G99 applications: why they get rejected and how to speed up approval

The gap between a customer signing your proposal and their system going live is largely determined by one thing: how cleanly your G99 application goes through. A first-time approval keeps that gap under six weeks. A rejection adds two to eight weeks. Two rejections and you are looking at three to five months on some networks.

For an installer doing 30+ solar installations a month, that is not a compliance problem. It is a cash flow problem and a capacity planning problem. You have panels ordered, an engineer scheduled, and a customer who has already told their neighbour the system would be running by now.

G98 vs G99: which applies to your installation

G98 covers smaller systems - those exporting no more than 16A per phase at the connection point. For a typical single-phase domestic install, that is up to around 3.68kW of inverter capacity. G98 works on a connect-and-notify basis: for a single installation you can install and commission first, then notify the DNO within 28 days of commissioning. (Installers running programmes of multiple installations can use G98's pre-notification route instead, which does involve applying before install.) In practice, most G98 notifications go through without a hitch.

G99 covers everything else: larger domestic systems, commercial installations, multi-phase connections, and any system where the inverter is capable of exporting above the G98 threshold - including battery storage installations where combined inverter capacity pushes past the limit. G99 requires formal application, technical assessment, and a connection agreement before you install. It is the process where rejections happen and timescales slip.

What triggers a rejection

DNOs assess G99 applications against technical standards and their own network capacity models. The vast majority of rejections are not about network capacity - they are about the quality of the application itself.

Wrong inverter model or outdated specifications

The DNO checks your inverter against the ENA Type Test Register - the Energy Networks Association database where manufacturers declare G98/G99 compliance for each model. If the model number in your application does not match exactly - a different variant suffix, a firmware-specific designation, or a model updated since you last submitted - the application comes back. This is the most common rejection reason and the most avoidable. Check the exact model designation against the current ENA Type Test Register, not against the manufacturer datasheet, the MCS product directory (a separate database serving a different purpose), or a previous G99 approval for a similar unit.

Incorrect export limitation configuration

If you are applying for a system with active export limitation - via a power diverter, a zero-export relay, or inverter-level export management - the application must specify the exact limitation method, the target export limit, and the protection settings. Vague entries like "export managed" or "zero export" without the technical configuration will be rejected. The DNO needs to know exactly how the limitation is enforced before it will accept the application.

Battery storage: capacity vs power

Applications for systems with battery storage frequently include the battery's storage capacity in kWh but omit the battery inverter's power rating in kW, or conflate the two numbers. The DNO needs the power rating to assess network impact. A 10kWh battery with a 5kW inverter has a very different effect on the network than a 10kWh battery with a 10kW inverter.

Missing or incorrect protection settings

G99 systems require specific protection relay settings for loss-of-mains detection and anti-islanding. The application must state the protection settings that will be applied, not the defaults the inverter ships with. Installers working across multiple inverter brands sometimes carry protection settings from one manufacturer's application to another - which will be wrong for every model where it does not match.

Connection point details

The DNO assesses your application against the actual connection point: your specific meter, supply cable, and local network topology. Applications that use a postcode or street address without the MPAN (Meter Point Administration Number) get bounced regularly. The MPAN is not the same as the meter serial number. If you are collecting it from a customer by email rather than from the meter on site, verify it before you submit.

Assessment timescales by network

The published target for G99 assessment is 45 working days from a complete application. In practice, timescales vary significantly by network. Indicatively, from what installers report on straightforward domestic applications:

• National Grid Electricity Distribution (formerly Western Power Distribution - Midlands, South West and South Wales) - typically four to six weeks
• UK Power Networks (London, South East and East of England) - six to eight weeks
• Northern Powergrid - six to ten weeks is common; complex applications can run longer
• Scottish Power Energy Networks - eight to twelve weeks is not unusual given the volume of solar applications in its territory

These are working observations, not published service levels - SSEN and Electricity North West sit in similar ranges, and any DNO's timescale stretches when applications arrive incomplete.

The clock only starts when the DNO deems your application complete. A rejection and resubmission does not pause the clock - it resets it. An application rejected at week three and resubmitted at week five is sitting at the back of the assessment queue again.

Getting the application right first time

The fastest path to approval is a complete, technically accurate application in a single submission. That means:

• Inverter model number exactly as listed on the current ENA Type Test Register
• Battery inverter power rating (not storage capacity) for any storage system
• Export limitation method with full technical specification, not a summary
• Protection settings specific to the inverter model you are using, not copied from a previous application for a different unit
• MPAN verified from the physical meter on site, not from email correspondence with the customer
• Any previous G99 approvals at the site referenced, since prior systems affect what the network will accept

For installers working across multiple inverter brands, a model-specific reference document for protection settings is worth the one-off effort. The copy-paste error - carrying settings from a Solis application into a Growatt application - is responsible for a substantial share of rejection letters.

Where the process breaks down at scale

For an installer doing 10-15 solar installations a month, G99 applications are manageable with a spreadsheet and a calendar reminder. At 30-50 installs a month, the volume creates a different kind of problem: tracking which applications are at which stage across multiple DNO territories, ensuring commissioning notifications go back to the right DNO on time, and catching approvals that are approaching expiry - connection offers and approvals are time-limited, and the window varies by DNO and offer type.

The commissioning notification - the step that formally tells the DNO the system has been installed and matches the approved specifications - is where the process most often breaks down for growing installers. It is easy to track the original G99 application because there is a firm pending outcome to watch. Commissioning notifications are less time-critical in the short term, get deprioritised against active jobs, and then three months later a customer rings asking why their export tariff is not set up.

Keeping G99 applications, commissioning notifications, and the corresponding electrical certificates in the same record as the customer, proposal, and scheduled engineer visit removes the gap where things are forgotten. If the DNO workflow lives in a separate spreadsheet from the job data, things will fall through the gap. If it is part of the job itself, your office team does not need to remember to check it - the status is visible every time someone opens the project. That is what Payaca's DNO workflow is built around.