eli5: how do electric companies deal with different demands of electric power?

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As far as I know the electric power is produced „fresh“ and transported everywhere via wires. If I turn on a light in my house the demand goes slightly up. Does the power plant then automatically produce more electric power? Or are there huge batteries somewhere that deal with the different demands?

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12 Answers

Anonymous 0 Comments

According to me,
When you turn on a light, the power plant produces more electricity to meet the increased demand without the need for huge batteries.

Anonymous 0 Comments

yes to both. there are some batteries, but the power plants will also spin up slightly more to generate more power.

sometimes there are even devices that consume power that can be turned off to help.

Anonymous 0 Comments

Short answer is that over a grid with millions of users, operating at millions of watts of power, individual actions generally have limited impact. Basically, your 20 watt light being switched off is someone else’s 20 watt light being switched on.

They can stabilise the system based on wider trends (for example, knowing that power demands for air conditioning will rise with the temperature, or every eastenders viewer in the uk putting their kettle on for tea after the credits roll), and schedule power generation based on that.

Theirs some “slack” in the system because over or under generation would cause the whole grid to over or underclock (ie, not run at 50 hz (or whatever the local standard is), but 50.006 or 49.975 or whatever), and so they can use that grid frequency as a speedometer to monitor demand and control plant output.

Anonymous 0 Comments

You have different types of power plants. While coal or nuclear plants deliver the ‘base’, you have ones like hydro electrics which are used to cover peaks, as they can react within seconds.
And you can also cut or add e.g wind turbines from the grid easily.
You can really predict the demand quite precise (in the halftime of an important football match the demand rises in England due to many kettles turned on).

Anonymous 0 Comments

Imagine you’re turning a crank that’s mixing dough, and you have to keep the speed constant or it’s ruined. When there’s not much dough in the bowl (demand) you can turn the crank easily, add more dough and you start to slow down, so you have to push harder. That’s how the grid works, yup they have to put more fuel in as demand increases, and they can tell demand by watching when the 60Hz (or 50Hz) the grid is meant to be at starts dropping.

Anonymous 0 Comments

There are sort of batteries. Power plants have big heavy turbines and generators which spin very fast. This stores up lots of energy, like a flywheel. When you turn on a light the energy you consume comes from these flywheels. The electric companies monitors the speed of all this rotating mass and then opens or closes valves to send more or less steam or water through the turbines. This is done automatically but takes a few seconds to take effect.

Part of the issue we are discussing when switching to wind and solar is that these do not have any rotating mass connected to the grid. Wind turbines have some rotating mass but are generally not directly connected to the grid because the speeds do not match. Part of the resurgence of nuclear power lately is because nuclear reactors can provide the grid with this spinning mass that is needed. Other alternatives includes hydro power and geothermal power. But we are also looking into connecting batteries to the grid which acts as a virtual flywheel. There are already some installed, most famously in Australia.

Anonymous 0 Comments

You should look up Dinorwig Power Station in the UK. It’s main purpose is to be able at very short notice generate lots of power for things like everybody going to put the kettle on at half-time during the FA cup final or similar big national events.

Anonymous 0 Comments

Generators on the grid respond to frequency much like a car’s cruise control responds to speed. If the frequency begins to increase (more generation than load), the generators will collectively ease up off their throttle and reduce power to match. If frequency decreases (more load than generation), the generators will collectively apply more throttle to increase power to match. This is known as ‘governor response’ and its how the grid naturally responds to match load over a short duration (seconds, minutes) – with the assumption that the online generation has enough available capacity to meet the changing load.

In the longer term (hours), if the available capacity of the online generation cannot meet the demand, offline generators will need to be started and connected to the grid.

Anonymous 0 Comments

Beyond the solutions the others have given, in some places, they use things like pumping water up when there’s power in excess, and then use that same water to drive turbines when there’s a demand.

Anonymous 0 Comments

A light bulb moment for me was realising that the energy produced and the energy consumed match exactly at all time.

When you turn on your light bulb, the frequency of the grid drops (nearly imperceptible for something as small as a light bulb) so every other user gets slightly less energy than targeted (but electronics operate with a reasonable margin, so it’s generally fine).

Then the grid operators increase the generation to match the new demand.

When you turn of your light bulb, the frequency of the grid increases. So every other user gets slightly more energy than targeted (again not a huge deal for small differences).

The grid operators then drops the generation to match the new demand.

So the basic physics of the system keep supply and demand matched. Then the grid operators ensure the balancing happens at the correct energy level.

In Australia the generation is dispatched on 5 minutes intervals. Within the 5 minutes, some generators are paid additional for more fine grained frequency control.