Power Factor (PF) = kW / kVA -- the ratio of useful power to total power drawn from the grid. After solar installation, grid kW drops but kVar (reactive power from motors) stays the same, causing PF to drop. When PF falls below 0.85, PEA/MEA charges 56.07 THB/kVar penalty. Fixable with 4 solutions, from rewiring (5,000 THB) to APFC upgrade (200,000 THB). CapSolar includes free PF assessment in every factory proposal.
Why Factory Power Factor Drops After Solar Installation
A factory with PF 0.92 before installing 500 kW solar may see it drop to 0.78 afterward. Solar reduces real power (kW) from the grid but does nothing about reactive power (kVar) that motors and compressors still consume.
PF = kW / sqrt(kW^2 + kVar^2). When kW drops (solar covers part of it) but kVar stays the same, PF decreases.
Grid kW = 500, kVar = 242, PF = 0.90
Grid kW = 200, kVar = 242, PF = 0.64
Most solar installers do not mention this in their proposals because it is not a typical EPC contract responsibility. But the factory will see kVar charges on the first electricity bill after commissioning.
Solar installers rarely mention PF impact in their proposals -- if they did, they would have to propose a fix, increasing the project cost.
Unexpected kVar penalties eat into solar electricity savings, slowing down ROI.
See full factory electricity cost breakdownPower Factor Basics -- What You Need to Know
Water pipe analogy: kW = useful water flow, kVar = pipe vibration (not useful but consumes pressure), kVA = total water pressure. PF = useful flow / total pressure. Higher PF (closer to 1.0) = more efficient.
Real Power (kW)
Power that actually does work -- runs motors, heats, lights. This is what you pay per kWh on your bill.
Reactive Power (kVar)
Does not do useful work, but is needed by motors, compressors, and transformers to create magnetic fields. This is what lowers PF.
What Creates Reactive Power (kVar)
Induction motors, compressors, transformers, lighting ballasts, and VFDs (Variable Frequency Drives) all draw kVar from the grid.
Reactive power congests transmission lines, increases current in cables, and causes transformer heating. That is why utilities penalize low PF.
| Load Type | Typical PF |
|---|---|
| Compressor room | 0.75-0.85 |
| Injection molding | 0.70-0.80 |
| Induction furnace | 0.60-0.75 |
| Conveyor belt | 0.80-0.90 |
| HVAC | 0.80-0.90 |
| LED lighting | 0.95-0.99 |
| Resistive heating | ~1.0 |
PEA/MEA kVar Penalty Rates -- Thresholds and Calculation
PF below 0.85 triggers kVar penalty charges.
56.07 THB/kVar (PEA and MEA use the identical rate).
Penalty triggers when reactive power (kVar) exceeds 61.97% of active power (kW), measured as 15-minute average.
Applies to Type 3 (medium), Type 4 (large), and Types 5-7 factories.
kVar fractions < 0.5 round down, >= 0.5 round up.
Worked Example: 500 kW Factory + 300 kW Solar
Grid kW = 500, kVar = 242 (PF = 0.90) Ratio = 242/500 = 48.4% < 61.97% NO penalty
Grid kW = 200, kVar = 242 (still the same!) PF = 200 / sqrt(200^2 + 242^2) = 0.64 Ratio = 242/200 = 121% > 61.97% PENALTY APPLIES!
Excess kVar = 242 - (200 x 0.6197) = 118 kVarMonthly penalty = 118 x 56.07 = 6,616 THB/monthAnnual penalty = 79,394 THB/yearThis penalty eats directly into your solar electricity savings!
Source: PEA/MEA/ERC 2026
How Solar Affects Your Capacitor Bank
Problem 1: CT Confusion
If solar connects after the cap bank CT, the controller misreads bidirectional current, causing incorrect capacitor switching that can damage capacitors.
Problem 2: Over-compensation
Cap bank may push PF into leading territory (capacitive), causing voltage rise and equipment stress.
