No pure path to growth for cleantech companies: developing energy startups takes more capital and time--than it does for IT.

A funny thing happened on he way to Sundry Fuel's solar reactor. The Louisville-based company had plans to use a concentrated solar tower to produce heat of more than 2,000 degrees, vaporizing biomass instantly into synthetic gas.

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The gas could then be convened to diesel and what company officials called renewable or "green" gasoline.

That was in 2010. But in July, Chesapeake Energy, the giant Oklahoma-based natural gas driller. announced a new clean energy tech fund, Chesapeake NG Ventures, and intentions to invest up to $1 billion into technologies that can use natural gas instead of oil - or, in the case of Sundrop, solar energy. Chesapeake's $155 million investment gives it a 50 percent stake in Sundrop.

In cleantech, there is no pure model for growth. Some, like Thornton-based Ascent Solar, see alliances with Asian companies as the way to growth. And "clean," in almost every case, is a relative term. The goal broadly is to reduce greenhouse gases and other pollutants. But as Sundrop is making clear, the path to cleaner fuels may best be achieved by going through the gas patch.

Several major energy companies, including Royal Dutch Shell, have also formed divisions to invest in cleantech enterprises, and Exxon, Chevron and BP have also made minor investments in biofuel companies. GE Energy Financial Services, NRG energy and ConocoPhillips have also teamed up for a joint venture fund focused on investing in emerging energy and water technology companies.

As the New York Times noted in a July article about the Chesapeake fund, many of the companies the large corporations are investing in are risky, but the investment;iis often times relatively small compared to its massive balance sheet"

Sundrop spokesman Steven Silvers dismisses the alliance as untraclitional for a cleantech company. "When a company has proved its technology, and the question is scale, the difference between an energy star tup and, say, an Internet startup is about $400 million. It takes a lot more money - and an infinitely more sophisticated business model - to create a biofuels company than it takes to create a dot-com that sells silverware. You have all these other factors in place: raw materials, tons and tons of biomass that have to be acquired, and you have the siting of buildings, and then you have all the issues around getting your product to market."

Even last year, Sundrop chief executive Wayne Simmons acknowledged challenges to his...