How electricity systems ensure enough generation, flexibility, storage and network capacity are available to meet demand reliably.
A 100 MW power plant walks into the grid's job interview with a magnificent résumé. The interviewer has one question: will you be there when electricity demand gets ugly? Capacity credit turns that awkward conversation into a reliability number, and explains why solar, wind, batteries, and gas plants cannot be hired by nameplate alone.
Buying enough electricity is not enough to run an electricity system. The grid also needs resources that can react in seconds, hold frequency, support voltage, replace a generator that suddenly disappears, and even help restart the system after a blackout. Those invisible jobs are called ancillary services—and as power systems add batteries, renewables, demand response, and power electronics, they are becoming much more visible.
Power systems traditionally solve tight hours by producing more electricity. Demand response flips the problem around: sometimes it is cheaper, faster, and smarter to temporarily use less—or simply use it later. That small change turns factories, air conditioners, water heaters, EV chargers, and eventually millions of homes into flexibility resources.
A power system can have more installed capacity than peak demand and still face electricity shortages. Resource adequacy asks the question that actually matters: will enough generation, storage, imports, and flexible demand be available when the system needs them most?