PV generation meters

A PV generation meter records the electrical energy generated by the installation. In a typical grid-connected home system it measures cumulative AC energy after the inverter. It is separate from the import meter, which records electricity bought from the grid, and the export meter, which records electricity sent to the grid.

These values are not interchangeable. Generation can be used in the home, stored or exported. Export is therefore not the same as generation, and import plus export does not reveal generation without additional measurements and assumptions.

The MCS recording requirement

MIS 3002 requires a means of recording and displaying total AC generation. The customer should be able to access and read it without special access equipment. The standard also addresses monitoring or notification of abnormal operation.

The means used can depend on the installation and any payment scheme. A physical meter used for billing or incentive payments has metrological requirements that an inverter portal does not automatically meet. A monitoring app can be useful while still being unsuitable as the legal payment register.

The handover should identify which display is the total-generation record, its units and how to obtain a reading if communications fail.

Legacy Feed-in Tariff systems

The Feed-in Tariff closed to new applicants in 2019, but accredited installations continue under their existing terms. Generation payments use the approved generation meter and its cumulative reading. Where export is deemed rather than metered, the generation reading may also feed that calculation under the installation’s FIT arrangements.

FIT owners should follow their licensee’s reading and verification process. If a generation meter fails or must be replaced, contact the FIT licensee before work where possible. Record the old meter serial number and final reading, the reason for replacement, the new meter details and opening reading, and retain installation and test evidence. Losing this audit trail can delay or complicate payments.

Altering the PV array, inverter or metering can also affect FIT records. The dedicated legacy repowering article covers that process.

Approved meters and installation

Meters used for prescribed measurement must satisfy the applicable measuring-instrument requirements and approval route. Schedule 1E of the Measuring Instruments Regulations 2016 covers active electrical energy meters. The project or scheme rules decide which approved meter and accuracy class are required.

The meter should measure only the intended generation boundary. On a simple PV system this is usually the inverter AC output before it joins household circuits. With multiple inverters, batteries, backup circuits or shared supplies, the schematic must show what each register includes.

Meter direction, phase arrangement, current transformers where used, pulse settings and register configuration should be commissioned. A meter that counts backwards, misses a phase or includes battery discharge can produce a plausible but wrong total.

Why the app may show a different number

An inverter portal, generation meter, smart meter and consumer energy monitor can disagree because they:

measure at different points
use different accuracy and sampling methods
include or exclude inverter standby use
handle battery charge and discharge differently
lose data during communication outages
round or estimate short intervals

A small difference is not automatically a fault. First draw the measurement boundaries and compare cumulative readings over the same period. For a payment, use the register specified by the scheme rather than choosing the highest value.

Reading and record keeping

The cumulative generation register normally increases over the life of the meter. Period generation is the later reading minus the earlier one, allowing for any meter exchange. Record the date, value, units, serial number and a clear photograph where required.

Sudden zero production, a frozen register or a large unexplained change needs investigation. Check inverter status and supply before assuming the meter itself has failed. Meter covers and live electrical equipment should not be opened by the owner.

For newer systems, generation records remain useful for fault detection, warranty evidence and comparing weather-normalised performance even where no FIT payment exists. Cloud data should be exported periodically if the owner relies on it as a long-term record.

Generation-meter record

a single-line diagram with every meter and measurement direction
generation-meter make, model, serial and opening reading
which register is used for FIT or another payment
whether battery energy can pass through the meter
how import and export are measured separately
reading, fault and replacement procedures
portal access and local data available without the cloud