G98 vs G99: Key Differences for UK Solar and Battery Systems
- When a Solar Installation Can Follow G98
- When a Solar Installation Needs G99
- How G98 vs G99 Solar Rules Apply to Different Home Projects
- Battery Storage Under G98 and G99 Connection Rules
- Information Needed for a G98 or G99 Grid Connection
- Planning Solar and Battery Storage Around the Correct DNO Route
- Conclusion
- FAQs
When integrating solar panels or battery storage into the electricity grid, there is more to consider than just hardware. Installers in Great Britain also have to consider if the proposed generation will be under G98 vs G99, two Engineering Recommendations, which offer two paths for connecting distributed generation to the local Distribution Network Operator.
For many smaller domestic solar installations, G98 provides a simpler route. Generally, larger systems, equipment not G98 Type Tested, or installations outside the limits of G98 will be a G99 connection for which the DNO will need to perform a connection assessment prior to installation of the generation equipment. Battery storage can also impact assessment, as inverter connected storage is assessed in the network connection regime.
This guide describes the requirements for a G98 vs G99 solar installation, the 16A-per-phase limit, notification and approval procedures and how a system extension may impact an installed connection. It also considers how adding battery storage to an existing solar home or planning solar and storage together should account for the correct DNO route from the beginning.
G98 vs G99 at a Glance
The easiest way to explain G98 vs G99 is to consider three aspects: the capacity and characteristics of the generating system, compliance of the system with the applicable Type Testing requirements and when the DNO enters the picture. G98 is generally a streamlined route for qualification of smaller installations, and G99 covers systems outside of this route.
The main difference between G98 and G99 for grid-connected generation
G98 is applicable to qualifying microgenerators that are installed at low voltage and are operating in parallel with the public distribution network, with a combined registered capacity of not more than 16A per phase, and the equipment complies with the relevant G98 Type Testing requirements. G99 applies to projects outside of those conditions, such as generation over 16A/phase and equipment not Type Tested for G98.
It is not just a question of domestic versus commercial solar. G99 may be required for a household installation as the generating capacity or equipment configuration does not conform to G98. Understanding how solar panels connect to home electricity also helps place the inverter and grid connection within the wider household system.
The 16A-per-phase threshold separating typical G98 vs G99 projects
Typically, the 16A per phase is the key threshold for a low voltage installation. This is typically linked to a registered single-phase generation capacity of around 3.68kW at a nominal supply voltage of 230V. If multiple generating units are installed on the same property, the total capacity per phase of the generating units should be taken into account instead of the individual inverter capacities.
A system at or below the threshold(s) of the applicable G98 may follow G98 if other requirements of G98 are met. Generation beyond the limit tends to enter G99. But it's not just about capacity: if the voltage is high, or the equipment isn't properly G98 Type Tested, it may still be a G99 route, even if the installation looks relatively modest.
Connect-and-notify under G98 compared with approval-before-connection under G99
The installer will usually be able to install and commission the generating equipment first, then notify the DNO within the specified post-installation period for a qualifying G98 installation. That's why G98 is sometimes referred to as a connect and notify process.
G99 changes the sequence. Before installation, the installer or applicant provides the DNO with the information regarding the proposed generation, to enable the network operator to consider the potential impact on the local network. The DNO then makes a connection offer or any relevant conditions of approval, which need to be addressed prior to the connection and commissioning of the generating equipment.
When a Solar Installation Can Follow G98
Once the basic distinction between G98 and G99 is clear, the next question is whether a particular solar installation actually qualifies for the simpler G98 route. The assessment depends on aggregate generating capacity, connection voltage and whether the equipment satisfies the relevant Type Testing requirements.
Small domestic solar systems that fall within the G98 generation limit
G98 can be followed with a typical domestic solar installation provided the total combined registered generation placed at a single premises is not more than 16A per phase on the low voltage network. This equates to about 3.68kW for a single-phase 230V supply, and 11.04kW on a three-phase supply.
The key is that the DNO takes into account the total generating capacity of the property. When there are multiple microgenerators or inverter connected devices, the total capacity of all devices will be evaluated instead of each ]device. Therefore, a simple small roof G98 solar PV installation could be eligible but an expanded multi-inverter PV system may not be.
Fully Type Tested microgenerators required for the standard G98 route
G98 is not determined by capacity alone. The generating equipment should also have the appropriate Fully Type Tested status, and comply with the relevant G98 technical requirements. ENA characterises G98 as the recommendation that covers the parallel operation of Fully Type Tested microgenerators with the public low-voltage distribution networks.
