Uncertainty-aware design assessment of local multi-energy system under joint energy and reserve market participation

This work presents a techno-economic framework to explicitly integrate energy and ancillary service markets into the design phase of local multi-energy systems (MES) under uncertain future market conditions. The methodology combines scenario-based stochastic design optimisation with operational evaluation to identify cost-optimal system configurations. A local energy community is used as a case study, demonstrating that accounting for ancillary service revenues during the design phase significantly influences optimal component sizing. While current energy arbitrage alone cannot economically justify a community battery energy storage system (BESS), incorporating reserve market revenues makes the BESS investment clearly profitable, thus outweighing the associated investment costs. However, as reserve prices decline and electricity price volatility increases, the economic value of BESS shifts from reserve provision to energy arbitrage. Although solar PV on its own is susceptible to volatile prices, its combination with BESS remains profitable across all evaluated scenarios. In contrast, oversized thermal components have not proven economically prudent under the assessed market conditions. Finally, slightly smaller BESS and solar PV provide a balanced trade-off between economic performance and minimising investment risks. These findings highlight the importance of explicitly accounting for market revenues during the design phase, as reserve markets in particular significantly drive investment decisions in local MES.