Best Industry Practice Manual: Management of network constraints on solar PV generation

In the last few years the amount of solar generation connected to the distribution high voltage networks has increased rapidly in both volume and capacity, and the major part of the income for the owners of these generation sites comes during the summer months. Traditionally the Distribution Network Operators (DNO) carried out planned maintenance and asset replacement on their networks during the summer months, when the customer load was at a minimum.

This gives rise to a conflict of interest between the DNOs, who have to constraint the network to carry out works, and the solar generators, who do not want their generation capacity constrained in the summer months, the period of highest generation output.

Research carried out by the Solar Trade Association (STA) indicates that in the period 2015 to 2017 the lost production of solar generators as a result of outages on the electricity distribution network equates to approximately 1% of the total installed capacity which represents approximately £10m per year across the industry.

Much good work has been done by both the DNOs and the solar generators to develop forums, web portals and other lines of communication to improve cooperation between the two parties. The STA and its members decided to develop this Best Industry Practice Manual (BIPM) to build on the work done so far to create a framework to formalise what constitutes good practice.

It is important that the DNOs and solar generators understand the perspective of the other, in order to improve the level of dialogue between them. The BIPM describes:

  • the legal and regulatory requirements that the DNOs must satisfy and the process they undertake to develop the annual programme of planned outages
  • the impact of constraints for the solar generators
  • the issues with communications that have been raised by both parties.

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The STA and the DNOs have each provided definitions of the terminology they use which should aid in understanding communications.

The types of connection, both in terms of the physical connection to the networks and the capacity of the network to export generation, are discussed and standard terms have been introduced to gain a better understanding of the reasons for constraints.

The BIPM has identified what is considered best practice for the holding and exchange of information on sites and contact details and allocates responsibilities on both the solar generators for ensuring this data is correct and updated when necessary.

The process and responsibilities for the notification of outages is described. One DNO has developed a web portal to communicate information on outages, which is considered a great step forward. The STA consider that the use of web portals for this process is the optimum way forward for two-way communication, but this is not possible at the present time due to concerns about computer system security. Using the one existing DNO portal as a basis the document details the data fields and facilities that the STA suggest should be included in developments of future portals.

The key part of the BIPM is that covering the liaison on mitigating the effects of constraints on solar generation. When the DNO issues the outage / constraint plan, it is the responsibility of each solar generator affected to determine the impact on their business of the outages and to determine whether they want to discuss whether any mitigation is possible with the DNO, and it is the responsibility of the DNO to respond to such contact.

Whilst mitigation measures may or may not always be possible this should be established by effective two-way discussions.

The solar companies are prepared to invest in funding mitigation where a positive cost benefit can be shown, both in immediate measures e.g. overtime or night time working, or in measures which may have both an immediate and long-term benefit, e.g. additional points of isolation in circuits. Such funding may be by individual or group of generators, where several are affected by the same constraint.

There is an issue regarding how the benefits of generator investment in the network could be fairly divided between those investing, and whether this would affect the constraint queue. This encompasses a range of legal and regulatory issues and this is highlighted as an area that will require considerable future discussion.

Communications during planned and unplanned constraints are discussed. The review of outages to identify any issues that can then resolved by discussion is an important part of the process.

A set of key performance indicators to measure the impact of scheduled and unscheduled outages. These indicators will provide a means of monitoring how the collaboration between solar companies and the DNOs is affecting the level of constraints and to identify where there has been a marked change in performance.

This is the first edition of the STA Best Industry Practice Manual and it is hoped that all solar generators and the DNOs will adopt the principles it contains. The principles contained in the BIPM may also be relevant to other generator technologies and the STA would welcome discussions with interested parties. There are still unresolved issues, but it is hoped that these will be addressed in future editions as experience is gained in its application.

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