UK ENA G99 Type B Commercial Solar Commissioning and Testing Guide

Key Takeaways

• ENA G99 applies to generators connecting to the public low voltage network at more than 16 amps per phase, which includes most commercial solar installations.
• Loss of Mains (LoM) protection must use Rate of Change of Frequency (RoCoF) set to 1Hz/s with a 500 millisecond time delay, replacing older vector shift methods.
• Distribution Network Operators (DNOs) charge Connection Offer Expenses for non-domestic applications, including initial and subsequent fees, with strict payment terms.
• DNOs reserve the right to witness testing of your system and protection settings, and non-compliance with G99 can lead to enforcement action, including de-energisation.

What is ENA G99 Type B Commercial Solar Commissioning?

Commercial solar commissioning in the UK, particularly for installations designated as Type B, involves ensuring that your generating equipment complies with the Energy Networks Association (ENA) Engineering Recommendation G99. ENA G99 sets out the requirements for connecting generators in parallel with public low voltage networks when the connection is for more than 16 amps per phase. This standard is a legal requirement for certain generators connecting on or after 27 April 2019. Commissioning confirms that the installed system meets these technical and safety standards before it can operate on the grid.

Understanding ENA G99 Requirements

The Energy Networks Association (ENA) is the trade association for energy networks in the UK. Its standards, such as G99, ensure the safe and reliable operation of the electricity grid. G99 superseded the previous ENA standard G59 on 17 May 2019. While G98 applies to smaller generators (16 amps or less per phase), G99 is for larger installations, including most commercial solar projects.

The Electricity Act 1989 places a duty on electricity distributors to make connections to their distribution systems. However, this duty has exceptions, such as when circumstances are beyond the distributor's control, or if the connection would breach regulations, or if it is not reasonable to require the connection. Compliance with G99 is essential for fulfilling the requirements of the Electricity Act and securing a connection.

Loss of Mains Protection and RoCoF Testing

A critical aspect of G99 compliance for commercial solar installations is Loss of Mains (LoM) protection. LoM protection is designed to check if a generator is still connected to the supply network. This applies to generating plants that run in long-term parallel with the distribution network and are within the scope of Engineering Recommendation G59 (now superseded by G99).

A significant change in LoM protection requirements mandates the removal of vector shift LoM protection. This must be replaced with Rate of Change of Frequency (RoCoF). The RoCoF setting requirement has been changed to 1Hz/s with a definite time delay of 500 milliseconds. All generation owners are required to ensure their equipment is compliant to avoid enforcement action.

The Accelerated Loss of Mains Change Programme (ALoMCP) provided funding for generator owners to make these necessary changes between October 2019 and August 2022. Although the programme is now closed to new funding applications, compliance remains mandatory.

DNO Connection Fees for Commercial Installations

Connecting a commercial solar installation to the grid involves specific fees, particularly for non-domestic connection applications. These charges are known as 'Connection Offer Expenses' or 'Assessment and Design (A&D) fees'. They cover the work involved in preparing a connection quote, including assessing network impacts, surveys, site visits, design, and quote preparation.

Electricity North West (ENWL), for example, recovers these costs through the quote's charges. This includes an initial charge, which is part of the total costs recovered upfront, typically ranging from £2,500 to £6,000. A subsequent charge covers the remaining balance of the Connection Offer Expenses, payable upon acceptance of the quote.

Payment terms are strict: the invoice for the quote charge must be paid within 30 days. If the charge is not paid within this timeframe, the connection offer becomes invalid. The applicant remains liable for the charge. Repeated non-payment (for three quotes) can lead to a requirement for advance payment for any future quotes. These charges apply to Extra High Voltage offers, High Voltage offers over 1MW/1MVA, requotes, cancellations (after the cooling-off period), and Gen+ initial assessments. Domestic connections (1-4 properties), budget estimates, cooling-off period cancellations, and service alterations or diversions are exempt from these quote charges.

DNO Witness Testing and Compliance

Distribution Network Operators (DNOs) play a crucial role in ensuring grid stability and compliance. It is a requirement of G59 (and by extension G99) that any material change to the G59 protection settings or generating equipment must be communicated to the DNO which supplies the site.

In some cases, the DNO reserves the right to witness the testing of the system and protection settings. This witness testing may be subject to a fee.

Non-compliance with G99 and LoM protection requirements carries significant consequences. Generator owners who are not compliant will be contacted to establish their current compliance status and will be required to cover the costs associated with the necessary changes. An enforcement programme will be initiated for non-compliant generators, which could ultimately result in the de-energisation of the generation assets. The enforcement process typically involves written notifications at Weeks 0, 4, 8, 16, and 22. If no evidence of compliance is provided by Week 26, the DNO will make arrangements to de-energise the generation site's Connection Point.

Compliance offers benefits such as more reliable generation, reduced likelihood of tripping, consistent income, a strengthened electricity network, cost savings for consumers, increased resilience, and the ability to integrate more renewable electricity onto the grid.

What you can check yourself, and what you cannot

As a commercial solar system owner, you can ensure that your installation records are meticulously maintained and that all communication from your DNO regarding compliance updates, such as Loss of Mains protection changes, is acted upon promptly. You can also ensure that invoices for connection fees are paid within the 30-day timeframe to avoid invalidation of your connection offer.

However, you cannot change inverter or protection settings yourself. Grid-protection settings are complex and must be set by an accredited installer or a qualified professional. Changing these settings without proper authorisation and expertise can breach your connection agreement with the DNO and compromise grid safety. Any material changes to G59 protection settings or generating equipment must be communicated to the DNO.

What the published sources do not tell you

The provided sources offer a comprehensive overview of ENA G99 and DNO connection processes. However, they do not explicitly define the specific technical thresholds or criteria that classify an installation as "Type B" within the G99 framework. While G99 generally applies to generators over 16 amps per phase, the precise distinctions for Type B are not detailed.

Furthermore, specific application forms, such as "Form B3" mentioned in the primary keyword, are not provided or linked directly within the available documentation. The process for appealing DNO decisions or charges is also not detailed. Detailed technical specifications for G99 Type B commissioning and testing procedures beyond the RoCoF settings are not present in these high-level overviews.