Solar Metering: PV Production & Net Consumption Monitoring

Part 1 — Metering solar PV output

A PV system has three distinct quantities and they are not interchangeable: production (what the array generates), consumption (what the building uses), and export (production that exceeds consumption and flows to the grid). Self-consumption is production minus export. Measure any two and you can derive the third — but only if the measurement points are correct.

Why the utility net meter is not enough

• It nets, by design. A utility net meter reports the difference between import and export at the service point. A building consuming everything the array makes shows almost nothing on it — production is invisible, so array performance cannot be verified from that meter.
• It cannot show degradation or a failed string. A 12% shortfall against expected yield looks like a slightly higher bill, not a fault. Dedicated production metering makes underperformance visible in the week it starts instead of at annual true-up.
• Incentive and SREC reporting wants gross production. SREC markets, performance-based incentives and many PPA settlements are paid on generation in kWh, and typically require a revenue-grade production meter — not a netted figure and not inverter telemetry alone.
• Inverter data is a diagnostic, not a record. Inverter kWh counters are useful and free, but they are uncalibrated, vendor-specific, and disappear when the inverter is replaced or its portal is retired. Reporting and settlement need an independent meter.
• Sustainability reporting needs both sides. Scope 2 accounting and green-power claims depend on separating on-site generation actually consumed from grid import — which is precisely what a single netted number destroys.

Bidirectional measurement, and where to put the meters

Any meter on a circuit that can carry power in both directions must be bidirectional — reporting import and export as separate, signed registers rather than one absolute total. A unidirectional meter on a PV-backfed circuit either sums both directions or clamps at zero, and both errors are silent.

• Production meter. On the inverter output or the PV combiner feeder, ahead of any load tap. This is the gross generation figure used for SREC and incentive reporting.
• Service / net point meter. At the main service, bidirectional, to capture import and export separately and reconcile against the utility bill.
• Load meters. On the loads or tenant panels you care about, so self-consumption can be attributed rather than assumed.

String, inverter or array-level monitoring

• Array level. One revenue-grade meter on the point of interconnection. Cheapest, satisfies reporting, tells you the system is down — but not which part.
• Inverter level. One meter per inverter output. The best value on most commercial rooftops: isolates a failed or derated inverter, and on a multi-inverter site lets healthy units act as the reference for the sick one.
• String / circuit level. Wireless self-powered sensors such as Panoramic Power clamp onto individual strings or combiner outputs, so soiling on one roof section, a shaded string or a blown fuse shows up as one line diverging from its neighbours. This is also the fastest retrofit path, because each sensor is a clip-on with no conduit run.

A worked example of circuit-level PV performance monitoring is in the solar performance monitoring case study.

CT placement and direction

• Direction matters more here than anywhere else. Every CT has an arrow, dot or "H1/source" marking. On a PV circuit, define which way is positive first — conventionally, generation toward the building — and install every CT consistently. A reversed CT on a bidirectional circuit reports production as consumption.
• Verify with real current. Commission mid-day with the array producing. Negative real power, a power factor near −1, or one phase disagreeing with the other two is a reversed or mis-phased CT, not a faulty array.
• Match the CT to the circuit, not the load. Size to the breaker or inverter continuous output rating. PV output sits near rated current for hours, so a CT running at the top of its range all afternoon should be sized with headroom.
• Keep phase mapping intact. Each CT must be paired with the voltage reference for the same phase. Cross-phasing produces plausible-looking but wrong kW. See current transformers for split-core, solid-core and Rogowski options.
• Rooftop and combiner environments. Enclosures at the array need UV-stable, wet-rated housings and CT leads routed away from inverter output conductors, which are electrically noisy.

Meters for all three tiers are in electric meters, and production data reaches a dashboard or BAS through the hardware in connectivity.

Part 2 — Solar-powered metering for sites with no power

The second meaning of solar metering has nothing to do with PV performance. It is the answer to a much more common problem: the thing you need to measure is somewhere with no available circuit and no building network. Running power and conduit to a remote meter routinely costs more than the metering itself, and often needs trenching, permits or an outage. A solar-powered remote metering panel removes that line item: a PV module, a battery sized to ride through several days of overcast weather, the meters and a cellular or LoRaWAN radio, pre-wired and bench-tested in one weather-rated enclosure.

• Agriculture and greenhouses. Irrigation blocks, greenhouse zones and field-edge water and power measurement, far from any panel. See the agriculture and greenhouse metering guide.
• Well pumps and lift stations. Flow and runtime at the source, where the nearest metering-capable panel may be a kilometre away.
• Remote tanks and process points. Level, flow and temperature at yard tanks, cooling ponds and outlying process skids.
• Parking and EV infrastructure. Lot lighting, canopy PV and EV charging loads spread across a site with no convenient submetering point.
• Temporary and construction metering. Trailer and phase-of-work energy accounting that has to be installed in a day and moved next quarter — no permanent infrastructure, no trenching.

Specifying one is the same exercise as any pre-built assembly — channel count, NEMA rating, CT selection, protocol — with two extra inputs: the daily energy budget of the meters and radio, and the site's worst-month solar resource, which together size the module and battery. Autonomy is usually specified at three to five days. See metering panels and enclosures for the panel build pattern, and the integration and data guide for backhaul options where cellular coverage is marginal.