Diesel vs Gas Generators: Which One for Standby, Prime and CHP?

In Short

Diesel and gas generator sets do the same job in different ways. Diesel starts fast, accepts large load steps and carries its fuel on site, while gas suits long running hours, heat recovery and sites with a pipeline supply. The better choice depends on whether the duty is standby, prime or CHP.

Diesel and natural gas generator sets do the same job by different means, and each wins in its own territory. Diesel starts fast, takes big load steps and carries its fuel with it; gas is cheaper to run where the pipeline is there, burns cleaner and suits long running hours and heat recovery. This guide compares them point by point and shows which suits which duty.

Starting and Taking Load

A diesel generator starts and accepts a large block of load within seconds - the reason it remains the standard for emergency and standby power, where the building or the data center must be back on before the UPS batteries run out. Gas engines, especially lean-burn engines built for efficiency, usually need longer to start and accept load in smaller steps; some gas engines are designed for fast start and large steps, but the class as a whole is less forgiving of a sudden full load.

Fuel: Storage Against Supply

Diesel is stored on site: a belly tank, a day tank, a bulk tank for days of autonomy. The set runs whatever happens to the outside world, as long as the tank holds out and the fuel is kept clean. Gas comes through a pipeline, which means unlimited running as long as the pipeline delivers and no tank, refuelling or fuel polishing - but also dependence on a supply that may be curtailed in the same crisis that takes the grid down. Where no pipeline exists, gas can be trucked as compressed or liquefied gas, at a cost.

Running Cost, Emissions and Maintenance

Per kilowatt-hour, pipeline gas is usually cheaper than diesel, and gas engines emit less particulate and, in most designs, less NOx - which makes them the choice for prime power, peak shaving and CHP, where the set runs many hours a year and its heat can be recovered. Diesel sets are cheaper to buy per kW and simpler to maintain at the low running hours of standby duty; for long running, their fuel cost and emissions after-treatment weigh more.

Maintenance intervals differ by engine, but gas engines run long hours and are maintained on a schedule by running hours; standby diesels are maintained by time, because they age while they wait.

Which One for Which Duty

Emergency and standby power for buildings, hospitals and data centers: diesel, for its start and load acceptance and its on-site fuel. Prime power on a weak grid, peak shaving and demand response: gas where a pipeline exists, diesel where it does not. CHP: gas, for its running cost and its recoverable heat. Bridging power while a grid connection waits: gas engines and trucked or pipeline gas are increasingly used. AXON builds containers and enclosures, fuel and exhaust systems and switchgear for both diesel and gas generator sets of any make.

In short

Diesel: fast start, large load steps, fuel stored on site - the standby standard
Gas: cheaper to run, cleaner, unlimited supply by pipeline - prime power and CHP
Gas depends on the pipeline; diesel on the tank and the fuel quality
Long running hours favour gas; low hours favour diesel
Trucked gas serves sites without a pipeline
AXON builds packages for both diesel and gas sets

What to send with an enquiry

Duty: emergency, standby, prime, CHP, bridging
Required power and the running hours per year
Fuel available: diesel only, pipeline gas, trucked gas
Load steps and the transfer time required
Emissions and noise limits of the site
Heat consumer, if heat recovery is considered

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Questions we are often asked

Is a gas generator cheaper to run than diesel?

Usually, where pipeline gas is available; the fuel cost per kWh is lower. For standby duty with few running hours the fuel cost matters less than the purchase price, where diesel is cheaper.

Can a gas generator be used for standby power?

Yes, with the right engine and controls, but most gas engines start slower and accept smaller load steps than diesel. The site's transfer time and load steps decide.

Are gas generators cleaner?

They emit far less particulate and generally less NOx than diesel; many sites still need after-treatment to meet local limits.

What if the gas supply fails?

The set stops. Critical sites either use diesel or keep a fuel backup; some gas engines can switch to an alternative fuel.

Which is better for CHP?

Gas, almost always: long running hours, low fuel cost and clean exhaust heat suit combined heat and power.