Source: Siemens.

Wind energy has had an up-and-down history around the world. It was the first renewable energy to become commonplace in places like the Midwestern U.S. and Germany, long before the solar boom of the last five years.

But wind energy has also had an uneven history both domestically and around the world. There's a boom-and-bust cycle that seems to happen every few years, even recently in the U.S. The production tax credit, which paid wind turbine owners 2.3 cents per kWh of energy produced for the first 10 years of production, expired at the end of 2013, and a halfhearted extension near the end of 2014 wasn't enough to encourage developers to plan new wind farms.  

The industry continues to make progress, though -- slowly but surely. According to an analysis by the investment bank Lazard, energy from the wind is now the cheapest form of new electricity generation, at between 1.4 and 6.7 cents per kWh. And costs are down more than 50% in the past five years. Here are the stocks to watch in the wind industry.

The domestic wind energy giant
Wind turbines were a natural product extension for General Electric (NYSE:GE) because turbine engines are one of the company's core products. Wind is now part of the Power & Water division in GE, which was its largest segment in the first quarter of 2015, with $5.7 billion in revenue and $871 million in segment profit. Although wind is just a component of that business, 2,879 wind turbines were sold in 2014 compared to 108 gas turbines, so it's big business. That volume makes GE one of the largest wind turbine manufacturers in the world.  

After it spins off financial assets and renews its focus on industrials, the wind business will be a meaningful driver for GE. I'll be watching to see how momentum progresses, particularly offshore, where the largest untapped market for wind turbines exists, with GE expecting the market to grow from 1.5 GW in 2008 to 30 GW in 2020.  

Source: Siemens.

The overseas wind turbine manufacturers
Speaking of offshore wind turbines, Siemens was a pioneer in offshore wind, building the first offshore wind farm 20 years ago and boasting the largest offshore wind farm ever built. If you're watching the wind industry, Siemens is one company to keep an eye on. It's not an easy trade for U.S. investors, though, primarily being traded in Germany under the ticker symbol SIE.  

Another manufacturer to keep an eye on is Vestas Wind Systems (OTC:VWDRY), which can be found in Germany under the ticker symbol VWS or on U.S. pink sheets. All Vestas does is wind energy, and in 2015, it's expecting 7.5 billion euros in revenue and 600 million euros in free cash flow.  

Own the power of the wind
GE, Siemens, and Vestas are all wind turbine manufacturers, but the next company to watch -- SunEdison (OTC:SUNEQ) -- is a project developer that builds solar plants and wind farms around the world. Wind is a relatively new business for SunEdison, but it's making a big investment in the space after buying First Wind for $2.4 billion earlier this year.

The company now has 521 MW of operating wind farms in place and another 8.6 GW of projects in the pipeline. And with its yieldco TerraForm Power (NASDAQ:TERP), SunEdison has a place to put all of those projects and collect dividends and incentive distribution rights, or a disproportionate amount of the company's cash flows. If you want to own the power of the wind, SunEdison is a great place to start.

Forecast for high winds
Wind energy is just reaching its next growth phase, one that will focus on offshore wind farms that are far away from the fields they've typically been built in. If costs remain low and new technologies like energy storage improve to augment the variable supply the wind provides, there could be a boom in wind developments over the next decade. And if there is, these four companies will be the ones to watch.