Optimal BESS Scheduling for Multi-Market Participation in the Nordics

Battery energy storage systems (BESSs) can provide fast frequency reserves and energy arbitrage in Nordic electricity markets, but their limited energy capacity requires accurate revenue forecasts and coordinated bidding across multiple sub-markets. This paper introduces a unified framework that employs generalized additive models (GAMs) to generate one-week-ahead forecasts of spot and FCR–N revenues in Denmark, Finland, and Norway using three years of hourly price and volume data. Forecast outputs feed a stochastic mixed-integer optimizer that co optimizes BESS participation in FCR–N, FCR–D, spot markets, subject to state-of-charge constraints, inverter losses, and differing pay-as-bid and pay-as-clear rules. Comparative analyses evaluate forecast accuracy and quantify the impact of forecast errors on BESS bid acceptance, market selection, and profitability under realistic seasonal price patterns. Results demonstrate that spot markets exhibit consistently higher predictability than frequency markets, and that forecast errors modestly affect bid acceptance but do not alter overall market participation. The proposed approach provides BESS operators and investors with a tool to assess revenue uncertainty and optimize multi-market strategies in Nordic power systems. Index Terms—forecast, BESS, multi-markets, Nordics.