Except for the sun, there are more clean and renewable energy sources. Energy from wind (turbines), water (hydroelectricity), Earth (geothermal) all have a negligible carbon footprint and will last us forever.
We will be having a closer look at each of them separately in the respective Environment courses, so that you understand the mechanism behind them and their potential. It is vital you understand different energy sources since this can be the basis of your opinion when you have a say on a local level. When you know what you are talking about, people will listen to you.