The real cost of diesel in an open-pit mine, and what grid power could change

Fuel is one of the biggest running costs in an open-pit mine. Knowing what it costs per hour of digging helps you judge whether electric machines would pay off.

This article works it out step by step for one large excavator, with a source or a stated assumption for every figure, and compares it with doing the same work on grid electricity. Change the inputs to match your mine.

How much diesel do big machines burn?

Caterpillar publishes typical fuel use for its mining machines, based on telematics data from machines at work. The table converts its figures to litres per hour. Caterpillar’s low, medium and high figures assume the machine idles 50%, 30% and 10% of the time.^[1]

Machines also burn fuel while they wait. A 2026 report by the US Lawrence Berkeley National Laboratory cites simulations in which haul trucks queuing at a shovel burned about 0.12 litres a minute, or about 7 litres an hour.^[9]

What diesel costs in 2026

• India. Industrial and bulk buyers pay a different price from motorists, and the gap widened sharply this year. Coal India says industrial diesel at most of its subsidiaries rose from ₹92 a litre in mid-March to ₹142 on 1 April 2026.^[10] In June, diesel cost ₹95.20 a litre at Delhi pumps while bulk sales were priced at ₹134.50, and on 11 June the government told industrial users to buy from bulk sale points rather than pumps.^[2]
• Australia. On 30 October 2026, the wholesale (terminal gate) price of diesel in Perth was 258.8 cents a litre including GST.^[11] Businesses can claim back fuel tax on off-road use: 53.7 cents a litre from August 2026.^[12]
• South Africa. In October 2026, the wholesale price of 0.05% sulphur diesel was about R31.95 a litre in Gauteng.^[13]

Electricity tariffs change too, but differently. In Chhattisgarh, for example, the state regulator sets the tariff for mines once a year, with a monthly fuel and power purchase adjustment on top.^[14]

Where the energy goes

A litre of diesel holds about 10 to 11 kWh of energy.^[15] Only part of it does useful work. A US Department of Energy study of mining cited 45% efficiency for diesel equipment but used 30%, because much of the equipment in use is older.^[16] A simulation study of large diesel-electric haul trucks assumed the engine and generator turn fuel into electricity at about 40% efficiency.^[17] The rest is lost, mostly as heat.

Electric drives waste much less. Under EU rules, most large low-voltage motors must be about 95–97% efficient at full load,^[18] and variable-speed drives are typically 95–97% efficient at full load.^[19] Allowing for cables and transformers on site, we estimate that roughly 85–90% of the electricity bought from the grid ends up as useful work.

So to replace one litre of diesel, an electric machine needs roughly 3.4 to 4.5 kWh from the grid if the diesel engine is 30 to 40% efficient, and about 5 kWh at 45%. We use 3.9 kWh per litre below: about 10 kWh of energy × 35% engine efficiency ÷ 89% electric efficiency. A simulation study of large haul trucks at Sweden’s Aitik mine found a similar ratio: 229 kWh from an electric road replaced 60 litres of diesel, about 3.8 kWh per litre.^[17]

Worked example: a 300-tonne excavator, diesel or grid power

Here is the comparison for a 300-tonne class hydraulic excavator in India. Every input is listed, so you can change any of them.

Two notes on fairness. The diesel prices are Delhi prices including taxes, while the grid cost excludes electricity duty and the monthly fuel and power purchase adjustment. And since 11 June 2026 industrial users have been told to buy at bulk prices, so the pump-price column is a best case for diesel.^[2]

On these assumptions, grid power does an hour of digging for about ₹6,700, against ₹15,300 to ₹21,700 on diesel. That is a saving of about ₹8,700 to ₹15,000 an hour, or ₹5.2 to 9.0 crore a year. Put another way, grid power does the work of one litre of diesel for about ₹41.

Is the scale realistic? Fortescue says each of its electric excavators saves around one million litres of diesel a year.^[20] Our example machine burns about 970,000 litres a year (161 litres × 6,000 hours).

What about CO2? The honest answer

Burning a litre of diesel releases about 2.7 kg of CO2.^[15] Our example excavator therefore emits about 430 kg of CO2 an hour.

Grid electricity is not free of CO2 either. India’s grid averaged 0.727 tonnes of CO2 per megawatt-hour in 2023-24, according to the Central Electricity Authority.^[21] At that rate, the 630 kWh the electric machine needs each hour come with about 460 kg of CO2.

So on India’s average grid today, moving an excavator from diesel to grid power saves money but not CO2: in our example it emits slightly more, about 460 kg against 430 kg an hour. In this example, CO2 savings start once the electricity emits less than about 0.69 tonnes of CO2 per MWh, for example with solar or wind supply, or in countries with low-carbon grids.

Some benefits do not depend on the grid at all: no diesel exhaust at the working face,^[22] less noise and heat, and no engine to service.

Diesel costs that are easy to miss

• Price risk. As 2026 showed, the price a mine pays for diesel can rise by half in a few weeks.^[10]
• Idling. Machines burn fuel while they wait, such as trucks queuing at the shovel.^[9]
• Fuel logistics. Storage tanks, fuel trucks, refuelling time and fuel management all cost money.
• Health and the working environment. Diesel exhaust causes lung cancer, according to IARC.^[22]

So is grid power always cheaper?

Not automatically. At 2026 diesel prices the energy saving is large, but it has to pay for electric machines, the power network and cable handling. A machine that works few hours a year, or a site far from the grid, may not make the case. A busy excavator in a long-life pit with good grid access is far more likely to.

The hardest part is often not the price of electricity but getting it to a machine that moves. That is the cable problem, covered in Trailing cables in open-pit mines. For an overview of all the options, see four ways to power open-pit mining machines.

Where FPCA fits

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