Electric vs diesel compressors: running cost, power and starting

What counts as an electric-driven compressor

An electric-driven compressor uses an electric motor instead of a diesel engine to turn the airend. On sites and in plants we see three practical forms:

• Portable or skid electric screw compressors. A complete package on a skid or a towable chassis, with its own starter or drive panel, intended to be moved between work areas or project phases. It needs a cable from the grid, a site substation or a DG set.
• Stationary electric screw compressors. The normal plant-room machine, installed on a plinth and connected to a receiver, dryer and distribution header. Some projects install a stationary unit temporarily in a container or shed for a long job.
• Electric reciprocating (piston) compressors. Smaller workshop and process duties, generally below the flows that portable site work needs.

A diesel-driven portable carries its own prime mover, fuel tank, batteries and cooling for both engine and airend. It is self-contained, which is exactly why it is the default on open sites. An electric package moves the energy problem off the machine and onto the site’s electrical system, so the selection becomes a joint air-and-power decision. “Electric” does not mean battery-powered, and it does not mean the machine can be plugged into any socket or any generator.

For the wider product picture, start with our portable air compressors hub and the diesel portable compressors guide.

Electric vs diesel: how do they compare on site?

The table below compares the two drives on the points that usually decide a site or plant requirement. It describes typical behaviour; the selected package’s documentation always governs.

Running cost: when does electric actually save money?

For the same delivered air (FAD) at the same pressure, the energy cost depends on specific power (kW per m³/min delivered) and the price of each kWh, whether that kWh comes from the grid or from diesel burned in an engine. A diesel portable converts fuel to shaft power in its own engine. An electric compressor running on grid power avoids that conversion on site entirely, which is why long-duty jobs on grid power usually cost less to run electrically.

The saving shrinks, and can disappear, when the electric compressor runs from a DG set. You then have two conversions (diesel to electricity, electricity to shaft power) and the generator’s own losses at part load. A DG set sized generously for starting may run lightly loaded most of the time, which is an inefficient place for a diesel engine. In that case a diesel portable is often the simpler and more economical answer unless the DG is already on site for other loads.

Work it out from measured or documented numbers rather than assumptions:

1. Establish the required FAD and working pressure at the tools, not the nameplate of a machine you happen to know.
2. Estimate running hours per month and the load pattern (full load, part load, idle).
3. For electric, take the package input power at that duty from its documentation and multiply by hours and your tariff, including demand charges if they apply.
4. For diesel, ask for the fuel consumption at the expected load, not at full load only. Typical litres per hour depend heavily on load.
5. Add servicing: engine servicing on diesel units is a real recurring cost on long hire.
6. Remember pressure: each extra bar costs roughly 7% more power, whichever drive you choose. See working pressure and pressure budget.

Our motor input and electrical measurement worksheet helps you record the electrical side of this comparison.

Site power and DG sizing: the interface that decides the job

The question is not whether electricity exists somewhere on site. It is whether the proposed connection can supply this compressor, at this location, through starting, normal running and changes in other site loads. Check these before you commit:

• Supply type and voltage. Three-phase supply at the motor’s rated voltage and frequency, with voltage held within the motor’s tolerance under load.
• Capacity at the point of connection. Transformer or feeder rating, the other loads already on it, and whether the compressor’s starting current will dip the voltage for everyone else.
• Cable route and size. Long runs to a moving work face cause voltage drop. Cable must be sized for current and length, protected mechanically and routed so vehicles do not cross it unprotected.
• Protection and earthing. Suitable incoming isolation, overload and short-circuit protection, earth-fault protection and a sound earth at the compressor. See compressor electrical starter and protection interfaces.
• Phase sequence. A screw airend must turn the right way. Reversed phase sequence is a classic commissioning mistake after a relocation; most packages have phase-sequence protection, but it must be checked.

Where the compressor will run from a DG set, size the generator for the starting method, not just the motor’s running kW. A direct-on-line start demands a much larger generator than a soft-started or VFD-driven motor, because the alternator must hold voltage while the motor draws its inrush current. Agree the starting method first, then size the DG with the generator supplier. Our team works across Reddy Generators and Reddy Compressors, so we can look at the compressor and the DG together rather than as two separate hire orders. More on this in electrical supply for temporary air packages.

One of our own projects shows the pattern: for a mechanical construction contractor on a large thermal power project in Karnataka, we supplied a 400 cfm electric compressor together with a 160 kVA DG set on hire, delivered and commissioned it, trained the operators and covered preventive and breakdown maintenance. The DG and compressor were planned as one package.

Starting current: star-delta, soft starter or VFD?

An induction motor started direct-on-line typically draws several times its full-load current, commonly in the region of six to eight times, for a few seconds. On a weak site feeder or a generator, that inrush causes a voltage dip that can trip other equipment, or stall the start altogether. Compressor packages therefore use a reduced-current starting method.

A VFD also changes the running economics. Instead of loading and unloading at fixed speed, the motor slows down when demand falls, so part-load power drops closer to the air actually used. That is valuable on plant duty with fluctuating demand, less so on a site job that runs flat out all shift. Drives bring their own needs: clean, cool panel air, harmonic consideration when running from a DG, and competent fault diagnosis. See variable-speed drive rotary screw compressors and VFD diagnostics.

Noise, emissions and working environment

An electric package has no engine, no exhaust and no fuel on board. That gives three practical advantages:

• No exhaust at the point of use. Tunnels, basements, enclosed sheds, food and pharma facilities, and hospital or city-centre works are poor places for diesel exhaust. The emissions of the electricity are produced elsewhere, at the power station or at a DG set you can place away from the work.
• Lower noise. Without the engine, the main noise sources are the airend, the cooling fan and the motor. That helps on night work near housing and in occupied buildings.
• No fuel handling at the machine. No refuelling on site, no fuel theft from the tank and no spill risk at the compressor.

