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Diesel Tank Sizing and Refuelling Planner
Running out of fuel at 2am is an avoidable problem. This works out the tank size you need for a target runtime and how often someone has to come and fill it.
Diesel Tank Sizing & Refuelling Interval
Work back from a target runtime to the tank size you need, and how often a bowser has to visit.
Usable volume and reserve
Indicative only. Confirm every sizing against the manufacturer's data and a qualified electrical engineer before ordering or installing.
How this calculation works
Two inputs decide it: consumption rate and how long you want to run between fills.
Tank volume = litres per hour × target runtime hours ÷ usable fraction
Usable fraction matters. You can’t run a tank to empty. Drawing the last of it pulls sediment and water off the bottom into the fuel system, and air into the injectors means a stopped engine and a bleed to restart. Plan on using around 80–90% of nominal capacity.
Base tanks versus bulk. Most rental sets have an integral base tank giving roughly 8 to 12 hours at typical load. For 24-hour operation, or to reduce refuelling visits, you need an external bulk tank with a transfer system.
Refuelling interval is an operations question, not just arithmetic. A tank giving exactly 24 hours means refuelling at the same hour every day, including Fridays and public holidays. Size for a comfortable margin — most sites aim for a 48-hour tank so a missed delivery isn’t an outage.
Storage regulations. On-site diesel storage in Abu Dhabi must comply with the UAE Fire and Life Safety Code of Practice enforced by the Abu Dhabi Civil Defence (ADCD), alongside international standards like NFPA 30/37 and local environmental guidelines. You must secure a formal No-Objection Certificate (NOC) and drawing approval from Civil Defence via an approved HAZMAT consultant before bringing or installing any fuel tank on-site. Bunding or secondary containment basins must hold a minimum of 110% of the total primary tank capacity to prevent any environmental spill or leak overflow. Tanks should ideally be located outdoors with strict safety distances from structural buildings. Indoor storage requires specialized fire-rated compartments (such as 2-hour fire-rated rooms) with self-closing doors. Systems must feature emergency thermal shutoffs, proper tank venting, anti-siphon devices, and appropriate fire extinguishers (e.g., ABC or 20-B rated) positioned within 3 to 15 meters of the storage area. Routine daily visual checks, leak detection instrumentation, and periodic structural integrity and water-separation servicing are mandatory to avoid sludge and contamination.
Whatever the threshold, bunding is good practice regardless: a secondary containment holding 110% of the tank’s volume, so a leak doesn’t become a contamination incident.
Fuel degrades. Diesel has a practical storage life of roughly 6–12 months before oxidation and microbial growth become a concern, and heat here accelerates both. For standby sets that rarely run, this matters more than for a site set turning over its tank every few days — treat fuel polishing or rotation as part of the maintenance plan.
Worked example
A 250 kVA set at 60% load, target runtime 48 hours between fills.
Consumption: 250 × 0.8 × 0.6 × 0.27 = 32.4 litres/hour. Fuel for 48 hours: 32.4 × 48 = 1,555 litres. Allowing 85% usable: 1,555 ÷ 0.85 = 1,830 litres nominal.
So a 2,000 litre tank gives comfortably over two days at this load, with margin for a higher load period or a late delivery.
The integral base tank on a set this size might hold 400–500 litres — around 14 hours. That’s a daily refuelling visit. The bulk tank turns that into twice a week.
Over a six-month project, that’s the difference between roughly 180 refuelling visits and about 50.
Common mistakes
Sizing to exactly the target runtime. No margin for higher load or a delayed delivery.
Assuming the full tank is usable. The bottom 10–15% isn’t, safely.
Forgetting weekends and holidays. A 24-hour tank needs someone there every single day.
Skipping bunding. A fuel spill is an environmental incident with real consequences.
Ignoring fuel age on standby sets. Fuel that’s sat for a year may not start the engine you’re relying on.
FAQ
How big a fuel tank do I need for a 250 kVA generator? At 60% load it burns roughly 32 litres an hour. For 48 hours of running, around 2,000 litres nominal allowing for unusable bottom volume.
How long does a generator run on a full tank? Integral base tanks typically give 8–12 hours at normal load. External bulk tanks are sized to whatever runtime you need.
Do I need a permit for a diesel storage tank in the UAE? Above certain volumes, yes — requirements around bunding, separation and permitting are set by Civil Defence and vary with quantity and location. Confirm the current requirement for your emirate before installing bulk storage.
How long can diesel be stored? Roughly 6–12 months before degradation becomes a real concern, and heat shortens that. For standby sets, plan on fuel testing, polishing, or rotation.