DNO Applications Explained for Businesses

For any solar PV, battery storage, or mixed renewable project in the UK, the DNO application is how a good design becomes an approved grid connection. It is also the stage that can slow a project down if the application is incomplete, the local network is constrained, or export expectations are not realistic from the start.

A Distribution Network Operator, or DNO, is the company responsible for the local electricity wires and infrastructure that carry electricity to homes and businesses. This is different from your electricity supplier, which bills you for energy use. The electricity distribution network is operated across 14 licensed DNO areas owned by several ownership groups, so the correct DNO depends on the site location rather than the energy supplier chosen by the customer.

In this blog we will talk you through what G99 applications are, when you need one, and how to put in an application that will not cause any project delays. We’ll go over the process step by step, and what to do if the DNO responds with no or limited export capacity. Finally, we’ve provided a quick and easy checklist to follow for a smoother route to DNO approval.

When do solar projects need a DNO application?

The UK solar approval process usually starts with the question does the installation fall under G98 or G99?

For small microgeneration, G98 is the simpler “fit and inform” route. ENA guidance describes G98 as applying to compliant microgenerators up to and including 16A per phase, which corresponds to 3.68kWp on a single-phase low-voltage supply or 11.04kWp on a three-phase low-voltage supply. For many domestic solar panel systems at or below that level, the installer can commission the system and notify the DNO afterwards, provided the equipment and installation meet the relevant requirements. However, most commercial installations are larger than this.

A G99 application is required when the generation capacity is above the G98 threshold or the installation does not meet the current G98 requirements. National Grid Electricity Distribution states that G99 applies to generation and storage installations rated above 16A, or 3.68kW, per phase, or installations that otherwise do not meet G98. For solar PV, this usually means the inverter’s continuous AC output rating. The inverter is the equipment that changes electricity from the panels into electricity the grid can use.

This means almost all commercial installations will need to register a G99 application with the DNO to find out whether they can export energy back to the grid.

In practical terms, DNO applications for solar panels tell the local network operator the generation capacity, whether battery storage is included, and whether the local transformer, cable and protection systems can safely support the connection.

They can then tell your business whether you can export energy to the grid, and if so, how much.

What the DNO is checking

A DNO’s job is to protect the safety, reliability, and power quality of the local electricity network. When lots of nearby homes or businesses add solar, batteries, EV chargers, or heat pumps, electricity starts to flow in different ways. This can put pressure on the local network and cause technical problems, especially if it was not built to handle large amounts of electricity flowing both in and out.

For a commercial solar connection, the DNO usually checks the system size, how much electricity it may export, where it will connect, how much power the site uses, the existing supply, and whether the network needs upgrades. If the project is larger or located in a constrained area, the DNO may need more detailed network studies before issuing an offer.

The ENA’s distributed generation guidance sets out the connection journey as a staged process. It also recommends identifying the DNO, reviewing available network information, and discussing plans with the DNO at an early stage.

The DNO application process step by step

1. Identify the correct DNO early

Do this before finalising the solar design, signing off project economics, or committing to an installation date. A site in London, for example, will not necessarily have the same network constraints as a site in the South West, North East, or Scotland. This is due to different local infrastructure, where some may have spare capacity, others may not.

For businesses planning commercial solar, early contact is one of the simplest ways to reduce delay. Ask whether the DNO offers budget estimates, capacity maps, pre-application support, constraints information, or early design discussions. This does not guarantee approval, but it helps the design team avoid submitting an unrealistic export request, and thus speeds up the approval timeline.

2. Build a technically complete design pack

A weak or inconsistent application can be paused while the DNO asks questions. A good submission normally includes:

• Site address and MPAN details.
• Existing supply capacity and phase arrangement.
• Proposed inverter rating and generation capacity.
• Battery storage details, if included.
• Maximum requested export capacity.
• Single-line diagram.
• Site layout and point of connection information.
• Inverter and protection settings.
• Type-test certificates and relevant ENA compliance evidence.
• Details of any export limitation scheme.
• Proposed commissioning approach.

For commercial sites, it is also useful to include load data if available. Half-hourly consumption data can show how much solar is likely to be consumed on site and how much is expected to export. That can support a more realistic DNO conversation. Take a look at what our in-house design team do for our clients.

3. Decide the export strategy before submission

The biggest mistake is assuming the DNO will approve the full export capacity requested. In some areas, full export may be accepted. In others, the DNO may approve a lower export limit, require reinforcement, offer a timed or flexible connection, or refuse the requested export capacity unless the design changes.

Where export is constrained, a G100-compliant Customer Export or Import Limitation Scheme can sometimes help. The G100 sets requirements for schemes that limit export to, or import from, a DNO distribution network, and says customers can choose to limit how much electricity flows through the grid connection instead of waiting for, or paying towards, network upgrades.