Type Testing is required to show that the equipment has been tested to the protection and operating characteristics required before being installed as part of the simplified connection route. It is therefore essential that installers check the Type Test reference for the inverter/generating unit and verify that the information corresponds to the inverter/generating unit for which a job is being completed. Even if the capacity of the project is low, the project could be subject to G99 if there is no suitable Type Test evidence.
Post-installation notification requirements for qualifying G98 solar systems
The DNO normally does not need to approve a project before it is installed for a qualifying single-premises G98 installation. Rather, the installer connects and commissions the system and submits the necessary Installation Document to the appropriate DNO.
For G98, notification is required within 28 days after the date of commissioning (which does not count towards the 28-day requirement). Site and metering information, generation capacity, Type Test and installer information, supporting diagrams and declaration of conformity.
One of the principal benefits of G98 for qualifying small systems is this connect-and-notify process. When generation is outside of these conditions, however, the installer must instead look to the more formal G99 application and approval process prior to connection.
When a Solar Installation Needs G99
If a proposed Solar installation is not under the standard G98 conditions, then the project enters the G99 connection process. However, the size of the installation does not have to be unusual to need G99 – some domestic installations need G99 due to inverter capacity, together with connection voltage or Type Testing status.
Solar generation exceeding the standard G98 threshold
The most common reason for a domestic solar installation to require G99 is generation capacity above 16A per phase. On a typical 230V single-phase supply, this means a system with registered generation above roughly 3.68kW moves beyond the standard G98 threshold.
The DNO does not count solar panels, but evaluates the entire generating installation. The combined registered capacity of several inverters/generating units will be relevant if they are operating at the same property. Additionally, G99 can be applied even when equipment is installed at a higher voltage, and even when the project seems quite small physically under G98.
G99 applications that require DNO assessment before connection
Whereas G98's connect and notify concept, G99 does not typically make exceptions for generation equipment installation and connection. The installer or applicant gives information about the system they plan to install, so that the DNO can determine the potential impact on the local distribution network.
ENA offers a simplified application form for smaller G99 Type A projects (up to 17kW single phase and up to 50kW three phase). With larger systems, there will be more technical information required. The process for connection can only proceed once the DNO has considered the proposal, made the connection offer or approval, and any outstanding network work has been resolved.
This prior-assessment stage is one of the clearest practical differences in g99 vs g98.
Different G99 generation categories as system size and complexity increase
Generating equipment is categorised in G99 as Type A, B, C and D, and as the amount of generating capacity increases and the impact on the network becomes greater, so do the connection and compliance requirements. Most residential comparisons of g98 vs g99 solar are most relevant to Type A, as it applies to smaller projects that are not part of the G98 route.
As the projects get bigger, from Type B to Type C and D, the level of technical studies, compliance and coordination with the network operators increases. The complexity is increased by the fact that larger generations are more likely to impact both distribution and transmission networks, says ENA.
The bottom line for homeowners is that a G98 rating does not indicate that a project will be exceptionally complicated, but it does alter the involvement of the DNO and when it is involved. These rules are now used in the next section for common household solar scenarios.
How G98 vs G99 Solar Rules Apply to Different Home Projects
G98 and G99 are put into practical situations in the home to make the connection route easier to understand. The DNO assessment will not be determined by the number of panels alone – the inverter size, current generation on the site and the method of connection of the additional generation can all alter the assessment.
Standard rooftop solar installations on a typical single-phase property
The maximum size of a rooftop PV system for a standard single-phase house that can qualify for G98 is a relatively small single-phase system with an aggregate registered generation at or below 16A per phase, which is typically around 3.68kW at 230V, where the PV equipment meets the applicable G98 Type Testing requirements.
This implies that a homeowner should not just count the panels to determine the connection route. The wattage of modern panels, the rating of the inverter and the registered generation capacity are key factors in network assessment. Households estimating suitable array capacity can first review how to calculate solar panel output before an installer determines the formal DNO route.
For many modest residential projects, these characteristics make G98 the more straightforward connection process.
Larger solar arrays and multiple-inverter systems that change the connection assessment
A larger rooftop array may require G99 when the system's registered generation exceeds the standard G98 limit. The same issue can arise when multiple inverter-connected generating units operate behind one connection point.
This is where g98 vs g99 solar assessment becomes more important than simply comparing array sizes. ENA guidance treats inverter-connected solar as a Power Park Module, with the relevant generating capacity determined from the units operating within the system configuration.
However, in some installations, approved export-limitation schemes, under G100 and certain G99 small generation schemes, may be applied, although export-limit does not necessarily make a system an ordinary G98 installation. Installer to make pre-connection assessment of the proposed configuration in accordance with DNO procedure.
