Clean energy standard (CES)

A clean energy standard, or CES, is a regulatory requirement obligating utilities, generation authorities, or load-serving entities to acquire a specific percentage of their supply from sources defined as being “clean.” CESs are sometimes called clean electricity standards. CESs have been mandated by numerous U.S. states that have created the requirements as a strategy to foster decarbonization, cleaner air, and local economic development.

While the exact details for CESs vary by state, they differ from a renewable portfolio standard (RPS) in that they allow a wider array of technologies to be used. The technologies may emit low or zero amounts of greenhouse gases and commonly include nuclear power, fossil-fuel generators with carbon capture and storage, and new energy efficiency projects. Often a CES requires that a certain amount of the clean energy be provided by renewable technologies – hence a CES can incorporate an RPS, and some states have both. 

CES mandates likely help greenhouse gas emissions associated with a region’s electric generation decline more quickly than if generation planning was solely based on market forces or on traditional reliability-based supply planning.