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EVs and the Grid: Implications and possible solutions [free access]

March 12, 2019

 

Sales of electric vehicles (EVs) have been increasing rapidly, in large part supported by governments to back their climate change mitigation agenda. While battery costs are falling, government policies and incentives have been a key driver in spurring the growth of EVs. Meanwhile, global carmakers have announced ambitious plans to improve their offerings and expand production. According to a study by the International Energy Agency (IEA), there will be about 125 million EVs in the world by 2030. This represents a huge jump from IEA’s estimate of 3.1 million EVs in 2017.

 

As the demand for EVs increases, so will the need for an adequate charging infrastructure. Early adopters of EVs have relied upon private charging connections. However, as EVs become more prevalent, the development of publicly available fast charging infrastructure becomes imperative and needs reliable grid connectivity. A fundamental question that needs attention is how this envisioned growth in EVs and the related charging infrastructure will impact the electricity grids.

 

Many studies have been conducted and papers have been written on this subject. Experts indicate that growth in demand for EVs will not have any major impact on the larger transmission and distribution network. But it will impact the local electricity grids, i.e. the ‘last mile’, at two distinct levels – demand for additional electricity and the power delivery system itself. The distribution network operators and utilities will need to be attentive of the growing numbers of EVs in their regions – whether these vehicles are charged at homes or at the public fast charging stations.

 

As active loads, EVs will no doubt place additional demand for energy on power grids. However, it is now widely acknowledged that they may not have a significant impact on the nationwide demand for electricity. Instead, the challenge is the local network, where there is a risk of overloading residential transformers. Many analyses conducted so far indicate that several EV owners charging simultaneously will have an impact on the local grid by changing the shape of the local load curve. EVs would increase the evening peak demand as EV owners charge their cars at the end of their workday. This change in the load curve will be most visible in the urban and suburban areas where many of the early adopters of EVs are likely to reside.

 

The Level 2 charging method is currently the preferred mode for charging EVs and is used by vehicle owners at their residential premises as well as at public charging facilities (see the box for definition of different levels of charging). A single EV with a Level 2, 240 V charging system consumes about 7 kVA. Most transformers at the local grid are designed to handle between 10 kVA and 50 kVA of load. There are thus concerns that new evening time peak loads created by several EVs charging simultaneously could overload the local transformers and even shut them down. Often, local distribution grids are not built to handle huge spikes in electricity demand. Excess load will impact the quality and reliability of electricity supply in the affected areas.

 

The issue does not end there. Residential transformers often do not have any in-built IT systems to inform the utilities about their condition and health. In many cases, utilities do not have any system in place to know when an overload occurs.

 

The seriousness of the matter increases as fast charging infrastructure at public places expands in the coming years. Public fast charging is especially important for certain businesses such as electric taxis and commercial fleets. High charging power requirements and unpredictability of demand from fast charging stations could severely impact grid operations. The distribution system operators may not be able to match up with the demand from fast charging stations, especially in urban areas where there are already risks of congestion. In a study in the US, it has been indicated that the local grids may be able to accommodate a few 50 kW chargers at frequent intervals, however, even a handful of fast chargers of 150 kW and 350 kW would likely require upgrades to the grid or even a separate transformer off the distribution line.

 

Upgrade of local grids to accommodate the increasing number of EVs could be, thus, challenging and expensive. Utilities would not only need to spend on evaluating the growing load requirements but also on the equipment and technology for expanding system capacity. Experts and technology providers are offering solutions to overcome these challenges. These issues can be countered with minimal infrastructure-altering schemes such as time-of-use (TOU) charging, smart charging and other possible demand management solutions.

 

In a TOU scheme, electricity rates vary by time of day or by local grid capacity. Owners of EVs are incentivised to charge their vehicles during off-peak hours with lower electricity rates. This usually requires pre-programming the start time through the charger or through the EV itself. While in most countries, TOU rates have fixed time periods that are designated as peak or off-peak, some regions around the world have real-time pricing with dynamically determined peak and off-peak times. There is, however, one limitation. While ToU charging reduces the load at peak hours, it might create a new high load during the off-peak hours.

