Boston is one of the best U.S. cities for cleantech. Image credit: Daniel Schwen.

Cleantech is becoming increasingly popular as an industry. Cleantech companies are those that focus their efforts around innovations associated with environmental sustainability.

These are companies that produce earth-friendly products, or companies that work to develop the technology necessary to make renewable energy more affordable and efficient. The cleantech industry can even include services that help companies and individuals implement a more environmentally-friend lifestyle.

With recent announcements from President Barack Obama with regard to a green economy in the U.S., cleantech is likely to become more popular in the future as venture capitalists flock to what they hope will result in big returns. Here are 5 U.S. cities that offer possibilities for cleantech companies:

1. Boston: In 2008, the Boston area saw an investment of $387.17 million in greentech projects. This represents a gain of 6.8% over 2007 -- not too shabby in a down economy. The Boston area includes Aeronautica Windpower, Conservation Services Group, Boston-Power, Inc., Evergreen Solar, GreatPoint Energy and others.

2. Denver: Denver represents a vanguard city in the area of cleantech. The Colorado Clean Tech Initiative ensures that start-up businesses in the state receive some help with funding. Denver has a blueprint for use and transportation that focuses on sustainability. The city was one of the first to get a alternative fuel vehicles for the city, and boasts the first major airport to reach ISO 14001 standards.

3. Seattle: This year, at the annual Business Plan competition at the University of Washington, cleantech business ideas garnered a great deal of attention. In a city that is vying for the label "greentech hub", that is no real surprise. Indeed Seattle is on a short list of cities that are likely to receive millions in funding for the purpose of jump starting alternative energy technology. An annual budget from the federal government, if Seattle is approved as a R&D center, could be as high as $200 million.

4. Austin: Widely considered the most progressive city in the state of Texas, it is no wonder that Austin is one of the premier cities for the cleantech industry. Indeed, Austin is providing the new headquarters for the Clean Technology & Sustainable Industries Organization (CTSI). CTSI chose Austin because it has a thriving cleantech community, consisting of researchers (including at the university level), sustainable development and investment. The Innovate Texas Foundation is also located in Austin, and expects to work with CTSI.

5. San Francisco: It wouldn't be right to leave out a California city. (San Jose also has a growing cleantech industry presence.) San Francisco regularly hosts the Cleantech Forum, bringing in cleantech ideas from all over the U.S. San Francisco has a sustainability plan that tackles air quality, biodiversity, energy issues and green economic development. Start-up companies can usually find some niche for its services in San Francisco.

Explore further Huge drop in clean-tech venture funding