# How do I calculate a solar cell plant's carbon footprint per watt?

Canonical: https://senseible.earth/answers/solar-cell-manufacturing-carbon-per-watt

Divide the plant's electricity and fuel emissions by the watts of cells produced, rated at standard test conditions. Electricity for furnaces, cleanrooms and chillers dominates. Purchased wafers carry most of a cell's embodied carbon, so report them separately in Scope 3.

## Inputs

- Monthly electricity bills, including open access or rooftop solar.
- Diesel and gas invoices.
- Watts of cells produced, from production records.
- Wafers bought, with supplier figures if available.

## Gases

Some cell lines use fluorinated gases for cleaning or etching. Losses of gases covered by the GHG Protocol count in Scope 1.

## Worked example (illustrative figures)

- Electricity in a month: 2,000,000 kWh.
- 2,000,000 × 0.710 = 1,420,000 kg CO2.
- Cells produced: 150,000,000 watts.
- 1,420,000 ÷ 150,000,000 = 0.0095 kg, about 9.5 g CO2 per watt.

## What Senseible does here

Senseible reads electricity bills (CEA grid factor 0.710 kg CO2 per kWh, CO2 Baseline Database version 21.0) and diesel, LPG and gas invoices (IPCC 2006 defaults) into a dated, fingerprinted Scope 1 and 2 record for each site. Intensity per unit uses the activity count you enter, and estimates are labelled as estimates.

- [Polysilicon CO2](https://senseible.earth/answers/polysilicon-production-co2-per-kg)
- [Module assembly per watt](https://senseible.earth/answers/solar-module-assembly-carbon-footprint-per-watt)
- [Grid electricity factor for India](https://senseible.earth/emission-factors/grid-electricity)

Sources: [CEA CO2 Baseline Database, version 21.0](https://cea.nic.in/cdm-co2-baseline-database/?lang=en), [GHG Protocol Corporate Standard](https://ghgprotocol.org/corporate-standard), [GHG Protocol Corporate Value Chain (Scope 3) Standard](https://ghgprotocol.org/corporate-value-chain-scope-3-standard)

Last reviewed 2026-10-22.