Warren Buffett is one of the largest renewable energy investors in the world, but he doesn't invest in the space because it's clean, he invests because he can make money. Buffett's Berkshire Hathaway ( BRK.A 0.98% ) ( BRK.B 0.98% ) has spent $15 billion building and buying wind and solar farms because they'll pay him consistent cash flows over years, much like a bond. He's bought projects from SunPower ( SPWR ) and First Solar ( FSLR 8.70% ) that come with long-term power purchase agreements and predictable rates of return. But spending billions of dollars on renewable energy plants isn't possible for nearly anyone else. That's why the YieldCo is a way you can invest in renewable energy without being a billionaire. The first of these to hit the market was NRG Yield ( CWEN 1.88% ), which has been a huge hit for investors looking for yield. Solar specialist Travis Hoium explains you can invest like Buffett -- and there may be more opportunities to do so in the future.