How Much CO2 a Rooftop System in Coimbatore Saves: The Official Numbers

Published September 15, 2025 · Updated October 6, 2026 · Reviewed by Karthikeyan E

Every unit of grid power in India releases, on average, 0.71 kg of carbon dioxide. That figure is published by the Central Electricity Authority, the government body that keeps the account. Multiply it by the units a roof makes and you have the saving. This page does that multiplication, shows the working, and explains the two things most other pages leave out: the panels' own footprint, and why the popular "trees planted" comparisons are not worth repeating.

The short answer

System	Units made a year	CO2 avoided a year	Over 25 years
1 kW	About 2,000	About 1.4 tonnes	About 34 tonnes
2 kW	About 4,000	About 2.9 tonnes	About 67 tonnes
3 kW	About 6,000	About 4.0 tonnes	About 100 tonnes

Based on 5.5 units per kilowatt per day in Coimbatore, the CEA factor of 0.71 kg per unit, and the panels' own lifecycle emissions taken off. The working is below.

Where the 0.71 comes from

The Central Electricity Authority publishes a CO2 Baseline Database for the Indian power sector every year. Version 21.0, released in November 2025, gives the weighted average emission factor of the grid for 2024-25 as 0.710 tonnes of CO2 per megawatt-hour, which is 0.71 kg per unit. It counts every station feeding the grid, coal and gas as well as hydro, wind and solar, so it is the average carbon content of the power that arrives at your meter.

Two details matter. First, there is no separate figure for Tamil Nadu: since December 2013 the regional grids have run as one Indian Grid, and the CEA publishes one factor for it. Second, the factor is falling, from 0.774 in 2013-14 to 0.710 in 2024-25, as more non-fossil plants come on line. The grid produced 1,739 billion units in 2024-25 and 255 billion of them came from renewable sources.

The working, step by step

Units a year: 3 kW × 5.5 units per kilowatt per day × 365 days = 6,022 units.
Grid CO2 avoided: 6,022 units × 0.71 kg = 4,276 kg, or about 4.3 tonnes.
The panels' own footprint: 6,022 units × 0.041 kg = 247 kg a year, spread over the system's life.
Net: about 4.0 tonnes of CO2 a year.
Over 25 years, allowing for panels losing about half a percent of output each year: about 100 tonnes.

The same steps give about 1.4 tonnes a year for a 1 kW system and 2.9 tonnes for a 2 kW. Shade, roof direction and dust move the yield, so treat these as central figures, not guarantees. What a 3 kW system includes is on the 3 kW system page.

What the panels themselves cost in carbon

Making, shipping and installing panels releases CO2. The IPCC's review of lifecycle studies puts the median for rooftop PV at 41 grams per unit generated over the system's life, against 820 grams for coal power. At 0.71 kg per grid unit avoided and 0.041 kg per unit spent, the panels repay their own footprint inside the first year and a half, and every unit after that is net saving. The tables above already subtract this.

Does exporting count?

Yes. Under Tamil Nadu's net metering rules, a unit you send out goes to the nearest consumer on the same line, who then draws one unit less from the grid. For the CO2 account it makes no difference whether your house or your neighbour's used the unit. The only units that do not count are the ones never made, so a system kept clean and free of shade saves more than one left dirty.

Your home's footprint before solar

Use in two months	Units a year	CO2 from grid power a year
400 units	2,400	About 1.7 tonnes
600 units	3,600	About 2.6 tonnes
800 units	4,800	About 3.4 tonnes
1,000 units	6,000	About 4.3 tonnes

A home on 800 units a cycle puts out about 3.4 tonnes a year from electricity alone. A 3 kW system makes more than that home uses, which is why the bill falls to the network charge and the carbon account goes slightly negative. The slab rates that go with those usage bands are in our 2026 tariff table.

Numbers you will see elsewhere, and why we do not use them

"Equal to planting 50 trees": published figures for how much CO2 one tree absorbs run from 10 kg to 150 kg a year depending on species, age and who is counting, so any tree number can be made to say anything. "Cars taken off the road": depends on the car and the kilometres. "An average household emits 7 to 10 tons": that is a United States figure for a house using three times the power of a Coimbatore home. "2.2 pounds per kWh": an American coal-plant number, not the Indian grid. The CEA factor is the only one that describes the power you actually buy.

How government policy is pushing the grid factor down, and what it pays you to join in, is in our note on the measures that support rooftop solar. If you are weighing a battery, read when a home needs storage first; it adds cost and a little carbon, not generation.

Questions people ask

Is the emission factor different for Tamil Nadu?

No. Since December 2013 the five regional grids, including the Southern grid, run as one Indian Grid, and the CEA publishes a single factor for it. Tamil Nadu's own wind and solar plants are inside that average.

Will the saving shrink as the grid gets cleaner?

Yes, slowly. The factor fell from 0.774 to 0.710 kg per unit between 2013-14 and 2024-25. If that pace continues, a unit your roof replaces in 2040 will avoid a little less CO2 than one today. The bill saving does not depend on this.

Does adding a battery change the CO2 saving?

Not the saving from generation; the panels make the same units either way. A battery adds its own manufacturing footprint and loses a little energy in charging and discharging, so a system with a battery saves slightly less per unit, not more.

Can I earn carbon credits for a home rooftop system?

There is no practical route for a 3 kW home. The CEA database exists so that registered projects can calculate emission reductions under the carbon market rules. For a household, the benefit is the bill and the avoided emissions, not a tradable credit.

Sources and disclaimer

CEA, CO2 Baseline Database for the Indian Power Sector, User Guide Version 21.0, November 2025. Weighted average emission factor 0.710 tCO2/MWh for FY 2024-25, Table S and Appendix C; one unified grid since December 2013.
IPCC Fifth Assessment Report, Working Group III, Annex III: technology-specific cost and performance parameters. Lifecycle emissions, median 41 gCO2-eq/kWh for rooftop PV and 820 for coal.
TNERC Order No. 8 of 2021: net metering for rooftop solar

Figures were worked out on 6 October 2026 from the CEA factor for FY 2024-25 and 5.5 units per kilowatt per day. The CEA revises the factor every year. RK Solar Solutions is an installer, not a carbon auditor; for a certified footprint, use the CEA database with your own metered data.

Want the bill side of the same sum? Enter your units in the calculator, or read how an installation is done.