Commercial Solar Monitoring: What to Track and What to Alarm On
Updated 10 November 2026 · SEO Dons Editorial
What should a commercial array measure?
Five measurements cover most needs.
- Generation at a meter. The Welsh Government's Energy Service recommends a half-hourly meter at each generating station in addition to any proprietary monitoring system. It is the record the contractor's platform can be checked against.
- Export and import at the connection point. They show what the building used and what left it. Export-limited sites need the reading anyway, because NGED says a limitation scheme measures power at the exit point of the installation.
- Irradiance in the plane of the modules. It lets output be judged against the sunshine received. IEC 61724-1:2021 updated its irradiance sensor requirements and its soiling measurement, and IEA PVPS Task 13 says soiling is highly heterogeneous across a plant, so assessing it takes several sensors rather than one.
- Module or ambient temperature. It explains seasonal swings, since the performance ratio typically reads lower in warm months.
- Inverter, string and event data. RC62 notes that many systems report everything from kWh generation to AC and DC string or module parameters, insulation resistance and event records, and calls live online monitoring very beneficial for early warning. Whether module-level data justifies fitting optimisers to every panel is weighed in solar optimisers on commercial roofs.
Whole-site energy monitoring is a separate subject. Everything here concerns the solar system.
Which KPIs matter?
- Specific yield. Sandia defines annual yield as the kWh produced in a year divided by the STC DC rating, in kWh per kWp, and notes it changes from year to year with the weather. The underperformance checklist shows the spread to expect.
- Performance ratio (PR). PVsyst defines it as the energy effectively produced divided by the energy that would be produced if the system always ran at its nominal STC efficiency, as in IEC 61724. It is the usual way to compare output with the sunshine received, and it takes in soiling and shading as well as inverter losses (see the losses guide).
- Availability. The Welsh Government note defines annual availability as the percentage of hours in a year a generating station is available to generate should environmental conditions allow. IEC TS 61724-3 likewise measures energy only while the system is operating and quantifies downtime in an availability metric.
- Measured against expected energy. IEC TS 61724-3 sets out a procedure for comparing measured with expected energy under actual weather.
PR is only as good as the irradiance behind it. PVsyst says satellite data typically have an accuracy of 10 to 20% for hourly values, against approximately 1 to 2% for a good solarimeter, so comparing measured and forecast PR is difficult, and a contract that uses PR must specify how it will be established on site.
Which alarms are worth setting?
An alarm is worth setting if someone has agreed to act on it. The thresholds belong to the designer and O&M contractor, set against the site's own first-year baseline. The candidates below come from what monitoring platforms and manufacturers document.
| Alarm | What it catches | Basis |
|---|---|---|
| Communications lost | A silent dataset that looks like zero output | SMA's portal lists an alert for communication faults between portal and system |
| Inverter event or fault | Trips, derating, string events | Manufacturers publish event codes, for example grid overvoltage, high inverter temperature and low insulation resistance in SMA's manual |
| Inverter against inverter | One unit lagging its siblings on the same roof | SMA's portal lists automatic inverter comparison with alerting |
| Performance ratio below a threshold | Soiling, shade, slow faults | SMA's portal lists a calculated PR with an alert when thresholds are exceeded |
| Export limiter state | Curtailment, or a scheme in fail-safe | NGED requires a limitation scheme to fail safe and cut export |
| Impossible meter readings | A wrong CT or phase, which can also send the limiter the wrong signal | Solis says a reversed CT misreads import as export |
Alarms go to the right people only if the owner can receive them. The Welsh note sets a minimum for a platform: push notifications by SMS or email to the owner's generic address, live remote monitoring of generation and faults through an app, and the ability for the owner to record, store and download the history of faults.
Inverter platform or independent data logger?
Inverter platforms read their own maker's fault codes directly. SMA's portal documentation lists data resolution options of every 5 minutes, every 15 minutes and 6 times a day, plus satellite-based weather data to rate performance without local sensors, though not in all countries. Solis publishes that its cloud data sits in ISO 27001-certified data centres in Frankfurt, with role-based access that isolates data for installers, asset owners and enterprise groups. Each platform has its own plans, limits and terms, and the inverter brands guide compares the ranges.
