G98 and G99 applications for Solar and Battery Storage

What is a DNO Application?

A DNO Application is a request to the local distribution network operator (DNO) when installing micro-generation devices in your home, such as solar panels or battery storage. There are 9 DNOs in the UK and Ireland that distribute electricity from the national transmission network to the electricity grid in your local area to serve homes and businesses.

This is no small feat, as the UK's energy system is fundamentally changing: The electricity consumption in the UK is expected to increase by 50% until 2035 according to the Climate Change Committee, while the share of intermittent electricity generation is projected to reach a multiple of what it is today. Since the existing electricity grid wasn't built with this level of consumption and decentralised, intermittent generation in mind, DNOs are careful about connecting too many new generation services to a grid that may struggle to accommodate this additional intermittent generation.

Hence, DNOs need to know about new residential solar and battery installations to make sure they can be connected to the grid without causing any disruption or overloading. Through the application, they can evaluate the potential impact of new devices on the existing grid infrastructure and if any upgrades to the local infrastructure are needed before granting approval.

While the need for these applications is apparent for the DNO, you might ask yourself why the application is important for you? A successful DNO application allows you to export excess electricity from your solar panels or battery storage back to the grid. Depending on your export tariff as well as the exported amount, you can make £100s in export revenues per year.

You may wonder now, what the application process looks like. This largely depends on the size of your system. Most commonly, homeowners need to do a G98 or G99 application. Let’s explore these two applications in detail.

The G98 Application

G98 is the application for small-scale systems and ensures that they can safely connect to the grid. It was developed by the Energy Networks Association (ENA) in the UK and standardises the requirements for connecting these systems for all network operators.

Do I need a G98 application for my system?

Any system with a current of up to 16A per phase falls into the small-scale category and needs a G98 application. Current is the flow of electricity measured in Amps (A). Think of the limit of 16A as a way to ensure your home’s electrical system and the local power network can handle the additional output of your system.

For most homes, this requirement translates to system that can produce up to 3.68 kW of power. The easiest way to find out if your solar or battery system has a power output of 3.68 kW or less is to check the size of your inverters in the product specifications or by asking your installer. Should you have more than system that generates electricity, the aggregate current of all your devices matters to determine the right application.

What is the G98 application process?

The application process for G98 is relatively straightforward and less complex compared to the G99 application. Additionally, the installer is responsible for making the application to the DNO and as a customer, you don’t need to be concerned about this. Yet, it might be helpful to know about the following 3 steps of the application process:

1. Installation: Unlike larger systems, you don't need to wait for approval before installation. The G98 process follows a "fit and inform" approach, meaning you can install your system and then notify the DNO afterwards.
2. Submission: You have up to 28 days after the installation to submit the G98 form and required documentation, including technical information about the system, a single-line diagram of the installation and proof for compliance.
3. DNO response: Once submitted, the DNO can take up to 4 weeks to assess the compliance status of your system.

How much does a G98 Application cost?

G98 applications are typically free of charge. The DNOs do not usually charge a fee for processing the applications for small-scale generators. While it is unlikely, some installers may charge an administrative fee for the submission.

The G99 Application

G99 is the application for larger-scale systems that exceed the G98 limits. It ensures that these systems can safely connect to the public electricity grid. Like G98, it was developed by the Energy Networks Association (ENA) in the UK to standardise connection requirements across all network operators.

Do I need a G99 application for my system?

Any system with a current exceeding 16A per phase, or with a power output greater than 3.68 kW requires a G99 application. This includes larger residential solar and battery installations and commercial solar projects where inverters often have larger power output than these limits. Given the differences in output size, there are some differences in the application process.

What's the G99 application process?

The G99 application process is more complex than G98 and varies depending on the size of your generation system, as the same application needs to be completed for some commercial solar and battery projects. In this section however, we focus on the G99 application processes for residential installations.

According to the rulebook, this involves the following steps:

1. Pre-application: Contact your DNO to discuss your project and get initial feedback on the project.
2. Application submission: Submit a detailed G99 application form and supporting documents to the DNO. In comparison with the G98 application, these documents are more extensive as they include additional information such as the generation profile.
3. DNO approval: Wait for approval from the DNO before starting the installation. They review your application and may request additional information. This may take between 4 to 8 weeks.
4. Installation: Once approved, you can install, commission and test your system.

