In short. A natural gas generator can only be as reliable as its gas supply. Before choosing a set, confirm the minimum dynamic pressure and maximum flow at the generator inlet, obtain a gas analysis, fix the duty as standby, prime, base load or CHP, and check the engine’s load acceptance against motor starts and UPS behaviour. In Hyderabad these sets suit long-hour prime and cogeneration duty better than occasional backup.
Start with the gas connection, not the kVA
The first question for a natural gas generator project is whether the fuel infrastructure can support the electrical duty continuously and predictably. A nominal connection to a city gas distribution network tells you that gas exists on the property. It does not tell you the pressure that will remain at the generator’s fuel train when the engine is drawing full flow and the kitchen, boiler or process burners are running at the same time. The gas chain runs from the distribution main through the utility’s meter and regulator, through site piping to a secondary regulator and filter, through the engine’s own gas train with its double block and bleed valves, and into the mixer or gas admission valves. Pressure is lost at every stage.
The variables we ask the gas supplier and the customer to confirm are the delivery pressure at the meter outlet, the minimum pressure guaranteed under contract, the maximum pressure the site regulator can see, the flow available in standard cubic metres per hour at that minimum pressure, the gas composition and heating value, and the supplier’s record of interruptions. Piped natural gas in India is typically methane-rich with a lower heating value in the region of 34 to 38 MJ/Sm³, but the figure must come from the supplier’s specification for the network in question.
Sizing the fuel supply to the engine
Engine fuel demand is best worked out from output and efficiency rather than from a figure copied from another installation.
Gas flow (Sm³/h) = P (kW) × 3.6 / (η × LHV)
P is the electrical output, η is the electrical efficiency of the engine-generator at that output expressed as a decimal, and LHV is the lower heating value in MJ/Sm³. Worked example (illustrative): a 250 kW set running at 200 kW with an efficiency of 36 percent at that load consumes 200 × 3.6 / (0.36 × 35) = about 57 Sm³/h. The site regulator and pipework must deliver that flow while holding the inlet pressure the manufacturer specifies, with other consumers on. Pipe sizing for gas at low pressure is sensitive to length and fittings, so a long run from the meter to a generator at the back of the plot often needs a larger bore than the connection itself.
Duty decides whether gas makes sense
| Duty | Typical annual hours | What matters most | Fit for natural gas |
|---|---|---|---|
| Emergency standby | Under 500 | Start reliability, load acceptance, fuel security during a grid event | Possible where supply is proven; diesel usually retained for critical loads |
| Prime power | 2,000 to 6,000 | Fuel cost per kWh, maintenance intervals, derating in summer | Strong where gas is priced competitively |
| Base load | 7,000 and above | Efficiency at rated load, overhaul planning, N+1 redundancy | Strong; multi-unit plants are usual |
| CHP | 4,000 and above | Simultaneous heat demand, heat recovery integration | Strongest overall energy case |
Transient performance is different
A lean-burn spark-ignition gas engine controls power by throttling air and fuel together, and it must avoid knock and misfire across the load range. It therefore accepts a sudden load step less willingly than a turbocharged diesel of the same rating. Where a diesel may take a 50 to 100 percent step in one block depending on its rating class, many gas engines are limited to steps of 20 to 40 percent at a time, with recovery periods between steps. The exact capability is published by the manufacturer as a load acceptance curve and varies widely between designs, so the figures above are only an indication of the gap.
This matters where the site has large direct-on-line motors, compressors, chillers or a UPS whose rectifier draws a block load on transfer. The screening method in transient response should be applied with the gas engine’s own data, and sites with a heavy UPS share should read UPS and non-linear loads before fixing the rating. Where load steps are unavoidable, a short battery buffer, staged ATS transfer or a larger engine are the usual answers.
Fuel security during an outage
Gas distribution networks are pressurised by compressors that themselves need electricity, and regulators, odorisation units and SCADA systems depend on power or batteries. In practice piped gas in Indian cities usually continues through local electrical outages because the compressor stations have their own backup and the pipeline holds line pack, but a wider infrastructure event or a pipeline maintenance shutdown can remove both utilities at once. For a hospital, data centre or continuous process this is a resilience dependency to be assessed, not an advantage to be assumed. Options include retaining diesel capacity for the critical load, specifying a dual-fuel set that falls back to diesel, or holding LPG as a secondary gaseous fuel where the engine is approved for it.
Comparing gas and diesel economics honestly
A fair comparison includes the delivered fuel cost per kWh at the real operating load, the capital and installation cost including the gas train and pipework, maintenance cost per hour including spark plugs, valve adjustment and oil changes, the value of recovered heat if the site can use it, the cost of emissions compliance for each option, and the cost of downtime risk from each fuel’s supply. Natural gas is not always cheaper than diesel per kWh, because the engine is less efficient at part load and gas tariffs for industrial consumers vary between networks. The comparison should be built from quotations and the gas contract, not from a general statement.
Common mistakes
- Sizing the set to the load and discovering afterwards that the network can only supply a fraction of the flow. The set is derated or a costly connection upgrade follows.
- Assuming the gas engine will take the same block load as the diesel it replaces. The first chiller start trips the set on underfrequency.
- Routing gas pipework in undersized bore over a long distance. Inlet pressure collapses at full load and the engine hunts or shuts down on low gas pressure.
- Comparing fuel on price per unit instead of cost per kWh generated. The business case looks better than the operating bills later prove.
What to send us
Send your electrical load list with the largest motor ratings and starting methods, the expected monthly operating hours, and the gas supplier’s connection letter or bill showing delivery pressure and sanctioned flow. Add a gas analysis if you have one, photographs of the meter and regulator installation, a sketch of the pipe route to the proposed generator location, and details of any UPS or thermal loads. Submit these through the application engineering enquiry and we will screen the supply against candidate engine ratings and advise what must be confirmed with the gas company.
Questions engineers ask
How much natural gas does a generator consume per kWh?
At or near rated load a modern gas engine-generator converts 35 to 42 percent of the fuel energy to electricity, which works out to roughly 0.25 to 0.30 Sm³ per kWh on pipeline gas of about 35 MJ/Sm³. At half load the efficiency falls and consumption per kWh rises. Use the manufacturer’s part-load fuel curve for the engine under consideration.
Can a natural gas generator start as quickly as a diesel?
Starting time is similar, typically 10 to 15 seconds to reach rated speed and voltage, but the time to accept full load is longer because the load must be applied in steps. Where a code or a UPS requires full load within a fixed time, check the engine’s documented load acceptance sequence rather than its start time.
Does summer heat in Hyderabad derate a gas generator?
Yes. Gas engines are sensitive to intake air temperature because of knock margin, and manufacturers publish derating above a reference ambient, often starting between 25 and 40 degrees Celsius depending on the design. At 42 degrees in May a set may lose several percent of its rating, so the rating must be checked at the site’s design ambient and not at the catalogue condition.
What safety equipment does a gas generator room need?
A gas train with filter, regulator, two automatic shut-off valves and a vent, a manual isolation valve outside the room, gas leak detection interlocked to the shut-off valves and ventilation, and purging and ventilation arrangements suited to a lighter-than-air fuel. Enclosures designed for diesel sets must be reviewed before a gas engine is fitted inside them.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.