The title premise needs correcting before the arithmetic starts
Diesel at ₦1,100 per litre is not the market the retrieved sources describe. A June 2026 conversion guide puts diesel above ₦1,400 per litre in most Nigerian markets and CNG at ₦380 per standard cubic metre. A September 2026 cost review puts petrol above ₦1,300 per litre in Lagos and Abuja, with depot prices between roughly ₦1,266 and ₦1,280.
That matters for a 10-truck operator because payback is linear in the diesel price. Run the model at ₦1,100 and you will understate the saving per litre substituted by roughly a fifth against a ₦1,400 pump. Run it at ₦1,400 and you will overstate it the moment the price falls. The diesel price is an input cell, not a headline.
So this is not a piece that hands you a payback figure. It is the model you run with your own numbers, and the three variables that actually decide whether ten trucks convert or two do.
First: a diesel truck does not convert to CNG. It converts to dual-fuel.
This is the technical fact that resets the whole conversation. A diesel engine uses compression ignition: air is compressed until it is hot enough to ignite injected diesel. CNG’s auto-ignition temperature is far higher than the compression environment provides, so a diesel engine cannot run on CNG alone without rebuilding the combustion system.
What the market sells is a dual-fuel kit. CNG is introduced into the air intake and a reduced quantity of diesel is injected as the pilot fuel that ignites the mixture. The conversion guide cited above states that dual-fuel conversion replaces 30–50% of diesel with CNG, and that when CNG runs out the engine reverts automatically to diesel with no interruption.
Read that last clause carefully. It is the risk mitigant and the ceiling at the same time. Your trucks will never stop needing diesel. The question is what share of each litre you displace, and how often the truck is actually near a station that can refill it.
The three variables that decide payback
For a ten-truck fleet, payback is not one number. It is a function of three things, and they interact.
1. Conversion cost per truck
Published ranges are wide and they are screening figures, not quotations. The June 2026 guide estimates heavy-duty articulated truck conversion at ₦2.5 million to ₦4 million and above. A September 2026 review puts heavy commercial buses and trucks at roughly ₦1 million to ₦1.7 million. A 2022 Guardian report quoted the NARTO president saying conversion cost about ₦5 million per truck at the time, and that no heavy-duty vehicle had been converted by government since the promise was made nearly two years earlier.
Those figures do not reconcile because they are not measuring the same thing: different truck classes, different cylinder configurations, different kit specifications, and four years of exchange-rate movement on largely imported components. Treat every published range as a screening number. Get three written quotes per truck class in your fleet before any capital is committed.
2. Substitution rate actually achieved in service
The kit’s rated substitution is 30–50%. What you achieve depends on route, load, driver behaviour, and whether the truck is on a corridor with reliable gas. A truck that runs the Lagos–Ibadan axis with a station at both ends will hold a high substitution rate. A truck on a thin-coverage route will spend most of its kilometres on diesel and carry the kit as dead weight.
This is the variable most operators get wrong, because they buy the kit and assume the saving. The saving is the substitution rate multiplied by the diesel price multiplied by litres burned. If the rate is 15% because the station is off-route, the payback stretches by a factor of two or three against the brochure case.
3. CNG station density on your actual corridors
The Presidential Initiative on CNG and Electric Vehicles states 90+ CNG refuelling stations and 400+ certified conversion centres nationwide. Ninety-odd stations across a country with roughly 11 million vehicles is good coverage on some corridors and thin elsewhere. The programme has activated a Northern Green Transport Corridor in Kano and is expanding along the Ajaokuta–Kaduna–Kano pipeline axis.
For your fleet, the national total is irrelevant. What matters is the count of stations within a reasonable detour of your regular routes, their uptime, and the queue at the pump. A station that is open but has a two-hour queue at 6am is a different asset from one that does not exist.
A sensitivity table you fill in yourself
The table below is a framework, not a forecast. Every input is operator-supplied. The point is to show how violently payback moves when you change the diesel price and the substitution rate together.
Assume, for illustration only: a truck burning 100 litres of diesel per day, 300 operating days a year, a conversion cost of ₦3 million, and CNG priced at ₦380 per SCM with a diesel-equivalent energy conversion that makes the per-kilometre gas cost roughly a third of the diesel cost at ₦1,400.
| Diesel price (₦/litre) | Substitution 20% | Substitution 35% | Substitution 50% |
|---|---|---|---|
| 1,100 | ~8 months | ~5 months | ~3 months |
| 1,400 | ~7 months | ~4 months | ~3 months |
| 1,700 | ~5 months | ~3 months | ~2 months |
Those figures are arithmetic on stated assumptions, not a claim about your fleet. Change the daily burn to 150 litres and every payback shortens. Change the conversion cost to ₦1.5 million and every payback shortens again. Change the substitution rate to 10% because your route has one station and the whole case collapses.
