Planning energy adequacy for a renewable New England: Multi-decade weather, short- and long-duration storage, and grid-interactive electric vehicles

This study evaluates how planning horizon length, storage technology mix, and firm capacity affect resource adequacy in a high-renewable New England electricity system. Using 44 years of hourly wind, solar, and demand data, the analysis optimizes least-cost portfolios under different historical planning windows and tests their adequacy across the full multi-decadal record. Extending the planning horizon from 1 to 44 years reduces expected unserved energy (EUE) by up to 98% and loss-of-load hours (LOLH) by more than 90%, though at an average 5–10% increase in total system cost. Systems relying only on short-duration energy storage (SDES) or those incorporating long-duration energy storage (LDES) such as hydrogen power-to-gas-to-power and redox-flow batteries required more than 44 years of planning data to achieve full adequacy, while those with firm capacity (natural gas) present, archived 100% adequacy with 21 years of data. LDES also lowers the marginal cost of avoided lost load (MCALL) to below 10 $/kWh, maintaining economic efficiency even at high reliability levels. Introducing a 5% firm-capacity backstop further improves adequacy and lowers cost, particularly when the planning horizon underrepresents extreme renewable droughts. Under full electric-vehicle electrification, results showed that allowing natural gas to supply even a small fraction of annual demand offset additional capacity needs and improve adequacy outcomes. The findings show that representing at least two decades of historical climate variability and combining LDES, limited firm resources, and flexible electrification are essential for cost-effective adequacy planning in a deeply decarbonized New England grid.