G98 or G99 for Home Battery Storage in Great Britain?

You cannot decide whether G98 or G99 applies to a home battery from its kWh capacity alone. In Great Britain, the installer has to assess the whole grid-connected generating arrangement: what is already connected, how the battery is connected, the aggregate Registered Capacity per phase, the number of units and phases, type-test status, and any agreed export or import limitation scheme.

This guide explains what those checks mean for a homeowner and what to ask before the installation proceeds. The current G98 and G99 Engineering Recommendations discussed here apply in Great Britain; Northern Ireland uses separate G98/NI and G99/NI documents. Check the current ENA catalogue for the Northern Ireland documents.

If you need the system basics first, see how solar battery storage works before comparing connection routes.

G98 or G99: the short answer

G98 is the Engineering Recommendation for Fully Type Tested micro-generating plant within its scope. The current G98 Issue 2 is scoped to Great Britain, expressly includes electricity storage, and defines a Micro-generating Plant as one or more micro-generators with an aggregate Registered Capacity no greater than 16 A per phase. It also states that the G99 procedures apply to micro-generators greater than 16 A per phase. See the current ENA G98 catalogue entry and scope.

For a homeowner, the practical lesson is simple: do not classify the new battery in isolation. The proposed route depends on the electrical generating arrangement connected to the property, not just the battery label or its stored-energy capacity.

What actually decides the G98 or G99 route?

Before choosing a route, the installer should build a picture of the whole installation. Six inputs matter most: existing generation, inverter topology, aggregate AC generating capacity per phase, the number of units and phases, equipment type-test status, and whether an export or import limitation arrangement is proposed.

1. Identify any solar PV, battery storage or other generation already connected.
2. Confirm whether the battery has its own AC inverter or shares conversion equipment with another generator.
3. Establish the aggregate Registered Capacity and how it is distributed per phase.
4. Count the generating units and confirm the supply and connection phases.
5. Check the relevant Fully Type Tested evidence for the intended connection route.
6. Identify any proposed G100 export or import limitation and confirm how the DNO will treat it.

Start with everything already connected

An existing solar installation can affect the assessment because the relevant generating arrangement may include more than the new battery. Ask the installer to review the existing inverter and any previous DNO connection information rather than treating the battery as a stand-alone addition.

If you already have solar panels, compare AC-coupled battery storage for existing solar systems before finalising the connection design.

Use aggregate AC generating capacity, not battery kWh

Battery capacity in kWh tells you how much energy the battery can store. It does not, by itself, decide G98 or G99. The connection assessment instead looks at the generating arrangement and the relevant AC output or current conditions, including the aggregate Registered Capacity per phase.

Check whether the battery has its own inverter

Topology matters. A battery connected through its own AC inverter can create a different aggregate generating arrangement from a battery that shares a hybrid inverter with solar PV. That is why two homes with batteries of the same kWh capacity may not follow the same connection route.

The safe question is not “What route does this battery use?” but “How is this battery connected alongside everything else at this property, and what is the resulting aggregate capacity per phase?”

Check the number of units and phases

G98 uses an aggregate per-phase concept. Multiple generating units do not each receive a separate 16 A allowance. The installer must consider how the complete plant is arranged and how its Registered Capacity is distributed across the relevant phase or phases.

For that reason, avoid shortcuts such as multiplying a single-phase threshold by the number of phases without checking the actual architecture. The connection arrangement and the relevant engineering requirements still have to be assessed together.

Check the equipment’s type-test status

G98 is for Fully Type Tested micro-generators that meet its requirements. The current ENA G98 scope refers to a Micro-generator Type Test Verification Report demonstrating that the design meets G98. This is a separate question from battery capacity and should be checked for the equipment and intended route. Review the current G98 scope on the ENA catalogue.

When can G98 apply to a home battery?

G98 can apply where the complete micro-generating plant falls within the current G98 scope and satisfies its requirements. For the domestic decision discussed here, that includes the Fully Type Tested requirement and an aggregate Registered Capacity no greater than 16 A per phase.

