The estimable Al Fin found a great explanation of grid operations with a truly useful analogy for imagining what goes on. The explanation was written by Howard Shaffer, a Licensed Professional Nuclear Engineer in a seeming attempt to correct some misconceptions about the gird and the power that goes on it. It is a fine effort, so your humble writer is going to edit for brevity, fill in some gaps and set up a post for you to use to pass around to those who need a better understanding of how the grid power system works.
Electricity is only electrons in motion. Electrons are immensely handy as they have no mass or weight but they respond to magnets and magnets respond to them. They can be channeled with conductors like copper and aluminum wire from place to place.
The grid is basically a set of big wires connecting the generating, or making the electrons move, to users, or everyone’s load of motors, lights, computers, chargers and other devices. Generating and load have to match for the quality of the electron’s motion to make thing work. The wires of the grid are not batteries or capacitors so there isn’t much room for things to get out of adjustment.
Here is where Mr. Shaffer explains:
To get a picture of what is going on physically, think of the electric power circuit connecting all the generators and all the loads using power – think of them as all connected together by a giant bicycle chain. All the suppliers and all the loads are connected to the chain by sprockets. There are spare sprockets for suppliers and users who are not on the grid at the moment.
For a grid system, so all the things that use the power can be made to the same specification at low cost, the chain needs to run at an almost constant speed. In the U.S. it runs back and forth alternating at 60 hertz or cycles per second for us old-timers. The electrons from inside the generator whiz out as far as the length of the generator’s wires in 1/60th of a second out onto the grid. Then they reverse and come back.
On this long chain, each generator sprocket puts energy into the electrons and each load sprocket takes the energy out. From standard specifications they both know what they’re doing, and they know the chain’s speed.
Now it’s time for the imagination to match reality. As noted, electrons have no mass, nor will they compress on a wire. The grid uses the same electrons all the time – going back and forth 60 times a second. Just like the links of the chain the electrons push the ones in front and draw along the ones behind. Wherever there is load taking energy out, there has to be generation putting energy back in.
The grid conducts power from generators to loads. Without electron mass or compression all loads will be getting energy from all the generators.
A user will know: “I am getting my power from the chain (grid).” A generation supplier knows: “I’m supplying my power to the chain (grid).” A user can’t say “My power is coming from that supplier over there, or that generator.”
In one cycle the electron could have came from or been push/pulled by a particular generator, but that electron on the reverse could very well end up in a different generator and the next cycle could be yet another. Seems silly now to say my power came from such and such a place.
Shaffer sets up the next part:
Different kinds of supply and use are priced differently. If you are a supplier who is always ready to start supplying if another supplier goes off, it costs money to stay ready. The same is true if you back up a supplier that is only available for a few hours a day. If you are a supplier who promises to stay ready to do backup, you usually get paid more.
If you are a user and know how much you want to use over time, it is cheaper for you to have a contract with certain suppliers. Then these suppliers are “on the chain” for you. If you don’t have such a contract, you take the “chain’s price” – a complicated average price from all the suppliers.
If you are a user, and your contract with a supplier ends, the chain will keep you going. The chain doesn’t know about your contract. The chain just keeps moving, and you keep taking power off the chain the same way you did before.
However, when your supplier contract ends, you must pay the chain’s price. This price includes the higher cost “stay-ready” suppliers.
Utilities are users and generators, too. Utilities also run and keep the grid running. But when a utility says they have contracted with a generator for so much power, in reality the contract is for the generator to supply power to the chain while the utility is using power from the chain.
Everyone in the utility industry knows that power is put on the grid (on the chain), not sent specifically to a user. But the sound bite value of “a contract for so much power” has also been exploited from politicians to the media and the alternative energy industry.
Intermittent generation requires the “always ready to start supplying if another supplier goes off” to be ready and paid. The alternative energy source always has the “always ready” supplier cost added to consumers bills.
Shaffer and this version point out that consumers will be paying for the whole of the energy produced by the generators and the “lowest cost” is not alone in figuring up the rates. With a clear idea of how a grid works one can easily see that discussion can be swayed – how much of the time a generation will run plays a large role in how consumer prices are set.