Smart electric vehicle (EV) charging, which adapts the charging cycle of EVs to both power system conditions and the needs of vehicle users, has the potential to flatten peak demand, fill load valleys and support real-time grid balancing. By optimising the charging process according to distribution grid constraints, utilising distributed renewable energy sources and considering consumer preferences, it reduces reverse power flows and mitigates voltage fluctuations, thereby enhancing grid capabilities. The Central Electricity Authority (CEA), in its report on the integration of EVs to the grid through reverse charging, provides an overview of EV services that can benefit the power system. It highlights the key challenges, expected benefits of vehicle-to-grid (V2G) technology for the power sector, and the important factors enabling V2G. The report focuses on the planning and operational aspect of integrating EV charging infrastructure with the distribution grid, which includes smart charging, EV services for grid support, technologies and EV infrastructure standards, and policy and regulations. Smart charging plays a pivotal role in reducing peak demand, filling load valleys and enabling real-time grid balancing. It can significantly reduce reverse power flows and transformer overloading, thereby enabling grid efficiency. Bidirectional V2G charging is one of the primary forms of smart charging. It is crucial for bringing clean transportation and the low-carbon economy together.
The transportation sector is aware of the low costs involved in generating electricity using renewable fuels. This presents an opportunity for the power sector to increase EV deployment, and serve a decentralised source of storage and flexible loads.
Power Line presents the key takeaways of the CEA’s recent report on Electric Vehicles Utilisation for V2G Services.
V2G system and infrastructure
V2G system architecture primarily consists of centralised and decentralised components. In centralised architecture, the aggregator is a key unit for managing EV charging and discharging processes. The aggregator with access to system data can optimise the smart charging performance and reach an optimum solution. Decentralised architecture or local systems optimise the charging cost through individual decisions that can impact the electricity cost.
The alternate current (AC) and direct current (DC) charging systems provide a choice between on-board and off-board chargers and a trade-off between the cost of the charging station and the vehicle. On-board charging is easily available due to the prevalence of AC charging systems. Smart charging prioritises slow charging over fast and ultra-fast charging because the latter can increase peak demand on local grids when several EVs are charging simultaneously.
A bidirectional system delivers electricity from the grid to batteries and vice versa, and can be facilitated using a double uni-directional or a single bidirectional convertor. A double uni-directional system can be costly and heavier in weight but a single bidirectional can be technically and economically beneficial. This technology assists in voltage regulation and prevents battery degradation.
Establishing a seamless communication system for the transfer of data between the grid and EVs is a complex and necessary task, which requires specific standards. The ISO/IEC 61850 and 15110 standards are laid out for EV charging station-grid communication.
The unpredictable nature of EVs demands a system optimisation algorithm for V2G services. Due to the increase in non-linear variables and system complexity, unit commitment plays an essential role in optimising the despatch schedule.
Expected benefits of V2G technology in the power sector
Congestion in the local grid due to an uncontrolled charging environment can result in load peaks and overload the transmission and distribution system. This would require additional generation capacity. This issue can be avoided by aligning the EV charging load and the distribution load profile. These can work as microgrid-connected storage units and perform a wide range of V2G services.
The integration of variable renewable energy can be accelerated through V2G charging. EVs can increase system flexibility by flattening the peak demand, thereby deferring investments in additional peak capacity. The technology also provides ancillary services like grid balancing by maintaining a steady voltage and frequency. Further, it can optimise power consumption by utilising locally generated renewable energy for self-consumption, reducing reliance on the electrical grid, and lowering energy costs by purchasing cheap electricity from the grid during off-peak hours to power homes when electricity rates are higher. Even as an EV’s battery capacity decreases, energy storage systems can extend the battery’s lifespan, promoting the use of second-use batteries.
Further, using V2G services as mobile power units in areas vulnerable to floods, cyclones, etc., can enhance resilience and provide power to the grid or specific shelters and critical buildings during power outages.
Factors enabling V2G
The Ministry of Power’s “Guidelines and Standards for Charging Infrastructure for Electric vehicles”, released in 2018, and the Ministry of Housing and Urban Affairs’ amendment to Model Building Bylaws for the inclusion of EV charging infrastructure are two of the government regulations that have enabled V2G in EV charging. Slow charging infrastructure can keep EVs connected to the grid for a longer period of time, thus increasing flexibility services to the system. Battery swapping, buffer storage at stations and nighttime charging can also reduce the peak demand stress.
Other important factors include close coordination between the electricity market and the e-mobility market to accommodate each other’s requirements. Revenue generation from multiple streams, including time-of-use tariffs, must be prioritised by regulators. Policies and regulations and appropriate price signals can play a key role in making a business case for V2G. Business models with power system requirements and ancillary service renumerations should be considered.
When many cars attempt to charge at the same time, the smart charging infrastructure rotates them to distribute capacity and avoid overloading the local feeders. By leveraging the synergies between EVs and renewable energy sources in the system, V2G policies may be synchronised with renewable energy sources to minimise the impact of additional load on the power system.
The discoms are responsible for providing electricity connections to EV charging infrastructure and establishing tariff structures, whereas charging point operators and e-mobility service providers can handle the day-to-day operations of the infrastructure.
Challenges
EV charging can impact grid investments due to congestion in the local distribution system, generation assets connected to low voltage levels, extra load from uncontrolled EV charging, voltage imbalances and power quality issues. The limited compatibility of mobility-as-a-service with EV-based flexibility can work against VRE integration by discouraging individual EV ownership in the transport system, resulting in fewer EV batteries connected to the system. Fast charging requires additional capacity from the grid, which further demands expensive protection devices for vehicles and charging stations, bigger cables and transformers. The varying charging patterns of commercial and non-commercial vehicles determine their flexibility. Constant charging and discharging, induced by V2G infrastructure can reduce battery life. Given the large amount of data available to the grid, V2G technology requires cybersecurity measures for seamless and secure data transfer.
Recommendations
The CEA has proposed the following measures to ensure flexibility through appropriate business models and technology, based on the opportunities, difficulties and benefits of V2G technology:
- Standardisation and cooperation within the EV charging ecosystem.
- A bidirectional charging system utilising open source and standard protocols.
- Modifications to a number of Indian standards concerning V2G.
- Management of charging and discharging by a central monitoring system to provide mobility and grid synergies.
- Use of battery switching or storage at charging stations to supplement grid charging.
- Advance integrated planning for the transportation and electricity sectors to prevent network congestion.
- Setting up of charging stations in strategic locations to enable two-way traffic between the grid and mobility.
- Increase in the availability of EV charging stations at work, as many vehicles sit idle for five to six hours each day.
- Investigation by manufacturers into how V2G-enabled EVs can carry out reactive power correction while keeping EV batteries charged and preventing further cycles of charging and discharging.
