How do powerplants adjust to the constant change in the demand of electricity?


I have heard that electricity comes directly from powerplants to our homes. No storage or battery of any kind. If I turn on an extra light, how does the powerplant adjust for such a small change in the demand? Does that mean every other device that is turned on and getting electricity from this powerplant gets a little less energy to compensate for my light?

In: 24

Well there’s infrastructure in between all of that. Yes it starts at a power plant, but there are substations before it reaches the consumers. At the substations, are devices called regulators that react to changes in consumer demand.

Powerplants react to changing demand, they follow a multiple stage plan (depending how much extra power is needed)

If the demand suddenly changes at first the missing/additional power is caught up by the rotational inertia of the generators of the whole electrical grid. They slow down or speed up wich changes the frequency of the grid but compensates the power balance. (Your extra lightbulb would slow all generators in your country by an extremely tiny bit)

Then powerplants are paid to run a control curve to get back to the desired frequency, the steeper it is, the more money they receive for that. That means, if the frequency is too low they will gradually increase power output to speed the generator up again.. Slow coal powerplants aren’t able to do that very steeply (lots of extra power on short demand) but gas powerplants are able to.

If that isn’t enough to restore the grid frequency withing minutes the grid operator calls on the control reserve, powerplants that are paid to stand ready to increase power on demand (so they are already fired up but deliberately only doing half load)

If that reserve looks like it’s going to be exhausted as well the grid operator can phone additional poweplants to power up outside of this planned program, or drop some load (ask industrial consumers to consume less, or in an emergency trigger a partial blackout)

Within the powerplant you can usually temporarily increase power output very easily, just Close/open a valve to push more steam towards the turbine. But longterm changes take a lot longer, heating up a new block from being completely cold takes about 8 hours, so it has to be coordinated properly who will fire up their boilers ahead of time so when the load comes they are ready already.

Well, first of all, power consumption is a well researched topic, and power plants do have [charts]([email protected]/Typical-Weekly-Load-Profiles-by-Season-for-New-York-FERC-Federal-Energy-Regulatory.png) with the expected hourly usage, so that they can ramp up more or fewer generators ahead of time, as necessary.

If they miscalculate, then yeah there will be possible power outages or brown-outs (not quite enough voltage) on the lines.

In terms of physics, the power that you consume translates to a “load” on the generator, i.e. harder or easier to spin that generator to create the electricity. So then it depends on the type of power plant; a hydro-electric plant for example may have to turn on more water flow to be able to still spin the generators as before, whereas coal or nuclear would have to “increase the heat” and steam pressures to spin the generators under more load (resistance to spinning).

If you increase load, the frequency of the grid decreases a bit, and power plants will increase power output to keep the overall grid at the right frequency(within some tolerance). They won’t notice a difference from one light, it will just take some more energy stored in the inertia of the spinning turbines.

Though there are some battery storage facilities in some places that actively react to smooth out short term fluctuations in power usage.

One method of balancing the hour to hour energy needs is **Pumped Storage Hydropower**. When power plants are producing more than is otherwise being consumed the extra electricity is feed to Hydro power schemes which are set up to pump water from downriver back up to the top dam. This pumping up of water is effectively storing energy which can be turned back into electricity again by opening the sluice gates and powering the hydro power turbines. This can be done during hours of peak demand to boost total electricity production.

>Pumped storage hydropower (PSH) is one of the most-common and well-established types of energy storage technologies and currently accounts for 95% of all utility-scale energy storage capacity in the United States. PSH facilities store and generate electricity by moving water between two reservoirs at different elevations. Vital to grid reliability, today, the U.S. pumped storage hydropower fleet includes about 22 gigawatts of electricity-generating capacity and 550 gigawatt-hours of energy storage with facilities in every region of the country.

To address your query on turning on a light. You’ve got constant voltage running into every home but the amperage going into every home can and does vary slightly. If you have an electric burner you should notice that it’ll take longer for your hot plate to heat up and bring a pot of water to the boil during peaks times like 6 to 8 pm versus if you doing the same during a time of low demand like midnight. Devices like phones or TVs or light bulbs draw an absolute negligible amount of power when compared with any heating elements and normally any variance in available amps would not in anyway be noticeable in the operation of these devices.

So you turning on a light means that your sister drying her hair in the room next door and your neighbor busy cooking food are going to take a fraction of millisecond longer to get their tasks done.

Edit add: You can think of it in comparison to water pipes where the voltage is the thickness of the pipes and the amperage is the water pressure.

>Does that mean every other device that is turned on and getting electricity from this powerplant gets a little less energy to compensate for my light?

Initially yes, however there are millions of electrical devices connected to the grid and they switch on and off every second so chances are, at the same time you turn on your light, someone else turns off their light. If for whatever reason you turn on your light and nobody else turns off theirs, then the total resistance on the grid increases which reduces the amount of power that every device on the grid gets. Most devices are able to tolerate a small drop in power so this isn’t really noticeable.

If the drop in power starts getting more noticeable then the grid will ask powerplants to increase output to compensate.

Very simply, every light you switch on increases the physical load that the generator must overcome to maintain the grid’s voltage.

Imagine a simple hand crank generator configured with a couple of switched lightbulbs that can be connected to the circuit independently.

As the power company, your job is to crank over the generator so the circuit produces 12 Volts at all times. With both lightbulbs disconnected, you don’t need much cranking force to make the generator produce 12 Volts. But as soon as you close a switch and connect the first lightbulb, the generator’s electricity has a new path to follow. Electricity flows through the lightbulb, and decreases the circuit’s Voltage.

Your duty to provide 12 Volts to the circuit means you must crank harder so the generator produces sufficent current to make up for the decrease in overall circuit resistance caused by opening an electrical path through the lightbulb. The required increase in current is inversely proportional to the lightbulb’s resistance.

Switch on the second lightbulb, and the force needed to keep everything at 12 Volts goes up again, because even more current must flow to “fill up” the electrical path opened by connecting the lightbulb.

In reality, electrical demand changes constantly. Powerplant generators are governed to maintain voltage. Slight drops in voltage cause the system to respond by applying more force to the generator so it can sustain voltage. Whatever current flows at that voltage represents total grid load.

You can’t consume more electricity than is produced, but you can also not produce more electricity than is consumed.

The power grid works at a large scale, so you turning on/off a light is not going to be significant as at the same time other people are also turning devices on/off.

A power plant of 500MW, might only be producing 450MW, and a slight increase in load can be absorbed by that power plant. As long as the load is within specs of the generator, it will deliver what is requested. The powersource driving the generator (steam, coal, gas) will have to work harder to deliver this extra load.

Compare this with riding your bike at a constant speed on a flat surface. If the road suddenly has a very slight incline, you need to push harder on your pedals, but you are still able to maintain the constant speed.

For larger changes in consumption (day/night), the consumption is actually predicted and the power companies ensure there are enough generators/power plants ready to accomodate the expected load.