When planning a larger residential solar and battery installation, you may hear your installer refer to a G99 application or say that the proposed system requires approval from the DNO.
The principle is straightforward: before certain generating systems operate alongside the electricity network, the local network operator must confirm that the connection can be accommodated safely.
What is a DNO?
DNO stands for Distribution Network Operator. The DNO operates and maintains the local electricity network that brings power to homes and businesses, including underground cables, overhead lines, substations, transformers and network protection equipment.
Your DNO is different from your electricity supplier. Suppliers such as Octopus Energy, British Gas, E.ON and EDF manage tariffs, accounts and bills. The DNO manages the physical local network. Each operator covers a geographical area, so homeowners do not normally choose which one serves them.
Why does the DNO need to know?
Solar panels and batteries can send unused electricity back through the property connection. Larger systems—or many systems in the same area—can affect voltage, transformer and cable loading, protection settings, phase balance and power quality.
The DNO’s assessment keeps the network within its safe operating limits. It is more accurate to describe this as managing voltage rise, thermal loading and protection than simply preventing “too many volts” or an explosion.
G98 and G99
G98 and G99 are engineering recommendations governing the connection of generating equipment.
G98 normally applies to fully type-tested equipment with a registered capacity no greater than 16 amps per phase. On a typical single-phase domestic supply, this is commonly described as approximately 3.68kW of AC inverter capacity. A qualifying single-property installation can generally follow a fit-and-notify process, with the DNO notified after commissioning within the required period.
G99 normally applies when generating equipment exceeds the G98 limit or falls outside its requirements. It generally requires an application and approval before connection. On three phase, the limit applies per phase, so it is not correct to assume that every installation above 3.68kW automatically follows the same route.
Panel capacity and inverter capacity are different
Solar panels are normally described by their combined DC capacity. The inverter converts that electricity into AC for use in the property or export to the network.
A 7kWp solar array could be paired with a lower-rated AC inverter. The connection route is not determined simply by counting panels. The inverter arrangement, battery equipment, phases and aggregate generating capacity must be considered.
Battery storage matters because a battery inverter may also be capable of exporting. Separate solar and battery inverters may therefore need to be assessed together.
Why might a larger home need G99?
A property with a heat pump, electric vehicles, air conditioning, electric cooking, a hot tub or workshops may have substantial simultaneous demand. A larger inverter can allow solar and battery storage to contribute more power at one time.
Battery capacity in kWh determines how much energy is stored; inverter power in kW determines how quickly it can be delivered. Both should be matched to the home’s demand, supply and connection approval.
What can the DNO offer?
The DNO may approve the requested capacity, offer a lower export limit, require protection settings, accept an approved export-limitation scheme, recommend three phase or identify network reinforcement work.
Two similar properties can receive different offers because they may be served by different cables, transformers or substations.
Can export be limited?
An approved G100-compliant export-limitation scheme can control the net power sent from the property. This may allow a larger solar and battery system to serve internal loads while restricting export to the level agreed with the DNO.
Export limiting is not a way to avoid the application. It is part of the declared design and must be assessed, installed and commissioned correctly.
Plan the connection before the sale
G99 should not be paperwork completed after a predetermined system has been sold. The likely connection arrangement can affect the inverter, battery, maximum export, project cost, timescale and future expansion.
OmniOrigin considers these requirements during design so the application reflects the system the homeowner actually needs.
Official guidance: Energy Networks Association and Ofgem.