Expanding an existing solar installation with additional generation capacity
On an existing G98 solar installation, if additional generation is installed later, then the installation can be reclassified. The addition of more panels, with no change in the appropriately limited inverter, can have different consequences than the addition of a second inverter, which increases the generation capacity of the property registered with the Department.
Therefore, before considering expansion, the installer should consult the DNO record and consider the existing and proposed generating equipment in conjunction with DNO. ENA's G99 guidance explicitly states that additions to existing generation necessitate rethinking the existing capacity and connection arrangement.
This is an important factor to consider regarding g98 vs g99. This is even more relevant when battery storage is added, as inverter connected storage can change the generation and export set-up that the network sees.
Battery Storage Under G98 and G99 Connection Rules
Battery storage can change the network assessment even when a property already has an approved solar connection. The installer needs to consider how the battery inverter interacts with existing generation, how much capacity is connected at the premises and whether export limitation forms part of the overall design.
Why inverter-connected battery storage matters in a G98 vs G99 assessment
The reason that battery storage is important in assessing a G98 vs G99 is that a battery connected to an inverter can import electricity for charging and export electricity when discharging. UK gov guidance says that battery storage must be registered with the local DNO and that it must be assessed at the property in conjunction with other energy devices.
If the PV and storage are installed together, the installer should think about an entire generation system and not the battery as a standalone product. The capacity & equipment configuration will be important to help decide whether the project can be connect and notify or if it needs a G99 application prior to installation.
Adding AC-coupled battery storage to an existing solar installation
When installing a battery system on top of an existing solar power system, an additional battery inverter will be added to the existing PV inverter. It may alter the aggregate generating capacity shown for the property and therefore the installer will need to check the existing DNO documentation prior to introducing storage. Based on the combination of configuration, the project can be considered a connect-and-notify route, or it may need prior approval from G99. There is also a fast-track G99 process for some Fully Type Tested integrated microgeneration-and-storage products which can be used for projects that meet the criteria for simplified pre-installation assessment.
Export limitation and combined generation capacity in solar-and-battery systems
Export limitation can be used to control the amount of electricity a solar and battery system exports to the distribution grid; however, export limitation does not equate to a larger installation being a standard G98 project. ENA guidance acknowledges G100 compliant export limitation schemes, where the total generation is more than 16A per phase.
The installer is still required to do a total solar and storage capacity assessment, understand inverter ratings and control schemes to choose a G98 or G99 route. Hence, the distinction between export capacity and installed generation capacity should be considered during the connection planning process as two related but independent quantities.
Information Needed for a G98 or G99 Grid Connection
When the most probable connection route is determined, the installer requires property and technical detail before preparing the paperwork for submission to the DNO. While G98 projects are relatively simple, any detail omitted from the description of the generating equipment and the site where it will be used is critical for G99 projects.
Inverter ratings and Type Test information used to assess the G98 vs G99 connection route
The inverter rating may be a factor to consider in determining the generating capacity which will be registered by the DNO. Installers are advised to check the manufacturer, exact model, rated output and phase arrangement of the equipment, and the appropriate G98 or G99 Type Test reference, and not to take approximate descriptions of equipment as representative. ENA will keep a Type Test Register for use in verification of conforming generating equipment.
For solar households, understanding how solar inverters work can also help explain why inverter capacity matters separately from panel wattage when planning a grid-connected PV system.
Site, supply and system details installers provide to the DNO
The DNO also requires sufficient data to be able to locate the property and how generation will interface with the existing supply. Common information includes the address where the installation is being set up, the contact information of the customer/generator, the arrangement of the supply, the phase arrangement, the number of Power Generating Modules, with each module's capacity, and the electricity storage capacity, if applicable. Also documented on G99 are the type of technology, manufacturer references and, where applicable, the location of isolation equipment.
When supplying accurate information, it is especially crucial where a property has existing solar or battery installations as the DNO will be required to consider the entire installation and not just the latest component.
Single-line diagrams and technical information required for more complex G99 applications
For more complex projects in G99 you may need more than just equipment details; technical evidence may be needed. A single-line diagram might be required to illustrate the relationship between the various elements: the generating units, the inverters, protection devices and the grid connection. For export limitation, the ENA documentation may also include a diagram and description of the control scheme and how it fails.
Additional details may include harmonics, voltage fluctuations, contribution and fault level and protection settings, depending on the project, enabling the DNO to determine whether the proposed system is fit for purpose to run on the local network.
Planning Solar and Battery Storage Around the Correct DNO Route
Once the connection requirements are clarified, then the solar and battery sizes can be designed based on the household connection and the route agreed by the DNO. This will prevent the equipment from being selected first and learning after that the inverter configuration is different and a different connection process must be performed.
