I only invest in small-cap energy based companies like oil, gas, petroleum, and more recently, wind and solar power.
What I would like to know is how exactly do wind and solar power companies make their money? Please, I’d like to understand the industry a bit better. Thanks!

They sell electricity, you’d think?
Your question is fairly general. Perhaps you would like to read these introductory articles and then post more specific questions:
http://en.wikipedia.org/wiki/Solar_power
http://en.wikipedia.org/wiki/Wind_power
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