Changing electricity markets call for new ways of handling supply and demand. The desired goal is to increase the utilization of renewable energy while ensuring reliable supply and minimizing the costs. We present an approach aiming at this goal that handles a large number of flexible energy offers from producers and consumers by aggregating them and scheduling these aggregates to minimize a cost function. We explore the influence of aggregation on the performance of scheduling, establishing that a trade-off between keeping the flexibilities of flexible offers and reducing their number is what yields the best results.