Microinverter

A microinverter converts solar-module DC into grid-compatible AC at the array. A unit may serve one module or have separate inputs for several modules. Each input normally has its own MPPT, allowing modules with different irradiance or orientation to operate more independently than modules sharing one string tracker.

The array’s AC outputs are connected through a manufacturer-specific trunk or branch cable. The system still needs isolation, protection, generation recording, grid connection and commissioning like any other PV installation.

What module-level tracking can and cannot do

In a conventional series string, modules share current and bypass diodes respond to sufficiently uneven conditions. Modern string inverters may also have more than one tracker. The effect of one shaded module is therefore more nuanced than “one panel loses power, so the whole string loses the same percentage”.

A microinverter prevents one input’s operating point from directly setting every other module’s operating point. This can help with persistent non-uniform shade, mixed orientations, different module characteristics or fault diagnosis. It cannot recover sunlight that does not reach a shaded module, and it does not make a poor roof layout good.

The gain should be estimated from a shade and layout model against a suitable string-inverter alternative. A universal yield uplift is not credible.

DC and AC ratings

The module’s maximum-power current and voltage, open-circuit voltage and short-circuit current must sit within the microinverter input limits after relevant temperature corrections. The module’s power rating may exceed the unit’s AC rating by design, but expected clipping and the manufacturer’s permitted input must be checked.

A multi-input microinverter does not necessarily allow arbitrary modules or orientations on every input. Tracker arrangement, shared limits and approved module combinations come from the datasheet.

On the AC side, branch-circuit current, cable length, voltage rise, protective devices and the manufacturer’s maximum units per branch govern the layout. Those limits vary by model and electrical design. Adding another roof module is not automatically possible because the conversion is distributed.

Grid connection uses the aggregate system

For DNO purposes, the relevant generation capacity is the aggregate registered capacity of all microinverters and other generation at the premises. Splitting it into small units does not avoid G98 or G99 requirements. The exact product also needs the applicable type-test evidence and settings for the connection route.

Loss-of-mains protection disconnects the grid-connected output when the supply fails. An ordinary microinverter array does not keep house circuits running during an outage. Backup requires a specifically designed islanding system, switching, controls and compatible storage or grid-forming equipment.

Roof-level equipment and isolation

Placing conversion at the module reduces the length of high-voltage series DC cable. It does not make the roof electrically dead in daylight: each module and its short DC leads continue producing voltage when illuminated, and AC circuits may be energised when connected.

Isolation and emergency behaviour should be described for the exact system. Overseas “rapid shutdown” claims should not be assumed to describe a UK requirement or every microinverter platform.

The trade-off for distributed conversion is more electronic equipment in a hot, exposed and difficult-to-access location. One unit failing may remove only its connected modules rather than the whole array, but replacing it may require scaffold or other safe roof access. Warranty length should therefore be read alongside labour and access cover.

Monitoring and dependence on the platform

Module-level data can reveal a failed unit, persistent shade or an underperforming module. The monitoring boundary should be clear: some portals show microinverter AC production, while site import, export and battery flows need additional meters or current sensors.

Data may depend on a gateway, local communications, internet access and the manufacturer’s cloud service. The owner should know which functions continue locally if the internet or service ends, whether installer access can be transferred, and whether replacement products remain compatible with the installed trunk and gateway.

Small differences between modules are normal. A portal image alone does not diagnose a defective panel without considering orientation, shade, dirt, temperature and communication gaps.

Batteries and future expansion

Because the PV array produces AC, a separate battery is commonly AC-coupled. Some manufacturer ecosystems coordinate PV, battery and backup products more tightly. Compatibility and operating behaviour should be shown for the exact components rather than inferred from the word microinverter.

Future expansion needs spare branch capacity, electrical supply and grid permission, compatible hardware and physical roof space. Product generations may use different connectors or communications, so “easy to add later” is not an expansion design.

Architecture boundaries

shade-model result against a suitable string design
input compatibility and AC clipping assumption
branch-circuit limits and cable design
G98 or G99 evidence for the aggregate system
monitoring hardware, data ownership and offline behaviour
expected roof-access cost for a failed unit
module, trunk and gateway compatibility for expansion
battery and backup architecture, if required