Why Can't I Install Any Size Solar System? Understanding Export Limits and DNO Approval

One of the biggest surprises for homeowners considering solar panels is learning that you can't always install any size system you want.

You may have heard terms like G98, G99, G100 or export limits, but what do they actually mean?

In this guide, we'll explain why these approvals exist, how they affect your solar installation, and why they help keep the electricity network safe and reliable.

What Is a DNO?

Your local Distribution Network Operator (DNO) owns and maintains the electricity cables, substations and transformers that supply homes and businesses in your area.

When you install solar panels, your home doesn't just consume electricity – it can also export surplus energy back to the grid. The DNO needs to ensure that the local electricity network can safely accommodate that exported power.

What Is an Export Limit?

An export limit is simply the maximum amount of electricity your solar and battery system is allowed to send back to the National Grid at any one time.

For example:

• Your solar panels may be capable of generating 8 kW.

• Your battery inverter may be capable of exporting 5 kW.

• However, the DNO may limit your export to 3.68 kW or 5 kW, depending on the capacity of the local network.

This doesn't necessarily mean your solar panels generate less electricity. Any surplus electricity can still be used within your home or stored in a battery. The export limit only controls how much electricity can flow back into the grid.

Why Are Export Limits Needed?

The electricity network was originally designed to deliver power to homes, not to receive electricity from thousands of rooftop solar systems.

If too much electricity is exported at the same time, it can lead to:

• Higher than acceptable grid voltage.

• Power quality issues.

• Protection equipment operating unexpectedly.

• Additional strain on local transformers and cables.

Export limits help keep the network stable while allowing more homes to benefit from renewable energy.

What Is G98?

G98 applies to smaller solar installations.

If your inverter's maximum export is up to 3.68 kW per phase, your installer can normally install the system first and then notify the DNO afterwards.

For most homeowners, this is the simplest approval process.

What Is G99?

If your system is larger than the G98 limit, it will usually require a G99 application.

Unlike G98, the DNO must approve the installation before work begins.

During the assessment, the DNO considers factors such as:

• Local network capacity.

• Existing voltage levels.

• Nearby generation.

• Transformer loading.

The application may be approved as submitted, approved with conditions, or given an export limit.

What Is G100?

Sometimes the local electricity network cannot accept the full export capability of a solar system.

Rather than reducing the size of the solar array, the DNO may allow an export limitation scheme known as G100.

A G100 controller constantly monitors how much electricity is being exported and automatically limits the inverter whenever the agreed export limit is reached.

For example:

• Solar array: 12 kW

• Battery inverter: 10 kW

• DNO export limit: 5 kW

Your home can still use the full solar generation and your battery can still charge normally. The system simply ensures that no more than 5 kW is exported to the grid.

Does an Export Limit Reduce My Savings?

Usually not. For most homeowners, the biggest financial benefit comes from using the electricity they generate rather than exporting it.

If your system includes battery storage, surplus energy can be stored instead of exported and used later in the day. This often means an export limit has very little impact on the overall financial return.

Can the DNO Refuse a Solar Installation?

Occasionally. If the local network is heavily constrained, the DNO may:

• Apply an export limit.

• Request a smaller inverter.

• Recommend network reinforcement.

• In rare cases, refuse the proposed connection.

Fortunately, modern G100 export limitation systems mean many installations can still proceed, even where the local network has limited capacity.

How Long Does DNO Approval Take?

Typical timescales are:

• G98 – Installed first, notification submitted afterwards.

• G99 – Typically a few weeks, although more complex applications can take longer.

• G100 – Usually assessed alongside a G99 application where export limitation is required.

Your installer should manage the entire application process on your behalf.

Why Choose Ulex Energy?

At Ulex Energy, we take care of every stage of the DNO application process.

As part of every quotation, we assess whether your proposed system is likely to require G98 notification, G99 approval or a G100 export limitation scheme. Where export limits apply, we'll explain exactly what they mean and design a system that delivers the best possible performance while complying with DNO requirements.

Our goal is to install the largest and most effective solar and battery system your property and local electricity network can support.

Thinking About Installing Solar?

If you're considering solar panels or battery storage and aren't sure whether your property will require DNO approval, we'd be happy to help.

Contact Ulex Energy for a free, no-obligation quotation, and we'll handle the technical side—including all DNO applications—so you can enjoy the benefits of solar with complete confidence.