SolarToolsHow This Tool Works
The Power Factor Calculator helps commercial and industrial customers analyze their power factor, calculate correction capacitor requirements, and estimate savings from PF correction. Power factor is the ratio of real power (kW) to apparent power (kVA) — it measures how efficiently your facility uses electricity. A PF of 1.0 means all power is used productively; 0.75 means 25% is wasted on reactive loads (motors, transformers, ballasts).
Utilities penalize poor power factor because reactive power (kVAR) loads the grid without doing useful work. Many commercial rate schedules include PF penalties or bill on apparent power (kVA) rather than real power (kW). Correcting PF from 0.75 to 0.95 can reduce demand charges 20%+ and eliminate penalties — saving $2,000–$15,000/year for a typical commercial facility.
Correction is achieved by installing capacitors that supply reactive power locally, reducing the reactive load on the grid. The calculator sizes the capacitor bank needed to reach your target PF and estimates the monthly savings from eliminated penalties and reduced demand.
- Real power (kW) — from your power analyzer, equipment nameplate, or utility bill.
- Current power factor — from a power quality analyzer or your utility bill (if they report it).
- Target PF — 0.95 is recommended. Most utilities require 0.90+. Check your rate schedule.
- System voltage — 480V is standard for commercial/industrial. 208V for small commercial.
- PF penalty rate — from your utility rate schedule. Some charge $/kVAR of excess reactive power.
The "capacitor size needed" is the kVAR rating of the correction capacitor bank. Install at the main service panel or at individual large motor loads.
When to Use This Calculator
Real, reactive, and apparent power
Real power (kW) does useful work — turning motors, heating, lighting. Reactive power (kVAR) maintains magnetic fields in motors and transformers but does no useful work. Apparent power (kVA) is the vector sum of both — what the utility must deliver. Power factor = kW ÷ kVA. A facility using 100 kW at PF 0.75 draws 133 kVA — the utility must deliver 33% more capacity than the useful work warrants.
What causes poor power factor
Inductive loads: motors (the biggest cause), transformers, fluorescent lighting ballasts, welding equipment, induction heaters. These loads draw current that's out of phase with voltage, creating reactive power. A facility with many lightly-loaded motors has particularly poor PF — motors draw reactive power even when idling. LED lighting (which has capacitive power supplies) actually improves PF.
How capacitors correct PF
Capacitors supply reactive power locally, so the grid doesn't have to. A 50 kVAR capacitor bank at the service panel supplies the reactive power that motors would otherwise draw from the grid. This reduces the apparent power (kVA) the utility must deliver, improving PF and reducing demand charges. Capacitors can be installed at the main panel (central correction) or at individual motors (distributed correction).
PF penalty structures
Utilities penalize poor PF in three ways: (1) kVAR charge — direct $/kVAR of excess reactive power. (2) kVA billing — demand charge based on apparent power (kVA) instead of real power (kW), so poor PF inflates the demand charge. (3) PF adjustment — demand charge multiplied by a factor based on PF. Check your rate schedule to understand which structure applies.
Sizing the capacitor bank
Capacitor size = current kVAR − target kVAR. For 100 kW at PF 0.75 targeting 0.95: current kVAR = 100 × tan(arccos(0.75)) = 88.2 kVAR. Target kVAR = 100 × tan(arccos(0.95)) = 32.9 kVAR. Capacitor size = 88.2 − 32.9 = 55.3 kVAR. Install a 55 kVAR capacitor bank at the main panel. Cost: $4,000–$8,000 installed. Payback: 1–3 years on penalty elimination.
Over-correction danger
Don't over-correct — a PF above 1.0 (leading) can cause high voltages, resonance, and capacitor damage. Target 0.95–0.98, not 1.0. If you have large intermittent loads (welders, large motors starting), use automatic power factor correction controllers that switch capacitors in and out as needed. Static (fixed) capacitors are fine for steady loads.
Frequently Asked Questions
Power factor (PF) is the ratio of real power (kW) to apparent power (kVA). It measures how efficiently your facility uses electricity. PF 1.0 = all power used productively. PF 0.75 = 25% wasted on reactive loads (motors, transformers). Utilities penalize PF below 0.90-0.95.
Inductive loads: motors (biggest cause), transformers, fluorescent ballasts, welding equipment. These draw current out of phase with voltage, creating reactive power (kVAR). Lightly-loaded motors are particularly bad — they draw reactive power even when idling.
Install correction capacitors. Capacitors supply reactive power locally, reducing the reactive load on the grid. A 55 kVAR capacitor bank at the service panel can improve PF from 0.75 to 0.95 for a 100 kW facility. Cost: $4,000-8,000. Payback: 1-3 years on penalty elimination.
kW (real power) does useful work. kVAR (reactive power) maintains magnetic fields but does no work. kVA (apparent power) is the vector sum: kVA² = kW² + kVAR². Power factor = kW ÷ kVA. The utility must deliver kVA, but you only use kW — poor PF means the utility delivers more than you use.
20-30% on demand charges (if billed on kVA) plus elimination of PF penalties. A 100 kW facility improving PF from 0.75 to 0.95 saves $200-500/month on penalties and $300-1,000/month on demand charges. Total: $6,000-18,000/year. Payback on $5,000 capacitor bank: 4-10 months.
Yes — over-correction above PF 1.0 (leading) causes high voltages, harmonic resonance, and capacitor damage. Target 0.95-0.98, not 1.0. For variable loads, use automatic PF correction controllers that switch capacitors in and out. Fixed capacitors are fine for steady loads.
Further Reading
Deep-dive articles and guides related to this calculator.