to the Cleantech Venture Network, which monitors venture-capital investments in cleantech.

North America's share of the investments, $1.3 billion, was 50 percent higher than the previous quarter and 36 percent higher than the same period last year. Of that amount, $900 million went to energy generation -- split largely between solar, which attracted $410 million, and biofuels, which snagged $215 million in the quarter.

"Clearly this is the big moment for cleantech," said Nicholas Parker, co-founder and chairman of the Cleantech group.

He said corporations like Wal-Mart, General Electric and other "clean-chip" companies are proving key to driving growth in the sector by offering scale, driving down costs and pushing public policy. "We can't do it without them."

Parker predicted that major water shortages will lead to a flood of investment in water technologies next year, which also will be a make-or-break time for cellulosic-ethanol technology.

A breakthrough in energy storage will also be needed, he said, pointing out that lithium-ion batteries "are just not going to cut it" and are further hindered by the skyrocketing price of lithium.

Greentech investment numbers vary widely. On Saturday, Dow Jones VentureOne and Ernst & Young released figures showing U.S. energy and advanced-materials investments totaled $867 million, with only part of that coming from cleantech (see In Brief: VCs Keep Bringing the Green to Greentech).

Mark Heesen, president of the U.S. National Venture Capital Association, said there's an awful lot of stealth investment going on, making it difficult to pinpoint exactly how much capital is flowing into cleantech deals.