How do power plants “know” the exact amount of energy that is in demand at a current moment by the millions of consumers within its distribution network since they must produce near this amount of energy (either too much or too little energy being pumped into the grid in comparison to the energy demand has negative consequences, if I understand correctly?)
Is there some sort of signaling system that can tell how much power is being drawn at a exact moment or will be drawn one second/minute into the future?
What happens if too much energy is produced at a current moment compared to the demand?
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They don’t produce exact actually…For natural gas powered generators they can ramp up and down quickly and for nuclear generators for example, ramping up and down takes a long time so they normally tend to output similar level of powers throughout the day. For wind farms it is even worse – they can’t really control the wind so they can’t control the amount generated.
Between grids electricity can be bought or sold (each grid is managed by an Independent System Operator), ISOs typically have power forecast models to forecast the consumption but that is not 100% accurate all the time, power trading is actually a serious trading business among some of the largest commodities players…and sometimes if too much power is generated that are not needed, the generators are willing to pay whoever that could consume that electricity. Sometimes when unexpected events happen (natural disasters for example could take down power lines or generators) and power lines become congested whoever owns the capacity to flow electricity to a much needed area could make millions of USD in a day.
Hope that helps.
The grid is all interconnected. The power flowing through the grid is responding, in real time, to the amount of current being drawn or produced by consumers and the power plants. In other words, they know how much power is being drawn by monitoring the electrical load at the generators.
Power or current draw is essentially resistance that the generators are pushing against. Think of a water wheel in a river; if there’s nothing attached to the wheel’s axle, it’ll spin very freely. But if there’s huge machinery attached, it will resist the flow of the current.
So when the power load reduces, the water flows faster. The generators, acting like reverse water wheels, will spin faster. The people at the power plant will then dial back the amount of steam fed to the turbines to slow down the generators, so that they don’t overload the power grid. Thinking back to the river example, that would be like a flood; it would damage or destroy the water wheels by the sheer volume/speed of water.
But the key point is that, within reason, they can monitor it at the generators themselves. So long as the load on the grid changes gradually, they can adjust. In cases like power line breaks or overloads, where there’s a sudden interruption or change in the grid, the generators can be protected by automated cut-offs. In this sense, it’s better to cut the power to the grid rather than risk damage to the generators (again, generators are acting like reverse-water wheels; they are also susceptible to “flooding” damage).
We use an AC system which runs at a specific frequency. This AC is connected to the magnets of the generator at the power plant which makes it rotate at the same frequency. Whenever you start using power in your home the increased current will cause the generator to slow down. However the turbine have a lot of mass so you need to use a lot of energy to reduce its speed. And this cause the frequency of the power grid to slowly go down as the turbine loses energy. The power plant operators notice this drop in frequency and open valves to make the turbines go faster again.
The short version is that you can tell if your network is over/under supplied by the frequency of the power in the network. If your network is oversupplied, the frequency increases as your generators have an easier load and begin to speed up. If your network is undersupplied, your frequency decreases as the load begins to tax your generators.
It gets more complicated as different components are added to the network, but at least from the power plant’s perspective, they can tell if they need to increase or decrease capacity simply by monitoring how hard their generation equipment is working.
They don’t know the exact amount.
The unpredictable sources (wind solar ect) produce their amount,
Nuclear and coal (which can ramp up/down but take hours or more) produce their bit
Gas plants then make up idealy just enough to fill the final gap
I’m practise to avoid brown outs they make some percent safety over this, and the extra is discarded/lost
Power management involves tuning each of these sources up and down to waste as little energy as possible, and use as much wind/nuc as possible to help the environment
They guess when more will be needed based on known events. For example half time in a popular football match is cause to ramp up power generation since everybody will get up to make a cup of tea. At night they increase when everybody starts to turn on the lights to see and decrease when everybody turns them off to go to bed. Changing the amount of power produced takes too long to react in real time.
The load is scheduled on a daily curve based on previous days’ curves. At the scale of a grid, the power usage usually follows a very similar curve every day. At the base of the curve are the ‘base load’ plants – nuclear, big hydro, big coal, and large gas turbine/combined cycle plants. Typically, these like to run at the same rate around the clock.
Then, higher up, you have smaller stuff, like renewables, small to mid sized hydro, and gas-turbine plants which are easy to vary the output of. Smaller plants are good at ‘following load’ – being dispatched to put out more or less power depending on minute-by-minute fluctuations of load. Sometimes, when the load pops above the curve for a couple of hours, ‘peaker’ plants (relatively simple plants that often contain just one gas turbine) can be quickly brought on line and supply the extra demand. Peaker plants are inefficient and therefore not normally turned on as base load plants.
The generation in a grid is nowadays controlled by a balancing authority, also known as an independent system operator. The ISO negotiates power contracts, keeps track of plants that are down for maintenance, and ensures that enough generation is available to meet the needs of the grid during the day.
There is a signaling system that monitors the grid – it’s called, in most contexts, a supervisory control and data acquisition (SCADA) system. Devices at stations called Remote Terminal Units gather data on voltage, current, frequency, etc. and report it to the various operating entities via computer programs known as Energy Management Systems (EMS). They also allow the grid assets to be controlled, such as opening and closing circuit breakers and ramping generators. So, a few guys in Sacramento, a few more in San Francisco and a few in Southern CA can monitor and control the entire CA transmission system.
Power plant doesn’t. System operator does. Each day operator estimates how much energy will be needed tomorrow and plans tomorrow according to that. Asks plants for prices, and builds a portfolio for each hour. Some plants have extra responsibilities called primary and secondary frequency control and they need to respond to commands of system operator. Other plants can spare some production for a different price. This works in both directions, system operator can ask power plants to cut production too.
Operator knows this by monitoring frequency of the system then predicting what will happen in the following minutes.
If a plant doesn’t produce enough, meaning what it promised, or produces more than it supposed to do, system enters into an imbalanced state. This mostly happens with renewables since you don’t really know how much sun or wind you will receive.
There are many ways to overcome this.
I’m a software developer working for a company that helps plants to plan their daily operations and helps with electricity market. My knowledge is not deep so it should make a nice ELI5
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