When comparing solar inverters for procurement, the headline efficiency figure — "98.8%" on a Sungrow datasheet — tells you almost nothing useful about real-world energy yield. That peak efficiency only occurs at one specific operating point: rated power, at a specific temperature, with a specific DC input voltage. A project that operates at 30% load during morning and evening — which accounts for a significant share of annual energy — may see actual conversion efficiency 1–2 percentage points lower.
Understanding weighted efficiency metrics — European Efficiency and CEC Weighted Efficiency — and how to read full efficiency curves is essential for accurate energy yield modelling and for making meaningful comparisons between Sungrow, Huawei, SMA, SolarEdge, and GoodWe inverters.
A solar inverter's efficiency is not constant across its operating range. It varies with:
Weighted efficiency metrics account for the time the inverter spends at each operating point, giving a single number that better predicts annual energy yield.
Developed by the European JRC (Joint Research Centre), European Efficiency weights efficiency at six load points representing typical Central European irradiance distribution:
η_Euro = 0.03×η₅ + 0.06×η₁₀ + 0.13×η₂₀ + 0.10×η₃₀ + 0.48×η₅₀ + 0.20×η₁₀₀
Where η₅ through η₁₀₀ are the efficiencies at 5%, 10%, 20%, 30%, 50%, and 100% of rated power. The weighting is biased toward 50% load (48% weight) because Central European irradiance is frequently at half-peak levels. Note: only 20% weight is given to full-load — in Germany or the UK, full-load conditions are rare.
European Efficiency is specified at Vmpp = nominal voltage (typically 600–800 V). It is used by PVsyst for energy yield calculation and is the metric quoted on European inverter datasheets.
The California Energy Commission (CEC) developed an alternative weighting reflecting California's sunnier climate, where the distribution of irradiance hours is shifted toward higher power levels than Germany:
η_CEC = 0.04×η₁₀ + 0.05×η₂₀ + 0.12×η₃₀ + 0.21×η₅₀ + 0.53×η₇₅ + 0.05×η₁₀₀
CEC efficiency adds a 75% load point (21% + 53% weight at 50–75%) reflecting the more frequent occurrence of high-irradiance hours in MENA, Australia, California, Chile, and South Asia. CEC Weighted Efficiency is used on the CEC inverter list (required for California incentive programmes) and is often a better metric for high-irradiance projects than European Efficiency.
| Inverter | Peak η | Euro η | CEC η (est.) | η at 10% load | η at 50% load |
|---|---|---|---|---|---|
| Sungrow SG350HX | 99.0% | 98.8% | 98.7% | 97.2% | 98.8% |
| Huawei SUN2000-330KTL-M3 | 99.0% | 98.8% | 98.7% | 97.5% | 98.9% |
| SMA Sunny Tripower 150 | 98.9% | 98.7% | 98.6% | 97.0% | 98.7% |
| GoodWe GW250K-HT | 99.0% | 98.8% | 98.7% | 97.0% | 98.8% |
| SolarEdge SE100K | 99.2% | 98.9% | 98.8% | 97.8% | 99.0% |
| Deye SUN-230K-G05 | 98.8% | 98.5% | 98.4% | 96.8% | 98.5% |
Note: η at 10% and 50% load are approximate values based on published efficiency curves and field data. Always request the full efficiency curve from the manufacturer for energy yield modelling.
The practical difference between 98.8% and 98.5% European Efficiency on a 10 MWp project producing 16,000 MWh/year is approximately 48 MWh/year. At USD 50/MWh PPA, this is USD 2,400/year — accumulated over a 25-year project life (discounted), worth approximately USD 30,000. For a 100 MWp project, the efficiency difference compounds to USD 300,000+ in lifetime revenue.
All inverter efficiency curves are specified at a reference temperature (typically 25°C ambient). At higher temperatures, efficiency decreases and the inverter's maximum continuous output power is derated:
For hot climates (MENA, South Asia, Australia Outback), temperature derating during peak irradiance hours (when temperatures are also highest) causes clipping losses that standard energy yield models underestimate if they do not include the inverter derating curve. For projects in climates where ambient regularly exceeds 40°C, request the manufacturer's full power vs temperature derating table and incorporate it into your PVsyst or SAM model.
Inverter placement also matters: outdoor-installed inverters on south-facing walls in hot climates absorb radiant heat from the sun, increasing internal temperature above ambient. North-facing installation, shading canopies, or dedicated ventilated enclosures can reduce operating temperature by 5–15°C and meaningfully improve annual yield.
Maximum Power Point Tracking (MPPT) efficiency is separate from inverter conversion efficiency. It measures how accurately the inverter tracks the module array's instantaneous maximum power point under changing irradiance and temperature. Typical MPPT efficiency is 99.5–99.9% for modern inverters, but poor MPPT algorithms cause additional losses during rapid irradiance transients (cloud edges, morning ramp-up, evening ramp-down). See our MPPT guide for detailed analysis.
| Project Location / Climate | Recommended Metric | Rationale |
|---|---|---|
| Northern Europe (Germany, UK, Poland) | European Efficiency | Low irradiance profile matches EU weighting |
| Southern Europe (Spain, Italy) | European Efficiency or CEC | Higher irradiance, either metric reasonable |
| MENA, South Asia, Chile Atacama | CEC Efficiency | High-irradiance profile, full-load hours dominate |
| Sub-Saharan Africa | CEC Efficiency | High GHI, frequent near-full-load operation |
| Australia (QLD, WA, NT) | CEC Efficiency | High irradiance; CEC originally designed for CA |
| East Asia (South Korea, Japan) | European Efficiency | Moderate irradiance, mixed-weather climate |
Econo Solar supplies Sungrow, Huawei, GoodWe, and Deye inverters direct from the factory with complete efficiency curve documentation (OND files, full efficiency tables at multiple DC voltages and temperatures). Our team can identify the optimal inverter model for your specific climate, DC/AC ratio, and grid code requirements.
For a factory quote with efficiency specifications, request pricing here.
At low loads (<10% of rated power), the inverter's fixed power consumption — control electronics, gate drivers, displays, cooling fans on standby — remains nearly constant while output power drops. These fixed losses represent a much larger percentage of the (smaller) output, causing overall efficiency to fall. At 5% load, a 250 kW inverter outputs only 12.5 kW, but its fixed consumption of ~200 W now represents 1.6% of output. This is why European Efficiency includes 5% and 10% load points with combined weight of only 9% — these low-load periods are real but contribute little to total energy.
For a typical commercial project in a temperate climate, improving Euro Efficiency from 98.5% to 98.8% (a 0.3 percentage point improvement) increases annual AC energy yield by approximately 0.3%. On a 5 MWp project producing 5,500 MWh/year, this equals ~16.5 MWh/year of additional revenue. Over 25 years at USD 60/MWh, the discounted value of 0.3% higher efficiency is approximately USD 15,000–18,000 — significant for a procurement decision between similarly priced inverters.
The MPPT voltage range is the range of DC input voltages within which the inverter actively tracks the module array's maximum power point. Outside this range (too low or too high), the inverter either does not produce power or operates at reduced efficiency. For a 1500 V system, a typical MPPT range is 200–1500 V. The inverter achieves its published peak efficiency at a specific Vmpp within this range (often 800–1100 V). At low Vmpp (early morning, high temperature), efficiency is lower by 0.1–0.5%. String sizing should keep Vmpp_min above the inverter's MPPT start voltage to avoid morning production delays.
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