| What it does |
Follows AGC signals every 4 seconds, absorbing or injecting power to hold grid frequency at 60 Hz |
Provides online capacity for post-contingency response |
Provides offline capacity; must reach full output within 10 minutes |
Provides backup capacity after 10-min reserves have responded |
Covers the gap between forecast supply and real-time demand; no real-time counterpart |
| Cleared in |
Real-time |
Real-time + Day-ahead |
Real-time + Day-ahead |
Real-time + Day-ahead |
Day-ahead only |
| Response time |
4 seconds |
10 minutes |
10 minutes |
30 minutes |
Real-time |
| Max response duration |
Continuous while dispatched |
30 minutes |
Undefined |
— |
| Volume requirement |
System-wide; set daily per hour90–95 MW range, avg 93 MW |
First Contingency Loss (~1,200–1,400 MW) × 115% NPF |
First Contingency Loss × 115% NPF, less TMSR |
≥50% of Second Contingency Loss160 MW Jun–Sep; 180 MW Oct–May |
— |
| 2025 avg price |
$14.12/MW-hr2025 capacity avg |
$1.78/MWhRT avg, all hours |
$1.07/MWhRT avg, all hours |
$0.94/MWhRT avg, all hours |
FER-based$3.3M BESS-side in 2025 |