The table’s real message is the spread. At ₦1,400 diesel and 35% substitution, payback is around 4 months. At ₦1,100 and 20%, it is around 8 months. The difference between a good decision and a bad one is not the kit price. It is the substitution rate you can actually hold.
What the subsidy and financing are worth — and what they are not
The June 2026 guide states a 50% conversion subsidy is offered to commercial transporters, and that CALM Fund financing at 9% is available through the Bank of Industry for fleet operators who cannot afford upfront costs. The Pi-CNG programme page confirms financing from 9% via the CALM Fund and states that conversion typically takes 4–6 hours at certified centres.
Model both as upside, not base case. Subsidy slots are administrative, time-limited, and allocated per centre per cycle. Eligibility rules and current availability must be confirmed directly with Pi-CNG or an accredited centre before you commit capital. A payback that only works with a subsidy you have not been awarded is not a payback. It is a hope.
If the 9% facility is available to you, it changes the capital structure question, not the operating case. At 9%, the financing cost is well below the return on a 4-month payback, so leverage is rational if the substitution rate holds. If the rate does not hold, leverage magnifies the loss.
The execution risks that eat the saving
Four items belong in the budget as separate lines, not as afterthoughts.
Pre-conversion engine diagnostics
A tired engine converts the saving into repair bills. Worn injectors, a leaking manifold, or a failing turbo will run badly on dual-fuel and may void the kit warranty. Budget a diagnostic and any necessary overhaul across all ten units before conversion. This is the line most operators omit and then blame the kit for.
FRSC re-certification
The conversion guide states the vehicle must be inspected and re-certified by the Federal Road Safety Corps after conversion, and describes this as both a legal requirement and insurance protection. Build the inspection time into the rollout schedule. A truck that is converted but not re-certified is not earning.
Insurer notification
Conversion is a material change to the vehicle. Failing to declare it can void a claim. Notify your insurer in writing before the truck returns to service.
Cylinder retest scheduling
Cylinders require periodic inspection and hydrostatic retesting. This is not a fit-and-forget component. Put the retest dates in the fleet maintenance calendar at the point of conversion, not when the first cylinder comes due.
On safety: the documented incidents in the retrieved sources trace back to a cylinder that had been welded and modified and was never approved for CNG service. The risk is concentrated in who converts the truck and with what parts. The Pi-CNG page states that all kits in its network are certified by the Standards Organisation of Nigeria and installed only at accredited centres. Use accredited centres, insist on certified unmodified cylinders with visible markings and test dates, and refuse anything welded or repainted over damage.
The decision rule for ten trucks
Do not convert the fleet. Convert the trucks whose routes have confirmed CNG coverage and whose daily diesel burn is highest. Defer the rest until corridor coverage improves.
Concretely: rank your ten trucks by daily diesel consumption. Overlay the CNG station map on their regular routes. The trucks at the top of the burn ranking that also run CNG-dense corridors are the first cohort. Convert two or three, run them for a quarter, and measure the actual substitution rate and station queue time. That measured rate is worth more than any published range, and it is cheaper to buy the information from three trucks than from ten.
If the measured substitution rate holds at 30% or better and the queue time is tolerable, commit the remainder. If it comes in at 15%, you have learned that for the price of three kits instead of ten, and the deferred trucks have lost nothing.
The diesel price will move again. The model should move with it. Re-run the payback whenever the pump price changes by more than 10%, and treat the conversion decision as a staged option rather than a single capital event.
FAQ
Can a diesel truck run on 100% CNG?
No. Diesel engines use compression ignition and CNG will not reliably auto-ignite in that environment. The conversion is dual-fuel: CNG displaces 30–50% of diesel, and the engine reverts to diesel automatically when CNG runs out.
What diesel price should I use in the payback model?
Your own recent pump price, not a published average and not the ₦1,100 figure in the original title. The retrieved sources put diesel above ₦1,400 per litre in most markets in mid-2026. Re-run the model when the price moves by more than 10%.
Is the 50% commercial subsidy available to my fleet?
Confirm directly with Pi-CNG or an accredited conversion centre. The subsidy is described in vendor and programme material, but eligibility and availability are administrative and time-limited. Model it as upside, not base case.
What is the single biggest risk to the payback?
Substitution rate achieved in service. A fleet that buys kits but runs mostly on diesel because stations are off-route has bought an option, not a saving. Measure the rate on two or three trucks before committing the rest.