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Summary

Inverter Temperature Derating reduces inverter AC power capacity when ambient temperature exceeds the nominal rating temperature. PlantPredict uses temperature-kVA curves provided by the inverter manufacturer, with curve selection based on site elevation. The model interpolates linearly between temperature-kVA points to determine the temperature-corrected maximum AC power. If ambient temperature is outside the curve range, the inverter is derated to zero (shutdown). The derating is applied before calculating maximum DC power limits for operating region determination.

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Inputs

NameSymbolUnitsDescription
Site ElevationzzmElevation above sea level
Ambient Air TemperatureTaT_a°CAmbient temperature
Inverter kVA Curves——Temperature-kVA pairs at multiple elevations
Rated AC PowerPAC,ratedP_{AC,rated}kVANameplate AC power rating

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Outputs

NameSymbolUnitsDescription
Temperature-Corrected PowerPAC,tempP_{AC,temp}kVADerated AC power capacity
Example Inverter Temperature / Elevation Derate Curve

Example Inverter Temperature / Elevation Derate Curves

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Detailed Description

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Curve Selection by Elevation

Inverter manufacturers may provide multiple kVA curves at different elevation ratings. If multiple curves are provided, PlantPredict selects the appropriate curve based on site elevation:
  1. From the available curves, select the curve with the lowest elevation rating that is still above the site elevation
  2. If the site elevation exceeds all available curve elevations, use the curve with the highest elevation rating

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Temperature Interpolation

If temperature outside curve range: Ta<Tmin or Ta>Tmax  ⟹  PAC,temp=0T_a < T_{min} \text{ or } T_a > T_{max} \implies P_{AC,temp} = 0 If temperature exactly on curve point: PAC,temp=kVA at TaP_{AC,temp} = \text{kVA at } T_a If temperature between curve points: Find bounding points: (Tprev,kVAprev)(T_{prev}, kVA_{prev}) and (Tnext,kVAnext)(T_{next}, kVA_{next}) where Tprev<Ta<TnextT_{prev} < T_a < T_{next} Use linear interpolation to solve for Derated AC Power Capacity: PAC,temp=kVAprev+Ta−TprevTnext−Tprev(kVAnext−kVAprev)P_{AC,temp} = kVA_{prev} + \frac{T_a - T_{prev}}{T_{next} - T_{prev}} (kVA_{next} - kVA_{prev})

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References

  • King, D. L., Boyson, W. E., & Kratochvil, J. A. (2004). Photovoltaic array performance model. SAND2004-3535, Sandia National Laboratories.