Fuel is 70–80% of a diesel generator’s lifetime cost — far more than the purchase price. Before you buy, you need to know how many litres per hour your genset will burn at real-world load. This guide gives you a consumption chart from 10 kVA to 2,000 kVA, explains the factors that move the numbers, and shows how to estimate annual fuel spend for your site.
How fuel consumption is calculated
Modern diesel engines consume roughly 0.21–0.26 litres per kWh of electrical output (specific fuel consumption, SFC). The exact figure depends on engine design, speed (1500 rpm units are more efficient than 3000 rpm), load factor and ambient conditions. High-pressure common-rail engines from Perkins, Cummins and MTU sit at the efficient end of that range; smaller air-cooled engines sit at the thirsty end.
The quick estimation formula:
Fuel (L/h) = kW output × SFC (L/kWh)
A 200 kVA (160 kW) genset at 75% load produces 120 kW, so at 0.25 L/kWh it burns about 30 L/h.
Fuel consumption chart by generator size
Typical figures for modern 1500 rpm diesel gensets. Actual consumption varies ±10% by engine brand and condition — always confirm against the engine datasheet.
| Genset size | Prime kW | 50% load (L/h) | 75% load (L/h) | 100% load (L/h) |
|---|---|---|---|---|
| 10 kVA | 8 | 1.3 | 1.8 | 2.4 |
| 20 kVA | 16 | 2.4 | 3.4 | 4.5 |
| 30 kVA | 24 | 3.6 | 5.0 | 6.6 |
| 50 kVA | 40 | 5.8 | 8.2 | 10.9 |
| 100 kVA | 80 | 11.2 | 15.7 | 20.9 |
| 200 kVA | 160 | 21.9 | 30.6 | 40.8 |
| 300 kVA | 240 | 32.5 | 45.4 | 60.4 |
| 500 kVA | 400 | 53.6 | 74.8 | 99.4 |
| 800 kVA | 640 | 85.2 | 118.9 | 158.0 |
| 1,000 kVA | 800 | 106.2 | 148.2 | 196.9 |
| 1,500 kVA | 1,200 | 158.8 | 221.6 | 294.4 |
| 2,000 kVA | 1,600 | 211.4 | 294.9 | 391.7 |
What makes consumption worse
- Low load running. Below 30% load, SFC rises sharply and unburned fuel glazes cylinder walls (wet stacking). Persistent low-load duty can raise per-kWh fuel use by 20–30% and shortens engine life.
- Altitude and heat. Above 1,000 m or 40°C, engines derate and work harder per kW delivered. Expect 1–3% extra consumption per 300 m of altitude.
- Poor maintenance. Clogged air filters, worn injectors and incorrect valve clearance each add 3–7%.
- Fuel quality. High-sulphur or contaminated diesel lowers energy content and fouls injectors.
Worked example: annual fuel cost
A factory runs a 200 kVA genset at 75% load, 8 hours per day, 365 days per year:
- Consumption: 30.6 L/h × 8 h × 365 days = 89,352 litres/year
- At $1.20/litre: $107,220 per year — several times the genset purchase price
This is why load-factor planning matters more than the sticker price. An oversized 500 kVA set doing the same job would idle at 30% load, burn more per kWh, and suffer wet stacking.
Five ways to cut fuel cost
- Right-size the genset so typical load sits at 50–80%. See our generator sizing guide.
- Parallel smaller units instead of one large set — run only the capacity you need. See generator paralleling explained.
- Hybridise with solar + BESS. A PV array plus battery can cut diesel runtime 40–70% on daytime-heavy loads.
- Service on schedule. Air filters, injectors and valve adjustment protect the SFC baseline.
- Monitor load factor with the controller’s logging — chronic low load means the set is oversized.
Econo Solar supplies diesel gensets from 5.5 kVA to 4,000 kVA across eight engine platforms — Perkins (ECP), Cummins (ECC), MTU (ECM) and more — plus the solar and storage hardware to hybridise them. Send us your load profile and we’ll spec the most fuel-efficient configuration.