Heat and dust still matter. In an Indian summer, ambient temperatures of 40–45 °C are common, and above 45 °C on open sites in Telangana and Andhra Pradesh. An electric package needs clear cooling-air paths, clean coolers and a ventilated panel; VFD and soft-starter electronics are often the first parts to complain when a canopy sits in direct sun with blocked louvres. Normal oil-injected screw discharge temperature is about 75–95 °C; a package that trends above that needs its coolers and ventilation checked before the high-temperature shutdown trips it.

When does electric win, and when should you stay with diesel?

Electric is usually the stronger choice when:

• the compressor will sit in one place, or move rarely, for weeks or months;
• a stable three-phase supply with enough capacity is within a sensible cable distance;
• exhaust, noise or fire risk at the work area is a concern;
• the job is plant standby or a planned shutdown where the plant’s own electrical supply is available;
• demand fluctuates and a VFD package can follow it.

Diesel is usually the stronger choice when:

• there is no grid power, or the supply cannot accept the compressor’s starting load;
• the machine moves along a pipeline, road, canal or drilling programme;
• the job is short and mobilisation speed matters more than running cost;
• the duty is high-pressure drilling or blasting in remote areas;
• a DG set would have to be brought in only for the compressor.

Mixed answers are common. A project may run an electric unit as the base load near the site substation and a diesel portable at the moving work face. Our diesel or electric rental air page covers that rental decision in detail.

What we check before supplying an electric package

1. Air duty: FAD and pressure at the tools, simultaneous use, hours and demand pattern.
2. Air quality: whether aftercooling, moisture separation, a dryer or filtration is needed downstream.
3. Supply: voltage, capacity, distance, protection and earthing at the connection point.
4. Starting method and, if a DG is involved, generator size for that starting method.
5. Placement: ventilation, sun and dust exposure, access for service, cable protection.
6. Commissioning: phase sequence, rotation, protection settings, trial run under load.
7. Service plan: on hire jobs we service every 300 running hours, with oil change and filter checks, and plan relocations so each one is re-commissioned.

How Reddy Compressors helps

Reddy Compressors, based at Tarnaka, Secunderabad, and serving industry since 2002, sells, rents and services electric and diesel compressors from ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and other makes as an independent multi-brand specialist, not an authorised dealer. We have tie-ups with all major and reputed brands. That lets us recommend the drive that suits your site instead of the one a single brand wants to sell.

• Rental: electric and diesel compressors from our own fleet, within 50–2,000 cfm and 2–30 bar, with compressor and DG planned together where needed. See the temporary air engineering centre.
• Sales: new electric stationary and skid packages, brand-new machines for long-term projects, and checked used and refurbished compressors.
• Service: more than 20 service engineers and technicians cover the whole of Telangana and Andhra Pradesh, with starter, VFD and motor diagnosis alongside airend work. Equipment, rentals and spares are supplied across India.
• Spares: identified from the make, model, serial number and nameplate, with fit confirmed before quoting.

What to send us

• Application and the tools or process the air supplies.
• Required airflow (cfm or m³/min) and working pressure (bar or psig).
• Running hours per day and expected duration of the job.
• Available supply: voltage, transformer or DG rating, other loads and cable distance.
• Site location, ambient conditions and any noise or exhaust restrictions.
• Whether you want to rent, buy new or buy used.

Frequently asked questions

Is an electric air compressor cheaper to run than a diesel compressor?

Usually yes, when it runs on grid power for long hours at a steady duty, because the site avoids burning diesel in an engine. The advantage narrows or disappears when the electric compressor must run from a DG set brought in only for it. Compare both options using documented input power, expected fuel consumption at the real load, servicing and your electricity tariff, rather than a general rule.

What size generator do I need to run an electric compressor?

It depends on the motor rating and, above all, on the starting method. A direct-on-line start needs a much larger generator than a star-delta, soft-starter or VFD start, because the alternator must hold voltage during the inrush. Agree the compressor package and its starter first, then size the DG with the generator supplier for that starting current, allowing for other loads on the same set.

Why does my electric compressor trip the supply when it starts?

Common causes are a supply too weak for the starting current, an undersized or very long cable causing voltage drop, a star-delta changeover set too early, or protection settings that are too tight. On generator supply, an undersized DG is a frequent cause. We check supply voltage during the start, the starter timing and settings, cable size and length, and the motor itself.

Can I use an electric portable compressor in a tunnel or enclosed building?

An electric package is generally the better choice for tunnels, basements and enclosed sheds because there is no engine exhaust at the machine and noise is lower. It still needs adequate cooling air and ventilation, a properly protected cable route and correct earthing. Any site-specific safety rules for the tunnel or facility apply to both the compressor and its electrical connection.

Is a VFD compressor worth it for site work?

A VFD pays back where demand varies, because the motor slows down instead of running unloaded at full speed. It also reduces starting current, which helps on weak supplies and generators. On a site job that runs flat out all shift, the running-cost benefit is smaller. The drive needs clean, cool panel air and competent diagnosis, so consider heat and dust on Indian sites.

Do you rent electric compressors as well as diesel?

Yes. Reddy Compressors rents both electric and diesel compressors from its own fleet, within 50–2,000 cfm and 2–30 bar, across Telangana, Andhra Pradesh and other states. Where the site has no suitable supply, we can plan the compressor and a DG set together. Tell us the air duty, hours, supply available and duration, and we will advise which drive suits the job.

Related pages

• Portable air compressors
• Diesel portable compressors
• Diesel or electric rental air
• Electrical supply for temporary air packages
• Variable-speed drive rotary screw compressors
• Stationary vs portable screw compressors