Effect of the Minimum Bid Size on the Wholesale Markets

Among Distributed Energy Resources (DERs), Electric Vehicles (EVs) are promising resources for flexibility provision. However, the small-scale capacity hinders their possibility to enter the electricity markets. This paper focuses on the understanding of the market barrier for EVs aggregators to participate in the wholesale markets: the minimum allowable bid size. The developed Hybrid Robust/Two-Stage Stochastic optimization model considers three uncertainties, including the availability of the EVs, the day-ahead (DA) market prices, and the imbalance price. Besides, this model gives output for the DA energy program minimizing not only the DA cost of energy procurement but also the imbalance cost realizations after delivery-time. Especially, the temporal correlations are reflected by the Copula model for generating scenarios for the upward and downward imbalance price. The results with different minimum bid sizes (100 kWh, 500 kWh, and 1000 kWh) and different fleet sizes (500 EVs, 1000 EVs) for the public, private, and mixed portfolios are analysed to understand the impacts of the minimum bid size on the business case for small players.