Reliably integrating variable renewables: Moving grid flexibility resources from models to results

At least eight kinds of demand- and supply-side grid flexibility resources can complement and firm variable renewables (wind and photovoltaics) at generally lower cost than fossil-fuel backup or bulk electrical storage, supporting largely if not wholly renewable electricity without a battery revolution. Validating dozens of simulation studies, at least 10 nations with modest or no hydropower now reliably use many times the US variable and total renewable fraction with attractive economics and improved reliability.