G98 and G99 Explained: DNO Applications for Solar Panels and Battery Storage

If you are planning to install solar panels, battery storage or a larger inverter, you may hear your installer mention G98, G99, DNO approval, export limits or connection offers.

These terms can sound complicated, but they are important. They can affect how quickly your system can be installed, how much power you are allowed to export, and whether there are any extra costs before your system can be fully connected to the grid.

This guide explains what G98 and G99 mean, why some applications take longer than others, how an IDNO can affect timescales, and what it means if the DNO offers different connection options.

What is a DNO?

A DNO, or Distribution Network Operator, is the company responsible for the electricity cables and local network in your area.

Your energy supplier sends the bill, but the DNO manages the network that brings electricity to your property. In the Midlands, the DNO is commonly National Grid Electricity Distribution.

When you install solar panels or battery storage, your system may export electricity back into the local network. The DNO needs to know about this to make sure the network can cope safely.

What is G98?

G98 is the simpler process for smaller generation systems.

For most domestic properties, G98 usually applies where the system can export up to 3.68kW per phase. On a standard single-phase home, this normally means an inverter output of up to 3.68kW. On a three-phase property, the allowance is higher because the export can be spread across three phases.

G98 is often described as a “fit and inform” process.

This means the system can usually be installed and commissioned first, and the installer then notifies the DNO afterwards. The DNO still needs to receive the correct paperwork, but there is normally no long approval process before the installation can go ahead.

For many standard domestic solar installations, G98 is straightforward. It is usually quick, relatively simple, and does not normally involve additional DNO connection charges.

What is G99?

G99 is the more detailed application process used when a system is above the G98 limits, or where the proposed system could have a greater impact on the local electricity network.

A G99 application is commonly needed when:

• the inverter output is above 3.68kW on a single-phase supply

• the customer wants a higher export capacity

• the system includes larger battery storage

• the property has a large domestic solar PV system

• the site is commercial

• the property has a three-phase supply with larger generation

• the DNO needs to assess the local network before approval

With G99, the installer cannot simply connect the system and inform the DNO afterwards. The application usually needs to be submitted and approved before the system can be fully commissioned at the requested export level.

The DNO reviews the proposed installation to check whether the local network can safely accept the additional generation. They may assess cable capacity, transformer capacity, voltage rise, existing solar in the area and whether export from the property could cause issues for neighbouring supplies.

Why does G99 take longer than G98?

G99 takes longer because it is not just a notification. It is a technical assessment.

The DNO needs to understand:

• what equipment is being installed

• the inverter size

• the maximum export capacity requested

• whether the property is single-phase or three-phase

• whether there is already generation on site

• how strong the local network is

• whether export needs to be limited

• whether network upgrades are needed

For a straightforward G99 application, approval may take several weeks. In many real-world cases, customers should expect something in the region of 8 to 16 weeks, depending on the DNO, the system size and the local network.

Some smaller systems may qualify for a faster route, often referred to as a fast-track G99 or fit-and-forget process. This can sometimes be dealt with in a few weeks, but it depends on the system design, the export level and the DNO’s own process.

More complex G99 applications can take significantly longer.

Delays are more likely where:

• the inverter is larger

• the export request is high

• the local network is already constrained

• the property is connected through an IDNO

• the DNO requires further studies

• reinforcement works may be required

• the application involves a commercial or three-phase connection

In some cases, a decision can take several months. We have seen examples where a customer has had to wait until 1st October for a decision on their DNO application. This is the real impact that DNO and IDNO delays can have, especially where larger inverter applications are involved.

What is an IDNO?

An IDNO is an Independent Distribution Network Operator.

Most properties are connected directly to the regional DNO. Some properties, particularly newer housing estates, business parks or private developments, may be connected through an IDNO instead.

The IDNO owns and manages part of the local electricity network. However, it may still need to liaise with the host DNO before approving larger generation or export capacity.

This can add another layer to the approval process.

How can an IDNO affect G99 wait times?