 

Smart charging is a programme when a vehicle can respond to signals from the utility to start, stop or reduce charging. This sort of control can be accomplished if either the EV or the charger is able to communicate with the grid. EV charging could be maximised when wholesale prices are low or when renewable energy generation is high. In order to not exceed utility transformer capacity, limits are often imposed on total electricity consumption at fast-charging installations.

 

Smart charging is increasingly being viewed as a key solution to mitigate the impact of EVs on grid infrastructure and defer investment. For example, a recent report by the UK energy regulator Ofgem warned that without a guaranteed flexible charging, or load-spreading approach – whereby EV users mainly charge their vehicles when there is excess generation in the system – meeting the government’s targets for EV penetration will probably entail expensive network reinforcements.

 

Combining fast charging at public charging stations with energy storage facilities could also mitigate grid impacts. During low demand periods, a storage device could be charged at a constant rate from the grid or from the on-site solar photovoltaic facility. The storage unit then discharges during peak consumption times. The flexibility offered by the storage device can diminish the stress on utility transformers and defer the need for infrastructure upgrades.

 

With smart charging, EVs can in fact become an asset for the grid. They could offer demand response and ancillary services, such as regulation, load-following and spinning reserves, to the grid. Known as Vehicle-to-Grid (V2G), this application allows for bi-directional flow of energy between the vehicle and grid such that the vehicle can both charge from the grid and discharge excess energy back to the grid. EV owners can make a profit by charging cars when the demand is low and electricity is cheaper and sell it to the grid when power demand spikes, saving the grid from the overload. Pilot studies have shown the willingness of EV owners to participate in coordinated smart charging.

 

It must be understood that smart charging would require some up-front investments. As explained above, smart charging essentially consists of controlling the time and rate at which an EV is charged. This enables the grid operators to handle EV charging according to the grid constraints and customers’ needs. This means that grid operators must have the right communication and control system in place to manage the charging process. This requirement also ties into the need for interoperable IT and data standards to coordinate data transfer between the grid, the charging point and the EV. For smart charging to be reliable and practical, interoperability is critical.

 

Thus, launching smart charging programmes will involve some investment from utilities. However, experts suggest that the payoff could mean that EVs would be less of a concern for the grid operators. EVs, in fact, could benefit the grid by making it more cost-effective, resilient and green.

 

EVs present unique challenges and opportunities for grid operators and utilities. While the increased demand for energy from EVs is manageable for the larger T&D grid, issues may arise at the local grid level. As several countries draft ambitious plans to bring millions of EVs on to their roadways in the years ahead, electric utilities will need to find solutions and build strategies to mitigate the risk to grid infrastructure. At the same time, it will be critical for governments and regulators to develop policies and incentives that will help optimise the services that the EVs could provide to the grid. And how these programmes are designed and promoted will have a significant impact on the management and operation of future grids.

 

 

 

 

Charging technology

 

EV chargers can be categorised as:

 

  • Level 1: Smaller units that plug directly into a standard 120 V outlet. These types of chargers typically require a longer period of time, 12-15 hours, to recharge the vehicle. Can charge up to 1.9 kW.
  • Level 2: Requires a 240 V electrical circuit and charge the vehicle battery much faster than a Level 1 charger, in 4 to 6 hours. Today, this is the preferred method of EV charging at both private and public facilities. It requires special equipment and connection to an electric power supply dedicated to EV charging. The voltage of this connection is either 240 V or 208 V. Typically charges between 3.3 kW and 7.2 kW, may go up to 11 kW or 22 kW.
  • Level 3: Fast charging an EV in 30 minutes or less. Works at higher voltage (480 V), making it impractical for residential charging. Involves significantly higher costs for charger and installation. Charges mostly at 50 kW. Higher ratings going up to 150 kW and 350 kW are being experimented with.