4. Submit the G99 application

For many projects, the installer submits the application through the relevant DNO portal or by the DNO’s stated method. Smaller qualifying systems may follow a faster small generation process, while larger commercial systems typically require a standard G99 application and a more detailed network assessment.

National Grid describes the G99 fast-track process as a route that may allow eligible small generation or storage installations to connect faster than through a standard G99 application, provided they meet one of the qualifying Small Generation Installation categories. ENA guidance also notes that, for certain fast-track storage-related applications, the time for DNO confirmation can be reduced from 45 days to 10 days or less.

5. Wait for assessment and respond quickly

For standard generation connection quotations, the typical regulated response window depends on voltage level and the type of works requested. ENA guidance states that where the DNO is asked to undertake both contestable (work that can be done by the DNO as well as approved contractors) and non-contestable work (work that can only be done by the DNO), quotation timescales are 45 working days for low-voltage generation connections and 65 working days for high-voltage and extra-high-voltage generation connections. This is due to the DNO needing to asses what work is needed, which contractors can do each part, how it will affect the network, and what it will cost.

That does not mean every project is fully ready to install after 45 working days. The DNO may issue an offer with conditions, ask for more information, quote for reinforcement, require export limitation, require witness testing, or identify third-party dependencies such as wayleaves or upstream network checks.

6. Accept the offer before installing or energising

Once a connection offer is issued, review it carefully. Check the approved capacity, export limit, and commissioning requirements. National Grid’s post-acceptance guidance states that a connection offer is valid for 90 days and that acceptance requires returning a signed acceptance letter with any payment due.

Do not assume that installing equipment is the same as having permission to operate it. For G99 projects, the system should not be commissioned until the required approval, agreements, and commissioning conditions are satisfied.

How long does a DNO application take?

A realistic project programme should allow time for more than the formal DNO response window. A standard low-voltage commercial application is commonly planned around the 45-working-day quotation window. Larger or more complex schemes may need 65 working days or longer if reinforcement, legal permissions, design revisions, transmission impact checks or supply-chain constraints are involved.

After offer acceptance, there can also be lead time for metering, connection works, and commissioning. For example, National Grid notes that generation connections may require completion certificates and 20 to 25 days’ lead time for energisation and G99 witness testing.

Common causes of delay or constraint

DNO delays are not always caused by slow administration. Many are caused by technical or commercial issues that could have been addressed earlier. Common problems include:

• Requesting more export capacity than the local network can support.
• Submitting an incomplete single-line diagram or missing type-test documents.
• Failing to include battery storage in the application.
• Confusing installed generation capacity with agreed export capacity.
• Designing around single-phase equipment where a three-phase solution would be more appropriate.
• Assuming a G100 export limiter removes all network concerns.
• Waiting until installation week to start the application.
• Not responding promptly to DNO clarification requests.

Ofgem has highlighted grid connection delays as a wider industry issue and has proposed reforms intended to improve accountability, real-time network information, and connection processes for clean power projects.

What to do if export is limited or cancelled

If the DNO limits export, the project is not automatically dead. It does mean the design and financial model need to be revisited.

A commercial battery storage system can be a strong mitigation option. Instead of losing excess solar generation at midday, a battery can store energy for later use on site. However, battery storage must be treated carefully in the DNO application because storage can also export, and AC-connected battery inverters may count as additional generation capacity. National Grid notes that generation, including energy storage systems, must comply with G98 or G99 as applicable, and that AC-connected batteries are counted alongside other inverter capacities.

Other mitigation options include:

• Reducing the requested export capacity.
• Installing a G100-compliant export limitation scheme.
• Using a smaller inverter while keeping a larger DC solar array where technically suitable.
• Moving from single-phase to three-phase supply where feasible.
• Phasing the project so an initial system can connect while reinforcement is planned.
• Increasing on-site consumption through EV charging, heat pumps or process loads.

Best practice checklist for a smoother approval

To reduce risk in the UK solar approval process, companies should:

• Contact the local DNO as early as possible.
• Confirm the site’s MPAN, supply capacity and phase arrangement.
• Model expected import, self-consumption, and export.
• Submit a complete technical pack first time.
• Ask the DNO or consultant about known constraints before fixing the design.
• Include batteries, EV chargers, and future load plans in the strategy.
• Design alternative export scenarios before the application is submitted.
• Keep the installation date flexible until approval is received.
• Track response deadlines and answer DNO queries quickly.
• Review the connection offer in detail before accepting.

A well-managed DNO application matches the solar and storage design to the real capacity of the local grid and protecting the commercial case for the project. If export is constrained, early design decisions around batteries, export limitation, and on-site consumption can often turn a difficult response into a workable solar grid connection.

If you’re struggling to do this by yourself, we can help. As part of any solar PV or battery storage project we install, we will carry out the entire DNO process on your behalf. Contact us now for help with your renewable project.