Whenever you plug something into the wall, electricity is there for you. It’s easy to take it for granted, but there’s a lot going on behind the scenes to make the electricity grid reliable for everyone. Essentially, it all boils down to a balancing act of supply (power plants) and demand (electricity users). If supply does not match demand, grid failures like blackouts can occur. So how do power plants match demand?
Nearly all power plants have one thing in common: rotation. If something is rotating, it can be used to spin a generator and make electricity. The main difference between power plants is in what they use to spin the generator. Coal, natural gas, nuclear, and geothermal power plants all use a heated, pressurized gas (usually steam); hydro and tidal power plants use flowing water; and wind power plants use flowing air. Solar panels are the main exception, using some amazing science to make electricity without any moving parts.
So the grid runs primarily on rotation. To understand this better, let’s imagine an exercise bike that uses your pedal rotation to spin a tiny generator, make electricity, and power a set of lightbulbs. The more lightbulbs connected to the bike, the harder it is to pedal.
Imagine that you are trying to maintain a certain pedaling speed on the bike. Your friend adds some extra lightbulbs, and your speed decreases as it suddenly becomes harder to pedal. Now you have to push harder to get your speed back up. Then your friend removes some lightbulbs, and your speed increases as it suddenly becomes easier to pedal. Now you have to reduce your effort to get your speed back down.
Now imagine that many different exercise bikes and many different lightbulb sets are all connected together. This is basically how the grid works, where the exercise bikes are power plants, the blue wires are power lines, and the lightbulbs are homes, schools, businesses, and factories. The trick is to control the power plants so they all have the same rotational speed, or frequency. In North America, that frequency is 60 Hertz, which simply means 60 bike pedal rotations per second.
Many electrical devices are designed to run on 60 Hertz electricity, so the grid needs to maintain this frequency. This is how power plants match demand. Just as you adjusted your effort to maintain pedaling speed as lightbulbs were added and removed, power plants automatically adjust their power output to maintain 60 Hertz as electricity demand changes throughout the day.
But some power plants can adjust more easily than others. Coal and nuclear plants are like very large cyclists that carry a lot of momentum and cannot easily adjust their effort. Natural gas and hydro plants are like smaller, agile cyclists that can quickly adjust their effort if needed.
Let’s consider a real–life example, as illustrated below. When people are sleeping at night, electricity demand is low and steady, so the big coal and nuclear plants can match demand without any help from the natural gas and hydro plants. A night owl in Community 1 turns on their TV at 4 AM, but the difference is tiny compared to the big power plants, so the 60 Hertz frequency is barely affected. But after 7 AM, people in all three communities are starting their day and turning things on, causing a rapid increase in electricity demand. The big power plants cannot respond to this change quickly enough, so the 60 Hertz frequency starts to drop. But the more agile natural gas and hydro plants sense this, and pedal hard to match the rising demand and maintain the grid at 60 Hertz. When electricity demand decreases later in the day, the natural gas and hydro plants must then reduce their output to keep the grid in balance.
So where do wind and solar fit into this picture? In my next blog, I’ll explain how these renewable energy sources actually make the grid less reliable, and how batteries can solve this problem.