Calculator Inputs
Example Data Table
| Item | Example Value | Unit |
|---|---|---|
| Real Power Demand | 250 | kW |
| Current Power Factor | 0.72 | - |
| Target Power Factor | 0.95 | - |
| Operating Hours Per Month | 300 | hours |
| Demand Charge Rate | 14 | per kVA-month |
| Reactive Penalty Rate | 0.03 | per kVARh |
| Capacitor Cost | 28 | per kVAR |
| Recommended Capacitor Size | 166.73 | kVAR |
| Monthly Gross Savings | 2,606.03 | currency units |
| Simple Payback | 1.80 | months |
These figures are illustrative. Actual tariff structures can include ratchets, penalties, taxes, and seasonal billing adjustments.
Formula Used
1) Apparent Power
S = P / PF
Where S is apparent power in kVA, P is real power in kW, and PF is power factor.
2) Reactive Power
Q = P × tan(cos-1(PF))
Where Q is reactive power in kVAR.
3) Required Capacitor Size
Capacitor kVAR = Qcurrent - Qtarget
This calculator also adds an engineering margin for a recommended bank size.
4) Demand Charge Savings
Demand Savings = (Sbefore - Safter) × Demand Charge Rate
5) Reactive Penalty Savings
Reactive Penalty Avoided = (Qbefore - Qafter) × Hours × Penalty Rate
This assumes the utility bills excess reactive energy above the target condition.
6) Payback and ROI
Payback = Installed Cost / Monthly Net Savings
ROI = Net Annual Savings / Installed Cost × 100
How to Use This Calculator
- Enter the real demand in kW for the load or facility.
- Provide the present power factor and your correction target.
- Enter average operating hours per month.
- Fill in the demand charge rate billed per kVA-month.
- Enter the reactive penalty rate charged per kVARh, if applicable.
- Add expected capacitor bank cost per kVAR.
- Set maintenance and engineering margin values.
- Press the calculate button to show results above the form.
- Use the CSV or PDF buttons to export the report.
Frequently Asked Questions
1) What is power factor cost?
Power factor cost is the extra billing burden caused by poor power factor. It usually appears as higher kVA demand charges, reactive energy penalties, or both.
2) Why does a low power factor increase electrical bills?
A low power factor raises apparent power for the same useful kW. Utilities may bill that higher kVA demand or penalize excess reactive energy because it burdens the network.
3) What does the target power factor mean?
The target power factor is the corrected operating point you want to reach. Many sites aim for 0.95 or better, depending on tariff rules and system design.
4) How is the capacitor bank size estimated?
The calculator finds reactive power at the current and target power factors. The difference becomes the base capacitor requirement, then an optional engineering margin is added.
5) Does correcting power factor always reduce kWh usage?
Not necessarily. This calculator mainly estimates billing reductions from demand and reactive penalties. Real energy savings depend on system losses, cable loading, and equipment conditions.
6) What tariff assumption does this calculator use?
It assumes two common billing components: a demand charge based on kVA and a reactive penalty based on avoided excess kVARh. Your utility bill may use a different structure.
7) What is considered a good payback period?
Many facilities view one to three years as attractive, though some corrections pay back much faster. The right threshold depends on project risk, utility rates, and capital policy.
8) When should an engineer review the result?
An engineer should review results when loads are highly variable, harmonics are present, detuned filters may be needed, or utility rules include seasonal and ratchet billing details.