Problem 3: Resonance Risk
Cap bank + solar inverter harmonics may create resonance, causing capacitor swelling, overheating, or explosion.
Capacitor bank explosion risk if resonance frequency matches inverter harmonics.
4 Solutions for Power Factor Problems After Solar
Reconnect Solar Before Cap Bank CT
Move solar inverter upstream of the cap bank CT. Cheapest fix: rewiring only, no new equipment needed.
Upgrade to APFC Controller
Replace fixed-step cap bank with Automatic Power Factor Controller (APFC) that handles bidirectional power flow.
Solar Inverter Reactive Power Compensation
Modern inverters (Huawei SUN2000, SMA Sunny Tripower, Sungrow, GoodWe) have Q(P), Constant Q, PF(P), and Q@Night modes for reactive power compensation.
Install Detuned Reactor + Capacitor Bank
Use detuned reactor (7% or 14% tuning factor) with cap bank to prevent harmonic resonance.
Comparing All 4 Solutions
| Solution | Cost (THB) | Complexity | Best For |
|---|---|---|---|
| Reconnect Solar Before Cap Bank CT | 5,000-30,000 THB | Low | Existing good cap bank, just needs reconnection |
| Upgrade to APFC Controller | 50,000-200,000 THB | Medium | Old fixed-step cap bank |
| Solar Inverter Reactive Power Compensation | Trade-off: 5-10% loss in real power (kW) capacity. No additional hardware needed. | Low | New installations designed for it from the start |
| Install Detuned Reactor + Capacitor Bank | 30,000-100,000 THB | Medium | Factories with heavy harmonic loads (VFDs, inverters) |
How to Check If Your Factory Has a PF Problem
Check your electricity bill for kVar charges.
Read PF meter at main distribution panel (MDB).
Check solar monitoring system (some inverters report site PF).
Install power quality analyzer for 7-day recording (rental 5,000-15,000 THB).
Red Flags
Capacitor Bank Sizing Guide
Required kVar = kW x (tan(arccos(current PF)) - tan(arccos(target PF)))Example: 500 kW factory, PF 0.78 to 0.95
kVar = 500 x (tan(arccos(0.78)) - tan(arccos(0.95))) = 500 x (0.802 - 0.329) = 237 kVar Select 250 kVar bank (nearest standard size)
Important: Size based on MINIMUM grid kW during peak solar, not peak demand.
Use APFC with small steps (12.5 kVar) for variable solar generation.
Add 10-15% safety margin above calculated value.
Recommended Brands
Schneider (Varplus), ABB, Epcos (TDK), Circutor, Ducati Energia
Prevention During Solar Design Phase
1. Record current PF and kVar readings for 30 days.
2. Note cap bank location, type, CT position, step sizes.
3. Specify solar inverter reactive power capability in EPC tender.
4. Define solar connection point relative to cap bank CT in SLD.
5. Include PF guarantee clause: "PF shall not drop below 0.85 at any grid import level."
5 critical questions to ask your EPC provider about PF management
Real Cost Impact -- PF Penalty vs Solar Savings
| Factory Size | Solar kW | PF Before | PF After | Annual Penalty | Fix Cost | Payback |
|---|---|---|---|---|---|---|
| 300 kW | 200 kW | 0.90 | 0.72 | ~65,000 | 50K-100K | 9-18 months |
| 500 kW | 300 kW | 0.90 | 0.64 | ~79,394 | 80K-150K | 12-22 months |
| 1,000 kW | 600 kW | 0.88 | 0.68 | ~145,000 | 100K-200K | 8-17 months |
Typically 3-8% of annual solar savings lost if PF is left uncorrected.
Most PF solutions pay back within 12-24 months.
Think of it as protecting your solar investment returns.
Fix cost is one-time. Penalty is every month. Fix pays for itself within 1-2 years.
Related Articles
CapSolar Includes Free PF Assessment in Every Project
No surprise kVar penalties after solar. We plan PF prevention from the design phase.