"Additionality" in the context of greenhouse gas (GHG) regulations means that a purchased renewable energy certificate introduces new renewable energy onto the electricity grid beyond what would have happened without the project or "business as usual". The U.S. Environmental Protection Agency (EPA) favors performance-based measures of additionality, such as the megawatt-hour (MWh) equivalent per REC. Critics argue "additionality" amounts to a subsidy for renewable energy, that business as usual (supply and demand) prevents unnecessary/duplicative renewable energy from being sold in some markets where overgeneration (excess supply in relation to demand) threatens
grid reliability. Whereas air and water pollution travels across state and national boundaries irrespective of its origin, the value of RECs and the emergence of RECs markets depend very much on the markets created state by state through legislative action to mandate a Renewable Portfolio Standard. Such a balkanized approach to establishing RECs markets and incentives state by state creates issues of equity as some states could legitimately claim that their neighboring states (and their electricity consumers) with voluntary RPS are operating as free riders of pollution prevention, paid for by states (and their electricity consumers) with mandatory RPS. We can learn from EPA's SOx and NOx cap and trade program regarding how the principle of additionality with a national standard provided a benchmark for measuring and validating the commodification of pollution prevention credits that lead to market-driven initiatives with proven results in improving regional and national air quality. In states with a Renewable Portfolio Standard, a RECs purchase enables the utility company to meet its minimum renewable electricity percentage without having to install that renewable generating capacity itself, regardless of the source of generating renewable energy. By analogy, in the EPA cap and trade program, a "clean" utility in one state can sell its NOx credits to a "dirty" utility in another state that would otherwise have to install additional smokestack scrubbers. The
United States Environmental Protection Agency claims to have the highest percentage use of green power of any federal agency. In 2007, it offset the electricity use of 100% of its offices. The Air Force is the largest purchaser in the US government in absolute terms, purchasing 899,142 MWh worth of RECs. Among colleges and universities, the University of Pennsylvania in Philadelphia is the largest purchaser of RECs, buying 192,727 MWh of RECs from wind power. The corporate leader is Intel, with 1,302,040 MWh purchased in 2007, and the largest purchaser among retailers is Whole Foods, which purchased 509,104 MWH, or enough RECs to offset 100% of its electricity needs. Research based on sample sets between 2004 and 2011 shows that Solar RECs purchased and retired voluntarily in the United States (i.e., not for compliance with a Renewable Portfolio Standard) do not lead to any significant additional renewable energy investment or generation. However, these findings may not be applicable given the changes in the REC market, such as supply, demand, efficiencies, and pricing dynamics. ==Criticism==