I. Introduction
With increasing fossil-fuel prices and climate change, many countries have started to rely on renewable energy sources (RESs) to meet the growing electricity demand [1], [2]. For example, Australia sets a target of a 20% share of renewable energy in its electricity supply by 2020 [3]. Such a widespread growth of RESs and advancements in smart-grid technology will open new opportunities for electricity trading between aggregators and electricity suppliers (ESs). However, the effectiveness of the trading largely depends on the willingness of ESs to participate. In reality, ESs are self-centered and want to maximize their benefits regardless of whether a certain demand is met or not [4]. Meanwhile, an aggregator is also a profit-seeking entity interested to maximize its utility. As such, considering the rationality of the different electricity entities, an incentive scheme is required to motivate them to trade energy.