Power Factor cosφ:
Complete Guide 2026
(€ / TND)
Eliminate STEG/Enedis penalties, unlock bonuses and optimise your ROI: a technical and financial guide for plant managers, energy managers and executives.
⚠️ France ≠ Tunisia: two distinct systems. In France (TURPE 7, 2026), the penalty applies from tanφ > 0.4 (i.e. cosφ < 0.928) and there is no bonus. In Tunisia (STEG), the bonus activates from cosφ ≥ 0.91 and the penalty from cosφ < 0.80. Select your country in the tables below.
Cosφ and tanφ: the two notations you must master
The power factor cosφ is the ratio between active power (real work) and apparent power (what flows through the cables). A cosφ close to 1 indicates an efficient installation. But in France, it is tanφ that serves as the billing reference — confusing the two leads to calculation errors.
- Active power P (kW): converted into mechanical work, heat, light.
- Reactive power Q (kVAR): magnetism of motors and transformers, without useful work.
- Apparent power S (kVA): vector sum: S² = P² + Q².
⚠️ tanφ: the reference measurement in France
Enedis bills based on tanφ = Q / P. The contractual threshold is tanφ > 0.4, which equals cosφ < 0.928 — not 0.92 as sometimes stated. This imprecision can represent several hundred euros in undetected penalties.
🎯 Universal target zone 2026: cosφ between 0.93 and 0.96 (tanφ between 0.36 and 0.29) — no penalty in France and STEG bonus in Tunisia.
P × (tanφcurrent − tanφtarget)
tanφ = 0.40 ↔ cosφ = 0.928 (France threshold)
tanφ = 0.48 ↔ cosφ = 0.900 (STEG bonus threshold)
tanφ = 0.62 ↔ cosφ = 0.850 (STEG penalty threshold)
tanφ = 0.75 ↔ cosφ = 0.800
Two distinct tariff systems: France vs Tunisia
Treating them as a single system is the main source of error in generic guides. The differences involve thresholds, the existence of a bonus, the calculation method and the billing period.
| Criterion | 🇫🇷 France: Enedis HTA (TURPE 7, 2026) | 🇹🇳 Tunisia: STEG green tariff MT (2026) |
|---|---|---|
| Penalty threshold | tanφ > 0.4 ↔ cosφ < 0.928 | cosφ < 0.80 ↔ tanφ > 0.75 |
| Bonus | ❌ Does not exist: only the absence of a penalty | ✅ Reduction on active energy price from cosφ ≥ 0.91 (−0.5%/hundredth) |
| Billing basis | Excess kVARh × TURPE 7 rate (~€0.018–0.021/kVARh — verify) | % on active energy price (cumulative by bands — art. 12 MT contract) |
| Measurement period | Peak hours only: HPH + HCH (~Oct.–Mar., approx. 50% of the time) | All year round, continuous monthly measurement |
| Recommended target value | tanφ ≤ 0.35 (cosφ ≥ 0.94) for safety margin | cosφ ≥ 0.91 for bonus · cosφ ≥ 0.95 for −2.5% on active energy |
| 2026 tariff reference | TURPE 7 (CRE, 2025–2029): enedis.fr | Current STEG tariff order: steg.com.tn |
| Regulatory context | EED III Directive (EU 2023/1791, transposed 2025–2026): reinforced efficiency targets | ANME programme; ISO 50001 labels encouraged |
📌 Important: Rates change regularly. Always consult your contract and the official STEG or Enedis schedules for the exact values applicable to your site. The amounts shown in this guide are indicative and based on public 2025–2026 schedules.
cosφ/tanφ bands and associated penalties
Select your country. Indicative amounts for a reference installation of 500 kVA / active power ~400 kW, operating ~500 h/month.
| Measured tanφ | Equivalent cosφ | Status | Indicative monthly impact (€) | Mechanism |
|---|---|---|---|---|
| tanφ ≤ 0.40 | cosφ ≥ 0.928 | ✅ No penalty | €0 | No reactive energy billing |
| 0.40 < tanφ ≤ 0.50 | 0.894 ≤ cosφ < 0.928 | ⚠️ Light penalty | +€80 to +€260 | Excess kVARh × TURPE 7 rate (HPH/HCH) |
| 0.50 < tanφ ≤ 0.75 | 0.800 ≤ cosφ < 0.894 | 🔻 Moderate penalty | +€300 to +€750 | Excess kVARh × TURPE 7 rate (HPH/HCH) |
| tanφ > 0.75 | cosφ < 0.800 | 🚨 Severe penalty | +€900 to +€1,800 | Very high kVARh volume × TURPE 7 rate |
| Measured cosφ | Equivalent tanφ | Status (STEG MT contract, art. 12) | Effect on active energy price | Indicative example* |
|---|---|---|---|---|
| cosφ ≥ 0.91 | tanφ ≤ 0.46 | Bonus | −0.5% per hundredth above 0.90 cosφ = 0.95 → −2.5% | cosφ = 1.00 → −5% | Reduction on active energy bill |
| 0.80 ≤ cosφ ≤ 0.90 | 0.48 ≤ tanφ ≤ 0.75 | Neutral zone | 0% (reference rate) | No impact on the bill |
| 0.75 ≤ cosφ < 0.80 | 0.75 < tanφ ≤ 0.88 | Light penalty | +0.5% per hundredth between 0.79 and 0.75 (max +2.5%) | cosφ = 0.75: +2.5% on active energy |
| 0.70 ≤ cosφ < 0.75 | 0.88 < tanφ ≤ 1.02 | Moderate penalty | Cumulative: +0.5%/hundredth (0.79–0.75) + 1%/hundredth (0.74–0.70) | cosφ = 0.70: +7.5% on active energy |
| 0.60 ≤ cosφ < 0.70 | 1.02 < tanφ ≤ 1.33 | Severe penalty | Cumulative: up to +22.5% at cosφ = 0.60 | cosφ = 0.60: +22.5% on active energy |
| cosφ < 0.60 | tanφ > 1.33 | Supply refusal | STEG may cut supply (art. VII + specifications Decree No. 64-9) | |
📌 Common objective: cosφ between 0.93 and 0.96 (tanφ between 0.36 and 0.29) guarantees no penalty in France and the STEG bonus (−1.5% to −2.5% on active energy) in Tunisia. STEG MT contract (art. 12): neutral zone 0.80–0.90 · bonus from cosφ ≥ 0.91 at −0.5%/hundredth · cumulative penalty from cosφ < 0.80.
