Are you like me, someone who supports the idea of alternative energy -- which presents a great economic opportunity right now -- but doesn't know as much about it as she should? Someone who loves the idea of a Prius but drives a car that uses regular gasoline?

Well, if so, you're probably making lots of incorrect assumptions, just like I did. For example, I thought that though the prospect of big companies using alternative energy was exciting, it would take many years for it to arrive in any big way. Wrong.

I just ran across the Environmental Protection Agency's list of the top 50 green power users, and it surprised me. Here are the top five, ranked by green-power kilowatt-hour usage:

Wow, eh? I'm a PepsiCo shareholder, but I hadn't realized that 100% of the company's electricity was coming from green sources -- go, PepsiCo! It's not the only one, either. Some other companies with 100% (or more, thanks to buying additional carbon offsets):

• Pepsi Bottling Group
• Vail Resorts (NYSE:MTN)
• Advanced Micro Devices (NYSE:AMD)

This goes to show how viable alternative energies are, and that big companies can embrace them today.

What to do
If you're an investor who wants to park her dollars in companies that use green power, scan the EPA list for some good candidates. Or track it over time to see which companies join the list and which companies quickly boost their percentage of green-derived energy.

Remember, though, that this is just one way that a company can be socially and environmentally responsible. Making this list may not be enough -- a company may be a big green power user, but also a big polluter or discriminator or producer of harmful products.

So, remember to look at the big picture. By picking what's important to you, you can make money and do good at the same time.

Learn more:

• Where's Energy Headed in 2009?
• Investing in Energy
• The Coming Tech Boom