  The ambitious targets for renewable energy penetration warrant huge
flexibility in the power system. Such flexibility does not come free. In this
paper, we examine the possibility of utilizing storage systems for achieving
high renewable energy penetration, and identify the trade-off between providing
flexibility and arbitrage against real-time prices. More precisely, we
investigate the relationship among the operation cost, storage capacity, and
the renewable penetration level. This illustrates the value of storage as well
as the true cost induced by the high renewable penetration targets.
