Guide to G98 and G99 DNO Approvals for UK Home Solar

Connecting solar panels, home battery storage, or vehicle-to-grid chargers to the electricity network in England, Scotland, or Wales requires formal permission from your local Distribution Network Operator (DNO). The DNO is the company responsible for the regional cables, towers, and substations that feed electricity into your street, distinct from your energy supplier who sends your bill.

Under regulations maintained by the Energy Networks Association (ENA), any electricity-generating equipment connected to the mains grid must comply with specific technical standards. The two primary pathways for domestic installations are Engineering Recommendation G98 and Engineering Recommendation G99. Understanding which pathway your installation falls into determines whether work can begin immediately or requires weeks of advance technical review.

Understanding the difference between G98 and G99

The boundary between G98 and G99 depends on the total rated output of your inverters, measured in kilowatts (kW) or Amperes (A) at standard single-phase mains voltage (230 volts).

Engineering Recommendation G98 applies to small-scale generation systems up to 16 Amps per phase. On a standard single-phase domestic supply, 16 Amps at 230 volts equates to an inverter capacity of exactly 3.68 kW. If the combined rated output of all inverters connected to your supply is 3.68 kW or less, the installation follows a simple, post-installation notification process often called fit and inform.

Engineering Recommendation G99 applies to any generation system exceeding 16 Amps per phase on single-phase supplies (above 3.68 kW), or exceeding 3.68 kW per phase on three-phase supplies. G99 is an advance application process. Your installer must submit detailed technical documentation and receive written approval from the DNO before any equipment can be physically connected or energized.

When calculating system capacity, the DNO counts the maximum AC rating of the inverter, not the peak direct-current capacity of the solar panels (measured in kWp). For example, a system with 5 kWp of solar panels wired to a 3.68 kW inverter qualifies under G98 rules, because the inverter cannot physically output more than 3.68 kW into the grid.

Comparing G98 and G99 application pathways

The following table outlines the core parameters, timescales, and technical requirements for both connection pathways under ENA regulations.

Step-by-step guide to the grid connection process

Navigating grid approval requires specific sequential steps to ensure safety, regulatory compliance, and protection of your equipment warranties.

• Step 1: Site survey and capacity assessment. An installer registered with the Microgeneration Certification Scheme (MCS) inspects your main consumer unit, fuse rating (typically 60A, 80A, or 100A), earthing arrangement, and local transformer head. The installer calculates the total proposed AC inverter capacity.

• Step 2: Selecting the connection route. If the total AC output is 3.68 kW or under, the installer schedules the installation under G98. If the proposed system exceeds 3.68 kW, the installer submits a G99 application to your regional DNO, such as National Grid Electricity Distribution, UK Power Networks, SSEN, SP Energy Networks, Electricity North West, or Northern Powergrid.

• Step 3: DNO grid study and formal response. For G99 applications, the DNO assesses local network constraints. They will issue one of three responses: full unconditional approval, conditional approval requiring an export limitation device (such as restricting export to 3.68 kW while allowing higher self-consumption), or a quote for network reinforcement if local infrastructure cannot support the load.

• Step 4: Installation and electrical testing. Once approved (or immediately for G98), the qualified electrician completes the physical installation. Electrical tests must comply with BS 7671 IET Wiring Regulations and Part P of the Building Regulations.

• Step 5: Commissioning and registration. For G98, the installer submits the commissioning form to the DNO within 28 days of turning on the system. For G99, the installer submits final commissioning documentation to close out the pre-approval file. The installer then registers the system on the MCS database to generate your MCS certificate.

What to ask your accredited installer

To ensure your project remains on schedule and compliant with network regulations, ask prospective installers these key operational questions before signing a contract:

• Which DNO covers this address, and what is their current average processing time for G99 applications?
• Is the proposed inverter listed on the Energy Networks Association Type Test Register for G98 or G99 compliance?
• If proposing a system over 3.68 kW, will you install an ENA G100-compliant hardware export limiter to secure fast-track approval?
• Does your quote include all DNO administration fees and drawing submissions?
• Are you registered with MCS, and will you provide an MCS certificate along with Part P electrical notification upon completion?

What this means for you

Understanding grid connection rules prevents unexpected delays and unexpected costs. If you want a quick installation without waiting for utility permissions, restricting your inverter capacity to 3.68 kW allows immediate fitting under G98 rules. However, if your household uses high amounts of electricity, has a heat pump, or charges an electric vehicle, applying for a larger G99 connection allows you to install a bigger solar array and battery inverter, maximising long-term self-consumption.

Householders accessing clean energy upgrades through workplace benefit programs, such as the Net Zero Home Scheme, receive guided assistance through these grid application steps, ensuring all DNO forms, MCS filings, and electrical certifications are handled by accredited installation partners.

Frequently asked questions

Can I install a 5 kW inverter under G98 rules if I limit export to 3.68 kW?

No. G98 rules apply strictly to the total rated AC capacity of the inverter equipment itself, regardless of software settings or export limiters. A 5 kW inverter requires a G99 application prior to installation, even if you intend to cap exported power to 3.68 kW using a G100-compliant limiting device.

What happens if an installer fits a G99 system without prior DNO approval?

Connecting a generation system exceeding 3.68 kW without prior written permission from the DNO breaches the Electricity Safety, Quality and Continuity Regulations 2002. The DNO has the legal right to disconnect your supply head until the system is isolated, and invalidation of MCS certification may prevent you from registering for export tariffs.

How long does a G99 application approval remain valid?

Once a DNO issues formal G99 approval, the permission is typically valid for 90 to 180 calendar days, depending on the specific network operator's terms. The installation must be completed and commissioned within this window, or an extension must be requested, to prevent the reserved grid capacity from being reallocated to other applicants.