Checking grid-connection requirements before finalising inverter and storage capacity
Before finalising equipment, the installer should consider the property supply, existing generation, proposed inverter ratings and battery configuration. Such factors are the ones which influence whether the project falls under G98 or requires a prior assessment under G99.
Future expansion should be taken into account in the same assessment. When planning for systems, selecting one that considers future expansion can minimize risk for future re-design of the connection if additional solar generation or battery capacity is needed.
EcoFlow STREAM 5000 for households planning solar and battery storage together
For households without existing solar, EcoFlow STREAM 5000 supports planning generation and storage as one coordinated installation. It provides 5.24kWh capacity, up to 4000W PV input and 3000W off-grid AC output, with Intelligent Mode+ managing household energy use.
Its storage can expand up to 90kWh, allowing capacity to grow as demand changes. The installer should still assess the complete inverter and generation configuration against the appropriate G98 vs G99 route before commissioning.
EcoFlow STREAM 5000 AC for existing solar homes adding battery capacity
EcoFlow STREAM 5000 AC is a retrofit-friendly storage solution for existing PV with 5.24kWh capacity and 800-3000 W grid-connected AC output. Local Mode and smart energy management support the synchronisation of existing solar power generation, storage and domestic energy consumption.
Before adding it, the installer must check the original DNO records and existing solar inverter. Another inverter-connected device may alter the overall site connection assessment, and the previous G98 or G99 (if applicable) should not be assumed to apply to the new battery.
Conclusion
Understanding G98 vs G99 helps homeowners and installers identify the correct DNO connection route before solar or battery equipment is commissioned. G98, in general, is applicable to qualifying smaller generation (below 16A/phase) and takes a 'connect and notify' approach, whereas G99 is for systems outside this path and is normally assessed by DNO prior to connection.
The correct route is not only determined by the number of panels, but also by comprehensive installation. Factors that may influence a project moving from G98 to G99 include inverter capacity, existing generation, battery storage, Type Test status and future expansions.
Grid requirements should therefore not be taken into account after equipment has been selected, but in the design of a solar and battery storage system for households. This ensures that capacity and inverter configuration and future expansion are compatible with the DNO requirements.
FAQs
Do off-grid solar systems need G98 or G99?
No, a genuinely off-grid solar system that operates independently and never runs in parallel with the public distribution network would not normally require G98 or G99 connection approval. These Engineering Recommendations apply to generating equipment connected in parallel with the electricity network.
However, the situation changes if the property retains a grid connection or the system can operate in parallel with it. In that case, the installer should assess the proposed configuration and determine whether G98, G99 or another relevant connection arrangement applies.
Does an MCS certificate replace G98 or G99 requirements?
No, MCS certification and G98 vs G99 address different parts of a solar or battery project.
MCS concerns installation and technology standards under the MCS framework.
G98 covers qualifying smaller generation connected in parallel with the distribution network.
G99 applies where the project falls outside the standard G98 route.
MCS battery-installation standards themselves recognise G98/G99 testing for electrical energy storage systems that operate in parallel with the grid. An MCS certificate therefore does not remove the need to complete the appropriate DNO connection process.
Does choosing a Smart Export Guarantee tariff determine whether G98 or G99 applies?
No, A Smart Export Guarantee tariff does not determine whether an installation follows G98 or G99. The connection route is based on generation capacity, equipment characteristics and how the system connects to the distribution network.
SEG is a separate arrangement for receiving payment for eligible exported renewable electricity.
The DNO connection process must still be completed correctly.
SEG suppliers set their own tariff rates and contract terms.
The installation must satisfy the applicable SEG eligibility and metering requirements.
Ofgem confirms that SEG payments are based on metered electricity exported to the grid.
What should a homeowner do if an existing solar system has no DNO paperwork?
First, check the installation handover pack, emails and records from the original installer for G98 or G99 correspondence. If nothing can be found, contact the relevant DNO using the property's address and MPAN and ask whether the generation is recorded on its network.
Homeowners planning an upgrade should resolve the missing paperwork before adding another inverter or battery. The installer can then compare the actual equipment with the DNO record and determine whether the existing connection needs to be regularised or updated before connecting further generation.
Can changing an inverter affect an existing G98 or G99 connection?
Yes, changing an inverter can affect an existing G98 vs G99 connection assessment because the replacement may have a different registered capacity, Type Test reference or operating characteristics.
Before replacing one:
Check the rating and Type Test details of the existing inverter.
Compare them with the proposed replacement.
Review the property's existing DNO connection documentation.
A like-for-like replacement may have fewer implications than installing a higher-capacity inverter, but the installer should still determine whether the DNO record requires updating. This becomes especially important if the replacement also accompanies additional solar or battery capacity.