In short. A gas power system is a fuel system, engine and heat system working together, not a diesel generator with a different tank. Before selecting a gas genset, confirm that gas reaches the site at the required pressure and flow, that its composition suits the engine, what the operating duty is, and whether the rejected heat can be used. Electrical sizing, protection and transfer remain as demanding as for diesel.
Why gas power is a different engineering problem
With a diesel generator the fuel is a finite liquid stored on site. Autonomy is a tank-sizing exercise and the fuel specification is well defined by IS 1460. With a gas generator the fuel usually arrives through a pipe owned by somebody else, or is produced on site by a biological or industrial process. Its pressure, flow and composition can vary from hour to hour, and the engine is a spark-ignition machine tuned to a narrow fuel envelope. The fuel therefore becomes a primary design input rather than a consumable bought later.
The gas fuel pathways we assess
Each gaseous fuel brings its own supply model, composition and treatment requirement. The pages in this section take each one in turn.
| Fuel | Typical source in India | Main engineering concern | Guide |
|---|---|---|---|
| Pipeline natural gas (PNG) | City gas distribution networks, industrial pipeline connections | Available pressure and flow at the generator inlet, supply continuity during a grid outage | Natural gas generators |
| Biogas | Distillery, dairy, poultry, food-processing and STP digesters | Hydrogen sulphide, moisture and low heating value; sizing to gas yield | Biogas generators |
| Biomethane and CBG | Upgraded biogas, compressed biogas plants | Verifying the upgraded specification against the engine’s natural-gas envelope | Biomethane power |
| LPG and propane | Bulk tanks or cylinder banks | Vaporisation capacity, storage licensing, butane-rich composition | LPG and propane systems |
| Dual fuel (diesel plus gas) | Existing diesel sets with approved conversion kits | Substitution rate versus load, knock limits, fallback to full diesel | Dual-fuel systems |
| Landfill and sewage gas | Municipal landfills, sewage treatment plants | Declining and variable yield, siloxanes, halogenated contaminants | Landfill and sewage gas power |
Four questions that come before any kVA figure
Is the fuel actually available?
Not in principle, but at the generator inlet, at the minimum dynamic pressure the engine’s fuel train needs, at the maximum flow the engine draws at full load, and for the full operating period, including the days when the process that makes the gas is down.
Is the fuel suitable for the engine?
Methane number, heating value, moisture, hydrogen sulphide, siloxanes and heavier hydrocarbons all affect knock margin, deposits, corrosion, oil life and the output the engine can give. The engine manufacturer publishes the acceptable fuel envelope, and a gas analysis is compared against it before the engine is chosen. Nameplate output is only valid on the reference fuel.
What is the duty?
Gas generation economics change completely between emergency standby, intermittent peak operation, prime power and continuous base load. A gas engine’s higher capital cost per kW is recovered through operating hours, so a set that runs 200 hours a year is judged on a different basis from one running 7,000 hours a year.
Can the heat be used?
Roughly 60 percent of the fuel energy leaves a gas engine as heat. Where the site has a simultaneous need for hot water, steam or chilled water, recovering that heat changes the overall energy case, which is the subject of trigeneration as well as CHP. Where there is no thermal demand, the heat is simply rejected and the comparison is made on electrical efficiency alone.
Fuel demand is an energy requirement
Gas consumption figures copied from one project to another are a common source of error because gas volume depends on reference conditions and heating value. The sound way to estimate fuel demand is from the electrical output and the engine’s efficiency.
V̇ = P / (η × LHV)
Here V̇ is the gas flow in standard cubic metres per hour, P is the electrical output in kW converted to MJ/h by multiplying by 3.6, η is the engine-generator electrical efficiency at that load, and LHV is the lower heating value of the gas in MJ/Sm³. Worked example (illustrative): a 500 kW set at 38 percent efficiency needs 500 × 3.6 / 0.38 = 4,737 MJ/h of fuel. On pipeline gas at about 35 MJ/Sm³ that is roughly 135 Sm³/h; on biogas at about 21 MJ/Sm³ it is roughly 225 Sm³/h for the same output. The efficiency and heating value must be confirmed for the actual engine and gas.
The electrical engineering does not change
A gas genset still has to be sized for the connected load and its transients, protected against faults, earthed correctly and transferred or synchronised safely. If anything the electrical work is more demanding, because spark-ignition lean-burn engines generally accept smaller load steps than a turbocharged diesel of the same rating. The usual generator sizing methods apply unchanged, with the added step of checking the manufacturer’s load acceptance curve against the site’s largest motor starts and UPS behaviour. Grid-parallel and multi-unit gas plants also need synchronising, load sharing and utility interface protection, which is covered under integrated power systems.
Screening a gas power project
Before we recommend a gas solution we establish the application, the electrical load and its profile, the thermal load if any, the expected operating hours, the gas source, a gas analysis, the available pressure and flow, the redundancy required, the grid interface and the site’s emissions consents. With those ten items in hand a project can be screened in a few days. Without them any proposal is a guess about the fuel, and the fuel is the one thing a gas project cannot afford to guess.
Common mistakes
- Selecting a gas genset from the electrical load alone. The gas network cannot deliver the flow at full load and the set runs derated or trips on low gas pressure.
- Treating pipeline gas as automatically available during a power cut. Gas supply usually continues, but compressor stations and regulators have their own failure modes, so critical sites need a documented fallback.
- Applying diesel load-step rules to a gas engine. The first large motor start pulls the frequency below the UPS tolerance and the critical load drops out.
- Comparing fuel costs per litre and per cubic metre directly. The comparison must be made per kWh generated, using each engine’s efficiency at the real operating load.
- Ignoring the heat. A site with a boiler running beside a gas genset is paying twice for energy that a CHP arrangement could supply once.
What to send us
Send a one-line description of the application, the electrical load list or a recent maximum demand record, the expected monthly operating hours and the gas source with any analysis or supplier specification you hold. Add the available gas pressure at the site boundary, any thermal loads such as boiler or chiller capacity, and photos of the proposed installation area. If you already own diesel sets, include their nameplate photos so that a dual-fuel route can be considered alongside new gas engines. Use the application engineering enquiry and we will come back with a screening and a list of what remains to be confirmed.
Questions engineers ask
Is a gas generator cheaper to run than a diesel generator?
Often, but not always. Gas engines have a lower fuel cost per kWh when pipeline gas is priced competitively and the set runs long hours, but they cost more per kW to buy, usually give less output per litre of engine displacement and need more frequent spark plug and valve attention. Run the comparison per kWh over the real annual operating hours rather than on fuel price alone.
Can a gas generator be used for emergency standby in India?
Yes, where the gas supply is dependable and the engine’s start and load-acceptance performance meets the site’s requirement. Most critical sites in Hyderabad still keep diesel as the primary standby source because the fuel is stored on site, and use gas for prime or CHP duty. The decision rests on the supply security analysis for the specific gas connection.
Do gas generators need CPCB approval?
Gensets sold in India are type approved against CPCB norms that cover diesel, gas and dual-fuel engines, and the operator still needs consent from the state pollution control board for installation and operation above the exempted sizes. Gas engines generally meet particulate limits easily, but oxides of nitrogen and carbon monoxide must be demonstrated for the certified configuration.
How much gas pressure does a generator need?
It depends entirely on the engine’s fuel train. Some small spark-ignition engines accept low pressure of a few tens of millibar, while larger lean-burn engines with electronic gas admission need higher regulated pressure. Take the figure from the manufacturer’s installation manual and verify that the site regulator can hold it at full flow with other consumers running.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.