Indonesia's electricity demand is growing rapidly, driven by robust economic growth combined with unprecedented urbanization and industrialization. Energy-efficiency improvements could reduce the country's electricity demand, thus providing monetary savings, greenhouse gas and other pollutant reductions, and improved energy security. Perhaps most importantly, using energy efficiency to lower peak electricity demand could reduce the risk of economically damaging power shortages while freeing up funds that would otherwise be used for power plant construction. We use a novel bottom-up modeling approach to analyze the potential of energy efficiency to reduce Indonesia's electricity demand: the LOAD curve Model (LOADM) combines total national electricity demand for each end use—as modeled by the Bottom-Up Energy Analysis System (BUENAS)—with hourly end-use demand profiles. We find that Indonesia's peak demand may triple between 2010 and 2030 in a business-as-usual case, to 77 GW, primarily driven by air conditioning and with important contributions from lighting and refrigerators. However, we also show that appliance and lighting efficiency improvements could hold the peak demand increase to a factor of two, which would avoid 23 GW of peak demand in 2030. These results suggest that well-understood programs, such as minimum efficiency performance standards, could save Indonesia tens of billions of dollars in capital costs over the next decade and a half.