Why does the power factor directly impact your bill?
Reactive energy penalties
In France: excess kVARh (tanφ > 0.4) × TURPE 7 rate (~€0.018–0.021/kVARh) during peak hours. In Tunisia: coefficient on the bill from cosφ < 0.85. A 630 kVA plant at cosφ = 0.75 incurs +2.5% on its active energy STEG bill (cumulative). The penalty applies from cosφ < 0.80 (STEG MT contract, art. 12).
Oversizing of subscribed power
To deliver 400 kW of useful power at cosφ = 0.80, your network must carry 500 kVA — 25% more than at cosφ = 1.00. This can force a higher subscription tier of 10 to 20% on your STEG or Enedis contract.
Joule losses in cables
Losses are proportional to I² × R. At cosφ = 0.80, total current is 25% higher than at cosφ = 1.00 for the same useful power — that's +56% more Joule losses, increased cable heating and reduced transformer lifespan.
How to measure your current cosφ in 2026?
1. Reading your STEG / Enedis bill
In France: locate the "reactive energy" line (HPH/HCH kVARh) and the monthly average tanφ. In Tunisia: check the average cosφ and the penalty/bonus amount. In 2026, Linky Pro meters (France) and STEG smart meters allow kVARh history to be exported for analysis.
2. IoT network analyser (Wattnow)
Continuous measurement of cosφ, tanφ, kVARh and harmonic distortion (THD) — per phase, in real time. Ideal for sizing correction precisely, validating post-installation ROI and producing monthly ESG reports. Accuracy class 0.5S.
3. True RMS clamp meter
Point measurement with cosφ/tanφ function at the main switchboard. Useful for a first diagnosis. Insufficient for precise sizing: cosφ varies considerably depending on motor load and can differ by ±0.10 from the actual monthly billed value.
Correcting your power factor: available solutions
Automatic capacitor bank
Standard solution: a controller measures cosφ/tanφ continuously and switches capacitive steps. Indicative cost: €3,500 to €13,000 (12,000 to 43,000 TND). ROI: 6–18 months. Choose a controller configurable to the country threshold (tanφ = 0.4 for France, cosφ = 0.85–0.92 for Tunisia).
Detuning reactors (anti-harmonic)
Mandatory if voltage THD > 5% or current THD > 15% (variable speed drives, inverters, EV chargers, industrial LEDs). In 2026, the widespread use of VFDs and EV charging makes this filter very often necessary. 7% reactors (standard) or 5.7% (5th harmonic). Extra cost: +15–25%. Standard NF EN 61921.
Individual correction on motors
Capacitor fixed to the terminals of a motor ≥ 30 kW operating at steady state. Cost-effective but inflexible. Beware of oversizing: risk of overvoltage at shutdown or excessive torque at startup. Calculate: Q (kVAR) = P × (tanφcurrent − tanφtarget).
Estimate your return on investment
cosφ Savings Simulator: 2026
Based on actual excess kVARh and TURPE 7 / STEG 2026 rates — not flat-rate estimates.
📈 2026 ballpark figures: A 630 kVA plant (~500 kW active) with cosφ = 0.85 typically saves €3,500–6,000/year in France (Enedis penalties), or 10,000–18,000 TND/year in Tunisia (STEG penalties + bonus). ROI typically between 8 and 16 months.
Real-world cases 2025–2026: Tunisia and France
STEG MT green tariff site, 3-shift production, variable speed drives present.
HTA Enedis green tariff B site, numerous variable speed drives and inverters.
Common questions about power factor
Official resources 2026
Further reading (Wattnow)
Ready to eliminate cosφ penalties from your bills (€ / TND)?
Wattnow continuously measures your cosφ and tanφ, calculates the precise ROI of a correction and supports you from the initial audit to post-installation monitoring in France and Tunisia.
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