Energy gateway hardware

An energy gateway is an enclosure that can coordinate metering, grid isolation, backup transfer and load control around a battery system. The name does not describe one standard set of functions. Some gateways switch the electrical supply; others are communication or metering devices only.

The product and single-line diagram must show what the installed gateway actually does.

Backup transfer

For a home to run from a battery during a grid outage, the maintained installation must first be disconnected from the public network. This prevents the inverter energising network conductors that engineers may expect to be dead.

A backup gateway can contain the contactors or relays that perform that transfer. It monitors the grid, opens the required live conductors, confirms the isolation state and permits the inverter to form a local supply.

When the grid returns, the system must verify acceptable voltage and frequency, stop or synchronise the islanded supply as designed, remove any temporary earthing link in the correct sequence and reconnect safely.

Transfer time is product-specific. It can also vary with operating state and load. A fast published value does not make the whole installation an uninterruptible power supply for sensitive electronics.

Earthing in island mode

Normal protection may rely on the distributor’s supply and earthing arrangement. Once the gateway separates the home from the grid, the inverter and islanding equipment must establish the earthing and neutral relationship needed for protective devices to operate.

MIS 3012:2025 defines a neutral-earth bond relay as a device that connects the EESS neutral to a means of earthing in island mode and disconnects it immediately before the maintained loads reconnect to the grid.

The exact solution depends on the supply earthing, inverter, switched conductors and manufacturer’s declared arrangement. It must not be improvised from a generic gateway diagram. Commissioning should test protection in both grid-connected and island modes.

Maintained and non-maintained loads

A gateway can back up selected circuits or the whole distribution board.

Selected-load backup moves lighting, refrigeration, communications or other chosen circuits to a maintained consumer unit. It limits the simultaneous load and makes battery duration easier to manage.

Whole-home backup keeps the main installation available but does not mean every appliance can run together. The inverter, battery, gateway contacts, cables and protective devices still have continuous and surge limits. Load shedding or user discipline may be necessary for cookers, showers, EV chargers, heat pumps and other large loads.

The design should state:

maintained circuits and priorities
maximum continuous and short-duration load
motor and compressor starting behaviour
which loads are automatically disconnected
expected action when the limit is exceeded
how the owner can conserve battery energy

An EV charger or heat pump should not be assumed suitable for island operation simply because the gateway has enough current capacity on paper.

Metering and control

Many gateways measure net flow at the grid connection and exchange that value with the battery inverter. The system uses it for self-consumption, export limitation and charge or discharge control.

Metering may use internal sensors, an external meter or current transformers. Commissioning must confirm:

each sensor is on the correct conductor
direction and phase assignment are correct
import and export signs agree across the gateway and inverter
communication-loss behaviour is safe
an export limit acts at the agreed connection point

On a three-phase supply, measuring only one phase or mapping phases incorrectly can produce misleading control even if the total shown in the app looks plausible.

Load shedding

A gateway may open contactors to disconnect lower-priority loads during a power cut or when import approaches a supply limit. That is different from asking an appliance to reduce demand over software.

A load-shedding design needs a defined priority and recovery sequence. Reconnecting several large loads together can trip the inverter or create repeated cycling. A failed communications link should leave the installation in the declared safe state.

Manual control can still be valuable. It lets an owner preserve charge during a prolonged outage, but the isolation and earthing functions must not depend on the owner making an unsafe switching sequence.

Black start and depleted batteries

Not every storage system can start an island after both grid and battery have shut down. Black-start capability depends on the inverter, BMS, minimum state of charge and whether solar can restart the system without an established AC reference.

Ask what happens when:

the outage begins below the backup reserve
the battery reaches its minimum state of charge overnight
solar returns the next morning
the battery or inverter is in a fault state
the gateway loses its communications supply

The answer should come from the tested product arrangement, not from the word “backup”.

Communication and cloud services

A gateway can provide Ethernet, Wi-Fi or cellular communication for monitoring. Those links are separate from its safety-critical transfer function.

The installation should continue in a defined local state if the internet or cloud is unavailable. Remote control, historic data or automated tariff schedules may stop even while grid isolation and basic battery operation remain functional.

Record local access, account ownership, firmware route and any subscription dependency at handover.

Siting and electrical integration

Transfer equipment is commonly installed near the supply intake or distribution equipment because it must intercept the relevant conductors and measure the connection point. The actual position follows cable sizing, fault current, voltage drop, service access, enclosure rating and the distributor’s requirements.

There is no universal gateway distance or enclosure position. Long meter tails and supply-side work need specific design and may require distributor or meter-operator involvement.

The gateway and associated battery arrangement must also follow the current battery fire-safety, access and environmental requirements that apply to the installation. A weatherproof rating does not by itself make every outside wall suitable.

DNO documentation

The gateway does not determine the G98 or G99 route on its own. The DNO considers the connected generation and storage power-conversion equipment, its type-test evidence and any export-limitation scheme.

As at 22 July 2026, qualifying equipment up to 16 A per phase can use the EREC G98 Issue 2 route. Other connections use the applicable G99 process. A G100 export limit can constrain net flow but does not automatically turn a larger registered-capacity system into a G98 installation.

Keep the DNO notification or agreement, schematics, export-control settings and gateway commissioning results with the handover pack.

Interfaces and service dependencies

For a proposed gateway, establish:

whether it switches power or only communicates
single or three-phase capability
continuous current and fault rating
selected-load or whole-home topology
isolation and neutral switching
island-mode earthing method
meter and export-control function
load-shedding outputs
black-start behaviour
local operation without internet
compatibility and responsibility for the complete system

The installed function and tested arrangement concern the complete system, not an enclosure viewed separately from the electrical work.