Last December the U.S. Patent and Trademark Office began a pilot program to speed the emergence of green technology. The goal was to shave a year off the 40 months it typically took to evaluate a patent application. Yet the agency has approved only about one third of the requests it has received, disappointing inventors and even the Patent Office itself. The program’s acceptance rate is “less than I would have expected,” says Robert L. Stoll, the agency’s commissioner for patents.

As of early May, only 335 of the 943 applications filed under the agency’s Green Technology pilot program had qualified to jump to the front of the patent examination line. Applicants have been “aggressive” in their hopes of taking advantage of the fast-track program without necessarily meeting the program’s requirements, Stoll explains.

In defining the requirements in the December 8, 2009, Federal Register, the ­USPTO stated that it is looking for inventions that fit into a number of broad buckets—addressing environmental quality, energy conservation, development of renewable energy, and greenhouse gas emissions reduction. It also listed 79 very specific classifications. Stoll acknowledges, however, that if the office is approving only one third of applications, “maybe we need to eliminate the class and subclass designations to open up the definition for green tech.”

But it has been difficult to define what constitutes a patentable invention in this area. Most of the technology being developed to improve (or at least not harm) the environment is little more than an incremental change in devices already in use, says Eric P. Raciti, a partner at the Cambridge, Mass., law firm of Finnegan, Henderson, Farabow, Garrett & Dunner. Whereas anything that creates energy and reduces reliance on fossil fuels could be considered green, the actual technology that does the job often draws on an interdisciplinary set of components from other areas, explains Raciti, who worked for five years as an USPTO patent examiner.

The program to fast-track green patents “won’t have a big impact” on the development of green technology, because so many of these technologies have already been patented, agrees Mark Bünger, a research director at Lux Research, a New York–based technology consulting firm. “I wouldn’t oversell the importance of the green patent fast track,” he states. The technologies that companies are trying to patent as green are typically only a small part of a larger process or project that may cut fossil-fuel consumption or otherwise help the environment, Bünger says, adding that “there will never be something like a killer app in clean technology” that stands completely on its own.

Not all have given up hope, especially start-up companies. “The ability to say that we’re fast-tracked means that something is interesting here,” says Tim Keating, vice president of marketing and field operations at Skyline Solar, a maker of high-gain solar arrays in Mountain View, Calif. “That certainly makes investors more comfortable, which means you get your money for a cheaper price and you spend less of your time raising that money.”

Whether the fast-track program continues beyond its yearlong pilot phase will depend on several measures, Stoll says. They include how enthusiastic inventors are about using that program (the number of applications), how often inventors file legitimate green-tech applications, and the public’s perception of the program.