Generator Fuel Consumption Calculator

Fuel is usually the largest line in a generator’s running cost — often more than the rental itself on a long project. This estimates consumption by set size and load factor, and puts a dirham figure on it.

How this calculation works

Diesel consumption tracks the real power the engine produces, not the set’s nameplate rating. A useful planning figure for a modern diesel genset is roughly 0.25 to 0.30 litres per kWh produced.

So: litres per hour ≈ kVA × 0.8 (to get kW) × load factor × 0.27

Consumption is roughly proportional to load, but not exactly. There’s a fixed overhead — the engine burns fuel just turning over and driving its own auxiliaries — so specific fuel consumption is worst at low load. A set at 25% load burns considerably more fuel per unit of energy delivered than the same set at 75%. This is one of the strongest arguments against oversizing.

Efficiency generally peaks somewhere around 75–80% load. That’s the band to aim for.

Cost. Multiply litres per hour by running hours and the current diesel price. UAE fuel prices are revised monthly, so this figure moves — the calculator uses the current rate.

What the calculator can’t include but you should budget for: delivery charges for on-site refuelling, tank rental if you need bulk storage, and the labour and downtime of refuelling itself on a set with a small base tank.

Worked example

A 250 kVA generator running a construction site, 10 hours a day, 26 days a month, at around 60% load.

Real power output: 250 × 0.8 × 0.6 = 120 kW. Consumption: 120 × 0.27 = 32.4 litres/hour. Daily: 324 litres. Monthly: 8,424 litres.

At a diesel price of AED 3.00 per litre, that’s roughly AED 25,272 per month in fuel alone.

Now compare against a 400 kVA set doing the same job at 37% load. Because specific consumption worsens at light load — call it 0.31 l/kWh — the same 120 kW costs about 37 l/hr, or AED 28,800 a month. Oversizing by one frame size costs roughly AED 3,500 a month in fuel, before you count the higher rental rate and the maintenance consequences of running lightly loaded.

Common mistakes

Calculating on nameplate rating. A 500 kVA set at 50% load doesn’t burn 500 kVA worth of fuel.

Assuming consumption scales perfectly with load. It doesn’t — light running is disproportionately thirsty.

Forgetting no-load running. Sets left idling between shifts burn fuel and do damage. Shut down or fit an auto start/stop.

Budgeting fuel at the pump price. Site delivery adds to it.

Ignoring fuel in the rent-vs-buy comparison. Over a year, fuel typically dwarfs both rental and depreciation.

FAQ

How much diesel does a 100 kVA generator use per hour? At 75% load, roughly 16 litres per hour. At 50% load, roughly 11–12. Consumption tracks load, not the nameplate rating.

How do I reduce generator fuel consumption? Right-size the set so it runs in the 50–80% band, shut it down rather than idling, keep filters and injectors serviced, and consider a hybrid battery system for sites with long low-load periods.

Why does my generator use more fuel per kWh at low load? Because part of the fuel burn is fixed overhead — the engine and its auxiliaries consume fuel regardless of output. Spread over less useful energy, the cost per kWh rises.

What’s the current diesel price in the UAE? Fuel prices here are reviewed monthly. The calculator uses the current rate; check the official announcement for the month you’re budgeting.