A 900 kVA set carrying a steady industrial load spends several times as much each month on diesel as the same output would cost on pipeline gas at typical delivered prices (check your own numbers, since fuel pricing moves fast). That gap is why so many plant managers have been handed a conversion quotation.
Converting a diesel generator to gas in Nigeria is a strong decision on the right site and an expensive one on the wrong site. The fuel arithmetic is not what separates the two. What separates them is load factor, distance to a gas main, the mechanical condition of the engine and whether the gas supply is firm enough to build a production plan on.
This article sets out the three routes available, what drives the cost of each, where the payback actually comes from and the conditions that decide whether you should proceed at all.
Three Routes, Not One
Vendors use the word conversion loosely. There are three technically distinct paths and they carry very different capital costs and risks.
Dual fuel retrofit. The diesel engine keeps its compression ignition and its injection system. Gas is introduced into the intake air through a mixer, and a reduced diesel pilot charge continues to ignite the mixture. Substitution rates of 40 to 70 percent of the fuel energy are realistic at steady high load. The engine reverts to 100 percent diesel automatically if gas fails, which is the main attraction. There is little or no derate.
Full spark ignition conversion. The engine becomes an Otto cycle machine. Compression ratio is dropped, usually from around 16:1 to between 10:1 and 12:1, which means new pistons. The injection pump comes off, spark plugs and coils go into adapted heads, and a new ignition controller, throttle body, gas carburettor and knock control system go on. Fuel cost per kWh falls furthest here, but you lose the diesel fallback entirely and you lose rated power.
Replacement with a dedicated gas genset. Often the cheapest honest answer. A purpose built gas engine has correct valve materials, the right piston geometry and factory support behind it. On sets below roughly 500 kVA, or on any engine past its economic life, a new gas genset frequently beats a full conversion on whole-life cost.
If you want the three costed against your measured load profile rather than against a brochure, request a technical proposal and we will scope the assessment.
What Converting a Diesel Generator to Gas in Nigeria Actually Costs
The table below assumes diesel at N1,200 per litre delivered, pipeline gas landed at $8.50 to $10.50 per MMBtu, CNG on a virtual pipeline at $13 to $16 per MMBtu, and an exchange rate near N1,550 to the dollar. Every one of those moves, so treat the table as a structure for your own arithmetic rather than a quotation.
| Route | Fuel cost, NGN per kWh | Power after change | Where it fits |
|---|---|---|---|
| Diesel, unchanged | 320 to 400 | 100% of rating | Baseline, and standby duty |
| Dual fuel retrofit on pipeline gas | 205 to 265 | 95 to 100% | High load factor, gas main within reach |
| Full spark ignition conversion | 130 to 170 | 70 to 85% | Sound engines above 750 kVA on firm gas |
| New dedicated gas genset | 125 to 165 | Rated | Diesel set near end of life |
| Either route on CNG | 195 to 275 | As above | No pipeline within reach, heavy consumption |
| LPG conversion | 285 to 360 | 75 to 88% | Rarely justified on fuel cost alone |
Capex is left off this table on purpose: it moves with engine class, distance to the gas main and whether CNG civils are needed, far more than it moves with the route itself. See our cost guide for the drivers, or request a proposal scoped to your engine and site.
In dollar terms that is roughly $0.21 to $0.26 per kWh on diesel against $0.08 to $0.11 on pipeline gas. The LPG row is worth pausing on. At bulk prices of N1,250 to N1,550 per kilogramme and about 0.23 kg per kWh, LPG lands within 15 percent of diesel. LPG conversions can make sense for supply security or where an installation already exists, but the fuel saving alone will not carry the capital cost.
The kit itself is often the smallest line in a conversion budget. The gas train, metering and pressure reduction skid, the buried spur to the distributor’s main, road crossings, gas detection, enclosure ventilation and the emergency shutdown system together usually exceed the price of the conversion hardware. Spur pipeline cost in a developed industrial area scales directly with distance, road crossings and ground conditions, so distance to the main is often the single factor that decides the project. Request a technical proposal for a figure against your own route.
