Project deliverable Open Access

Specification of grid constraints

Jesus Varela Sanz

ASSURED project aims to develop and test an interoperable high power charging point for heavy-duty vehicles. Buses could charge in 30 seconds, 5 minutes or 30 minutes using powers up to 600 kW. High power systems and short charging times imply special grid operation conditions that should be taken into account.

The objective of this deliverable is to establish a basic context and a set of requirements coming from electricity grids to influence positively the high power charging system design in order to grant an easy and smooth integration of this kind of equipment into electricity distribution systems.

In order to understand the “State of the Art” of electric-HDV (e-HDV), the real on-going exploitation experiences are reviewed, to continue with a brief analysis of existing roadmaps, technical press recommendations and European projects learnings. The deployment of e-HDV is still starting, but a representative set of these experiences in cities has been reviewed to understand the “state of the art”. Several aspects are briefly reviewed: the number of e-buses, the number of charging points installed, the charging policies (overnight, opportunity charging) used in each city, the technologies that have been employed (pantographs, etc.), the power of the current systems, the expectations and plans of the cities on the electrification of public transport, etc. China is the clear leader in the use of e-buses with the 98 % of the world total, while USA and Canada could be the next in the list with a few hundreds of electric HDV. In Europe, UK is the first in the list with 213 e-buses, followed by Germany, Belgium and Netherlands.

This study gives an overview of the status of e-HDV, but it necessarily should be completed with an overview of the tendencies of deployment of other types of electric vehicles and the charging infrastructure as well as the energy and power required. Looking at the drivers of transport electrification progress, the evolution of electric cars has been significant in Norway where has been incentivized with tax exemptions, and it is expected a relevant progress in the next years in Germany, France and U.K. Different studies show that there is a real risk of an important increase of power peaks in the consumption profiles due to the introduction of EVs with special impact on the LV grids. Several studies about the evolution of EV market are presented. For 2030, some studies foresee an increase of battery-EVs that will cover 50% of cars’ market while diesel vehicles, that nowadays cover more than 50% of the European market (depending on the source), will reduce its share below 30%. The tendency for urban buses is quite similar with a market prediction even higher for e-buses.

In terms of global energy demand, an increase is also expected, but the impact in the system can be easily maintained under control. The only consideration about it is that EV load repartition strongly affects the peak load and the required capacity to fulfil the system needs.The point of view of the European Association of Green Vehicles (EGVI) extracted from their roadmap is presented, focusing on the charging and grid related aspects. They raise the importance of the charging infrastructure and the regulatory efforts made by EU to encourage Member States to expand the network of charging points. They also recommend public education, vehicle sharing and increasing the autonomy of EVs. In the longer term, they foresee the need of bidirectional smart charging to implement vehicle to grid (V2G) services.

Reviewing other technical information and research projects, interesting inputs can be found. For example, the use of stationary batteries to reduce the peaks of fast charging or bus-high power charging, or the suggestion to connect the high power chargers to MV grid. A proper management of the electrical loads to reduce the impact on the grid is becoming a key topic. For example, the “overnight” and “opportunity charging” offer possibilities to accommodate the needs in a cost-effective way and with different impact on the grid, for e- HDV, while “Smart charging” can allow a penetration of 50% of EV without grid reinforcement.

In order to understand the reasons that explain the slow pace of transport electrification, and the limitations that prevent or delay the process, the point of view of DSOs, electricity providers, electricity service providers, bus operators and manufacturers has been obtained, sometimes through their European associations. DSOs consider that flexibility should be taken into account when deploying the charging infrastructure. They identify the power as the challenge and propose the use of “Smart charging”, regulation and tariffs to activate it, and the involvement of the DSO in planning and control of charging points assets (not the exploitation of the service).

Energy and Energy Service Providers detect a set of technical, environmental and economic limitations. They consider that the roles of the involved stakeholders should be analysed, especially in a context of access limitations to the cities, growing of EV fleet and lack of charging infrastructure that has to be deployed to foster the EV market.

For the automotive industry, the cost reduction and compatibility are key drivers. They foresee a growing in the electrification of public bus transport in the cities that should be pushed by standardisation and interoperability. They observe important advantages in the electric powertrain technology (operation speed, torque, noise, vibrations, gases emission, etc.) but the technology should be robust, reliable and safe to receive the bus-operators investments. The cost, efficacy, need of raw materials, and other aspects are reviewed as well. They remark that electric vehicle is still not emission free.

Bus operators discuss the possibility of eliminating diesel from the cities, and claim for a legislation on clean air. Public transport should offer comfort, service and good prices. Consequently, when investing they take into account the cost of ownership (including maintenance) and the expectation of satisfaction of their customers. When analysing the investments on e-buses, they consider the different possibilities of charging and consequences in type of charging, size of battery, battery aging, space for passengers, difficulty of moving existing bus-stops, etc.

The impact of charging infrastructure on generation and transmission grids is possible, but it is clearly higher on Distribution grids. The needs of DSOs for the expansion and operation of grids are analysed. The expectations of EDSO4SG for 2030 is an increase of 1% to 10% in energy, which can be easily managed and an increase of up to 20% in peak load which should be properly treated.

A massive deployment of EV could require LV (typically <1kV) grid reinforcement or larger LV grid connection(s), for example in charging zones. Traditionally, LV grid has been poorly supervised or controlled, but “Smartening the LV grid” will be necessary in the short medium term. On the other hand, at MV (<66kV), the impact of high power charging systems on the most common grid constellations and extensions must be assessed.

The grid side requirements for the design of a high power charging point and the reasons for these needs have been reviewed arriving to conclusions that are summarised at the end of this document. The needs of a transformer inside the enclosure of the charging point or the relevancy of connecting it to MV grid are some of these conclusions.

The main limiting factors at LV level and at MV level have been analysed. The first conclusion is that a direct, short-term congestion challenge is not expected with AC- chargers for cars, but the capacity and power quality could be main challenges, especially dealing with e-HDV in urban areas.

The needed measurements in the charging point and the parameters to be considered as well as the limits to be respected have been detailed in the study. The IEC 6100 standard and the European Standard EN 50160 are the main sources of these guidelines. ASSURED solutions should respect the limits emerging of these norms.

The main aspects to be considered when connecting charging stations to the distribution grid have been explained: grid overloads, grid voltage drops, consumption peaks, N-1 needs, reactive power, harmonics, in-rush current and voltage unbalance. Congestion, voltage drops and consumption peaks are the most frequent issues are developed more in deep.

As far as ASSURED project plan to design high power (up to 600kW) installations to be placed in the cities where citizens walk around, appropriate safety and security measures should be implemented. The main problems that may appear and suggestions about the ways of avoiding incidents have been developed.

To conclude, the future of the EVs, and cities have been explored as a source of additional requirement, given that new services may appear. Some of them could be related to electric car uses, but also bus-stops and bus infrastructures may be involved and the future has to be considered at least in terms of potential modular expansions of the systems. A shared use of infrastructures will probably be compulsory for electricity system optimization and general infrastructure cost reduction, leading to a few additional requirements related to payment, identification of vehicles and roaming understood as interoperability among European retailers.

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