# Is grid-charged battery backup lower carbon than running a DG set during power cuts?

Canonical: https://senseible.earth/answers/battery-backup-vs-dg-set-emissions

Usually yes, and clearly so when the DG set runs at light load. Battery backup emits 0.710 kg CO2 per kWh divided by its round-trip efficiency, about 0.81 kg at 88 percent. A DG set emits 2.68 kg per litre divided by kWh per litre: 0.89 kg at 3 kWh per litre, 1.34 kg at 2.

## The two formulas

- Battery: kg CO2 per kWh delivered = 0.710 / round-trip efficiency. The losses are extra grid kWh, so they count.
- DG set: kg CO2 per kWh delivered = 2.68 / kWh generated per litre of diesel, from your own fuel and energy meter readings.

## Load decides the DG side

A DG set sized for the whole plant often carries a small backup load during a cut, and its kWh per litre drops sharply below about half load. Read litres per kWh from your logbook for actual cut hours, not the data sheet at 75 percent load. At light load the battery wins clearly; at good load the two can be close.

## What the battery side must include

- Round-trip efficiency from the manufacturer for the actual chemistry: lithium systems usually do better than older lead-acid inverter banks.
- Standby losses: charger, inverter idle draw and self-discharge, which add grid kWh even on days without a cut.
- If the battery is charged from rooftop solar that would otherwise be exported, those kWh carry no grid emissions, which lowers the battery figure further.

## Which scope each sits in

Diesel burnt in your own DG set is Scope 1. Grid power used to charge the battery is Scope 2. Switching from DG to batteries moves emissions from Scope 1 to a smaller Scope 2 figure, so report both lines rather than a single net change.

## Worked example: 12,000 kWh of backup a year

- Battery at 88% round-trip efficiency (assumed): 12,000 / 0.88 = 13,636 grid kWh
- 13,636 x 0.710 = 9,682 kg CO2 (Scope 2)
- DG set at 2.2 kWh per litre during cuts (assumed from logbook): 12,000 / 2.2 = 5,455 L
- 5,455 x 2.68 = 14,619 kg CO2 (Scope 1)
- Difference: 14,619 minus 9,682 = 4,937 kg, about 4.9 t CO2 a year lower with the battery

Add standby losses to the battery side if the charger runs all year.

## What Senseible does here

Senseible calculates both sides from your bills: diesel invoices at 2.68 kg CO2 per litre as Scope 1 and grid kWh at 0.710 kg CO2 per kWh (CEA version 21.0) as Scope 2, so the shift shows up in the monthly record.

- [DG set emissions per kWh vs grid](https://senseible.earth/answers/dg-set-emissions-per-kwh-vs-grid)
- [Does battery storage cut Scope 2?](https://senseible.earth/answers/does-battery-storage-reduce-scope-2-emissions)
- [DG specific fuel consumption](https://senseible.earth/answers/diesel-generator-specific-fuel-consumption)
- [Estimate DG diesel from run hours](https://senseible.earth/answers/estimate-dg-diesel-from-run-hours)

Sources: [CEA CO2 Baseline Database for the Indian Power Sector, version 21.0](https://cea.nic.in/cdm-co2-baseline-database/?lang=en), [IPCC 2006 Guidelines, Volume 2 (Energy), default fuel factors](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html), [BEE Guide Book 3, Energy Efficiency in Electrical Utilities, chapter on DG systems (beeindia.gov.in)](https://beeindia.gov.in)

Last reviewed 2026-10-18.