An IDNO can sometimes make the process slower because the application may need input from both the IDNO and the host DNO.

That does not mean every IDNO application will be delayed. Some are straightforward. However, where the customer wants a larger inverter, higher export capacity or a more complex connection, the IDNO may need to refer the application back to the host DNO for further assessment.

This can create longer wait times than customers expect.

For smaller G98 systems, this is less likely to cause a major issue. For G99 applications, especially larger domestic or commercial systems, it can become a significant factor in the project timeline.

This is why it is important to check early whether the property is connected to a DNO or an IDNO.

What is a DNO connection offer?

For some G99 applications, the DNO may issue a connection offer.

This sets out:

• what the DNO is willing to approve

• the maximum import capacity

• the maximum export capacity

• the connection point

• any required works

• any charges

• any conditions attached to the connection

A connection offer does not always mean the customer has been refused. It often means the DNO has approved the connection, but only if certain works, costs or conditions are accepted.

Example: DNO connection offer options

A recent connection offer we reviewed included a three-phase connection with:

• Maximum Export Capacity: 10kVA

• Maximum Import Capacity: 18kVA

• Connection: three-phase, 230/400V

• DNO: National Grid Electricity Distribution

The customer was offered two options.

Option 1: The DNO undertakes all works

Under Option 1, the DNO would carry out all of the required connection works.

This included both:

• non-contestable works

• contestable connection works

In the example reviewed, Option 1 was priced at:

£6,216.39 excluding VAT£7,459.67 including VAT

This option is usually the simpler route for the customer because the DNO takes responsibility for the full package of works.

However, it is also more expensive. The customer is also dependent on the DNO’s schedule, which can affect timescales.

Option 2: The DNO undertakes non-contestable works only

Under Option 2, the DNO would only carry out the non-contestable element of the works.

In the example reviewed, this included inspection of assets installed by an Independent Connection Provider.

The customer, or their appointed Independent Connection Provider, would then be responsible for designing and constructing the contestable works from the point of connection.

In the example, Option 2 was priced at:

£873.00 excluding VAT£1,047.60 including VAT

This option can be much cheaper from the DNO’s side, but it is not automatically easier. The customer or their appointed provider must arrange the design, construction and any required legal documentation.

This could include wayleaves, easements, leases, transfers or other site-specific agreements.

For some projects, Option 2 can reduce cost and give more control over the works. For others, it may add complexity and require more coordination.

The key point is that the options are normally mutually exclusive. The customer chooses one route.

What are contestable and non-contestable works?

This is a common area of confusion.

Non-contestable works are works that only the DNO can carry out. These may include final connection, inspection, approval, network studies or energisation.

Contestable works are works that can often be completed by an Independent Connection Provider instead of the DNO. These may include elements such as design, trenching, ducting, cable installation and some construction works.

Using an Independent Connection Provider can sometimes reduce cost or improve timescales, but the work still has to meet the DNO’s requirements.

What happens if a G99 application is restricted?

Sometimes, the DNO may approve a system but not at the full export level requested.

This could mean:

• the inverter must be export limited

• the system can generate but only export a set amount

• the battery may not be allowed to export at full capacity

• extra equipment may be needed to control export

• the customer may need to pay for network reinforcement

• the system design may need to be changed

For example, a customer may want a larger solar and battery system with a higher export capacity. The DNO may say the system can be installed, but only if export is capped at a lower level.

The system may still be very worthwhile, especially if the customer uses a lot of electricity on site or has battery storage. However, the return from export payments may be lower than expected.

What could restrictions cost?

Restrictions can create direct and indirect costs.

Direct costs may include:

• export limitation equipment

• additional monitoring equipment

• revised design work

• DNO re-application fees

• electrical engineering time

• network reinforcement charges

Indirect costs may include:

• reduced export income

• a longer payback period

• delays to installation

• delays to commissioning

• reduced benefit from a larger inverter or battery

In some cases, the DNO may say the requested export level is only possible if the local network is upgraded. These reinforcement costs can vary significantly. They may be relatively modest, or they may run into thousands of pounds depending on the work required.

