Aspen produced a major study for the American Public Power Association (APPA), with additional support from the Utility Air Regulatory Group, entitled “Implications of Greater Reliance on Natural Gas for Electricity Generation.” The 90-page study is a comprehensive look at the possibility of electric utilities replacing their coal-fired baseload generating capacity largely with natural gas-fired generation, even assuming low annual load growth and a resource portfolio in which 20% of load is served with energy from renewable sources. The study shows that without carbon capture and sequestration or large numbers of carbon offsets, 15 Trillion Cubic Feet (Tcf) per year more natural gas must be burned by generators in order to achieve the 2036 carbon targets and that 14 Tcf more would be burned if all coal were switched to gas today. These figures represent a roughly 60% increase in the amount of natural gas burned in the U.S. today. The study evaluates which U.S. states would have inadequate pipeline capacity and underground gas storage to support this burn and estimates that nearly $750 billion would need to be spent on natural gas and generating infrastructure in order to support a gas burn of such a magnitude. The study identifies operational issues related to the natural gas/electricity interface that will become more troublesome as more utilities replace aging coal-fired generating with natural gas and points out that it is more economical to replace coal-fired generation with natural gas combined-cycle units than to retrofit or repower a coal-fired unit.