G99 and Commercial Solar: Getting a Business System Connected

Almost every commercial solar system needs approval from the local network operator before it can be connected. In London that is usually UK Power Networks. The approval process is called G99, after the engineering standard behind it, and it is the part of a commercial project most likely to set the timetable.

The good news is that it is predictable if you plan for it. Your installer makes the application, the network operator assesses it, and you only need to be ready to make a few decisions along the way.

Key points

• The simple notification route, G98, only covers small systems: up to 16 amps per phase, which is about 3.68 kW on a single-phase supply or 11.04 kW on a three-phase one. Most business systems are bigger.

• Above that, the system needs the network operator’s approval before it is connected, not after.

• With UK Power Networks, systems from 5 kW up to 50 kW go through its online Smart Connect portal. Larger systems go through its full generation connection process.

• If the local network needs upgrading, the network operator will quote for the work, and it has to be paid for before it is booked in.

• Export limitation can let you install more panels than the connection would otherwise allow, which suits businesses that use most of their power on site.

• Start the application early. It is easier to plan an installation date around an approval than the other way round.

Why business systems need approval

Every solar system feeds power into the same local network your building draws from. The network operator needs to know that adding your system won’t overload cables or transformers, or push voltages out of range for your neighbours.

For small systems, that check is light. The installer fits type-tested equipment and notifies the network operator after commissioning. That is the G98 route, and our guide to G98, G99 and DNO approval explains the thresholds in detail.

A business system on a warehouse, office or school roof is almost always well above the G98 limit, so it falls under G99. The difference that matters to you is timing: under G99, the network operator assesses the system first, and it can’t be connected until that assessment is complete.

How it works with UK Power Networks

UK Power Networks runs two routes for businesses, depending on size.

5 kW to 50 kW: Smart Connect

The installer applies through UK Power Networks’ online Smart Connect portal. UK Power Networks reviews the application and says whether any changes are needed to its network. If they are, it gives a price for the work, which has to be paid in full before the work is booked in.

Over 50 kW: the full generation connection process

Larger systems go through UK Power Networks’ generation connection process. In outline:

1. Application. The installer submits the G99 application with the system design and equipment details.

2. Assessment and quotation. UK Power Networks designs the connection and sends a quotation for any work needed.

3. Acceptance. You accept and pay for the connection. At this size, UK Power Networks may also need to check with National Grid, and the quotation can change as a result.

4. Network work, if needed. Where reinforcement is needed, UK Power Networks gives an estimated timescale.

5. Commissioning. The system is tested before it goes live, and UK Power Networks may attend to witness some of the tests.

Who does what

We do:

• design the system and choose equipment that meets G99

• prepare and submit the application, and deal with the network operator’s questions

• plan any export limitation, and the battery if there is one

• commission the system and send the network operator the commissioning paperwork

You’ll need to:

• give us details of your electricity supply, usually from a recent bill and the meter

• authorise the application on behalf of the business

• decide whether to accept any network operator quotation for upgrade work

• give access for the survey, installation and any witness testing

What affects the timeline

There is no single answer to how long G99 takes, because it depends on the system and on the local network. The things that make the biggest difference:

• System size. Larger systems need more detailed assessment, and over 50 kW the process involves more steps.

• Local network capacity. Where the network is already busy, the network operator may need to reinforce it or limit what you can export.

• Your supply. The size of your existing connection affects how much generation it can comfortably take.

• Batteries. A battery is part of the assessment too, and how it is set up to charge and discharge matters.

• Completeness. An application with full equipment data and a clear design moves faster than one that comes back with questions.

Export limitation: fitting more panels on the same connection

Many businesses use most of their solar power during the working day. If the system rarely exports much, it can make sense to fit an export limitation scheme. This is a control system that stops the site exporting more than an agreed amount, even if the panels are producing more than the building is using.

Because the network operator plans around the agreed export rather than the full size of the system, export limitation can make a larger system possible on a connection that couldn’t otherwise take it. It can also help avoid network upgrades. The trade-off is that any surplus above the limit is curtailed rather than exported, so it suits sites with a strong daytime load, or ones that add a battery to soak up the surplus.

How to plan a commercial project around G99

1. Survey and design first. We need the roof, the supply and your usage pattern to design a system that is the right size.

2. Apply early. Submit the application as soon as the design is settled, before fixing an installation date.

3. Decide on export. Choose between full export, limited export and a battery with your usage in mind, not just the size of the roof.

4. Allow for network work. If upgrades are needed, build them into the programme and the budget conversation.

5. Book the installation around the approval. Starting work before approval is a risk if the network operator asks for changes, and the system can’t be switched on until its assessment is complete.

Frequently asked questions

Does every commercial system need a G99 application?

Almost every one does. Only very small systems, up to 16 amps per phase, use the simpler G98 notification route.

Who submits the application?

Your installer, on behalf of the business. You authorise it and provide details of your supply.

Can we install before approval?

Work can sometimes start, but it is a risk if the network operator asks for changes to the design. Either way, the system can’t be connected and switched on until the assessment is complete.

What if the network can’t take our system?

There are usually options: a smaller system, export limitation, a battery, or paying for network reinforcement. We’ll set those out once the network operator has responded.

Do batteries need approval too?

Yes. A battery that can export to the grid is part of the generation the network operator assesses.

We work on warehouses, offices, schools and other commercial buildings. See our pages on solar for warehouses and office and commercial buildings, or browse all the sectors we cover.

Request a commercial solar assessment. We’ll look at your roof, your supply and your usage, and tell you what the connection is likely to involve before you commit.