This is why it is important to understand the DNO position before assuming that a larger inverter can export at full capacity.

Does a restricted G99 mean the system is not worth installing?

Not necessarily.

A larger solar or battery system can still make sense even where export is limited.

The value depends on how much energy the property uses, when it uses it, and how the system is designed.

A home with high daytime usage, an electric vehicle, a heat pump or a large battery may still benefit from a larger system because more of the energy can be used on site rather than exported.

For commercial sites, export limitation may have very little impact if the business uses most of the generated power during the day.

The important point is that export approval should be considered early. A good design should look at more than just how many panels fit on the roof. It should consider inverter size, battery capacity, export limits, DNO process, IDNO involvement and possible future restrictions.

What should customers ask before accepting a quote?

Before agreeing to a solar or battery installation, it is worth asking:

• Is this system G98 or G99?

• What inverter size is being proposed?

• What export level is being applied for?

• Is the property single-phase or three-phase?

• Is the property connected to a DNO or an IDNO?

• Could the DNO restrict the system?

• Are DNO application fees included?

• What happens if the DNO requests reinforcement?

• Could export limitation be used instead?

• Who manages the DNO application?

• What happens if the application is delayed?

These questions help avoid surprises later.

Who manages the G98 or G99 application?

In most cases, the installer should manage the application or notification on behalf of the customer.

For a G98 system, this usually means submitting the required notification after installation.

For a G99 system, this means preparing and submitting the application, providing technical information, liaising with the DNO or IDNO, responding to queries and explaining the outcome to the customer.

At M+S Renewables, we manage this process as part of the system design and installation journey.

How M+S Renewables can help

At M+S Renewables, we design solar and battery systems with the DNO process in mind.

We look at the proposed inverter size, the likely export requirements, the property’s supply type and whether the site is connected to a DNO or IDNO. Where G99 is required, we can submit and manage the application, liaise with the network operator and explain the options if a connection offer or restriction is issued.

In some cases, the best approach may be a fast-track G99. In others, it may be a standard G99, export limitation, a three-phase design, or a revised system layout.

If a DNO connection offer includes contestable and non-contestable works, we can help explain what the options mean so the customer can make an informed decision.

G98 and G99 are not just paperwork. They can affect cost, timescale, system performance and export potential. Understanding the process early helps ensure the system is designed properly from the start.

Frequently Asked Questions

Do I need G98 or G99 for solar panels?

It depends mainly on the inverter size and export capacity. Smaller systems are usually covered by G98. Larger systems, or systems that export above the G98 threshold, usually need G99.

Does battery storage need a G99 application?

It can do. If the battery or hybrid inverter can export above the G98 limit, a G99 application may be required.

Can I install before G99 approval?

For systems that require G99, approval is normally needed before the system can be fully connected and commissioned at the requested export level.

What is a fast-track G99?

A fast-track G99 is a quicker route for certain smaller systems that meet specific criteria. It is not available for every installation.

How long does a G99 application take?

A straightforward G99 application may take several weeks. Many customers should expect around 8 to 16 weeks. Complex applications, IDNO involvement or network constraints can take longer.

Why can an IDNO delay a G99 application?

An IDNO may need to coordinate with the host DNO before approving larger export capacity. This adds another layer to the process and can extend timescales.

What happens if the DNO restricts my export?

The system may still be approved, but export may be capped at a lower level. This can affect export income, system design and payback period.

Who pays for DNO connection works?

This depends on the connection offer. The customer may be asked to pay for assessment fees, connection works, reinforcement, or the use of an Independent Connection Provider.

Can restrictions be removed later?

Sometimes, but it may require a new application, further assessment and additional cost.

Should I still consider a larger system if export is limited?

Possibly. If you use a lot of electricity on site or have battery storage, a larger system may still provide strong benefits even with an export limit.