Monitoring

Inverter level, string level and module level

Granularity is the first decision, because it sets both the cost and what a fault will look like on the screen.

• Inverter level is the baseline and comes with every inverter: total AC output, daily and cumulative yield, efficiency, temperature and fault codes. It tells you the plant is working. It does not tell you which of forty panels is the problem.
• String level means per-MPPT voltage and current, which most modern inverters report and which larger units expose per individual string. Two strings on the same orientation should track within a few percent, so divergence localises a fault to one string on one roof face.
• Module level requires optimisers or microinverters and gives voltage, current and yield per panel. That is what you need on roofs with chimneys, dormers or partial shading, and it is the only view that names the individual panel to be replaced.
• Cost against value: on an unshaded south roof with two clean strings, string level answers almost every question. On a complex roof with several orientations, module level pays for itself the first time somebody has to find one failing panel.

Consumption monitoring needs a meter

An inverter measures only what it produces. It cannot see the kettle, the heat pump or the wallbox, so any figure for self-consumption, import or export has to come from a separate measurement at the grid connection point. That is a smart meter on the main incomer, downstream of the utility meter and upstream of every load and of the inverter's own AC connection, wired back to the inverter or logger over RS485 Modbus RTU.

• Without a meter the portal shows production only. Self-consumption ratios in that case are estimates, not measurements.
• With a meter you get bidirectional power per phase, so the portal can separate production, direct self-consumption, battery charging and export.
• Phase count follows the supply, not the inverter. A three-phase supply needs a three-phase meter even behind a single-phase inverter.
• Sub-metering a heat pump, a wallbox or a tenant unit takes an additional meter on that circuit, which most portals will display as a separate channel.

Data loggers and gateways for multi-inverter sites

A single residential inverter with a communication stick needs nothing further. Once there is more than one inverter, or once meters, batteries and third-party systems have to appear in one place, that job belongs to a data logger or gateway.

• Aggregation: the logger polls several inverters over an RS485 daisy chain or over Ethernet and presents the site as one plant, with combined yield and per-device detail.
• Device capacity: loggers are rated for a number of devices, commonly tens of inverters per unit. Check the limit and the supported device list before designing the bus.
• Local storage: a logger buffers readings when the internet is down and uploads them afterwards, so a dropped line does not leave a permanent hole in the record.
• Export control: on larger installations the logger, not the individual inverter, applies the site-wide power limit using the meter reading at the connection point.
• Commercial sites: where commercial energy storage is involved, the gateway usually also coordinates charge and discharge and reports the battery to the same portal.

Open protocols against closed portals

Most manufacturers give you a free cloud portal and an app. That is convenient and it is also a dependency: the portal defines what you can see, the account owns the plant, and the manufacturer decides how long the history stays and whether an API exists. For a family house that is usually acceptable. For a commercial site, a housing association or anyone with an energy management system, it is worth checking what the hardware exposes locally before buying.

• Modbus TCP over Ethernet is the common open route. The inverter or logger acts as a server on the local network and any client, from a building management system to open-source software, can read the registers.
• Modbus RTU over RS485 is the same protocol on a two-wire serial bus, used for meters and for inverters without an Ethernet port. Daisy chain the bus, use shielded twisted pair and terminate long runs with 120 Ω.
• SunSpec is a standardised register map layered on Modbus, so a compliant device can be read without a brand-specific mapping document.
• REST APIs published by the portal let you pull historical data into your own reporting, though rate limits and, on some platforms, a paid tier apply.
• MQTT appears on some loggers and third-party gateways and suits pushing live values into a local energy manager without going through the cloud at all.

Alerting, remote diagnostics and service contracts

For an installer carrying a service obligation, monitoring is the tool that makes the obligation affordable. The value is not the dashboard, it is knowing about a fault before the customer does and arriving with the right part.

• Alert rules: zero production in daylight, communication lost, a string deviating from its neighbour, inverter fault codes, isolation resistance warnings and, on batteries, an abnormal state of charge.
• Fleet views: installer portals list every plant under one account with status, so one screen replaces opening thirty customer logins.
• Remote diagnostics: reading fault history and firmware versions remotely turns many callouts into a phone call, and some brands allow parameter changes or firmware updates over the same link.
• Evidence: a manufacturer handling a performance claim asks for time series data. Continuous logging from the day of commissioning is what supports it.
• Access rights: separate installer and owner accounts from the start. Sharing one login is what makes a later handover or a change of installer painful.

Data retention and export

Retention policies differ sharply and are rarely read before commissioning. Portals typically keep high-resolution data, values every 5 or 15 minutes, for a limited window of months, then condense to daily, monthly and annual totals held for years. If you need five-minute data from three years ago for a warranty case, condensed totals will not serve.

Check three things before you rely on a platform. Whether the portal offers CSV or Excel export and at which resolution. Whether an API is available and whether it is included or charged for. And whether the hardware can log locally as well, over Modbus TCP into your own database, which is the only arrangement that keeps the record independent of the manufacturer's business decisions. Also settle who owns the plant account, because the account holder, not the site owner, usually controls the data and the ability to transfer it.

Quick comparison of monitoring levels

Swipe the table to the left