Where the applicable G98 procedure is used, it is commonly described as a connect-and-notify route. That should not be read as a promise that every project can proceed without any prior DNO discussion; the installer still needs to confirm the correct procedure for the actual installation.

When does G99 need to be considered?

G99 needs to be considered when the generating equipment falls outside G98 scope or does not comply with G98. That can include an installation whose aggregate capacity exceeds the G98 limit, but G99 should not be reduced to one universal domestic wattage band.

The applicable G99 connection process is followed before the relevant installation is connected. The exact process and timing depend on the project, the DNO and any required network assessment, so this guide does not give a generic approval timescale or fee.

Why adding a battery to existing solar can change the route

If an existing PV system already has an AC inverter and the new battery introduces another AC power-conversion unit, the assessment may need to consider their outputs together. That is why an installer should review the existing generation as part of the new battery design rather than checking only the new device.

Worked example: 3 kW solar plus a 3 kW battery inverter

MCS MIS 3012:2025 gives a specific example: a 3 kW solar PV system and a 3 kW electrical energy storage system are connected in parallel to the same single-phase AC supply. MCS states that the combined maximum theoretical output is greater than 16 A, so G99 applies in that stated scenario. See MIS 3012:2025 from MCS.

Where does G100 export limitation fit?

G100 is not a third simple power band and it is not a shortcut that automatically turns a G99 installation into G98. The current G100 Issue 2 Amendment 2 sets technical requirements for customer export and import limitation schemes where there is an agreed need to restrict current flow at the connection point or prevent network voltage limits being exceeded. The DNO assesses whether a limitation scheme is suitable for the relevant network circumstances. See the current ENA G100 scope.

What should your installer do with the DNO?

The Distribution Network Operator (DNO) needs information about the generating arrangement being connected to its network. The installer should therefore establish the existing system and the proposed battery configuration before deciding what notification or connection process applies.

Before installation

1. Record the existing solar, storage or other generation already connected.
2. Confirm the proposed inverter arrangement, number of generating units and supply phases.
3. Work out the relevant aggregate Registered Capacity per phase.
4. Check the equipment’s type-test evidence for the intended route.
5. Identify whether a G100 export or import limitation arrangement is part of the design.
6. State the proposed G98 or G99 route and follow the applicable DNO procedure before the project proceeds to connection where required.

After commissioning

The relevant notification and commissioning paperwork should be completed under the applicable procedure, and the homeowner should keep the DNO correspondence with the installation records. For an MCS installation, MIS 3012:2025 says that notification to the DNO under the relevant G98 or G99 procedure is undertaken by the MCS Contractor. Read the current MCS battery storage standard used for this point.

DNO approval, MCS and SEG are separate

These processes are related, but they do different jobs. MCS certification is not the same as a DNO connection decision, and a G98 or G99 outcome does not itself create a Smart Export Guarantee (SEG) payment.

Ofgem explains that generators who want SEG payments apply to a SEG licensee, which has its own application process and terms. That is separate from deciding the G98 or G99 connection route. See Ofgem’s SEG guidance for generators.

Questions to ask before you accept a battery quote

A good quote should make the connection assumptions visible. You do not need to calculate the route yourself, but you should be able to ask how the installer reached it.

Note: The applicable connection route depends on the actual installation and the relevant DNO. This guide explains the framework; it is not a site-specific connection approval.

Keep the installer’s written explanation with the quote so you can compare the assumptions behind the proposed connection route before moving on to product selection.

Once the DNO route and installation requirements are clear, you can compare home battery storage options.

Explore more UK home battery storage guides.

Written by Jason

Jason is Vice President at Sunpura Energy and leads product and technology strategy. He works on home battery storage, energy management, smart metering and practical ways households can use solar and grid electricity more intelligently. His articles explain technical topics such as battery sizing, off-peak charging, export, retrofit and backup boundaries in clear, practical terms for UK readers.