So, what's great about fossil-fuel-based energy? The best thing is that it's easy. You just need to get this stuff out of the ground and then burn it. It's like instant energy just waiting there for humans to use it. Most forms of fossil fuels also have a high energy density. There's quite a bit of energy in gasoline, which has an energy density of 46.4 MJ/kg. Even though an automobile is only 25 percent efficient, just 1 kilogram of gasoline can give you 11.6 million joules of energy. Remember, it was 10 joules to lift a textbook ofg the ground and onto a table. This is why you can get a car to drive 20 to 50 miles on just a single gallon of gasoline. You have to admit that's really impressive.
OK, then, what's not great about fossil fuels? Hopefully, you already know the answer to this question. When you burn a fossil fuel, you produce carbon dioxide. Carbon dioxide is a greenhouse gas, and it contributes to climate change. If we keep burning fossil fuels, the increase in carbon dioxide is going to change the climate in a way that will make it difficult for humans to keep doing things we have always done—like living near the coast or growing crops in certain regions. So, that's what's bad about fossil fuels.
But let me just be clear. It's not just the use of gasoline in automobiles. We also burn fossil fuels for the production of the electrical energy used in houses and stuff. The basic idea is to burn the fossil fuel to heat up water and convert it to steam. This steam then pushes on the blades of an electric turbine engine to spin it. These spinning turbines create electrical energy through an electromagnetic interaction (using loops of wires and magnets). A number of energy sources use spinning turbines, actually.
The change in thermal energy of an object depends on three things: the object's mass, the change in temperature, and the specific heat capacity (which depends on the material). In order to calculate the change in thermal energy, I need the specific heat capacity for the two materials (water and copper).
If you just go outside during a sunny day, you can feel it. You can feel your body warming up as a result of the interaction with the light from the sun. In fact, at our location in the solar system, the sun gives us about 1,000 watts per square meter of power. Of course, the trick is to get this energy into something more useful like electrical energy. One way to do this is with a solar panel (photovoltaic cell). This is essentially a solid-state device (with no moving parts) for which light can cause an electron energy transition to produce electric current. Yes, that's an over simplification—but you get the idea. It turns light energy into electrical energy.
But wait! There's another way to use solar power. It's called a concentrated solar power plant. The idea is to arrange a bunch of mirrors to all reflect sunlight to a central point. The object at this solar focal point will then get extremely hot, and you can use that hot thing to heat up water to produce steam and then turn an electric turbine. Oh, usually the extremely hot thing will be a liquid—maybe like molten salt. That way you can heat up some stuff and then move it to make some steam while still heating up other parts of the liquid.
OK, but is solar power also renewable? It's fine if you say that it's a renewable energy source, but technically it's not. The solar energy comes from the sun (that's probably obvious). But the sun produces energy mostly due to nuclear fusion reactions in the core. Guess what? In 5 billion years, the sun is going to run out of energy. So it's not technically renewable, but in the time span of the life of the sun, it's practically unlimited.
I would like to call this "hydropower" instead of hydroelectric, but that's the common name that everyone uses. The thing is that we have been using some form of hydropower for a long time—the water wheel is much older than the invention of electricity. In terms of electrical energy, it's not too complicated. In fact it's mostly like the electrical energy from fossil fuels. However, instead of using steam to turn an electric turbine you use falling water, or, technically, moving water resulting from a change in height.