Monitoring a C&I Solar Plant: String-Level Data, Alerts and What Reports You Should Get

A C&I solar monitoring system should log inverter and, where the hardware allows, string data every few minutes, hold a history you own, raise alerts for outages and under-performance, and produce a monthly performance-ratio and availability report. Write data access, alert response times and the report format into the contract, because a dashboard alone does not tell you whether the plant performs.

The four layers of monitoring

"Monitoring" covers four different things, and quotes often differ because one bidder prices one layer and another prices all four. Ask which are included.

String-level data costs more hardware, especially with central inverters, and adds communication points. With string inverters you often get per-MPPT data without extra cost. Decide how deep to go on the size of the plant and the cost of a lost string; the more strings per inverter, the more a single bad string hides.

A benchmark from a public tender

The SECI tender for a 700 MW (AC) project in Gujarat (Tender No. SECI/C&P/OP/11/023/2025-26) shows how a large buyer writes a SCADA specification. It asks for monitoring of electrical and environmental parameters at intervals not greater than one minute; a one-minute logging interval with local buffering and time-synchronised backfilling after a communication outage; server archiving at 15-minute resolution for two years, with full one-minute data kept around any alarm event; alarms on equipment faults in less than five seconds; configurable threshold alerts; a browser-based interface; downloadable Excel and PDF reports; and performance ratio and CUF calculated on the fly. For the string monitoring boxes it lists string current, bus voltage, output current, cabinet temperature, disconnector status and surge protector status as parameters brought to SCADA.

A 700 MW plant is not a factory roof, and you should not copy that specification. Use it as a ceiling: it tells you what is technically normal, so you can decide which items you need and ask a bidder to price the rest as options.

Performance ratio and availability, defined

Two numbers belong in every monthly report. Performance ratio (PR) compares the energy delivered with the energy the plant would produce at the irradiation it received. It needs a measured plane-of-array irradiance, ideally from a calibrated sensor kept clean; without one, PR can only be estimated from satellite data, which is a weaker basis for a guarantee. Availability is the share of daylight hours in which the plant, or each inverter, was able to generate, and the contract must say what counts as downtime and what is excluded, such as grid outages. The SECI tender, for example, sets an acceptance criterion of at least 99% system availability during its test period, a reminder that availability is defined and tested, not asserted. Our guide to performance ratio guarantees shows how to word and test them.

Alerts: who gets them and who must act

An alert is useful only if someone must respond. The SECI document is explicit that alarms and alerts on faults and threshold crossings must be raised, and that the list of parameters is finalised with the owner. For a C&I contract, write these items:

• Which events raise an alert: inverter trip, communication loss, a string below a set share of its neighbours, PR below a floor, export meter fault.
• Who receives it: your maintenance lead and the O&M contractor, by SMS or app, with an escalation path.
• Response times in hours for acknowledgement and for a site visit, tied to your production hours. Contracts typically state both.
• A fault log with root cause, date closed and energy lost, shown in the monthly report.

Data ownership, access and API

If the contractor owns the logger account, you own nothing when the contract ends. Ask for the following in writing: you own the data; you can export raw data in CSV, and by API if your plant is part of a group dashboard; the logger and portal credentials are in your name or handed over at the end of the O&M term; and the system keeps local buffer data and fills gaps after a communication failure. The SECI document requires the contractor to give the owner passwords for operating software and enough documentation for later modification, and lists industry-standard protocols such as Modbus, MQTTS, HTTPS and IEC 60870-5-104 for talking to field equipment; those are reasonable asks at any scale. Also decide retention: two years of archived data is the benchmark in that tender, and a longer history is cheap and useful for warranty claims.

The monthly report, and reconciling it with the DISCOM bill

• Generation by inverter, with a comparison against the previous month and the same month last year.
• Performance ratio and availability, with the irradiance source stated.
• A loss breakdown that separates soiling, shading, equipment faults and grid outages, so the cause is on the page and not only the total.
• The fault and alert log: what happened, the response time, the date closed and the energy lost.
• Cleaning dates and any inspection findings, such as thermal-imaging results (see what thermography finds).
• Export and import reconciled against the DISCOM bill, and open issues with owners and dates.

Ask for a sample report before you sign. A contractor who cannot show one has not defined what you will receive, and the solar AMC cost calculator is a useful check on what the reporting and visits should cost to run.

Your SCADA is not the billing record; the DISCOM's meter is. Haryana's rooftop regulations, as one example, require the DISCOM to show on each bill the electricity injected, the electricity supplied, the net quantity billed and the credit carried over. Compare those lines with your monitoring export every month. A persistent gap means a meter, CT, communication or data-mapping problem, and finding it early protects both your credits and your warranty evidence. Our net metering and monitoring page explains how the metering side works.

How Secured Engineers helps

We design the monitoring scheme with the plant, in-house, and file the DISCOM net-metering application in-house, so the meter points, communication and reports are planned together. Solar can be delivered under one contract with the rest of the MEPF scope from our Noida (Delhi NCR) and Ludhiana offices. The company has delivered 535+ projects across 18+ states, with 89.77% repeat clients. For an existing plant we can review the monitoring set-up and report format, and quote any additions.

To scope monitoring for your plant, see net metering and monitoring, then send your plant details or current report on WhatsApp, call +91 70099 85817, or ask for a free proposal. For a new plant, our solar calculator frames size and savings first.