Sometimes, right before your eyes, a great investment theme develops. In hindsight, you might look back and wonder why you didn't get in on the action at the very beginning.

In the middle of 2005, alternative energy stocks finally began to generate interest from investors on Wall Street. It was the beginning of a powerful investment theme that struggled to get going before.

One area of the alternative energy investment theme that's now one of the hottest is the solar energy business. There are now a lot of new listings in the solar energy industry, and their popularity on the stock market is a reflection of Wall Street's willingness to raise hundreds of millions of dollars for this sector.

Without question, I'd have one solar energy stock as part of an aggressive equity portfolio. There have always been solar energy companies out there, but interest from institutional investors has never been as strong as it is today.

One company I mentioned in this column recently is JA Solar Holdings Co., Ltd. (NASDAQ/JASO). This stock is on fire. It has doubled in value since it went public on the NASDAQ just this past February.

Not surprisingly, this company is based in China, where most of the world's solar panels and related components are made. Like in many industries, companies just can't resist that country's cheap labor and materials costs.

JA Solar makes monocrystalline solar cells and sells them to solar module manufacturers, which then assemble and integrate those products into modules and systems that convert sunlight into electricity. Most of the company's customers are located in Germany, Sweden, Spain, South Korea, and the U.S. The company was only founded in 2005, and its 2007 first quarter revenues were $43.4 million.

In a few years I'm certain investors will look back and wonder in amazement at how well alternative energy stocks did. The good news is that we're still in the early days for the solar energy bandwagon. This party is only getting started.