LOW VOLTAGE GRID CONNECTION OF PHOTOVOLTAIC POWER SYSTEMS ETSU Report No. S/P2/00215/REP EATL Report No: 5010 Contractor: EA Technology Ltd Prepared by: A Collinson, EA Technology J Thornycroft, Halcrow Gilbert The work described in this report was carried out under contract as part of the New and Renewable Energy Programme, managed by the Energy Technology Support Unit (ETSU) on behalf of the Department of Trade and Industry (DTI). The views and judgements expressed in this report are those of the contractor and do not necessarily reflect those of ETSU or the DTI. First Published September 1999 Executive Summary This report forms the final report of the project entitled “Technical Criteria for the Electrical Integration of Photovoltaic Systems into Electricity Supply Networks”, supported by ETSU and the DTI (contract number S/P2/00215/00/00). The project was jointly supported by EA Technology’s Core Research Programme, carried out on behalf of the UK Electricity Supply Industry (ESI). Note, the Core Research Programme subsequently developed into EA Technology’s Strategic Technology Programme in 1997. Introduction & Background The use of photovoltaic (PV) systems is well established for stand-alone applications, but in recent years there has been growing interest in grid-connected PV systems using DC to AC inverters. Building-integrated PV systems for the domestic market have been identified as offering a large potential power source in the UK. However, the integration of photovoltaic power systems into local electricity supply networks in the UK is currently in the early stages of development. The current high costs of PV systems mean that relatively few requests have been received by UK electricity companies to date for the connection of such systems. However, the increasing international activity related to cost-reduction of PV systems, especially in the area of building integration, means that significant reductions in basic system costs will continue to be made. If the current trend in cost reduction continues it will not be long before PV systems are a true commercial proposition. Consequently, any increased use of PV systems is likely to have a significant impact on the design, operation and management of electricity supply networks. The electricity supply industry has identified several technical and commercial issues which have caused them some concern. These issues needed resolution before grid connected systems could become more widespread. Consequently in 1994, the DTI established a programme of work to investigate and overcome the barriers to the introduction of grid connected PV and release this potential, as well as supporting other projects designed to stimulate the new technology. With this in mind, and taking into account the greater practical experience of grid- connected PV systems of countries overseas, the UK Government made the decision to become involved in the international collaborative research work which was being established to investigate the technical issues related to grid-connected PV, with the aim of tackling these issues to ensure that no unnecessary technical barriers existed to inhibit the future expansion of grid connected PV systems in the UK. Involvement in this work would have the added benefit of encouraging UK research and manufacturing companies to develop PV power systems for the UK and overseas markets. Objectives of the Work The project was designed to:- • explore the concerns of the UK ESI and address the concerns where possible • raise awareness of the potential for application of PV in the UK • provide the UK input to Task V of the IEA PV Power Systems Implementing Agreement and benefit from the results of that programme. In detail, the objectives set down were:- • To develop specific research and demonstration activities which will resolve concerns over technical problems • To assist the ESI to participate in the development of international standards and norms which will eventually apply in the UK via participation in their IEA work on pre-standards • To add to technical understanding of PV and grid connection in the ESI engineering centres • To assist the existing UK PV industry and new entrants to learn from the Task V technical activities and to channel the industry’s input to Task V discussion and decisions • To encourage co-operation between the PV industry and the ESI in the development and acceptance of new products • To develop the guidelines and reference materials for application of grid connected PV systems in the UK • To improve awareness in the UK PV industry and ESI of export opportunities • To develop recommendations for improved procedural practices Summary of Work It is generally accepted that grid interconnection of photovoltaic (PV) power generation systems enables effective utilisation of the generated power. It enables constant and automatic adjustment of electric power from the utility grid side and the PV system side. However, technical requirements of both the utility power system grid and the PV system must be satisfied to ensure the safety of the PV operator and the reliability of the utility grid. Clarifying the technical requirements for grid interconnection and solving the problems are therefore very important issues for the widespread application of grid-connected PV systems. In order to address the technical issues and develop a consensus view, the project established a consultative group of representatives from the ESI. This group has been instrumental in both guiding the technical work and raising awareness in the industry. This report also summarises the important findings from the first stage of activities of the International Energy Agency Implementing Agreement on Photovoltaic Power Systems working group examining “Grid Interconnection of Building Integrated and Other Dispersed Photovoltaic Power Systems” (commonly known as Task V) and critically examines these issues from a UK perspective. The Task V work took place between 1993 and 1998 and covered a review of existing techniques and rules related to grid interconnection of photovoltaic power generation systems and included both theoretical and experimental investigations. The main objective of this work was to provide technical input into the development of technical guidelines for the grid-connection of photovoltaic (PV) inverter generators. These technical guidelines have subsequently been taken on board by the electricity supply industry, who are about to produce Engineering Recommendation G77, entitled , “UK Technical Guidelines for Inverter Connected Single Phase Photovoltaic (PV) Generators up to 5kVA” to provide an industry-endorsed guide to grid-connected PV in the UK. The technical guidelines produced as part of this work formed the original basis for G77. Summary of Results A major output from the project has been the Draft G77 “UK Technical Guidelines for Inverter Connected Single Phase Photovoltaic (PV) Generators up to 5kVA” which is currently being prepared for publication as formal guidance to the ESI. The provisional draft guidelines were launched to an audience of ESI representatives and PV industry representatives at a workshop 1999 hosted by EA Technology in February 1999. As well as this, the sharing of experiences between the members of this group and the PV specialists has helped to smooth the path for new PV installations during the life of the project. Conclusions and Recommendations The UK Consultative Group in conjunction with the IEA PVPS Task V working group has successfully completed the first stage of work by identifying grid interconnection issues of PV systems and drafting possible recommendations for improvement. During the period of this work it has been observed that some countries have developed new guidelines for grid interconnection and some countries have revised their guidelines due to the increased knowledge of requirements for grid interconnection of PV systems. The introduction of small-scale, grid-connected PV systems have also progressed in the UK and on a larger scale abroad. AC modules, a new concept of a PV module with a tiny embedded inverter (typically up to 100Wp output power), have been developed and are now sold in some countries, including the UK. There are still many issues still to be resolved such as islanding issues, interconnection of many PV systems in a concentrated area, cost evaluation of grid interconnected PV systems and so on. These issues will be studied in future work, both within the UK PV Experimental Programme (Phase 2) and the newly established UK Strategic PV Network Study, in collaboration with the continuing work of the Task V Working Group. In general there is a need to look at the effects of a range of PV penetration scenarios on system operation and performance, with concentrations of multiple PV systems operating in UK climatic conditions. The development of the technical guidelines document highlighted the main areas of concern for electricity companies. These areas of concern are: • voltage level control • power quality, including harmonics, power factor and DC injection • the real risks associated with islanding • safety, including earthing and generator isolation • rate of change conditions (e.g. fast moving clouds) and flicker • capacity of the existing LV network to accept PV systems • future design of LV distribution networks containing PV systems • the impact on infrastructure costs • the impact on operating and maintenance costs • effects on spinning reserve and unloading of conventional plant