The growth of renewable energy has intensified the need for solutions that can address temporal and spatial mismatches between electricity supply and demand, arising from the intermittency of renewables. While battery storage has emerged as a key tool to store renewable electricity for future use, storage developers face diminishing and uncertain returns. In this paper, we first demonstrate how local competition and transient transmission capacity congestion lead to low and uncertain returns for Stationary Energy Storage System (SESS) operators. Using six years of price data from the PJM Interconnection and a staggered diff-in-diff approach, we estimate that an additional storage installation reduces existing SESS’s annual profit at that location by $7,820 per megawatt on average. We then estimate how Mobile Energy Storage Systems (MESS)—an innovative business model that allows grid-scale batteries to be relocated—can increase operators’ returns and improve grid-level congestion by providing geospatial flexibility. We introduce a dynamic programming-based forecasting framework for MESS developers’ relocation and operating decisions and show that, even when relocation costs are high, MESS’s profit consistently outperforms even the best-sited SESS by 11-47%. In part, this profit increase is driven by MESS capturing up to 22.5% more value from congestion prices than SESS, better aligning developer and grid incentives. Our findings quantify how competition and transience of price patterns limit storage profitability and highlight how leveraging mobile storage inventory in the energy transition can help storage developers, grid planners, and policymakers to accelerate storage build-out, renewable integration, and grid flexibility.
