Community Choice Aggregation (CCA) is a system adopted in California that allows cities and counties to aggregate the buying power of customers to secure alternative energy supply contracts. CCAs now serve over 5% of Americans in more than 1,300 municipalities. CCAs act as public utilities that negotiate with suppliers rather than relying on traditional utility models. CCAs can provide cleaner energy, often from local renewable sources, at a lower cost than traditional utilities. California's law enables CCAs and requires automatic enrollment with an opt-out option. Many California local governments explored CCAs in 2007 to increase their use of renewable energy beyond utility standards.