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Diesel · LPG · natural gas · hybrid
Which fuel, and why it matters more than the badge.
The fuel decision affects running cost, storage, maintenance, noise, emissions and how long you can go unattended. It is worth more thought than it usually gets.
The short comparison
| Diesel | LPG | Natural gas | |
|---|---|---|---|
| Storage | Tank on site, bunded | Bulk tank or cylinders | None — piped supply |
| Shelf life | Degrades over months; needs treating and polishing | Indefinite | Not applicable |
| Energy density | Highest — most run time per litre of storage | Lower than diesel | Unlimited while the main holds |
| Emissions | Highest particulates and NOx | Much cleaner than diesel | Cleanest of the three |
| Noise | Loudest | Quieter | Quieter |
| Maintenance | More frequent; oil and filters | Longer intervals, cleaner burn | Longest intervals |
| Resilience | Independent of any network | Independent of any network | Depends on the gas network |
| Best for | Long autonomy, heavy load, remote | Remote sites, standby that sits unused, CHP | Sites with mains gas and regular running |
Diesel
Still the default for good reasons: highest energy density, widest choice of equipment, and the lowest capital cost per kVA. For long autonomy on a remote site, nothing else comes close on run time per litre of storage.
The drawbacks are real though. Fuel degrades — diesel left in a standby tank for two years will not be the fuel you put in, and injector problems follow. It needs treating, testing and occasionally polishing. It is the noisiest and dirtiest option. And on a lightly loaded standby duty it is prone to wet stacking.
LPG
The most underrated option for standby specifically, for one reason: it does not go off. A standby generator might sit unused for a year or more. LPG will be exactly as good then as the day it was delivered, which removes an entire category of problem.
It burns considerably more cleanly than diesel, which means longer service intervals and less to go wrong on infrequent starts. It also suits CHP well. The trade-off is lower energy density, so you need more storage for the same run time, and the equipment costs a little more.
Natural gas
Where a mains gas supply exists, natural gas removes fuel storage, refuelling and degradation from the equation entirely. It is the cleanest and quietest, and for anything running regularly it is usually the cheapest to run.
The resilience caveat
A natural gas generator depends on the gas network. In most electrical outages that is fine — the two networks are independent. But in a major incident, or where gas supply is itself interrupted, your backup power goes with it.
For genuinely critical resilience, on-site fuel storage removes that dependency. Some sites run natural gas as the primary with a diesel or LPG set behind it.
Hybrid — the fourth option
Strictly it is not a fuel, but it belongs in the comparison because it changes every row of that table. Adding battery storage means the engine runs a fraction as often, which reduces fuel use, noise, emissions and servicing regardless of which fuel you choose.
On many sites the right question is not "which fuel" but "how much of this should be battery rather than engine at all". See hybrid conversion.
What we would ask you
- How often will it run? Occasional standby and continuous prime power point at different fuels.
- How long unattended? This sizes the storage and often decides the fuel on its own.
- Is there mains gas? If so, it changes the shortlist immediately.
- Any noise or emissions constraint? Neighbours, planning conditions, or a contractual requirement.
- How easily can a delivery reach you, and what does each visit cost?
- Is there a heat demand? If yes, CHP may change the whole answer.
Not sure which fuel suits?
Tell us how you would use it. The answer usually falls out of the duty rather than the price list.
Ask an engineer