Smart Inverters Explained: What They Do That Standard Inverters Don't

Every solar installation has an inverter. But increasingly, the inverter your installer fits is expected to do far more than convert direct current from your panels into the 230V alternating current your kettle uses. A new generation of smart inverters communicate with your Distribution Network Operator (DNO), respond to grid-stability signals, log granular performance data, and open the door to demand-flexibility income — capabilities that a basic box simply cannot offer. If you are comparing quotes or planning an upgrade, understanding the difference matters more than ever.

What makes an inverter "smart"?

The short answer: two-way communication with the grid and the ability to act on it. A standard grid-tie inverter follows a fixed rule — export whatever the panels produce, up to a hard-wired limit agreed with the DNO at connection time. A smart inverter replaces that fixed rule with a live conversation. It can receive a signal and adjust its output within seconds, redirect surplus energy to a battery or EV charger, report performance data to a cloud portal, and accept firmware updates over the air — all without manual intervention.

In UK regulatory terms, most of these capabilities cluster around two grid codes: G99 (the DNO connection standard for systems above 3.68 kW per phase) and G100 (the Engineering Recommendation governing Customer Export Limitation Schemes, now in Issue 2). G100 in particular is where smart inverter features move from optional extras to legal requirements for many installations.

G100 and dynamic export limiting

G100 is the regulation that most directly forces inverters to be smart. When a DNO cannot grant you unrestricted export — because the local network is already congested — it may offer a connection on the condition that you install a Customer Limitation Scheme (CLS). Under a fixed-limit arrangement, your inverter simply caps export at, say, 3.68 kW regardless of what the network can actually handle at any given moment. That wastes potential generation.

Dynamic export limiting, enabled by G100, replaces the fixed cap with a real-time control loop. A G100-compliant controller monitors the power flow at your meter, calculates how much headroom the network has, and continuously adjusts the inverter's output to use every kilowatt the DNO's network can accept at that instant — without ever exceeding the agreed maximum. If export levels approach the ceiling, the system must reduce output (or redirect energy on-site) so the connection stays compliant; under G100 Issue 2, an excursion beyond the limit must be corrected within 15 seconds, and the system must enter a fail-safe state if the breach persists beyond 60 seconds.

G100 Issue 2 also extended the standard beyond export to cover import limitation — relevant for sites with EV chargers or heat pumps that could exceed the agreed import capacity during peak demand. The standard now requires enhanced fail-safe functionality and supports wireless communications, provided backup protection mechanisms are in place. DNOs retain the right to request compliance tests at any time, particularly after system changes.

For larger residential or commercial systems requiring G99 approval, DNOs may additionally impose reactive power control and frequency response obligations. Smart inverters can absorb or inject reactive power to manage local voltage rise — a requirement that becomes more common as more solar is added to already-loaded suburban feeders. Under G99, inverters may also be required to operate in Limited Frequency Sensitive Mode (LFSM), curtailing active power output automatically when grid frequency rises above 50.4 Hz or falls below 49.5 Hz to help stabilise the network.

Remote monitoring and open protocols

Smart inverters expose their data — and accept commands — through standardised interfaces. The most widely adopted in the UK are Modbus TCP (a wired or Wi-Fi LAN protocol) and the SunSpec Alliance data model, which defines a common register map so third-party energy-management systems can read any compliant device without manufacturer-specific code. Leading brands sold in the UK — including SolarEdge, Huawei (SUN2000 series), SMA, Sungrow, and Fronius — publish SunSpec-compliant implementations.

Manufacturer cloud portals layer on top: SolarEdge's monitoring portal, Huawei FusionSolar, SMA Sunny Portal, and Sungrow iSolarCloud all provide generation dashboards, yield forecasting, fault alerts, and — crucially — remote firmware updates. This last feature matters because grid code requirements evolve; an inverter that cannot be updated in the field may need physical replacement when the rules change, whereas a smart inverter can receive a software patch overnight.

If you are also thinking about home battery storage, smart inverter compatibility is essential — a hybrid inverter coordinates the charge and discharge schedule of the battery alongside solar production and grid tariffs, something a basic string inverter cannot do.

Demand Flexibility Service and Virtual Power Plants

The most financially interesting capability of a smart inverter is grid-service participation. The National Energy System Operator (NESO) operates the Demand Flexibility Service (DFS), which since November 2024 runs as a year-round in-merit service rather than a seasonal emergency measure. Homes with smart inverters and batteries can participate through registered electricity suppliers: during a DFS event (typically one to two hours, around four to six times per month), the aggregator signals the system to charge from the grid or export stored energy, and the homeowner is rewarded for the flexibility provided.

Beyond the DFS, a growing number of aggregators run Virtual Power Plant (VPP) programmes that pool hundreds or thousands of home batteries into a single dispatchable resource. Axle Energy, for instance, offers £1 per kWh dispatched during stress events plus a monthly minimum payment; SolarEdge launched its own VPP for UK SolarEdge Home Battery owners directly through the DFS. Battery chemistry matters less than inverter API quality for VPP eligibility — brands that expose a well-documented control interface (Modbus or a proprietary API) can be enrolled, while closed systems cannot.

These services complement, rather than replace, export income. A smart inverter can simultaneously optimise self-consumption, maximise Smart Export Guarantee earnings, and hold battery capacity in reserve for a scheduled DFS event — decisions that a fixed-output standard inverter is structurally incapable of making.

Which brands lead on smart features in the UK?

All five of the major brands sold by UK installers now offer G100-compatible hybrid inverters, though the depth of third-party integration varies:

SolarEdge — Power Optimiser architecture; SunSpec Modbus TCP certified; direct DFS/VPP programme; SetApp commissioning.
Huawei SUN2000 — SunSpec Modbus TCP; FusionSolar cloud; widely used in UK residential G99/G100 schemes.
SMA — SunSpec Modbus TCP; open Home Manager 2.0 for local automation; strong G99 track record.
Sungrow — SunSpec Modbus TCP; iSolarCloud; increasingly popular in UK residential installs.
Fronius — Modbus RTU and TCP; Solar API for third-party integration; Symo Hybrid for battery coupling.

Do you need a smart inverter?

If your system is under 3.68 kW per phase and your DNO has not imposed an export limit, a G98 string inverter will connect without G100 compliance. But as systems grow larger — and as battery storage, EV charging, and heat pumps are added — the probability of a DNO requiring G100 dynamic export control rises sharply. Beyond compliance, the monitoring, grid-service, and VPP capabilities of a smart inverter represent genuine long-term value: the ability to earn from flexibility services, update firmware as grid codes evolve, and integrate with a whole-home energy management system.

For most households adding solar today, especially with a battery, specifying a smart inverter from the outset costs little extra and avoids a costly replacement later.