What are G98, G99, and G100 approvals?

How long does G99 approval take for solar installations?

When installing solar PV systems, it is essential to understand which approval process applies—G98 or G99—depending on the size and type of installation.

The size of the system is not normally the summation of the solar panels installed, but the output of the installed inverter. E.g. 4 kWp of solar panels will normally result in a 3.6 kW inverter.

G98 for Domestic Properties

For most domestic solar installations (under 3.68 kW single phase or 11.04 kW three phase), a G98 applies. This is a simple post-installation notification to the Distribution Network Operator (DNO). You do not need prior approval, and the installer notifies the DNO on your behalf.

✅ G98 is ideal for standard home installations, battery storage, and small-scale solar arrays.

G99 for Larger or Commercial Installations

If you are planning a larger system—over 3.68 kW single phase or 11.04 kW on a three-phase installation—common on large homes with high energy usage, farms, and commercial sites—you will likely need G99 approval. This involves formal DNO permission before installation.

1. While timelines vary, the key steps in the G99 process include:

2. Application Submission – Once submitted, the DNO has a statutory obligation to respond within 45 working days.

3. Follow-Up Questions – The DNO may ask for more technical details about your proposed system and grid connection.

4. Decision & Upgrades – The DNO assesses local grid capacity and outlines the acceptable connection terms required. If upgrades are necessary (e.g. a transformer upgrade or export limitation), these will be stated in the Connection Offer.

5. Connection Offer – The Connection Offer will detail the conditions under which the Solar PV installation can be installed, including maximum system size, the amount of exported energy allowed, and/or any physical changes to the DNO infrastructure. These changes can sometimes involve additional cost to the customer; this will also be detailed in the offer.

6. Contestable or Non-Contestable Acceptance – You normally have 90 days to accept the offer and usually 1 year to install and commission the system.

7. Installation & Final Approval – Systems can often be installed while awaiting upgrades, but they cannot be turned on until final approval is granted.

8. Installation Confirmation – Once the system has been installed and commissioned, the installer will confirm the commissioning parameters to the DNO. Once received, the DNO will then issue an export MPAN (Meter Point Administration Number).

   At Chiltern Solar, we guide you through the entire process—whether you are a homeowner looking to add panels to your roof or managing a larger agricultural or commercial project.

G100 – Export Limitation Explained

G100 is a UK standard that controls how much electricity your solar system can export to the grid. This is a constraint the DNO will apply in to maintain grid stability If the local grid can’t handle all the power your system generates, a G100 Export Limitation Scheme (ELS) is used to cap your exports to an agreed level. This helps avoid the need for expensive grid upgrades.

When Do You Need G100?

You’ll need G100 if:

• Your system could export more than the local grid can safely handle.

• This may be dictated by either a thermal and/or fault condition in the local area.

• The G100 constraint can be anywhere between 0% and 100% of the Solar PVs maximum output..

How Does It Work?

A G100 system:

• Limits export power within 5 seconds.

• Defaults to a safe level if there’s a fault.

• Uses approved equipment that meets national standards.

Why It Matters

G100 lets you install larger solar systems in more places by staying within grid limits. At Chiltern Solar, we offer expert support and G100-compliant solutions to help you get the most from your investment.

📩 Get in touch to discuss your solar installation and find out which approval process applies to your property.