While both the Energy Efficiency Existing Ship Index (EEXI) and the Carbon Intensity Indicator (CII) are crucial measures introduced by the International Maritime Organization (IMO) to drive decarbonization in shipping, they differ fundamentally in their scope, calculation, and what they measure. EEXI is a technical, design-based standard for a ship's energy efficiency potential, calculated once, whereas CII is an operational, performance-based rating of a ship's actual carbon intensity over a year. Both play a role in determining a ship's environmental compliance and rating.
Understanding EEXI (Energy Efficiency Existing Ship Index)
The EEXI is a one-time calculation that applies to existing ships of 400 gross tonnage and above falling under MARPOL Annex VI, aiming to ensure they meet a specific minimum energy efficiency standard.
- Nature: It is a technical measure based on the ship's design parameters and installed power. Think of it like a vehicle's factory-rated fuel efficiency.
- Purpose: To assess the energy efficiency potential of a ship's design and ensure it complies with a minimum efficiency standard. This applies to ships for their first annual, intermediate, or renewal survey after January 1, 2023.
- Calculation: EEXI is calculated using a formula that considers the ship's engine power, capacity, and design speed. It indicates the amount of CO2 emitted per unit of transport work.
- Compliance: A ship is assigned an attained EEXI value, which must be below a required EEXI value set by the IMO. If a ship does not meet the required EEXI, modifications such as engine power limitations (EPL) or shaft power limitations (ShaPoLi) may be necessary.
- Result: A ship either complies or does not comply with the EEXI requirements. There isn't an annual rating system for EEXI itself; it's a one-off verification.
Understanding CII (Carbon Intensity Indicator)
The CII is an operational measure that assesses a ship's actual carbon intensity annually, assigning a rating from A to E. This rating reflects how efficiently a ship transports goods or passengers, considering the CO2 emitted relative to the distance traveled and capacity.
- Nature: It is an operational measure reflecting a ship's real-world performance. This is comparable to a vehicle's actual fuel efficiency achieved during driving under varying conditions.
- Purpose: To monitor and reduce the carbon intensity of ships during their operation. It promotes continuous improvement in fuel efficiency and operational practices. The annual operational Carbon Intensity Indicator (CII) is added with a CII rating.
- Calculation: CII is calculated annually based on actual fuel consumption, distance traveled, and cargo carried (or gross tonnage for certain ship types). The formula yields an attained annual operational CII, which is then compared against a required CII.
- Rating System: Based on the attained CII, ships receive a rating from A (superior) to E (inferior).
- A/B: Encourages continuous operational improvement.
- C: Acceptable performance.
- D/E: Indicates a need for improvement. Ships rated D for three consecutive years or E for one year must submit a corrective action plan as part of their Ship Energy Efficiency Management Plan (SEEMP).
- Compliance: Shipowners are encouraged to achieve C or higher ratings, as poor ratings can trigger corrective actions and potentially impact commercial attractiveness.
Key Differences at a Glance
| Feature | EEXI (Energy Efficiency Existing Ship Index) | CII (Carbon Intensity Indicator) |
|---|---|---|
| What it is | A technical measure based on design. | An operational measure based on actual performance. |
| Scope | Assesses the ship's potential for energy efficiency. | Assesses the ship's actual carbon intensity during operation. |
| Timing | One-time calculation and certification (at a specific survey point). | Annual calculation and rating. |
| Basis | Ship's design parameters (engine power, capacity, speed). | Actual fuel consumption, distance traveled, cargo carried over a year. |
| Goal | Ensure existing ships meet a minimum efficiency standard for their design. | Drive continuous improvement in operational carbon efficiency over time. |
| Outcome | Compliance (ship meets required EEXI) or non-compliance (requires fixes). | Annual rating (A to E) with requirements for corrective action if low. |
| Impact | May require hardware modifications (e.g., EPL/ShaPoLi) or technical changes. | Primarily influences operational practices (e.g., speed optimization, route planning, trim). |
| Reference | Focuses on energy efficiency potential. | Focuses on carbon intensity from actual operations. |
The Interrelation and IMO's Decarbonization Strategy
Both EEXI and CII are part of the IMO's short-term measures to reduce greenhouse gas emissions from international shipping, effective from January 1, 2023. As highlighted, two factors are involved related to the rating: first, EEXI determines energy efficiency by calculating the ship's attained index, and second, the annual operational CII is added with a CII rating.
- EEXI sets the baseline; it ensures that the design of an existing vessel is up to a minimum efficiency standard.
- CII then measures how well the vessel performs operationally against that standard year after year, encouraging continuous optimization.
Together, they create a comprehensive framework addressing both the technical design aspects and the operational realities of vessel emissions. Shipowners must ensure their vessels are technically capable (EEXI compliant) and operated efficiently (achieving good CII ratings) to meet international regulations and contribute to a more sustainable shipping industry.
For more detailed information, consult the official IMO guidelines on EEXI and CII.
