Grid connection approval is one of the least glamorous parts of a commercial solar or battery storage project — and one of the most consequential for project timelines. Businesses that discover the UK Power Networks G99 application process only after their installation date has been booked can face delays of weeks to months, with panels or batteries on site and no legal authorisation to switch them on.

This guide explains exactly what the G99 process involves for Essex commercial sites, how it differs from the simpler G98 notification used for smaller systems, what the DNO application timeline looks like in practice, and what your installer should be doing on your behalf to keep the project on track.

When a commercial solar or battery storage system connects to the electricity grid, it becomes part of a network that UK Power Networks (UKPN) — the Distribution Network Operator for Essex, East Anglia, and parts of London — is responsible for managing safely. A new generation or storage asset on that network affects how power flows, what protection systems need to respond to, and in some cases whether the local infrastructure can handle the additional capacity without reinforcement.

The G99 application process is UKPN’s formal mechanism for assessing and approving these connections before they happen. It requires the installer to submit technical details of the proposed system — inverter specifications, protection relay settings, export capacity, battery round-trip characteristics — so that UKPN’s engineers can model the impact on the local network and either approve the connection as proposed, approve it with conditions, or require modifications before approval is granted.

The process exists because an unapproved connection can affect voltage stability, compromise protection systems that keep the network safe during faults, and in worst cases create safety risks for other network users and engineers working on the local infrastructure. It is not bureaucracy for its own sake — it is a genuine engineering sign-off that protects both the business installing the system and the wider network.

Two engineering recommendations govern how solar and storage systems connect to the UK distribution network: G98 and G99. Understanding which applies to your system is the starting point for managing the grid connection process correctly — and getting this wrong is one of the most common mistakes made by inexperienced commercial solar installers.

The DNO application timeline for Essex commercial solar and battery storage projects through UK Power Networks follows a broadly consistent sequence. Understanding it allows you — and your project manager — to plan realistically around it rather than discovering the constraints after an installation date has been confirmed.

Most Essex commercial G99 applications are approved within 4–8 weeks without significant complications. However, certain site characteristics and system specifications consistently trigger longer assessment periods, requests for additional information, or conditions that require further action. Knowing these in advance allows your installer to design around them or flag them early.

Export capacity relative to network headroom. Every section of the distribution network has a finite capacity for generation to export onto it. If your proposed system’s maximum export figure is large relative to what the local network can absorb, UKPN may require export limitation — a setting on the inverter that caps the amount of power the system can push to the grid at any moment. For battery storage systems, this can sometimes be avoided by demonstrating that the battery will absorb surplus before it reaches the grid, reducing effective export. This requires accurate modelling in the application.

Protection relay requirements. Larger commercial systems — typically above 50 kWp or those with battery storage — may be required to install a protection relay between the system and the grid connection point. This is a piece of equipment that monitors grid conditions and disconnects the system rapidly during a fault to prevent the generation asset from feeding a fault on the network. The relay must be set to UKPN’s specifications and tested before commissioning. This adds equipment cost (typically £1,500–£4,000 depending on specification) and requires an additional commissioning step.

Network reinforcement. In some parts of Essex — particularly rural areas served by longer, lower-capacity feeder cables — the local network may lack the headroom to accommodate a large commercial system at all without reinforcement. UKPN will identify this during their assessment and quote for the reinforcement works separately. Reinforcement timelines and costs vary significantly; in the most constrained cases, it can add months to the project. This is rare for mid-size commercial systems but worth being aware of for very large installations above 150 kWp.

Incomplete or inaccurate applications. The most avoidable source of delay. UKPN will issue a request for further information if the submitted technical pack is missing documents, contains inconsistent specifications, or does not include required data sheets for the inverter or protection equipment. Each request for information pauses the assessment and resets part of the timeline. A thorough, well-prepared application from an experienced installer avoids this entirely.

Managing the UK Power Networks G99 application is part of what separates a competent commercial solar installer from one that specialises in residential work and treats commercial projects as a scale-up of the same process. The questions below are worth asking any installer you are considering for an Essex commercial solar or battery storage project.