The Challenge
A facility's 250 kVA main generator was sized for simultaneous peak load of all equipment (worst case). Actual operating load during grid failures was 50–90 kW — only 20–35% of generator capacity.
What Became Visible
Load factor analysis revealed that the 250 kVA generator operated continuously below 35% nameplate capacity during grid events. Operating at this low load factor causes: incomplete combustion (carbon buildup), poor fuel efficiency (only 28–32 kWh/liter vs 48+ at rated load), and premature engine wear. The generator was burning more fuel, producing more emissions, and aging faster than a properly-loaded unit would.
What Changed
Generator sizing was recalculated based on actual typical peak load (80–90 kW). A 125 kVA generator was identified as appropriate for normal peaks; the 250 kVA unit was reserved only for facility-wide simultaneous peaks (rare, <2% of grid-failure events).
How it worked: The facility installed a 125 kVA second generator alongside the 250 kVA unit. Control logic was updated: use the 125 kVA unit for normal grid failures (80–90 kW load) and automatically bring the 250 kVA unit online only if load exceeds 100 kW. This kept generators operating at 75–90% load factor during normal events, improving efficiency and reducing maintenance stress.
Results
on appropriately-sized unit
vs 28–32 at part load
from optimal load operation
from operating at rated load
Generators sized for worst-case peak and operated at part-load continuously wear out faster and consume more fuel. Matching generator capacity to typical load extends engine life and reduces fuel consumption.
Operational Reality
Most facilities operate their backup generators 20–50% oversized. Operating at part-load reduces efficiency 25–40% and accelerates maintenance intervals.