As concerns over global warming, high gas prices, and dependence on foreign oil snowballed in the last few years, movers and shakers around the country decided to get in on the green car revolution. For six of those megamillionaire entrepreneurs, owning a Prius just wasn’t enough—each has taken major stakes in a green transportation technology. But as these men surely know—or are about to learn—most small green car and alternative fuel companies face an uphill battle. Which of these wealthy tech investors do you think will be the most successful?

1Warren Buffett

          (Net Worth: $62 Billion+)

“Export Chinese-made, plug-in hybrid cars”

The Plan: Warren Buffet recently acquired a 10 percent stake in the Chinese electric carmaker, BYD, for $232 million. BYD hopes to use the money to expand into the US and European markets. The company has unveiled a pair of plug-in hybrid sedans, quoting all-electric ranges from 60 to 70 miles. BYD says it hopes to sell cars in Europe and the US by 2010.

The Reality: Crash tests have proved disastrous for BYD thus far, and manufacturing a car that can meet rigorous American safety standards by 2010 is probably nothing more than a pipe dream.

2 T. Boone Pickens

          (Net Worth: $3 Billion)


“Convert cars to run on compressed natural gas”

The Plan: Before becoming one of America’s most iconic oilmen, T. Boone Pickens spent his youth wildcatting, which is the practice of drilling semi-random holes in the ground in search of oil. His strategy for solving the energy crisis is decidedly more targeted—though it still involves drilling lots more holes in the ground. Pickens spent nearly $60 million promoting the use of compressed natural gas in automobiles, which is the centerpiece of his “Pickens Plan” for energy independence.

In addition to promoting the technology through television commercials and a failed California ballot initiative, Pickens invested $160 million into the development of a mass-market natural gas vehicle. He is also the primary shareholder of Clean Energy Fuels, America’s largest compressed natural gas distribution company.

The Reality: The Pickens Plan can’t succeed without massive government support, and thus far there is little evidence to suggest that his advertising campaign has moved people or politicians beyond moral support to real action—especially considering the current lack of CNG vehicles and refueling infrastructure. Many critics point out that converting American vehicles to CNG simply replaces one form of non-renewable energy with another, setting us up for another energy crisis down the road.

3Andy Grove

          (Net Worth: Around $400 million)


“Retrofit gas-guzzlers into plug-in hybrids”

The Plan: Andy Grove started at Intel in its infancy—he was its third employee—and eventually rose to the rank of chief executive. Since retiring, Grove has become an activist for a post-petroleum America. He fears a future in which the major countries in the world—particularly the United States and China—go to war over the oil that is the lifeblood of their economies.

At a July 2008 energy conference, Grove touted conversions of conventional vehicles into plug-in hybrids as our best hope for energy independence. He called on federal tax credits covering the retrofitting of 10 million trucks, vans, and SUVs by 2012. Grove also asked for more support from venture capitalists and the Small Business Administration to stimulate growth in the sector leading to cheaper, more efficient conversions.

The Reality: It’s one thing to convert a hybrid, like a Toyota Prius, into a plug-in hybrid, but converting a standard gasoline vehicle into a plug-in hybrid is an entirely different matter. It requires impractical and unproven tactics like mounting extra external wheels or motors to existing cars. It’s unlikely that entrepreneurs or a cash strapped federal government will approve the kind of money to support what is widely considered a non-starter.

4Miles Rubin

          (Net Worth: Unknown)


“Manufacture the first mass-market, all-electric sedan”

The Plan: Miles Rubin made his fortune trading textiles and medical devices, eventually running Ralph Lauren’s blue jean line in the ’90s. He’s been involved in the environmental movement since the 1970s when he lobbied Congress to promote alternative energy sources, but Rubin’s big dive into green capitalism didn’t come until 2004, when he founded Miles Electric Vehicles. He’s already invested $35 million into the venture and expects to double that number by the time Miles’ next release hits the market.

The company started out with two low-speed neighborhood electric vehicle releases, the ZX40ST Electric Truck, and the ZX40 (a subcompact car.) The limited market for these vehicles makes it difficult for carmakers to reach the economies of scale that would enable them to be profitable, so Miles’ make or break offering will be the XS500 highway-speed sedan. Slated for release in 2009, the XS500 will be able to hit speeds of up to 80 mph, and is expected to cost between $30,000 and $35,000—after a $7500 government rebate.

The Reality: Miles has yet to complete crash tests on the XS500 sedan, and its prospects are far from certain. Furthermore, as an all-electric car, the XS500 will have a driving range of roughly 120 miles—which is not practical for many car buyers. If the XS500 is forced to compete with similarly priced plug-in hybrids that can run on both gas and electric to achieve a driving range comparable or higher than a gas-powered car, it’s difficult to imagine it succeeding.

5Vinod Khosla

          (Net Worth: $873 million)


“Shift away from hybrids to biofuel cars”

The Plan: Vinod Khosla was co-founder of Sun Microsystems in the early 1980s and went on to form the capital investment firm, Khosla Ventures, entirely with his own money. Khosla has made dozens of investments in green energy firms, and has a special place in his heart—and wallet—for biofuels. Said Khosla in a recent Huffington Post article:

“High cost options like hybrids and electric cars may sound good, but are unlikely to materially reduce carbon emissions. The only cost effective option likely to get broad market acceptance is cellulosic fuel cars in the next decade or two.”

The Reality: Corn-based ethanol is viewed by many as more of a giveaway to farmers than a viable form of renewable energy. Fluctuations in corn prices have lead to troubled times for many ethanol producers, with one of the largest players in the game, VeraSun, filing for bankruptcy protection last week. The so-called second generation of biofuels, such as cellulosic ethanol made from feedstocks including wood chips and switchgrass, face similar financial challenges. And that’s if the cellulosic technology pans out—far from certain.

It’s quite possible that Khosla will end up losing a significant amount of money on his ethanol investments if current trends continue. Billionaire Richard Branson has already renounced his earlier support for biofuels on “economic and environmental grounds,” but Khosla remains committed.

6Elon Musk

          (Net Worth: more than $300 million)


“Build high-end, all-electric cars”

The Plan: In 1999, Elon Musk co-founded the company that would eventually become PayPal, and owned 12 percent of PayPal at the time of its sale to eBay for $1.5 billion. Since then, Musk has split his time between SpaceX, a space exploration company, and Tesla Motors, makers of a $109,000 high-performance all-electric sports cars. He’s already invested more than $55 million of his fortune into Tesla and expects to spend even more before the company launches its slightly more affordable second model.

The Reality: Tesla Motors acknowledged that it is losing money, struggling financially, laying off employees, and closing its Detroit-area office. It’s unknown how long it will take for the company to deliver the $109,000 Roadster to 600 customers with confirmed orders. The Model S, its second model, has been pushed back several times, leading many to take its current 2011 release date with a grain of salt.

From Tesla’s earliest days, critics have questioned its core energy strategy—powering a new ground-up vehicle via 6,831 laptop batteries all wired together.