DG Running Cost per Unit Calculator
Put a rupee figure on every unit your diesel generator delivers. Enter the fuel you measured at your usual load, the kW delivered over the same run, your fuel price and the maintenance cost per running hour — then the hours it runs in a year, if you want the annual cost.
What this tool estimates
Your DG's running cost per kWh delivered — measured fuel at your fuel price plus maintenance that scales with running hours, divided by the kW delivered — and, if you give annual running hours, the running cost for the year.
What it cannot decide
- What the set burns at a load you have not measured: fuel per unit changes with loading, so measure at the load you run.
- The cost of owning standby — the set, room, panel and financing — which stays out of the per-unit figure on purpose.
- Whether solar or a battery can take over DG hours: that depends on how the plant is designed to run alongside the set.
- Whether the set's condition, fuel quality or maintenance practice is right.
Result
| Step | Value |
|---|
| Fuel price | Fuel use −10% | As measured | Fuel use +10% |
|---|
Standby capital cost — the set, its room and panel, financing — is not in these figures. It is the cost of having backup at all, and spreading it over the few hours a standby set runs would make the per-unit figure meaningless. Compare it separately.
Method version 6 October 2026. A screening estimate, not a design: see the limits below.
How this calculator works — and where it stops
What it calculates
The running cost of a diesel generator per kWh delivered, from the fuel you measured at your load, your fuel price and the maintenance cost that scales with running hours — and, with annual running hours, the running cost for the year.
Inputs
- Measured fuel consumption, litres per hour — litres used over a steady-load run (tank dip or flow meter) ÷ the hours run, at the load the set normally carries.
- Net power delivered over the same run, kW — the set's kWh meter ÷ the same hours. Zero is refused.
- Fuel price, ₹ per litre delivered to site.
- Variable maintenance, ₹ per running hour — lube oil, filters, service visits and any overhaul reserve ÷ running hours. Zero is allowed.
- Running hours a year (optional) — blank means no annual figure, not zero.
Method
- Fuel cost per hour = litres per hour × ₹ per litre.
- Running cost per hour = fuel cost per hour + maintenance per hour.
- Running cost per unit (₹/kWh) = running cost per hour ÷ net kW delivered.
- Fuel per unit = litres per hour ÷ kW, shown with its inverse in kWh per litre for comparison with the maker's figure at the same load.
- For the year: running cost = running cost per hour × running hours; units = kW × hours; fuel = litres per hour × hours.
- Sensitivity: the cost per unit with the fuel price and the measured fuel use each 10% lower and higher — nine cases.
Assumptions
- The measured run represents how the set normally runs. Fuel per unit changes with loading — engine makers publish fuel consumption against percentage load — so a run at one load says nothing about another.
- The kW is the average electrical output over the same period as the fuel measurement.
- Maintenance entered per hour is the part that scales with running. A fixed yearly contract that does not depend on hours belongs with the cost of standby.
- Standby capital cost — the set, room, panel and financing — stays out of the per-unit figure: spread over the few hours a standby set runs, it would make the figure depend on how rarely the set runs.
Limitations
- No universal litres-per-kWh figure is used or offered as a default: a set that has not been measured has no answer here.
- Does not model part-load fuel curves, start-up and cool-down fuel, fuel losses or the tax treatment of fuel.
- Does not compare with grid or solar units. A grid-tied solar plant stops in a grid outage (CEA 2013 connectivity regulations, regulation 11(6)(e)), so it cannot carry the outage load a DG covers unless the plant is designed to run with the DG or with batteries. The DG vs Solar calculator compares daytime running costs.
- Does not assess emission norms or any restriction on running the set.
Worked example
Produced by running this calculator with the inputs below.
Inputs
- Measured fuel 25 litres per hour at the usual load
- Net power delivered 100 kW over the same run
- Fuel price ₹90 per litre
- Variable maintenance ₹250 per running hour
- Running hours 500 a year
Working
- Fuel cost per hour = 25 × ₹90 = ₹2,250.
- Running cost per hour = ₹2,250 + ₹250 = ₹2,500.
- Cost per unit = ₹2,500 ÷ 100 kW = ₹25 per kWh — fuel ₹22.50 and maintenance ₹2.50.
