A building achieved EDGE certification three years ago and obtained 30% energy savings.

EDGE Zero Carbon certification requires specific prerequisites and operational data to verify performance. The EDGE Certification Protocol details the requirements: "To apply for EDGE Zero Carbon certification, a project must first achieve EDGE Advanced certification, which requires at least 40% energy savings. Additionally, EDGE Zero Carbon certification mandates at least one year of operational data at 75% occupancy to confirm energy performance, after which carbon offsets can be purchased for the remaining energy use to achieve zero carbon status" (EDGE Certification Protocol, Section 2.3: Certification Levels). In this scenario, the building’s energy savings have increased to 60% with solar panels, qualifying it for EDGE Advanced (40% minimum). The next step is to gather one year of operational data before applying for EDGE Zero Carbon, making Option C (after achieving EDGE Advanced certification and gathering one year of operational data) correct. Option A (as soon as one year of operational data) skips the EDGE Advanced requirement: "EDGE Advanced is a prerequisite for EDGE Zero Carbon" (EDGE Certification Protocol, Section 2.3: Certification Levels). Option B (no wait time) is incorrect, as operational data is mandatory: "Operational data is required to verify performance for Zero Carbon certification" (EDGE User Guide, Section 6.3: Advanced Certifications). Option D (at the same time as EDGE Advanced and after two years) is wrong, as only one year of data is needed: "One year of operational data at 75% occupancy is sufficient for EDGE Zero Carbon" (EDGE Certification Protocol, Section 2.3: Certification Levels). Thus, Option C is the correct timeline.