DG power backup in luxury residential projects: a technical primer.

"100 per cent power backup" is one of the most frequently quoted specifications in Indian luxury residential marketing. It is also one of the least understood. In practice, the phrase means very different things depending on which engineering team wrote the specification and which commercial team approved it. This brief unpacks the technical meaning of DG backup in an Indian high-rise residential context — what "100 per cent" actually covers, how the sizing is done, what redundancy looks like, what noise and emission standards apply, and what a buyer should verify at the specification stage.

The grid reliability question.

Uttar Pradesh grid reliability in the Noida-Greater Noida belt has improved markedly since 2015, with average consumer interruption frequency now around 8 events per year and average interruption duration around 4 hours cumulatively. This is a meaningful improvement over the Delhi NCR baseline a decade earlier, but it is not zero. On peak summer evenings — typically June — voltage sags, transformer tripping and load-shedding events still occur with regularity. For a luxury residential tower where the AC load, the fire suppression system, the water pumps, the ventilation and every apartment's refrigeration must remain functional without interruption, grid dependence is not acceptable.

The engineering response is a dedicated on-site diesel generator (DG) set that can supply the entire tower load within approximately 10 seconds of a grid failure, run for the duration of the outage, and then re-synchronise back to the grid cleanly once the grid returns. This is the fundamental service that "100 per cent backup" promises — but the implementation details matter.

What "100 per cent" actually means.

There are four different definitions of "100 per cent backup" circulating in Indian real estate marketing, and they are not equivalent.

For a genuine luxury project, "100 per cent backup" should mean the fourth definition — the full connected load of every apartment, including all air conditioners, all kitchen appliances, all lighting and all entertainment, operates on DG identically to grid. Anything less is marketing, not specification.

DG sizing and redundancy.

The DG set is sized against the calculated building demand, which is the connected load multiplied by a diversity factor. For a G+35 residential tower with 96 apartments, each with a connected load of approximately 15 kW, the total connected load is 1,440 kW. The diversity factor accounts for the reality that not every appliance runs simultaneously — for luxury residential, the factor is typically 0.55 to 0.65. This produces a peak demand of approximately 850 kW per tower, plus common area loads of approximately 150 kW, for a total of 1,000 kW per tower.

The DG set is then sized at the peak demand plus a 25 per cent margin for start-up inrush and future growth, producing a prime rated DG capacity of 1,250 kW per tower. A single DG of this rating would satisfy the peak demand. However, best practice on luxury projects is to provide two DGs in parallel — each rated at 750 kW — such that either unit can carry a reduced load if the other is down for maintenance. This N+1 redundancy eliminates the single-point failure that a single large DG introduces. The two units synchronise automatically and share load according to their real-time capacity. On Fab Luxe, each tower has a redundant DG pair.

Synchronisation and grid transition.

The transition from grid to DG must be fast enough that sensitive loads — medical equipment, computers, refrigeration — do not notice. Static transfer switches or automatic transfer switches with 10 to 20 millisecond switching time handle this transition for critical loads. For the entire building, a typical DG set needs 8 to 12 seconds to start, stabilise and accept load — during which time the lifts pause between floors, the AC units restart, and the public lighting briefly dims. This is the standard experience and is acceptable.

When the grid returns, the DG synchronises back to the grid voltage and frequency, then transfers the load back to the grid, and finally shuts down. This closed-transition return prevents a visible power dip during grid restoration.

Noise and emission standards.

A DG set in a residential environment produces three nuisance outputs: engine noise, exhaust emissions, and vibration. All three are regulated and all three must be actively managed.

Noise.

CPCB standards for DG acoustic enclosures limit the noise emission to 75 dB(A) at 1 metre from the enclosure. In residential settings, this is further reduced in luxury projects to 65 dB(A) at 1 metre through acoustic canopies, exhaust silencers and plantroom sound treatment. The DG room itself is typically isolated from the tower structure using floating slab construction and spring isolators under the DG base.

Emissions.

CPCB Part III emission norms for DGs limit NOx, CO, SO2 and particulate matter at specified levels. From 2024, CPCB Part IV norms (based on engine capacity) have become applicable for new installations, and require catalytic converters or selective catalytic reduction (SCR) after-treatment on DGs above 800 kW. Fab Luxe DG sets are specified to CPCB Part IV norms with SCR after-treatment on both units per tower.

Fuel and run-time.

The DG fuel tank sizing is determined by the required autonomous run-time. For a typical luxury residential project in Uttar Pradesh, the specification is 24 hours of full-load runtime without refuelling. For a 1,250 kW DG running at 220 litres per hour at full load, this requires approximately 5,300 litres of diesel storage, held in a bunded underground tank with leak detection and fuel polishing.

What the buyer should ask.

• Is 100 per cent backup defined as "full apartment connected load, no limit"?
• Is the DG sized with N+1 redundancy, or is there a single unit?
• What is the CPCB emission compliance class?
• What is the noise limit at 1 metre, and is it audible from the lowest apartment?
• What is the autonomous runtime at full load?
• Is there a static transfer switch for critical apartment loads?
• What is the annual DG maintenance schedule, and who bears the fuel cost?

These questions have technical answers that should be documented in the project specification. On Fab Luxe, each of the above is answered in the electrical design basis report and available to buyers at the specification stage. For the complete MEP specification, see the project specs page. Related: the AQI-managed indoor air engineering brief which explains why continuous backup is essential for the ventilation system.