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Power is used as it's made
Made and used instantly
If a device is plugged in, the light from its screen was a drop of water in a turbine or a breeze across a windmill microseconds ago. Nobody calls the utility before switching on a computer or phone, so the extra demand arrives with no warning, and production has to rise to match it immediately.
Millions of people connected to the same grid smooth out the swings that any one person creates. Even so, following the load in real time remains a major challenge.
The smarter grid
Software, sensors, and devices that communicate with each other are making the grid smarter. On the supply side, computers take in tremendous amounts of data to help decide how to manage it. On the demand side, a smart grid gives consumers a clearer picture of how much power they use and what it should cost at different times of day or year, since most people have little feel for either.
How do plants sense that demand just rose?
Every generator on the grid spins at a speed tied to the grid's frequency, which is 60 hertz in North America. When demand jumps, the generators carry a heavier load and slow down slightly, so the frequency dips just below 60. Control systems at the plants detect that dip and open steam valves, water gates, or fuel supply to push more power in. Those systems repeat this correction every few seconds, all day.
Why do operators keep spare plants spinning?
Grid operators hold back reserves so that a sudden loss of a large generator doesn't leave the grid short. Some plants run below full output on purpose, which lets them raise production within minutes when it's needed. Other units sit on standby, ready to start on short notice. Capacity that is already connected to the grid and spinning is called spinning reserve.
How does time-of-day pricing show up on a bill?
Older meters recorded a single running total that a meter reader collected once a month, so a utility couldn't tell when anyone used power. Smart meters record usage in intervals, commonly between fifteen minutes and an hour. That interval data makes it possible to charge more during the late afternoon and evening hours, when demand typically peaks in many regions. Those same readings also let customers see their usage hour by hour.
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