Investigation of technical barriers and solutions for high penetration of photovoltaic systems in the UK

Rising concerns on climate change due to greenhouse gases have led to the UK Climate Change Act 2008 which sets a target to cut CO2 emissions by 80% of 1990 levels by 2050. Photovoltaic (PV) systems form one of the main technologies capable of delivering the target. Though the ability to deliver reductions in the installed costs of PV will determine the level of sector growth, this growth could be limited by several technical factors. As about 90% of the number of PV systems installed in the UK belong to the category of residential systems with individual ratings less than 4 kW, this study focuses on this sector. This sector represents 20% of the total installed capacity in the UK. This research aims to identify the key technical barriers and associated solutions to increase PV penetration in a distribution network in the UK. The research defines the realistic worst-case scenario to evaluate the performance of the distribution network with PV and then quantifies the percentage of PV penetration at which the presence of PV may adversely affect the performance of the distribution network. The steady-state analysis conducted shows that the voltage at parts of the feeder violates the statutory limits at 20% penetration for the realistic worst-case scenario, followed by reversal of net active power and low power factor at the secondary of the substation when penetration level is over 30%. The results indicate that the minimum load of the feeder under consideration during hours of daylight and the more common irradiance level at that geographic location should be used rather than a hypothetical worst-case scenario to evaluate the maximum allowable contribution of PV systems in the feeder. Analysis of the performance of distribution networks under fault indicates that the tripping time of the relay may be delayed under the presence of PV. However, the probability of false tripping of the relay is very low. This research also identifies solutions to increase the contribution of PV systems in the energy mix and evaluates the effectiveness of the solutions. The solutions in the order of decreasing effectiveness are changes to tap changer settings, reactive power control and PV generation curtailment. A strategy to increase the contribution is proposed. This includes changes to the settings of the tap changer (increases the PV contribution from 20 to 40%) followed by active power curtailment (which would increase PV contribution from 40 to 60%). A phased approach like this would enable the regulators to plan for the transitionary period to increase the contribution of PV