- Fuel per unit = 25 ÷ 100 = 0.25 litres per kWh, or 4 kWh per litre.
- Running cost for the year = ₹2,500 × 500 hours = ₹12.5 lakh, for 50,000 kWh and 12,500 litres.
Result. ₹25 per kWh delivered and ₹12.5 lakh a year in running cost at 500 hours — with the capital cost of the set kept separate.
Sensitivity — what moves the answer
- Fuel dominates: here fuel is ₹22.50 of the ₹25 per kWh, so a 10% change in the fuel price moves the cost per unit by ₹2.25 — to ₹22.75 or ₹27.25.
- Fuel use moves it the same way: 10% more litres per hour for the same output gives ₹27.25 per kWh, and 10% more on both price and use gives ₹29.73.
- Output matters as much as fuel: the same 25 litres per hour delivering 80 kW instead of 100 kW costs ₹31.25 per kWh — which is why fuel must be measured at the load the set actually runs.
How engineers use the result
To put a defensible rupee figure on each DG hour and unit before deciding on load segregation, maintenance, a solar–DG controller or storage — and to compare a set's measured fuel per unit with its maker's figure at the same load.
When a professional design must replace it
Before the figure is used to justify an investment: an engineer should check how the fuel and kWh were measured (instrument, duration, steady load), whether that load is representative of the year, the maintenance cost basis, and — for any solar or battery alternative — whether the plant can actually run alongside the DG.
Sources
- BEE Guide Book 3 (Energy Efficiency in Electrical Utilities), Chapter 9: DG Set System — section 9.4: a two-hour steady-load trial logging fuel (by dip or flow meter) and kWh every 15 minutes, analysed as kWh per litre; engine makers' curves of fuel consumption against loading
- CEA (Technical Standards for Connectivity of the Distributed Generation Resources) Regulations, 2013 (notified 30 Sep 2013) — regulation 11(6)(e): a distributed generation resource must cease to energise the electricity system within two seconds of an unintended island — why grid-tied solar is not backup
- Cost per unit = running cost per hour ÷ kW delivered — definition; no tariff or regulation is applied
Questions people ask before using it
What information do I need before using the DG running cost calculator?
Fuel used over a steady-load run, by tank dip or a fuel flow meter, divided by the hours run; the kWh the set's meter recorded over the same run, divided by the same hours, for the average kW delivered; what you pay per litre of fuel delivered to site; the costs that scale with running hours — lube oil, filters, service visits and any overhaul reserve — divided by hours; and, for the annual figure, the running hours from the hour meter or log book. This is the same measurement BEE's guide book uses to assess a DG set: a two-hour steady-load trial with fuel and kWh logged every fifteen minutes.
Which site conditions could change the cost per unit?
Loading first: engine makers publish fuel consumption against percentage load, and a set run well below its best operating point — idling on a small night load, say — burns more fuel for each unit than the same set loaded near that point. Then the fuel price and quality, the set's condition (injectors, filters, turbocharger), hot or dusty intake air, unbalanced or harmonic-rich loads, and frequent short runs with starts and cool-downs. Measuring at the load you actually run captures most of this; one litres-per-kWh figure applied to every set does not.
What should I send an engineer for a project-specific review?
The DG log book with hour-meter, kWh-meter and fuel-fill entries; fuel bills; maintenance or AMC invoices; the set's datasheet with its fuel-consumption figures at part load; the single-line diagram showing what the DG feeds and where the changeover sits; and recent electricity bills or demand records, so the hours the DG runs can be set against what the grid supplied.
Optional: ask an engineer to look at it
The result above is yours with no form. If you want an engineer to check it against your drawings, schedules or bills, send a request. Nothing is sent until you press the button.
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The work itself
Read before you specify
The terms behind it
Delivered work with this scope
- Full MEPF Package for JMH Prime, Jeewan Mala Hospital — Karol Bagh, New Delhi— Jeewan Mala Hospital
- SBJ Nirmal Rotavator-Parts Distribution Warehouse — Ludhiana— SBJ Nirmal Products (SBJ Forging Pvt. Ltd.)
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