Where the Payback Really Comes From
Payback is fuel saving per kWh multiplied by annual kilowatt hours, less capital and outage cost. The second term is where most projects live or die, and it follows load factor, not engine size.
Worked example (hypothetical): a plant runs a 900 kVA prime set with a measured average load of 460 kW over 416 running hours a month, on diesel at 0.29 litres per kWh, against about 191,360 kWh a month.
The plant fits a dual fuel retrofit. The vendor’s proposal assumes 65 percent gas substitution. Over a measured 90 day period the achieved monthly average is 46 percent, because the plant runs two lightly loaded night shifts and loses gas pressure twice. The blended fuel saving is still substantial, but well short of what was quoted.
Capital covers the kit and installation, the gas train and metering skid, a spur with a road crossing, and gas detection, ventilation and shutdown work, plus a period of rental hire during commissioning. Weighed against the achieved, not the promised, fuel saving, the retrofit still pays for itself well inside a year, and the plant keeps a diesel fallback on every hour the gas is not there.
Two things that model must include and usually does not. The gas contract carries a minimum daily quantity, so during a planned shutdown the plant pays for gas it never takes. And the achieved substitution rate, not the promised one, is what pays for the project. Ask for a performance guarantee expressed as measured substitution at your load profile, with a retest clause.
Now the opposite case. Worked example (hypothetical): a standby set runs behind a reasonably stable feeder for about 900 hours a year at an average of 175 kW, around 157,500 kWh annually. At that load factor substitution rarely exceeds 35 percent, and the resulting fuel saving is small against the capital needed for a spur, gas train and certification. Payback stretches to several years on an engine that may only have a few years of life left, and the gas train needs certification whether the set runs or not.
A site like that should not convert. The same money spent on generator maintenance, fuel polishing, load bank testing and a properly sized changeover returns more and carries less risk. Below roughly 2,000 running hours a year, conversion economics generally do not close.
Gas Conversion for Nigerian Diesel Generators: The Conditions That Decide It
Is the engine convertible at all? Not every block is. Full spark ignition conversion needs pistons for the lower compression ratio, heads that will accept plug adapters, and valve seat materials that survive without the cooling and lubricating effect of diesel. If the OEM does not support it and no established kit exists for that block, stop there. An engine beyond about 30,000 hours without a planned overhaul should be overhauled first, because a conversion on a tired engine simply converts a diesel problem into a gas problem.
Gas quality, not just gas supply. Methane number, Wobbe index, moisture, H2S and particulate content all govern kit selection and knock margin. Associated gas rich in propane and butane has a low methane number and will knock, forcing ignition retard and derate. Insist on a gas analysis before anyone specifies hardware, and on a supply agreement that guarantees minimum pressure at the fence, not only volume.
Contract firmness. Minimum daily quantity, take-or-pay exposure, the distributor’s own maintenance shutdowns and force majeure terms all belong in the payback model. Licensing and midstream supply conditions sit with the Nigerian Midstream and Downstream Petroleum Regulatory Authority, and the national gas supply picture is set out in the International Energy Agency’s Nigeria profile. Above 1 MW the permit position also changes, which we cover in our note on the captive power permit in Nigeria.
Derate and sizing. A full conversion typically leaves 70 to 85 percent of the former diesel rating, so a 1,000 kW engine becomes a 780 to 850 kW engine. If your peak already sits at 80 percent of the diesel rating, conversion alone will not serve the plant and you need a sizing review before, not after.
Safety scope. A gas installation on a genset is a process safety job, not a mechanical one: double block and bleed, slam shut valve, over and under pressure protection, hydrocarbon detection in the enclosure and the generator hall, forced ventilation at a defined air change rate, hazardous area classification around vents and reliefs, and commissioning by a competent gas engineer. It needs an outage window and specialist personnel on site. It is not a weekend retrofit.
