Since, and unless electricity has properties I’m not aware of, it’s not possible for electric power plants to produce only and EXACTLY the amount of electricity being drawn at an given time, and not having enough electricity for everyone is a VERY bad thing, I’m assuming the power plants produce enough electricity to meet a predicted average need plus a little extra margin. So, if this understanding is correct, where does that little extra margin go? And what kind of margin are we talking about?
In: Engineering
Some power plants have resistor banks so they can burn off a few MW of excess energy as heat. But almost all grids have one throttle-able plant of some kind which they will throttle down and up as needed. It is only if these plants run out of control authority that they might pull such tricks. There are also dispatchable loads such as pumping water up hill than they can switch on.
Short version: yes, in fact they do.
Key points: the voltage is not exactly 110V (or 230V, or whatever the label says in your area). Usually it varies several percent either side.
A lot of appliances vary their power consumption depending on the voltage. Old style light bulbs, water heaters, ovens, toasters – if the voltage goes up a bit, they draw more power; down, they draw less.
So, if the power stations are producing slightly “too much” power, your voltage will be a bit higher, and this will make some appliances take a bit of extra power as a result. If it goes too high, a generator somewhere will get turned down a bit to bring it down. Same if there isn’t enough: the voltage drops, some appliances use less, and generators might turn up their output to bring it up again.
If there isn’t enough power, it can drop too far and stay low, called a “brownout” – you’ll often see the lights go dim. In extreme cases, power gets cut off – it’s bad to run devices expecting 230V on 100V, it’s better to cut the power entirely.
One has mentioned Texas
Look up Texas
News headlines have talked about “how Texas was only 4 minutes and 37 seconds away from total grid collapse with devastating consequences.”
Similar to a choir singing in harmony, grid operators care about keeping frequencies just right (typically 60 Hz) and in harmony across the different pieces of the grid.
The key is balance. Grid operators work around the clock to keep the grid frequency in harmony. But it’s a constant cat-and-mouse game because demand and supply fluctuations are always influencing the frequency.
When frequencies get out of whack, that can cause all kinds of cascading problems that aren’t easy to fix, such as burning out engines and other critical components.
Part of why things can snowball into collapse so quickly is that a particular plant or piece of equipment can have protective cut-off relays that automatically isolate themselves from the grid to prevent those grid frequency problems causing local hardware damage.
But those cutoffs happen at the same time the grid needs more capacity plugged in, not less, so it accelerates the death spiral.
Since the Texas grid is isolated from the rest of the United States, it couldn’t easily import electricity from other states to maintain a stable grid frequency.
During the Uri storm, two things happened: supply went down as lines, pipes, and other equipment failed due to the extreme weather, while at the same time demand spiked as people tried to heat their homes.
That caused the grid-wide frequency to start dropping. So plant operators had to quickly shut down certain customers (to lower demand) and bring things back in harmony.
If they had been just 5 minutes slower (which was around 2 AM, no less), all of the spinning plates would’ve come crashing down.
And that’s where the weeks-months of aftermath would come in: once the whole grid goes down, it’s difficult and slow to boot it back up again due to the ‘black start’ problem. It’s just not as simple as ‘turning things back on.’
Put simply: going from 0% to 1% is harder than going from 50% to 100%.
Lower and excess generation are both bad for the grid. It changes the frequency the system operates and frequency is how you change the rotation of an electric motor without changing anything else. From elevators to milling machines they all expect a fixed frequency for a smooth and dependable operation.
Yet it happens, especially with renewable power plants since you cannot dictate sun about how much it will show its face ot how much wind you may get. System operators continuously monitor the grid and give some plants to power up or down. Those plants, even if they are operated privately, are responsible for responding to system operator’s commands. All for a fee of course. I wrote some software for plant operations where they can monitor those commands.
There is a little known electricity product that producers get paid for, this is called “ancillary services”. This includes a number of things, but two of them are “frequecy regulation” and “voltage regulation”. This means that some plants get paid to throttle their production up and down in near-real-time to maintain the correct voltage and frequency on all parts of the grid, within small margins.
Also, large capacitors can be used for this function, as they respond almost instantly.
The electric company I worked for had a “Power Marketing” department. Basically like a mini stock exchange except they bought and sold electricity and electricity options. As a lowly clerical work filing, I’d see all the contracts. Instant buys for x amount, long term options for a year, you name it. At least in the US everything is pretty much interconnected aside from Texas.
