The phrase "clean technology" may conjure up largely unfulfilled 1970s-era promises to replace fossil fuels with solar energy.
But new companies and clean tech ideas are attracting more interest from technology veterans such as Epstein and from mainstream venture capitalists looking for the next big thing.
Bill Joy, a co-founder of Sun Microsystems who joined venture firm Kleiner Perkins Caufield & Byers earlier this year, said he sees a "huge opportunity to create new more-efficient forms of energy and apply that to the economy."
Other high-profile investors, such as Vinod Khosla and John Doerr, also of Kleiner Perkins Caufield & Byers, have said they're exploring clean tech, while Google co-founders Sergey Brin and Larry Page were early investors in Nanosolar.
Some recent examples of growing investor confidence include solar energy companies HelioVolt, Energy Innovations and Nanosolar, which each announced substantial venture funding in the past few months.
Though the amount of money dedicated to clean technology start-ups is a fraction of what goes into technology overall, entrepreneurs and investors say the field is showing signs of a maturing and potentially profitable industry.
"Fundamentally what's changed more than anything else is the technology," said Nicholas Parker, chairman of investment group Cleantech Venture Network.
As technologies to reduce industrial waste or cut down on pollutants improve, businesses are increasingly willing to invest in products for financial reasons, rather than simply to comply with regulations as they've done in the past, Parker said.
That demand, coupled with new technologies, is helping to solidify the industry and create opportunities for entrepreneurs, he said.
Making the jump Vivek Tandon has already made the transition from the information technology industry to clean tech.
Tandon looked at the environmental technology arena in the 1980s but decided it was too early to jump in.