We present a unified model for flexibility services in the power system, identify two existing categories (ramping and loading) and introduce a new category (stalling). Each service is characterised by duration, capacity and effort, with associated prices. We show that the effort of stalling, measurable in kWh2, is a significant cost component for balancing through storage and demand response (DR). In future energy systems - with increased reliance on renewable generation - storage and DR resources are expected to become an important component of power system flexibility and balancing. Existing resource allocation mechanisms are mainly based on pricing in kW (for ramping) and in kWh (for load). Simulations demonstrate that conventional pricing mechanisms yield inefficient allocations of storage and DR resources for power balancing. In contrast, we show that introducing an additional pricing component in e/kWh2 (for stalling) improves the allocation efficiency.

Smart energy systems integrate renewables and demand response. Most European electricity markets coordinate the resulting time-varying flexibility in demand and supply by organising day-ahead trade with Walrasian mechanisms, using simultaneous call auctions and sealed bids. These mechanisms give bidders no information on each other's values and flexibilities until after clearing. In this paper we simulate two alternative day-ahead market mechanisms which share information, such that bidders obtain a better position before entering the intraday market. One mechanism uses an ascending shared market price signal rather than sealed bids. The other auctions off future timeslots consecutively rather than simultaneously. We perform a case study on 400 households with electric vehicles, either with or without volatile wind generation. Results show that a price-taking flexible consumer can obtain higher utility in the market with simultaneous ascending-price auctions, because online price information reduces uncertainty over available energy and prices.