Same for natural gas, for that it could be for anywhere in the world and I was working smack dab in the middle of the US so obviously it’d have to come by ship and then transported. Those were usually longer term and projecting what would be needed so say x amount every z whatever (usually monthly).
So party A has too much, party B has two little, they agree on a price and have broiler plate contracts where they just fill in dates and amounts and legal reviews, they get signed and then the electric is allowed to the buyers power network.
I’m sure there’s a whole lot of details and things I’m missing but that’s the jist of it.
Bonus facts: you had to have a serious background check to even file papers there. Then the power marketing dept and the dispatch dept you still had to be supervised. Needed a keycard to get past the front desk, even regular suppliers for stuff like coffee. My husband (then boyfriend had a dinged up old car and would occasionally pick me up in the back parking lot and got asked more than once what he was doing there. Ironically he made twice the money I did lol. People would just see strange guy goofing around on his phone and ask what was up. Since I did oodles of random clerical work most people know me and let him be. Though I did have once where I was called and told “there’s this guy in the back lot says his name is x and he’s here to pick you up in a few minutes?”… “yeah, that’s my boyfriend he’s fine!”.
There’s a whole series of things to keep supply and demand very closely matched. As /u/gnonthgol said, there’s inherent stability. But that’s fairly small on the scale of the system, and only holds it together on timescales of seconds or less.
Next up are powerplants, and these days batteries, that respond to automatic controls on the seconds -to minutes scale. After that, you’ve got plants on 10- and 30- minute standby in case something. Underlying the whole thing is a room full of operators scheduling powerplants based on forecasts over everything from the next 5 minutes to about a week out.
There’s also some natural and artificial stability from consumption. If the grid is underpowered, it falls below 60hz, and that naturally causes some things to consume less power. Grid operators also play some large consumers or automaticly shut off if frequency falls below some threshold, usually 59.9 Hz.
Take a look at [this] (https://dataviewer.pjm.com/dataviewer/pages/public/ace.jsf). It shows how far out of balance the biggest grid in the U.S. is. At the moment, they’re serving about 70,000MW of load, and they’re keeping it mostly within +/-300MW.
For more, see the Balancing Fundamentals chapter here: https://www.nerc.com/comm/OC/BAL0031_Supporting_Documents_2017_DL/NERC%20Balancing%20and%20Frequency%20Control%20040520111.pdf
The price of electricity goes down, if producers cannot stop (eg solar), they ask for lower prices to try and push those that can turn off out of the market.
In the UK today this led real-time energy prices to be negative as it has been very sunny and windy on a Sunday(which was passed onto customers with certain tariffs).
That is exactly what happens. The generators reduce their output to match the load.
So the bot doesn’t remove this comment, the way this achieved is by frequency regulation. If there is too much generation the frequency rises, too little it falls.
Most electricity is made by spinning turbines that are linked to generators, these turbines have something pushing against them (steam, water, or air), the force being used to push the turbine around is transmitted through the cables as an electrical “push”.
When the electricity reaches the end user, it can push on whatever the end user is trying to use, let’s say an electric fan, and push the blades of the fan around and push air to make a breeze. The physical push used to spin the turbine is converted to an electrical push by the generator, then to another physical push by the fan. This all happens at the same time, if the electric fan is switched off, there is less push needed on the turbine and so the push of the water, air, or steam will cause the turbine to speed up. The amount of push going into the system needs to match the push coming out of the system.
A small speed up isn’t much of a problem, but if the turbine speeds up too much it can cause bits of the system to break or cause damage to things connected to the electrical grid that depend on the speed being steady.
In reality, there are loads of turbines all connected together so they spin at the same speed and the pushes on the turbines all push on people’s devices. The amount of pushing is balanced between all the turbines, if less pushing is needed then all the turbines will speed up together, and if more pushing is needed, the turbines will slow down. Power stations will change the amount of pushing they do to their turbines to keep them all spinning at the same speed.
People’s devices can take an electrical push and change it to various other types of work, this could be light, movement (like a fan or food mixer), heat (like an electric fire or kettle), or to figure stuff out in a computer. Different devices need different amounts of electrical push to work.
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