In practice, your installer can speed up this process by fast-tracking your application with some DNOs. The fast-track can be chosen for Small Generation Installations (SGI) and can shorten the time-to-approval from the DNO to 2 weeks. Alternatively, your installer may install the system without the DNOs approval, limit its inverter’s output to the 3.68 kW allowed under G98 and only remove this limit once the G99 application has been approved.

What happens if my G99 application gets rejected?

While G99 application rejections are uncommon, they can occur due to various factors. These may include local grid capacity constraints, inaccurate applications, or concerns about the impact of your system on the grid’s stability. Systems without battery storage might face additional scrutiny due to higher pressures on the grid from the intermittent solar generation. However, if your application is rejected, don't be discouraged, there are several options for you to consider.

1. Change the design of your system

This approach is only feasible if you are still in the planning stage and haven't yet installed your system. You might want to discuss with your installer to downsize the system's output to below 3.68 kW to qualify for a G98 application or upgrading to a three-phase electricity connection which can accommodate larger capacities.

2. Restrict your inverter at 3.68 kW

You can comply with G98 requirements by limiting your system's export capacity to 3.68 kW, while still benefiting from a larger system. For solar PV installations, consider adding a larger battery to maximise self-consumption of generated electricity. This in turn will reduce your exports to the grid.

3. Drop the connection to the electricity grid

This option is viable for combined larger solar and battery systems, but not for standalone batteries. By operating off-grid, you can optimise self-consumption of solar-generated electricity without DNO approval.

4. Pay the grid operator for grid expansion

The DNO might propose that you pay for local grid upgrades to handle your system's full capacity. This could involve a significant investment ranging from £100s or £1000s. We would recommend comparing the upgrade costs against the export revenues from your system. If you are on a good export tariff, the investment might pay off after all!

5. Re-apply for a G99 in the future

You can wait for future grid improvements, instead of paying yourself for immediate upgrades in your area. As the grid’s capacity expands over time, your chances of G99 approval are likely to increase. However, it may take years or decades until you can connect your system.

How much does a G99 Application cost?

Unlike G98, G99 applications can involve fees from DNOs and installers. Depending on the DNO and your system’s size, the application fee can range from £0 to £1000s. As explained above, they may also charge you for equipment and local infrastructure improvements, as a condition of approving your application. Since these costs vary significantly, you might want to get the application approved and know the project’s total cost before starting.

We at Capture Energy recommend always discussing the applications with your installer or a qualified electrical engineer. We help our customers manage these applications end-to-end free of administrative charges. Get in touch now so that we can help you with your application and start exporting electricity this summer!

Frequently asked questions

Do I need a G98 or G99 application for a standalone home battery?

Yes, you typically need to submit a DNO application for a standalone home battery system, given that it is connected to the grid. The type of application depends on the battery system's capacity:

• Battery inverter <3.68 kW: If your battery system's inverter is rated at 3.68 kW or less for a single-phase connection (or 11.04 kW or less for a three-phase connection), you'll need to submit a G98 application.
• Battery inverter >3.68 kW: If your battery system's inverter exceeds the 3.68 kW limit, you'll need to submit a G99 application.

The application is necessary because a battery system can both draw electricity from and export power to the grid. So even if you don’t expect to export electricity from your battery, the DNO needs to be aware of the system to manage the local grid’s stability.

Do I need to re-apply for G98 or G99 if I replace my inverter?

It depends on the new inverter's size. If the new inverter is the same size or smaller, you don't need to submit a new application. However, you should let the DNO know about the change and the details of the new inverter model. If the new inverter is larger and exceeds 3.68kW for a single-phase connection (or 11.04 kW for three-phase), you'll need to submit a G99 application. If the new inverter is larger but still within G98 limits, you should submit an updated G98 application to reflect the changes in your system.

Generally, we recommend contacting your DNO before making the inverter replacement. Alternatively, you might want to discuss this with an MCS-certified installer, who can help you with questions on application and installation. Don't hesitate to get in touch with our experts by answering the quick form below: