UK Grid Connection Feasibility Studies and DNO Point of Connection Guide

Key Takeaways

• Distribution Network Operators (DNOs) manage your local electricity network and approve all grid connections for solar.
• Your solar installation must comply with specific engineering recommendations like G98, G99, or G100, depending on its size and connection date.
• Outdated Loss of Mains (LoM) protection must be updated to Rate of Change of Frequency (RoCoF) settings to avoid de-energisation.
• Feasibility studies and connection offers from DNOs involve specific technical assessments and can include costs for design and network upgrades.

Understanding Grid Connection Feasibility in the UK

Connecting a solar photovoltaic (PV) system to the electricity grid in the UK requires approval from your local Distribution Network Operator (DNO). This process ensures your installation is safe, compliant with national standards, and does not negatively impact the stability of the wider network. Feasibility studies assess how your proposed solar system will interact with the existing infrastructure, considering factors such as network capacity, fault levels, and thermal limits.

The Role of Distribution Network Operators (DNOs)

Distribution Network Operators (DNOs) are responsible for the local electricity distribution network. This includes the poles, wires, and substations that deliver electricity to homes and businesses. For any new generation equipment, such as solar PV, connecting to the grid, the DNO must approve the connection. Electricity North West (ENWL), for example, "owns, operates and maintains the North West’s electricity distribution network." The DNO assesses your application against national engineering recommendations and may provide a connection offer that outlines the technical requirements and any associated costs.

Key Grid Connection Standards: G98, G99, and G100

Grid connections for solar PV systems in the UK must comply with specific Engineering Recommendations (ERECs) issued by the Energy Networks Association (ENA). These standards ensure safe and reliable operation.

The Energy Networks Association (ENA) is "the trade association for the energy networks." The ENA previously maintained a Type Test Register (TTR) which "closed on 16/04/2024." Its functionality and data have been "migrated to Connect Direct," a platform where you can "register new devices, update existing devices and register new users/manufacturers."

Loss of Mains Protection: Compliance and Updates

Loss of Mains (LoM) protection is a critical safety feature for any generator connected to the grid. It is "designed to check if a generator is still connected to the supply network." If the main grid supply is lost, LoM protection ensures your generator disconnects automatically, preventing dangerous "islanding" where your system continues to power a section of the grid that is otherwise de-energised.

Older LoM protection systems often used "vector shift" technology. However, current requirements mandate that "Where LoM is provided by vector shift, it must be removed and/or replaced with Rate of Change of Frequency (RoCoF)." The updated "RoCoF setting requirement has been changed to 1Hz/s with a definite time delay of 500 milliseconds."

The compliance deadline for these updated EREC G59 requirements "was 1 September 2022." Failure to comply can have serious consequences. If "no evidence of compliance provided or evidence is not sufficient to demonstrate compliance with the Distribution Code, the DNO will make arrangements to de-energise the generation site's Connection Point in accordance with Distribution Code DGC12." This means your solar system could be forced offline. "Any generators who are not compliant and therefore require updates to their protection will be subject to an enforcement programme which could ultimately result in the de-energisation of generation assets."

Safety Warning: Updating LoM protection settings involves critical grid-protection parameters. These changes should only be performed by an accredited installer or qualified electrician. Incorrect settings can compromise grid safety and lead to enforcement actions from your DNO.

Addressing Network Constraints with Flexible Connections

As demand for electricity grows, "it can put pressure on the existing infrastructure and limit available capacity leading to constraints." These network constraints can make it difficult for new solar installations to connect, or they may require expensive network upgrades.

To address this, DNOs offer "flexible connections." These connections, often managed through Active Network Management (ANM) systems, allow generators to connect to the grid under specific conditions. Instead of requiring costly physical upgrades, ANM systems dynamically manage the export or import of electricity from your solar system based on real-time network conditions. This can involve "curtailed connection offers," "export limited connection," or "timed connection" where your system's output is adjusted to maintain grid stability. This approach helps to maximise the use of existing network capacity.

What the Published Sources Do Not Tell You

While Statutory and engineering documentation provides crucial information on DNO roles and connection standards, specific details on "Connection Offer Expenses" and "Assessment and Design (A&D) fees" are mentioned but not quantified. The exact costs for feasibility studies, network upgrades, or specific connection types (e.g., System Normal, Export Limited, Import Limited, Timed Connection) vary significantly by DNO and the complexity of the project. These figures are typically provided in a DNO's specific connection offer.

Furthermore, the full list of DNOs across the UK is not provided, with Electricity North West serving as a detailed example. The specific forms for G98 and G99 applications are not directly linked, nor are the detailed "Connections Charging Statement" documents that outline DNO pricing structures. These documents are usually found on individual DNO websites.

Statutory and engineering documentation also mentions the "Electricity Act 1989" and related regulations but does not detail their specific provisions or "designated strategic plans."