“The first mention of distinguishing the attributes from electricity came in 1995 or 1996 as part of the discussion about how to design a California renewable portfolio standard (RPS). Stakeholders made a number of proposals, including credit trading, to the California Public Utilities Commission (Renewables Working Group 1996). Although the RPS was not adopted at that time, the idea resurfaced in early1997 during discussions about implementing environmental disclosure (electricity labels) in New England. Stakeholders were wrestling with the challenge of verifying the fuel mix and emissions data claimed by electric service providers. The first proposal was to follow the money by an audit of power purchase agreements that would document the chain of custody—the so-called contract-path or “settlements” method of verification. Because this would be impractical for electricity purchases from the spot market, one of the stakeholders suggested that the fuel and environmental attributes be traded separately from the commodity (Enron 1997).
A year after this discussion took place, electricity markets in California, Massachusetts, and Rhode Island were opened to retail choice—but California was the most active. The day before the California market officially opened on April 1, 1998, Automated Power Exchange (APX) opened a separate market for green power. This was a wholesale market for scheduled electricity deliveries, designed to serve electric service providers seeking to differentiate themselves and their products. The APX Green Power Market traded electricity generated by renewable resource technologies as defined by the California legislation and renewable energy programs (Pepper 1998). Recognizing the greater flexibility and market liquidity of separating the environmental attributes from the commodity, APX began operating a market for “green tickets” in May 1999 (APX 1999). These wholesale green tickets were purchased and rebundled with commodity electricity for retail green power sales.
In June 1999, the Texas Legislature adopted Senate Bill 7, a restructuring law that included a renewable portfolio standard. The law also resulted in the first renewable energy credit-trading program in the United States. The Texas PUC adopted rules for a credit-trading program in December 1999.” Source: Ed Holt, Lori Bird: Emerging Markets for Renewable Energy Certificates: Opportunities and Challenges . NREL, 2005: https://www.nrel.gov/docs/fy05osti/37388.pdf