I was thinking on the drive home for work that the ever increasing number of electric vehicles will likely mean an increasing demand on the energy infrastructure’s of countries.
But what is actually happening in the electricity grid if supply can’t meet demand? Is it simply the devices furthest away from the generation of power won’t receive current?
Whilst this is ELI5, I also wouldn’t mind a slightly more technical answer. Thanks!
In: 9
Presuming an AC system, as is used for most electric grids:
The first effect is that the frequency drops. Most of this effect comes from physical turbines that produce most of the power, whether in hydroelectric dam, fossil fuel plant, thermal solar-thermal generator, geothermal generator, or nuclear plant. When there is more demand, it increases the electromagnetic resistance in the generator, thus slowing it down. The opposite happens if there is an oversupply of electricity.
Minor fluctuations of frequency happen all the time, though typically not by much. The US grid runs at 60hz with a tolerance of 0.050hz – that is, it is allowed to normally vary from 59.95hz to 60.05hz. This is also corrected over a longer period to ensure it averages out to 60hz.
More major changes can start to cause problems. While a lot of modern technology doesn’t care much at all what frequency it gets as input, such as computers, others do care: motors will run at a different speed, as will many AC clocks.
If the frequency changed too much, various power plants will start to disconnect. Any given powerplant is only designed to operate inside a fairly tight range and will be forced to disconnect to prevent damage if the frequency goes outside that range. Naturally, having a powerplant disconnect when there already is not enough power will worsen the problem, so that is something you really want to avoid – you’ll basically end with a blackout.
To avoid such a cascading failure, parts of the demand grid will get cut off at some point before that by flipping breakers feeding areas. Generally, this will be done by rolling blackouts. That is, the power company will cut off some neighborhoods for a few hours then switch to a different set of neighborhoods. In this way, everybody gets power for some time, minimizing damage, though nobody will be completely happy. Some areas have, optionally or required, high power draw appliances, such as air conditions, able to be controlled by the power company to balance load.
In other cases, the power company will institute a brownout, reducing the voltage, which naturally results in lower power demand. This is not commonly used as it is much more likely to damage modern equipment than a frequency change or complete power outage.
In a DC system, the entire thing is much simpler: the excessive draw will drop voltage across the system, with the effect being stronger the higher your resistance is.
Overall, any predictable usage is very unlikely to cause problems. The real issue comes down to the hard to predict demand, such as heaters and air conditioners. These can draw a lot of power suddenly and can do so with much less predictability than car charging patterns.
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