Generator Sizing for Pakistani Industrial Standby 2026 — Genset vs Solar+Battery Hybrid Decision
How do I size a generator for Pakistani industrial backup?
Pakistani industrial generator sizing has 4 steps: (1) Calculate total connected load in kVA (not kW); (2) Apply diversity factor (usually 0.7-0.85 — not all loads run together); (3) Add 25% headroom for motor starting kVA; (4) Round up to nearest standard genset size (50/75/100/125/150/200/250 kVA). Rule of thumb: a 100 kW factory needs ~125-150 kVA genset. But the bigger decision in 2026 is genset vs solar+battery hybrid: at PKR 18-22/unit diesel cost vs solar at Rs. 5-7/unit lifetime, hybrid pays back in 18-30 months for sites with regular 4+ hour outages.
Step-by-step Pakistani genset sizing
Step 1: Total connected load (kVA)
List every backed-up appliance with running kW and assumed PF:
Example: small marble factory - 2× bridge cutter motors 22 kW each × 0.85 PF = 51.8 kVA - 1× edge polisher 15 kW × 0.82 PF = 18.3 kVA - 1× air compressor 37 kW × 0.85 PF = 43.5 kVA - 1× water pump 7.5 kW × 0.80 PF = 9.4 kVA - Lighting + office 10 kW × 0.95 PF = 10.5 kVA - Connected total = 133.5 kVA
Step 2: Diversity factor
Most factories don't run all motors simultaneously. Typical diversity factors:
- Marble factory (sequential cutting + polishing): 0.65-0.75
- Textile mill (continuous operation): 0.80-0.90
- Workshop / fabrication: 0.50-0.70
- Hospital / data centre: 0.85-0.95
- Commercial building: 0.55-0.70
Applied to example: 133.5 × 0.75 = 100.1 kVA actual peak demand
Step 3: Motor starting headroom
The largest motor's starting kVA must be accommodated even when running other loads. For the 37 kW air compressor:
- Direct-on-Line (DOL) starting: 37 × 6 = 222 kVA inrush (will trip genset)
- Star-delta starting: 37 × 2 = 74 kVA inrush (acceptable)
- Soft-starter: 37 × 1.5 = 55 kVA inrush (best)
With star-delta on biggest motor + diversity-adjusted base load: 100 - 37 (excluded as starting) + 74 (starting kVA) = 137 kVA worst-case during start.
Round to next standard size: 150 kVA genset.
Step 4: Pakistani-specific derate adjustments
- Altitude derate: -1% per 100 m above 300 m elevation (irrelevant most plains; -10% in Murree)
- Ambient derate: -3% per 5°C above 40°C. Pakistani summer 45°C = -3% derate
- Humidity derate: -2% in monsoon coastal humidity
- Combined Pakistani summer derate: typically 5-8% off nameplate
For our 150 kVA genset, real summer-derated capacity = ~138 kVA. Still adequate for 137 kVA demand, but margin is tight. Consider 175 kVA for safety.
Genset BoM — 150 kVA Pakistani diesel standby
| Component | Spec | Typical PKR |
|---|---|---|
| Diesel genset 150 kVA | 3-phase 400V, ISO 8528 G3 class | 3,500,000 - 5,000,000 |
| Sound-attenuated canopy | Outdoor IP54, 75 dBA at 7m | Included or +300,000 |
| ATS (Automatic Transfer Switch) | YCQ6 4P 250A motorized | 42,000 |
| Genset controller (DSE / ComAp) | Auto start, mains-fail sensing | Included |
| Genset DB box | 4P MCCB 250A + breakers + RCBO | 35,000 |
| Cabling (genset to MDB) | 95mm² 4-core, 20m run | 85,000 |
| Diesel tank | 500L day tank + 2000L bulk | 150,000 |
| Civil / foundation / exhaust | Concrete pad + exhaust pipe + vent | 120,000 |
| Total genset install | ~PKR 3,950,000 - 5,750,000 |
The 2026 alternative: Solar+Battery Hybrid Backup
For sites with 4+ hours daily outages (very common across Pakistan post-IMF tariff hikes), a solar+battery hybrid often beats diesel on 5-year total cost of ownership:
| Solution (for 100 kW peak factory) | Upfront PKR | Running cost / unit | 5-yr total |
|---|---|---|---|
| Diesel genset only (150 kVA) | 4,500,000 | Rs. 18-22/unit (diesel + maintenance) | ~9-12M assuming 4h daily run |
| Solar 60kWp + 50kWh battery hybrid | 8,500,000-12,000,000 | Rs. 5-7/unit lifetime (panels + battery cycle cost) | ~10-13M (cheaper than diesel after year 3) |
| Solar 30kWp + 25kWh battery + small backup genset 50 kVA | 7,500,000 | Rs. 7-10/unit blended | ~8-10M (BEST risk-adjusted) |
Numbers approximate; depend heavily on outage duration profile, daylight hours, panel-array sizing. Hybrid wins when daytime outage exposure is high (Pakistani 9am-5pm load-shedding common); diesel-only wins for sites with primarily evening/night outages.
Decision tree: which backup option for your Pakistani site?
- Outages <2 hours per day average: UPS only (no genset needed). Save the genset cost.
- Outages 2-6 hours, mostly during daytime: Solar + battery hybrid. Sun and shedding overlap.
- Outages 4+ hours, mostly evening: Diesel genset + small battery for switchover gap. Solar doesn't help when sun's down.
- Outages unpredictable, 8+ hours: Diesel + solar + battery (full hybrid). Diesel sized to 60-70% of peak load; solar covers daytime running.
- Critical site (hospital / data centre): Diesel genset MANDATORY (regulation) + UPS + ideally solar for fuel-cost reduction.
ATS sizing rule for genset switchover
Automatic Transfer Switch sized to 1.25× of full-load amps at genset capacity:
- 150 kVA / 400V LL × √3 = 217A full-load. ATS = 1.25 × 217 = 271A → use 300A 4P ATS
- 100 kVA / 400V = 144A FLA → 180A 4P ATS (round to standard 200A)
- 200 kVA / 400V = 289A FLA → 360A 4P ATS (round to 400A)
CNC YCQ6 4P 250A typical for 150 kVA, YCQ6 4P 400A for 200-250 kVA gensets.
Common Pakistani genset installation mistakes
- Under-sized for motor starts — diesel genset can be over-loaded for 2-3 seconds during DOL start. Multiple motor DOL starts together = genset stalls.
- Wrong fuel quality — Pakistani diesel sometimes high-sulphur; ensure genset has fuel filter capable of <10 ppm; use Euro-VI compliant diesel where possible.
- Inadequate exhaust ventilation — diesel exhaust + heat in confined space damages alternator insulation; provide 2× cooling air flow.
- Tank sized for 4 hours not 24 hours — load-shedding often extends; 500L day tank gives ~24h at 50% load.
- Skipping the ATS — manual changeover is OK for tiny sites; >10 kVA needs ATS for personnel safety + auto restart.
- Genset earthing skipped — must have separate earth electrode for genset neutral, bonded to main earth bar at a single point only.
Related
3-Source Changeover Wiring (Grid + Solar + Gen) · Marble Factory Switchgear BoM · YCQ6 ATS family