Non-generating resources such as thermostatically controlled loads (TCLs) can arbitrage energy prices and provide balancing reserves when aggregated due to their thermal energy storage capacity. An aggregator that wants to quantify this flexibility in order to place optimal bids before gate closure, would be affected by market timing. The market timing can be quantified by parameters such as lead time and contract period. This paper explores the impact of market timing on TCL aggregate power consumption and reserve capacity bids and quantifies trade-offs between market timing and flexibility. We first optimize the power consumption and reserve capacity offers at given lead times and contract periods, varying from 24 hours ahead to real-time. We then introduce uncertainty in prices and TCL availability, formulate a two-stage chance-constrained optimization problem of a risk-averse aggregator, implement it on a rolling horizon basis, and evaluate how the trade-offs change. The results show that shorter lead times and contract periods positively impact TCL profit as well as flexibility if the prediction horizon is sufficiently long. The proposed method can be used by aggregators to decide on optimal bids and incentive payments to consumers to reward flexibility.
Due to increased use of variable renewable energy sources, more capacity for balancing and ancillary services (AS) is required. Non-generating resources such as thermostatically controlled loads (TCLs) can arbitrage energy prices and provide AS due to their thermal energy storage capacity. This paper explores the impact of energy/AS price notice time, i.e. the time between when the price is announced and when it takes effect, on the TCL energy consumption and AS capacity bids, and quantifies trade-offs between notice time and flexibility. We first optimize the energy consumption and AS capacity offers at a given notice time, varied from 24 hours ahead to real-time. We then introduce uncertainty in TCL availability, formulate the stochastic optimization problem, and evaluate how the trade-offs change. We find that price notice time impacts TCL profits, but does not significantly affect the total AS capacity offered over the day. However, AS capacity offers are impacted by uncertainty, which is likely to increase with notice time.
Electric vehicles (EV) can be considered as energy storage with availability, energy and capacity constraints that can provide flexibility to the power system in the form of balancing products when aggregated. In this paper, we develop a two-stage stochastic optimization problem that maximizes the profit of a risk-averse EV aggregator for bids on the day ahead in both energy and Frequency Containment Reserve (FCR) markets. Unidirectional charging is examined, while we take into account uncertainty from prices and vehicle availability. Case studies are carried out in different Nordic bidding areas based on historical EV charging data. We identify a strong temporal alignment of EV availability and high FCR-N prices. Results show that consumption is shifted largely towards early hours of the morning. When compared to a reference cost of charging case, up to 50% of the cost of charging can be recovered in Norway, and 100% in Sweden.
System operators have the option to trade balancing reserves among countries and operators. In order to trade balancing reserves with other system operators the markets should be harmonized. While the spot and intraday markets are already harmonized within the Nordics, the balancing markets still display differences. The differences can be subtle, yet they may play a significant role for the planning, operation, modelling and control of the power system. In this paper, we conduct a thorough literature review on Nordic balancing markets and summarize the market rules and requirements. This review can help operators and modellers to better represent the Nordic power system.
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