The Role of Electric Vehicles in Global Power Systems

Andreas Thingvad

    Research output: Book/ReportPh.D. thesis

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    Abstract

    The transition of the personal transportation sector to electric vehicles (EVs) cause a number of technical challenges for the power system but also holds the key to unlocking a stable and efficient system based on renewable distributed energy resources (DER). The thesis starts by investigating the energy requirements for public charging, before focusing on the behaviour of private and semiprivate infrastructure where the flexibility and service provision ultimately will be focused. Charging an EV is regarded as trivial with chargers installed on private property, which is found to be the case for 78% of the Danish cars. Hence, the owners would rarely need to charge outside their household as EVs with 300 km range are able to complete the daily driving distance without range extending charging in 98.4% of the days. Car owners in the cities often do not have this option and rely on the public charging infrastructure. The thesis analyses driving, parking and car ownership data based on a Danish national transport survey with 58,761 interviews to quantify the need, in terms of energy demand, for public chargers on a national level and in the largest Danish cities. The potential of reducing the need for public charging points by installing destination charging at existing shared parking facilities next to the household and next to the workplaces is found to be up to 87%. EV owners that can charge at home might experience the adverse effects that uncontrolled charging may have on the local distribution grid. Controlling the charging processes can not only mitigate this impact, but also be used to deliver several kinds of services to the power system such as local congestion management, increasing the consumption of DER or maintaining the power balance between production and consumption. With a bidirectional vehicle-to-grid (V2G) charger, EVs can become power buffers and deliver grid services for extended periods. Primary frequency regulation is the most profitable service that can be delivered by EVs, but the service can lead to fully charged or depleted storages. Several years of frequency measurements of the Nordic synchronous zone are analysed to determine statistical bounds of the energy content on different time scales, determining the required battery capacity. Real frequency and market data are used for calculating the revenue under the Nordic and the British regulatory framework. Revenues are both calculated for a best case scenario where the future energy requirements are known in advance (1106 €/a) and for an implementable case where the controller reacts to the experienced energy content (948 €/a). The second controller is experimentally validated, and is found to have a response time of 2 s from a frequency deviation is measured in a remote location to the active power is measured on the grid side of the V2G charger. Accelerated battery degradation, resulting in a reduced capacity, is the main concern when discussing V2G services. This thesis gives a unique empirical insight into the long-term effects on batteries performing frequency regulation. To this end, an empirical method for measuring the battery capacity of series produced EVs via the DC charge port was developed. The reproducibility of the method is demonstrated with repeated tests on new and aged vehicles and the results are compared with the EVs internal estimates, read via the on-board diagnostics port. The capacity test method is used to evaluate the battery degradation of a fleet of commercially owned EVs which, as a part of the world’s first commercial operation, have been used for frequency regulation for five years. The EVs have, together with ±10 kW V2G chargers, been delivering primary frequency regulation for 15 hours per day with a daily energy throughput of 50.6 kWh. The usable battery capacity, initially found to be 23.0 kWh, after two years is reduced on average to 20.7 kWh and after five years is reduced to 18.9 kWh. The cost of increased battery degradation due to the service provision is found to be 86 €/a which together with the cost of energy
    conversion losses in the charger reduces the profit to 599 €/a.
    Original languageEnglish
    PublisherTechnical University of Denmark
    Number of pages194
    Publication statusPublished - 2021

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