What the Emissions Factor Measures
The grid emissions factor (sometimes called the grid emission intensity or marginal emission factor) represents how many kilograms of carbon dioxide are released into the atmosphere per kilowatt-hour of electricity consumed from the national grid. For a grid that runs entirely on diesel and heavy fuel oil, as Antigua's effectively does, this number is determined by the carbon content of the fuels and the thermal efficiency of the generators converting heat to electricity.
Diesel fuel combustion releases approximately 2.68 kg CO2 per liter burned. APUA's generation units operate at a thermal efficiency of roughly 35-38%, meaning it takes about 0.28-0.30 liters of diesel to generate one kWh of electricity. Multiplying: 0.29 liters × 2.68 kg CO2/liter = approximately 0.78 kg CO2/kWh at the generator. Adding transmission and distribution losses (approximately 8-10% of generated electricity is lost before reaching consumers), the effective emissions factor at the meter rises to 0.82 kg CO2/kWh. This is the number now used in our model.
Why the Previous Figure Was Too Low
The previous model used 0.79 kg CO2/kWh, which was based on APUA generation data from 2021-2022. The CDB's 2024 report reveals that the proportion of heavy fuel oil (HFO) in Antigua's generation mix has increased relative to cleaner diesel over that period, as APCL's older HFO-burning generators have run more hours due to maintenance issues with newer units. HFO has a slightly higher carbon intensity per unit of electricity generated than marine diesel oil, pushing the emissions factor upward. The 3.8% revision from 0.79 to 0.82 is not dramatic, but it's meaningful for calculating project-level carbon savings.
For a standard 5kW residential system generating 7,008 kWh per year, the revised emissions factor increases calculated annual carbon savings from 5,536 kg CO2 (using 0.79) to 5,747 kg CO2 (using 0.82) — an increase of 211 kg, or about 3.8%. Over 25 years, that represents an additional 5.3 tonnes of CO2 avoided per system. With roughly 180 residential systems installed in 2025 alone, the updated factor increases total annual avoided emissions for new 2025 installations by approximately 38 tonnes CO2 per year.
How Carbon Savings Factor Into Investment Decisions
For most Antiguan homeowners, the financial return is the primary driver of solar investment decisions — and carbon savings don't directly show up on a bill. But emissions data matters in two important ways. First, for businesses subject to international environmental reporting (including tourism operators affiliated with international hotel chains that have sustainability commitments), documented carbon savings are a reportable asset. Several Antigua hotels have used their solar installations' verified emissions reductions in ESG reports to international investors and tour operators.
Second, carbon markets are evolving. The Caribbean Climate Exchange and various voluntary carbon market mechanisms are beginning to create pathways for small island nations to monetize verified emissions reductions. While the mechanics remain complex and the administrative overhead currently exceeds the revenue for a single residential system, commercial installations above 50kW are increasingly being assessed for voluntary carbon credit eligibility. An accurate, documented emissions factor is the foundation of any such verification process, making data quality maintenance a practical concern, not just an academic one.