An independent logger reads the inverters, meters and sensors itself, so the record is the same whichever inverter or O&M contractor is in place. That needs open interfaces. Fronius, for example, describes its Solar API as an open REST API that reads data directly from the inverter over the network and lists Modbus RTU, Modbus TCP and a push service alongside it, while SMA's table shows its monitoring API as optional for some products. Ask in writing what is available, on what terms and for how long.
IEC 61724-1:2021 defines classes of PV performance monitoring system as guidance for monitoring system choices, and removed Class C. A specification should name the class it wants and the sensors that follow from it.
What should the monitoring clause in an O&M contract say?
The Welsh Government's Energy Service published a contract note in February 2026 for public sector and community owners of renewable generation. Its points work as a checklist for any owner:
- Access. The note warns that monitoring platforms are designed to serve the contractor, not the owner, and that some contractors will not give the owner access while most give limited access. State the access, and who keeps the history if the contract ends.
- Reports. Monthly reports should let the owner verify generation and export against expectation, with availability reported and attributed as the contract says.
- Verification. The note says independent verification of the contractor's availability calculation reduces errors in attributing downtime, and that the owner should record downtime in an operational diary as it happens. A separate generation meter makes that possible.
- Communications. It recommends the contractor takes responsibility for the communications line to its monitoring equipment, so a comms failure is not attributed to the owner in the availability calculation.
- Performance terms. If PR is used, say which irradiance source, where the sensor sits and how it is calibrated.
The maintenance guide covers the rest of an O&M programme, and the commercial PV systems page shows where monitoring sits in a specification. What the whole contract costs, and how to compare two O&M quotes, is covered in the commercial solar O&M costs guide. You can send an enquiry through the site's form to request quotes that state their monitoring terms.
Sources
- International Electrotechnical Commission: IEC 61724-1:2021; IEC TS 61724-3:2016 (publication pages), checked 22 October 2026.
- IEA PVPS Task 13: Soiling Losses: Impact on the Performance of Photovoltaic Power Plants (January 2023), checked 22 October 2026.
- PVsyst SA: Performance ratio; PR warranty (for its own model only), checked 22 October 2026.
- Sandia National Laboratories, PV Performance Modeling Collaborative: Annual yield; Performance ratio, checked 22 October 2026.
- Welsh Government Energy Service: Renewables: operation, monitoring and maintenance contracts (17 February 2026, for public sector and community organisations), checked 22 October 2026.
- RISCAuthority and MCS, published by the Fire Protection Association: RC62, version 2 (2023) (copy hosted by Solar Energy UK), checked 22 October 2026.
- SMA Solar Technology AG: Sunny Portal powered by ennexOS with SMA Data Manager; with Sunny Tripower X; Sunny Tripower CORE2 STP 110-60 manual, grid overvoltage event; temperature event; insulation resistance event (manufacturer pages, own product only), checked 22 October 2026.
- Fronius International: Fronius Solar API (JSON), open interfaces (manufacturer page, own product only), checked 22 October 2026.
- Solis: SolisCloud monitoring platform and data logger security; Smart meter phase rotation and CT polarity verification (manufacturer pages, own product only), checked 22 October 2026.
- National Grid Electricity Distribution: Export limitation, checked 22 October 2026.
Common questions
Is the inverter app enough for a commercial roof?
It is a start. Welsh Government guidance recommends a half-hourly generation meter in addition to any proprietary monitoring system, and warns that contractor platforms may give the owner only limited access. Irradiance and temperature sensors are needed to judge output against the sun.
Does a site need an irradiance sensor?
To calculate performance ratio on site, in practice yes. PVsyst says satellite data typically have an accuracy of 10 to 20% for hourly values, against approximately 1 to 2% for a good solarimeter, though satellite data can serve as a first check. Placement without shade and good calibration matter.
How often should data be recorded?
SMA's portal lists intervals of every 5 minutes, every 15 minutes and 6 times a day, and Welsh Government guidance recommends half-hourly meter data. Shorter intervals show clipping and curtailment better. Settle the interval, and how long history is kept, in the contract.
Who owns the monitoring data?
The contract decides. The Welsh Government note says some contractors will not give the owner access to their platform. The contract should let the owner see, export and keep the data, including after the contract ends.