Hybrid inverter

A hybrid inverter combines a solar inverter and a battery power-conversion system. It accepts DC from a PV array, manages a compatible battery on its DC side and supplies AC to the home and grid.

Putting those functions in one unit can simplify a new solar-and-storage installation. It also makes compatibility and failure consequences more important because one inverter coordinates both assets.

Energy paths

Solar DC can be used in three main ways:

converted to AC for household loads
sent through the battery interface for storage
converted to AC for export

When solar is insufficient, the inverter can draw from the battery. Many models can also charge the battery from the grid, but that is a product and firmware capability rather than an automatic feature of every hybrid.

The control system decides which path is active using meter data, battery limits, schedules, export controls and operating mode. A current transformer facing the wrong way or placed on the wrong conductor can make the inverter act on an incorrect view of import and export.

DC coupling

The battery is coupled before the inverter’s AC output. Solar energy stored during the day does not need to pass through a separate solar inverter and then back through an AC-coupled battery inverter.

Fewer conversion stages can reduce losses, but there is no universal efficiency advantage to publish. Actual results depend on PV voltage, battery voltage, charge rate, standby use, inverter loading and where energy is measured. Compare like-for-like round-trip figures for the complete system, not a peak conversion figure from one component.

DC coupling can also retain some solar that would otherwise be clipped at the inverter’s AC export ceiling, provided the battery can accept the surplus and the manufacturer’s DC input limits are still met.

Battery compatibility is specific

A hybrid inverter does not work with any battery that has a convenient capacity. Compatibility includes:

battery voltage range
maximum charge and discharge current
cell and BMS limits
CAN or RS485 communication protocol
approved firmware versions
number and arrangement of modules
isolation, fusing and cable requirements
manufacturer responsibility for the combination

MIS 3012:2025 classifies battery systems partly by who packages the battery, BMS, power-conversion equipment and islanding arrangement. In a mixed-manufacturer system, responsibility for proving compatibility moves towards the competent designer and installer.

A communications link is not optional where the approved system uses it to exchange safe current, voltage and temperature limits. If communications fail, the system should enter the declared safe state rather than continue charging from fixed assumptions.

PV input design still applies

The PV side has the same design constraints as a solar-only string inverter. The design must check:

maximum open-circuit voltage in the coldest design condition
operating voltage inside each MPPT range
short-circuit and operating current limits
permitted strings per tracker
connector and DC cable compatibility
array power and any permitted oversizing

A battery does not make it safe to exceed the inverter’s absolute PV voltage or current limits. It may absorb power that reaches the inverter above the AC demand, but only inside the declared DC envelope.

New installation or retrofit

A hybrid inverter is a natural option when solar and battery storage are installed together. One unit can reduce duplicated hardware and let the designer coordinate PV, storage, export control and monitoring from the start.

Adding storage to an existing solar array presents a different choice. Replacing a working solar inverter with a hybrid may disturb existing strings, monitoring, warranties and Feed-in Tariff evidence. An AC-coupled battery can leave the existing solar system intact.

If the old inverter is already due for replacement, moving to a compatible hybrid may be sensible. The decision should compare complete system design and remaining equipment life, not assume that either coupling method is always cheaper or more efficient.

One point of failure

If the hybrid inverter stops, solar conversion and battery charging or discharging normally stop together. The home remains supplied by the grid unless a separate fault has affected it, but both low-carbon functions can be unavailable until the inverter is repaired.

An AC-coupled arrangement has separate solar and battery inverters. One can sometimes continue when the other fails, although common metering, gateway or network equipment can still create shared dependencies.

The design and handover should explain fault behaviour, safe isolation, local operation and the support route. A long component warranty is only useful while an obligated legal entity can provide the promised remedy.

Backup is a separate design function

A hybrid inverter may have an EPS output, but the word “hybrid” does not mean the home will run in a power cut.

Backup requires an islanding arrangement that:

disconnects the maintained installation from the public network
prevents dangerous backfeed
establishes the required earthing arrangement in island mode
keeps voltage, frequency and fault protection within limits
limits loads to the inverter and battery capability
reconnects safely when the grid returns

Some products support selected maintained circuits. Others can form part of a whole-home arrangement with a gateway. Transfer time is product-specific, and a fast stated value does not make the system an uninterruptible power supply for every connected device.

The IET’s island-mode guidance explains why the neutral-earth arrangement cannot be assumed from normal grid-connected operation. It must be designed and tested for the exact equipment and supply earthing.

Grid connection

The DNO considers the registered capacity of all generation and storage power-conversion equipment behind the connection, not just the planned export limit.

As at 22 July 2026, EREC G98 Issue 2 applies to qualifying small-scale generation up to 16 A per phase. Larger or otherwise non-qualifying connections use G99 and need the appropriate permission before operation. A G100 limitation scheme can cap net export, but it does not automatically reduce the registered capacity used to choose the connection process.

Replacing a solar inverter with a hybrid or adding a battery inverter changes the generation arrangement. The revised design identifies the DNO route and type-test evidence, while the handover includes the completed notification or connection agreement.

Metering and export control

The inverter needs a reliable measurement of net power at the connection point. That value is used for self-consumption control, export limitation and battery schedules.

Commissioning should test:

import and export direction
response when household load changes
battery charge and discharge limits
export-limit response and failsafe behaviour
operation with the PV array at low and high output
behaviour after loss of meter communication

The smart meter used for billing is not automatically the control meter used by the inverter. Their values can differ because they measure at different intervals and boundaries.

Electrical and compatibility data

Compare a proposed hybrid using the full system, including:

PV voltage and current design
approved battery and firmware combination
continuous charge and discharge power
minimum stable power and standby consumption
number of phases
export-limitation evidence
backup arrangement and maintained-load limit
local controls and cloud dependency
commissioning data and support responsibility