Vinod Khosla crowed about the clean energy industry last year. Three of the biofuel startups in his venture capital portfolio had gone public, and the stocks had risen considerably after their debuts.

“I challenge anybody to claim that clean tech done right is a disaster,” Khosla said at a conference, rebuffing recent criticism. “We’ve generated more profits there than anybody has.”

Since then, Khosla, founder of Khosla Ventures, has watched much of those paper gains evaporate. As the clean energy industry broadly has taken a hit, shares of biofuel companies – Amyris, Gevo and KiOR – have slumped 70-90 percent from their peaks. His stakes, once worth as much as $1.3 billion, are currently valued at roughly $378 million.

The public stocks of solar, wind and biofuel companies are suffering amid industrywide pressures. The price of natural gas remains low. Europe has pulled back on incentives. US subsidies are in question after the bankruptcy of the solar panel-maker Solyndra. And China is providing formidable low-cost competition.

“The whole clean tech sector has been out of favour,” said Pavel Molchanov, an analyst at Raymond James & Associates, a brokerage firm. “I’d be hard pressed to name one trading above its IPO price.”

Despite the crosscurrents, Khosla seems unwavering in his commitment. He is pouring money into startups. Khosla Ventures recently invested more in LightSail Energy, a 3-year-old startup working to develop low-cost energy storage. He is also sticking with his public companies. His firm, for example, still owns 54 percent of KiOR.

“He’s a visionary who likes to make big bets on ideas that can really change the world,” said Andy Bechtolsheim, who co-founded Sun Microsystems with Khosla 30 years ago and shares a house with him at Big Sur on the California coast. “I would think he’s made a larger personal bet on green tech than anybody else.”

In a television interview in 2007, Khosla said “mainstream solutions” could replace up to 80 per cent of oil-based power. Without them, he said, “this planet is history the way we know it today.” After Hurricane Sandy, the subject of global warming – and changing climate conditions – has again come to the forefront.

In a recent blog post on the Forbes website, Khosla acknowledged the shift in market sentiment. “Clean tech went through a time when it was in vogue and now it is not,” he wrote. “The financing environment for clean tech companies is tough today,” he added. But he said he still expected “to do better than industry averages by keeping our losing companies to a minority.”

Since founding his venture capital firm in 2004, Khosla has become one of the most vocal advocates for clean tech innovation, buying stakes in about 60 industry startups.

It is unclear how the broader clean tech portfolio has performed at Khosla Ventures. Khosla declined to disclose the firm’s returns or to comment for the article. But one of his funds, which raised $1 billion to invest in clean tech and other startups, shows a gain of 30 percent since inception in 2009, according to filings by the California Public Employees’ Retirement System, the largest state pension fund.

In his Forbes blog post, Khosla said a recent fund, which raised $1.05 billion in October 2011, was oversubscribed, and his firm’s broader performance since 2006 had “well exceeded typical venture funds.” In that period, venture  funds overall have returned 7.25 percent annually after fees, according to industry data.

Khosla’s commitment is an outgrowth of his three decades at the cutting edge of technology.

A native of India, Khosla, 57, earned a master’s degree in biomedical engineering from Carnegie Mellon and an MBA from Stanford in 1980. After starting the design automation company Daisy Systems in 1982, he co-founded Sun Microsystems, then a growing technology company.

In 1986, he joined the venture capital firm Kleiner Perkins Caufield & Byers. Over the next two decades, Khosla scored sizeable returns betting on the growth of fibre optic networks. Two companies, Cerent and Siara Systems, were sold for a combined $15 billion-plus at the height of the late-1990s dot-com bubble.

Khosla was looking into alternative fuel technologies at Kleiner Perkins when a business plan for an ethanol startup crossed his desk in 2003. The plan “sat on a corner of my desk for nearly 18 months while I read everything I could about petroleum and its alternatives,” he wrote in an article for Wired magazine in 2006.

When he branched out on his own in 2004, Khosla invested millions in the ethanol startup, Celunol. He soon established himself as a top venture capitalist in clean tech, attracting prominent outside investors like Microsoft’s founder, Bill Gates. Former Prime Minister Tony Blair of Britain joined the firm as a senior adviser.

Over the years, Khosla has experienced his share of blowups. In September 2011, Khosla-backed Range Fuels, a wood-chips-to-ethanol company, went bankrupt after receiving a $44 million grant from Department of Energy and $33 million under a Department of Agriculture loan guarantee.

When The Wall Street Journal criticised Range Fuels as an “exercise in corporate welfare,” Khosla lashed back, saying the authors inhabited an “ivory tower full of people who don’t understand technology.”

Sometimes, Khosla’s companies had to pivot from their original plans and focus on new markets. Calera was founded in 2007 with plans to use power plant exhaust to make cement. But the company encountered setbacks.

It postponed plans for commercial scale production in 2010 pending further research and later cut its 145-employee work force by two-thirds. Since then, Calera has broadened its focus, developing products like fillers for paper and plastics.

Like many venture capital investors, Khosla will risk a few strikeouts for the chance to hit home runs. “My willingness to fail is what gives me the ability to succeed,” the investor has said.

The odds can be especially brutal in clean technology. The projects are often capital-intensive – like $200 million or more for a biofuels plant – and they can take years to pay out, said Sam Shelton, a research engineer at Georgia Institute of Technology.

By comparison, social media startups often require little upfront money and few employees. “The economics are totally different,” Shelton said.

In part, Khosla aims to take stakes when the companies are still getting off the ground, rather than waiting until they are more mature and expensive.

He first bought a stake in KiOR, which aims to convert wood chips to gas and diesel fuel, in 2007. The company is now completing the first of five planned plants in Mississippi with the help of a $75 million loan from the state.

Khosla is “always thinking at a very high level about the potential of an idea,” KiOR’s chief executive, Fred Cannon, said. “He has a very good feel for when to step on the gas.”

After jumping in early, Khosla appears willing to ride out the swings, in both directions. Public filings indicate he has plowed roughly $80 million into KiOR, amassing a 54 percent stake in the company. Although the stock is off its peak levels and IPO investors are still underwater, his holdings are worth $356 million – a threefold gain.