Does a detailed model of the electricity grid matter? Estimating the impacts of the Regional Greenhouse Gas Initiative

•We use a realistic 5000-node model to predict future operation and generator entry.•We describe uses of such a model, for analysis of policies and investments.•We use it and an otherwise identical 300-node model to predict effects of a CO2 price.•We find that the predictions of the two models differ significantly.•We discuss reasons and implications.