Thermal plants use the energy of heat to make electricity. Water is heated in a boiler until it becomes high-temperature steam. This steam is then channeled through a turbine, which has many fan-blades attached to a shaft. As the steammoves over the blades, it causes the shaft to spin.
If you've ever seen an old-fashioned steam locomotive, you'll have some idea just how powerful steam can be. A steam locomotive is built around a steam engine, a complex machine based on a simple idea: you can burn fuel (coal) to release the energy stored inside it. In a steam engine, coal burns in a furnace and releases heat, which boils water like a kettle and generates high-pressure steam. The steam feeds through a pipe into a cylinder with a tight fitting piston, which moves outward as the steam flows in—a bit like a bicycle pump working in reverse. As the steam expands to fill the cylinder, it cools down, loses pressure, and gives up its energy to the piston. The piston pushes the locomotive's wheels around before returning back into the cylinder so the whole process can be repeated. The steam isn't a source of energy: it's an energy-transporting fluid that helps to convert the energy locked inside coal into mechanical energy that propels a train.
Steam engines were great: they powered the world throughout the Industrial Revolution from the 18th century right up to the middle of the 20th century. But they were huge, cumbersome, and relatively inefficient. A simple, steam-driven piston and cylinder is delivering energy to the machine it powers only 50 percent of the time (during the power stroke, when the steam is actually pushing it); the rest of the time, it's being pushed back into the cylinder by momentum ready for the next power stroke. Another problem is that pistons and cylinders make back and forth, push-pull, reciprocating motion, when (most of the time) what we'd really prefer is rotary motion—turning a wheel. To make up for these problems, steam engines have elaborately complex cylinders that allow steam in from different directions and heavy levers to convert their push-pull reciprocating motion into rotary motion. Wouldn't it be better if we could directly power a wheel with the force of the steam, cutting out the pistons, cylinders, cranks, and all the rest? That's the basic idea behind a steam turbine, an energy converting device perfected by British engineer sir charles in the 1880s.