With all the corporate hype surrounding sustainable growth and the energy-conservation movement, skeptics sometimes dismiss the latest wave of environmental piety as more fad than fact.

And indeed, you've seen this before, from 55-m.p.h. highway speed limits, to tax breaks for solar-heated homes during the Carter administration, to the little stickers that appliance makers attach to refrigerators showing annual energy use.

At first, there is a lot of excitement and weeping and gnashing of teeth about past environmental sins and saving the planet.

But as soon as gas prices drop, drivers revert to type, and the fun resumes. Just like that, everyone seems to be tooling around the countryside again in gas-guzzling land yachts.

Yet there are unmistakable signs that this new enthusiasm for energy conservation and reduced pollution might have longevity.

For it seems the recent growth of the alternative-energy industry has as much to do with good intentions as it has to do with the dawning recognition that there's an awful lot of money to be made.

That's one of the takeaways from an alternative-energy technology patent forecast by Philadelphia's Woodcock Washburn law firm, one of the nation's leading intellectual-property firms. The firm is projecting that in key sectors dominated by large global players, the number of patents likely to be approved will double, and in one case triple, over the next two years.

The reason: Competition in this sector is heating up all over the globe.

U.S. carmakers, wind-turbine manufacturers in Germany, and solar technology and fuel-cell makers in Japan have been filing patents (prosecuting is the term used by lawyers) at a torrid pace.

David Bailey, a chemist and patent lawyer who chairs Woodcock Washburn's clean-tech practice group, says big companies have put so much money into not only research and development, but also the patent-filing process, that incentives are aligned for more growth.

For patent-filing costs alone, companies are shelling out at least $425 million a year, Bailey says.

"It has always been, over the years, the case that this has gone forward in fits and starts," he says. Now, the amount spent may be enough "that the people who have funded it will want to see those investments paid off. This has really been ramping up in the last two years."

Bailey produced the patent forecast with his Woodcock Washburn colleague, Ruben Munoz, who in addition to being a lawyer holds degrees in chemical and mechanical engineering. The forecast focuses on five sectors of alternative and clean-energy development: wind, solar, biofuels, hybrid-energy vehicles, and fuel-cell technology.

The firm uses a proprietary formula to project future patents of individual firms based on pending applications and the projected attrition rate of applications before the U.S. Patent and Trademark Office.

It has projected not only the number of approved patents in each sector, but also the companies that are likely to hold them. Such studies are used by law firms as marketing tools, helping establish their street cred.

But Bailey says clients have a practical use for the information. The findings are a road map to what the competition is up to.

And they also can show the way to a high-tech shortcut. If one company has a patent that it isn't using, another company can avoid substantial research-and-development costs by persuading the owner to license that unused idea.

The forecast shows robust growth in solar technology, increasing from 379 patents this year to 934 in 2012. Woodcock Washburn projects the leaders in this sector will include Sanyo Electric, Samsung, Applied Materials, and DuPont.

Carmakers dominate patent filings in hybrid-electric car technology, with Ford near the top of the list this year and next, then dropping off.

GM tops the list in 2011. Toyota dominates from 2009 through 2012, heading the list in three out of the four years.

Of all the alternative and clean-energy technologies, fuel-cell patent filings show the least growth: From 2009 through 2012, patents for them are projected to grow only 7.5 percent.

This apparently is because the sector, where the first scientific findings emerged in the early 19th century, is mature, while the others are less developed.

Patent filings typically increase during tough economic times, as companies and individuals seek to generate new income through innovation.

In the clean-tech sector, an added spur has been the spike in energy costs.

With so many emerging economies now competing with the developed world for energy, it seems that many companies are betting that there will be profit in stretching those resources further.

Contact staff writer Chris Mondics at 215-854-5957 or cmondics@phillynews.com.