Weighted vs Peak Microinverter Efficiency: What an RFQ Should Compare

Two microinverter quotations can show the same peak efficiency and produce different annual energy. Peak efficiency is one operating point; a PV system spends much of the year at partial load, different DC voltages and elevated temperatures.

For a distributor or EPC, the useful question is not “Which datasheet has the largest percentage?” It is “Which evidence describes conversion performance across the operating envelope of this project?”

Separate the four efficiency questions

An RFQ should distinguish:

• Peak conversion efficiency: the best measured DC-to-AC result under stated conditions.
• Weighted efficiency: several load-point results combined with a defined weighting method.
• MPPT effectiveness: how closely the control follows the module's available maximum-power point.
• Night and standby consumption: energy used when PV power is absent or too low to export.

The California Energy Commission identifies conversion efficiency, standby power and MPPT performance as separate inverter metrics. A supplier should therefore not use peak efficiency as a substitute for all three.

Ask for the curve, not only the badge

Request efficiency at multiple power levels and, where available, at more than one DC voltage. Record the test method, laboratory, model, firmware, ambient condition and measurement uncertainty. Confirm whether auxiliary gateways or controllers are inside or outside the stated power consumption.

RFQ evidence	Procurement question	Warning sign
Efficiency curve	Does it cover the project's normal load range?	One isolated peak value
Weighted value	Which weighting method was used?	“European/CEC” without report reference
MPPT result	What input range and irradiance profile were tested?	Tracking claim with no conditions
Standby/night power	What remains energized after sunset?	Gateway demand omitted
Model traceability	Does the report match the quoted hardware?	Family-level document only

Weighted values from different methods are not directly interchangeable. The weighting profile is a mathematical model, not a prediction for every climate, orientation or DC/AC ratio.

Put efficiency in the project operating envelope

Map the expected module power distribution to the inverter curve. A high-power module on a small AC channel may operate near the upper end more often, while a shaded balcony system may spend longer at low power. Include temperature, module orientation and the selected DC/AC ratio; the clipping guide covers that boundary separately.

Do not convert a small efficiency difference directly into an annual-energy promise. Cable loss, clipping, availability, soiling, shading and grid curtailment may be larger. Use the same yield model and assumptions for every candidate.

Verify samples with repeatable measurements

The objective of incoming evaluation is not to recreate an accredited efficiency certification. It is to detect inconsistency. Use a calibrated DC source or controlled PV simulator, a suitable AC power analyzer, stable voltage and a defined warm-up period. Measure several load points and repeat them on multiple samples.

Record uncertainty before ranking products whose reported difference is only a few tenths of a percentage point. The OEM sample evaluation plan provides a broader gate for identity, protection, monitoring and thermal checks.

Add these fields to the RFQ

Ask each supplier for:

1. Peak and weighted efficiency with named method
2. Load-point curve and relevant DC-voltage conditions
3. MPPT efficiency or tracking test evidence
4. Night, standby and communication-device consumption
5. Exact model, hardware and firmware covered
6. Laboratory and report reference
7. Temperature or derating conditions that affect the curve
8. Any tolerances applied to published figures

Send the target module, climate, orientation and expected operating range through TMG Contact. A defensible comparison uses consistent evidence and project assumptions—not the largest number in a product table.