4 - Vehicle-to-grid systems: ancillary services and communications

Summary

Introduction

Recent studies have shown that about 70% of the total oil extracted worldwide is consumed in the transportation sector [1]. With rising oil prices, the USA and many other countries have set long-term plans to electrify their transportation system and manufacture electric vehicles (EVs) to reduce their oil consumption. It is foreseen that by 2013, approximately 700,000 grid-enabled electric vehicles will be on the road in the USA. The expected trend in the automotive market share for EVs is shown in Figure 4.1 [2]. A large number of EVs can not only help to reduce the amount of oil and gas consumption, but also provide great opportunities for the power grid, as the batteries of millions of EVs can be used to boost distributed electricity storage. Depending on the type and class, the battery storage capacity for an existing EV varies from 1.8 kW [3] to 17 kW [4, 5]. Note that, currently, the only major electricity storage unit in most power grids are the pumped storage systems [6].

In general, EVs have the capability to work in two main modes of operation: standalone mode and grid-connected mode [7]. These two modes and their transition cycles are shown in Figure 4.2. In the stand-alone mode, the storage capacity of EVs is used as a back-up energy source at the time of electricity shortage or blackout. In addition, it helps to smooth down possible fluctuations in local renewable generation units, such as rooftop solar panels and wind turbines [8–11].