C I R E D 22 nd International Conference on Electricity Distribution Stockholm, 10-13 June 2013 Paper 0699 CIRED2013 Session S2 Paper No 0699 USING ELECTRIC VEHICLES TO MITIGATE IMBALANCE REQUIREMENTS ASSOCIATED WITH HIGH PENETRATION LEVEL OF GRID-CONNECTED PHOTOVOLTAIC SYSTEMS Salem ALI Nicola PEARSALL Ghanim PUTRUS Northumbria University-UK Northumbria University-UK Northumbria University-UK ali.salem@northumbria.ac.uk nicola.pearsall@northumbria.ac.uk ghanim.putrus@northumbria.ac.uk ABSTRACT This paper considers the use of electric vehicles as mobile energy storage to mitigate the effects of output power production associated with high penetration level of grid- connected photovoltaic (GCPV) systems. Power flow analysis of a typical the low voltage distribution network is carried out to investigate the voltage level at each busbar along the low voltage feeders. A model of typical UK low voltage distribution network has been developed in the MATLAB program environment. The voltage profile of the network model was investigated with and without GCPV systems connected. Then, electric vehicles are integrated into the network model and the voltage level was investigated when these vehicles are in charging condition while the PV systems remain grid-connected. The paper presents a description of the network model and the results of simulations. INTRODUCTION Electrical energy storage technology has the potential to facilitate the high penetration level of variable renewable energy sources, such as wind turbines and grid-connected photovoltaic (GCPV) systems, which are an alternative option for generating the power near the customer load and reducing greenhouse gas emissions from the electric power sector. In the UK, electricity generation is still largely from fossil fuels, which causes the release of harmful gases into the atmosphere [1]. The use of PV systems and other types of renewable energy sources such as wind turbines will help to reduce the gas emissions thereby helping government to achieve 15% of its energy from renewable sources to meet their binding 2020 target [2]. Although PV systems and wind turbines are intermittent electricity sources and their output power varies with sunshine intensity and wind speed respectively, PV power generation may be less challenging for grid integration because sunlight is more predictable than wind. In addition, PV systems have many technical advantages such as flexibility, simplicity to install in any area where the solar irradiation is available, being non-polluting, emitting no noise during electricity generation and requiring little maintenance. However, since operators of the electrical grid must constantly match electricity supply and demand, installing a high penetration level of GCPV systems into low voltage distribution networks within a relatively small area, referred to hereafter as clustered, may have an impact on the power quality and reliability of the existing distribution network. Normally the direction of power flow is from higher to lower voltage levels in the distribution networks. This system architecture was a technical and economic choice. However, as the amount of locally installed GCPV systems is increasing rapidly, some of the GCPV output power will be consumed locally within the building and any excess will be injected into the grid. Feeding power to the grid could happen during the hours of daylight when the generated power is higher than the load demand due to a high solar irradiation level, especially in sunny weather conditions (summer season). In this case, the main issue to be expected is that the export of active power to the grid could result in reverse power flow and may cause an excessive voltage rise along a distribution network feeder violating the voltage limits. In this paper, the UK low voltage distribution network is taken as a case study to investigate this issue, together with the integration of electric vehicles as a mobile storage system to absorb the surplus power and keep the voltage in the permitted range. Generally, the rated output of a typical UK domestic GCPV system is in the region of a few (1-5) kW [3], based on the average space available on the roof of a residential house and the system efficiency. Figure 1 shows a typical daily load profile [4] and the output power of a 3 kW PV system on a clear summer day in the UK. The summer load profile is considered as it provides a good example of when there is more energy being produced by the PV than is consumed by the local load across the middle of the day. Fig.1. Typical house load profile and PV production for a 24 h period (summer season)