DG Set for a Factory: Capital Cost Drivers and the Running Cost That Matters More

A DG set's purchase price is the smaller part of what it costs a factory over its life. Capital cost moves with kVA rating, prime or standby duty, emission-compliant engine, acoustic enclosure, control panel and installation civil works. Running cost, driven by fuel at the actual loading, maintenance hours and idle runtime, is paid every year and usually decides the real cost of a unit of backup power.

What moves the capital cost of a factory DG set?

We do not quote DG prices; they change with engine makers, copper and steel, and the exact specification. What can be said is which decisions move the number and what to ask the supplier for.

Why does emission and noise compliance appear in the price?

Two national rules sit behind two lines of the quotation. The Ministry of Environment, Forest and Climate Change notified revised emission standards for engines used in generator sets up to 800 kW gross mechanical power through G.S.R. 804(E) of 3 November 2022, referred to as CPCB IV+. The Central Pollution Control Board's system-and-procedure document covers type approval and conformity-of-production testing. Insist on the type-approval certificate for the engine family you are buying, not a general claim of compliance.

Noise is regulated separately. Under the Environment (Protection) Rules, the Central Pollution Control Board's procedure for diesel generator sets up to 1000 kVA sets a limit of 75 dB(A) at 1 m from the enclosure surface for new sets, with an integral acoustic enclosure supplied at the manufacturing stage. For sets not covered by that rule, the enclosure or room treatment must be designed for at least 25 dB(A) insertion loss, or for meeting the ambient noise standard if that is stricter, and the set needs an exhaust muffler with at least 25 dB(A) insertion loss. The State Pollution Control Board regulates these limits. Our note on CPCB IV+ emission norms for DG sets goes further.

How do you work out the running cost of a unit from a DG set?

Running cost per kWh has two parts. The first is fuel: litres burned per kWh at the loading the set actually runs at, multiplied by the price of diesel. The second is maintenance: the cost per running hour of oil, filters, servicing and a share of overhaul, divided by the kWh produced in that hour. Add them and you have a cost per unit that you can compare directly with grid tariffs and with solar.

1. Find the real loading. A set sized for the worst case often runs at a low share of its rating. Fuel consumption per kWh worsens at low loading, so a 500 kVA set that mostly carries 150 kW is costing more per unit than its data sheet at full load suggests.
2. Take the specific fuel consumption at that loading from the manufacturer's curve, not from a rule of thumb.
3. Multiply by the current diesel price for your site, and add the maintenance cost per running hour from the AMC offer.
4. Add idle and test runtime. Weekly test runs and warm-up hours burn fuel without producing useful power.
5. Compare with the alternatives. The same arithmetic for grid power, solar and storage is in our DG running cost versus grid and solar note.

Our DG running cost calculator performs this calculation with your inputs, and the DG sizing calculator helps check the rating against the load. Sizing matters twice: oversizing raises the purchase price and lowers loading, which raises the running cost per unit.

The hours the set runs change which cost matters. A standby set that runs only during outages burns little fuel in a year, so its lifetime cost is dominated by the purchase, the yearly service and the cost of keeping it ready, including test runs and fuel quality management. A set that carries a plant for several hours every day because the grid is unreliable is the opposite: fuel becomes the largest line, and spending more on a correctly sized, efficient set pays back through lower fuel burn. Estimate annual running hours from your outage record before you compare quotations, and ask each supplier to state the assumptions behind its fuel figures.

What approvals and rules add to the cost?

Regulation 34 of the Central Electricity Authority's Safety Regulations, 2023 leaves to each state the capacity above which a generating unit must be inspected by the Electrical Inspector before commissioning. Below it the owner self-certifies, with a report on the prescribed form. Either way, test records, earthing results and protection settings must be ready. Our guide to what gets checked on DG sets lists the points. In Delhi NCR, the Commission for Air Quality Management has issued directions on DG set operation, including during pollution episodes, so check the current direction before assuming a set can run freely when the grid fails.

Where a plant also has solar, the DG must be interlocked so the two do not fight. See solar with DG sets for what goes wrong, and DG versus battery storage if outage hours are few.

How Secured Engineers helps

Secured Engineers designs electrical systems in-house, including DG and transformer layouts, and files CEIG, Fire NOC and DISCOM applications in-house. MEPF and solar can be delivered under one contract, which keeps the DG, solar interlock and LT panel in one design. We work from offices in Noida (Delhi NCR) and Ludhiana, and have delivered 535+ projects across 18+ states, with 89.77% repeat clients. Our transformers and DG sets page describes the scope.

The most useful step before buying is a budget review: send the supplier quotations or BOQ with your load data, and we will check the rating, the scope split and the running-cost assumptions. Message us on WhatsApp, call +91 70099 85817 or ask for a free proposal with the review.