The maintenance regime changes. Spark plugs need attention every 1,000 to 2,000 running hours, coils and leads become consumables, valve lash checks tighten, and the oil moves to a low ash gas engine grade with its own drain interval. Cylinder exhaust temperature deviation becomes your early warning of a misfire, and a converted engine kept on the old diesel schedule will not hold its efficiency. Conversion also generally voids any remaining OEM warranty and must be declared to your insurer, so get both positions in writing before the kit lands.
To have these conditions checked against your actual site before you commit capital, book a plant assessment.
A Third Scenario: When the Numbers Are Unusually Good
Worked example (hypothetical): a plant runs a genuinely continuous load of about 690 kW for roughly 7,200 hours a year, close to 5 GWh, with two 1,250 kVA sets and firm gas available at the fence.
The plant converts the younger of the two engines to full spark ignition, accepting a derate from 1,000 kW to about 800 kW, and keeps the older set on diesel as backup. The fuel saving at that load factor is large, and even with a five week outage window covered by rental cover, the programme pays for itself very quickly.
That result is real, and it is also rare. It requires a continuous load, a sound engine, a spur that is already there and a plant able to release one set for five weeks. During commissioning the plant finds estate pressure dipping below the mixer’s minimum on weekday afternoons, so it retains diesel changeover capability rather than assume gas will always be there.
For a wider comparison of prime movers at this scale, see our piece on gas turbines against diesel generators, and for the baseline you are trying to beat, our breakdown of diesel generator cost per kWh.
Solar PV with storage will shave daytime kilowatt hours and can cut run hours, but it does not replace firm generation for a process load, and array sizing here must allow for harmattan soiling and wet season output. Treat it as a fuel reduction measure alongside conversion, not a substitute for it.
Deciding Without Guessing
Start with 30 days of metered data: kWh at the generator outgoing feeder, litres consumed, running hours and a load profile at 15 minute resolution. That dataset gives you your load factor, your true cost per kWh and a test of whether the substitution rate in any proposal is achievable here.
Then get a written distance and pressure position from the gas distributor covering your estate, a mechanical condition assessment of the engine and a gas analysis. Only then should anyone price a kit. A power plant audit produces all four inputs in one exercise, for a fraction of the cost of a conversion that turns out to be unsuitable.
Frequently Asked Questions
Can any diesel generator be converted to run on gas?
No. Full spark ignition conversion requires lower compression pistons, heads that accept plug adapters and valve materials suited to dry gas combustion, so kit availability for your specific engine family decides the matter. Dual fuel retrofits are more widely applicable because the diesel system remains in place, but even those need an engine in sound mechanical condition. An engine with poor compression, heavy blow-by or a worn turbocharger should be overhauled before any conversion is considered.
How much does it cost to convert a diesel generator to gas in Nigeria?
Cost depends heavily on scope. A dual fuel retrofit needs the gas train, metering and safety systems; a full spark ignition conversion adds pistons, ignition hardware and controls on top. Distance to the gas main is often the largest single variable, since spur pipeline cost scales with kilometres, road crossings and ground conditions. CNG supply adds decompression, storage and civils on top of either route. Firm figures require a site survey, a gas analysis and a distributor connection quotation, which is what a technical proposal is built from.
Will the generator lose power after conversion?
A dual fuel retrofit normally costs little or no rated power. A full spark ignition conversion typically leaves 70 to 85 percent of the previous diesel rating, so a 1,000 kW engine becomes a 780 to 850 kW machine. Low methane number gas reduces that further because the control system retards ignition to protect against knock. Check your peak demand against the derated figure before committing, not afterwards.
What happens when the gas supply fails?
A dual fuel set reverts to 100 percent diesel automatically and keeps running, which is why it suits sites with uncertain supply. A fully converted spark ignition engine stops, so it needs either a retained diesel set, an alternative gas source or an accepted outage. Model the plant cost of that outage before choosing the route, and write minimum pressure as well as minimum volume into the gas supply agreement.