How the calculation works
The calculator starts from the coincident peak load — not the nameplate sum of every appliance, which is the single most common sizing mistake on Ukrainian farms. Divide peak kW by the typical diesel-genset power factor of 0.8 to get base kVA, then overlay the motor-start surge of the largest motor: ×3.0 for direct-on-line (DOL), ×1.75 for soft-start, or ×1.2 for variable-frequency drive (VFD). Next comes UA-climate derating: −4% per 5°C above 25°C (a Lisostep 32°C summer trims ≈5.6%), −1.5% per 10% RH above 35% (UA summer at 65% RH trims 4.5%), −1% per 100 m above 1,000 m altitude (≈0% anywhere on UA farmland), and a fuel penalty of +5% on natural gas or +12% on biogas. The derated kVA then gets a +25% headroom cushion for future-load expansion and part-load efficiency, and the final value rounds up to the nearest UA-market catalog size: 22/33/45/60/80/100/125/150/165/200/250/350/500 kVA. The default rating class is PRP — ESP is ruled out by the 960 h/yr winter exposure baseline that has held since October 2024, which exceeds the ESP 200 h/yr ceiling by almost 5×.
- 1
Pick a farm archetype
Poltava-A (500 ha + 50 dairy), Dnipro-B (1,500 ha + dryer + pivot), Cherkasy-C (1,000 cows + 5,000 ha), or enter custom values.
- 2
Verify coincident peak
This is the simultaneous peak — not the nameplate sum. Use a diversification factor of 0.4–0.6 for unrelated loads.
- 3
Enter the largest motor-start load
Typical candidates: irrigation pivot end-tower, cold-room compressor, milking vacuum pump, dryer blower. Drives the surge kVA headline.
- 4
Select the motor-start type
DOL is cheapest but surges ×3; soft-start ×1.75; VFD ×1.2. VFDs shave 25–40% off genset size on motor-heavy farms.
- 5
Pick the ISO 8528 class
PRP is the wartime default. ESP is voided by the 960 h/yr exposure. COP only if you run fully off-grid.
- 6
Cross-check the wartime-continuity checklist
168 h fuel autonomy, EPS ≤20 ms, LFP battery, cold-weather kit, 25 m separation, ATS open-transition — mandatory, not optional.
When to use this tool
- Size a backup genset for a 1,500 ha farm with a grain dryer through the 2025-26 winter
- Decide PRP vs ESP for dairy critical-load continuity
- Compare a single 200 kVA unit vs 2× 100 kVA + battery hybrid
- Audit an existing genset for correct sizing (not oversized → wet-stacking)
Limitations
Frequently asked questions
Why PRP and not ESP for wartime?
Why the +25% headroom?
What is wet-stacking and how do I avoid it?
Do I need a tropical radiator?
Sources & references
- 1ISO 8528-1:2018 — Reciprocating internal combustion engine driven alternating current generating sets (performance classes G1–G4, rating classes ESP/PRP/LTP/COP)
- 2Cummins Power Generation — Application Engineering Bulletin AEB-9 (motor-starting, altitude + temperature derating, transient response)
- 3Caterpillar Electric Power — LEBE0005 Generator Set Application Guide (oversize + wet-stacking cylinder-glazing repair schedule)
- 4Ukrenergo — 2025-26 rolling-outage schedule baseline (960 h/yr winter exposure, GSS5 graphic stabilization schedule)
- 5NBU — official USD / EUR reference rates (43.89 UAH/USD, 51.76 UAH/EUR April 2026 baseline — floats daily)
