Hi Jun, derate is very subjective - he's some reasoning behind it:
1. Generalized Industry Estimates
• Many solar designers use a default system derate factor to estimate real-world performance losses, even though actual losses depend on specific site conditions.
• Historically, the National Renewable Energy Laboratory (NREL) suggested a default system derate factor of ~0.77 to 0.88 (i.e., 12% to 23% losses), depending on component efficiency and environmental factors.
2. Typical Sources of Losses
A 10–15% derate factor typically accounts for:
• Module Nameplate vs. Actual Output (~1-3%): Manufacturers’ power tolerances and real-world degradation.
• DC Wiring Losses (~1–3%): Resistance in conductors.
• Inverter Efficiency (~2–5%): Conversion losses from DC to AC.
• Mismatch Losses (~1–2%): Variability between modules.
• Temperature Losses (~3–10%): High cell temperatures reducing voltage and efficiency.
• Other Factors: Like degradation, shading, and transformer losses.
3. Convenience Over Accuracy
• Designers often default to a quick 10–15% value instead of running detailed PV system modeling tools (e.g., PVsyst, SAM).
• This avoids spending excessive time on minor refinements for early-stage feasibility studies or sales quotes.
• In preliminary designs, it’s considered “close enough” unless specific site conditions suggest otherwise.
4. Variability in Site Conditions
• Losses vary by location, climate, and installation quality. A system in Arizona with little cloud cover and frequent cleaning may have lower losses (~10%), while one in a humid, polluted area with frequent overcast conditions could be higher (~15–20%).
• Some designers use 12% as a middle-ground default if no site-specific data is available.
5. Software and Default Assumptions
• Some solar design tools (e.g., Aurora Solar, Helioscope, PVsyst) use default loss factors in this range unless a user customizes them.
• Many companies standardize a single derate value (e.g., 13%) across all projects to maintain consistency in estimations.
Hi Jun, derate is very subjective - he's some reasoning behind it:
1. Generalized Industry Estimates
• Many solar designers use a default system derate factor to estimate real-world performance losses, even though actual losses depend on specific site conditions.
• Historically, the National Renewable Energy Laboratory (NREL) suggested a default system derate factor of ~0.77 to 0.88 (i.e., 12% to 23% losses), depending on component efficiency and environmental factors.
2. Typical Sources of Losses
A 10–15% derate factor typically accounts for:
• Module Nameplate vs. Actual Output (~1-3%): Manufacturers’ power tolerances and real-world degradation.
• DC Wiring Losses (~1–3%): Resistance in conductors.
• Inverter Efficiency (~2–5%): Conversion losses from DC to AC.
• Soiling Losses (~2–5%): Dust, bird droppings, and pollution reducing panel output.
• Mismatch Losses (~1–2%): Variability between modules.
• Temperature Losses (~3–10%): High cell temperatures reducing voltage and efficiency.
• Other Factors: Like degradation, shading, and transformer losses.
3. Convenience Over Accuracy
• Designers often default to a quick 10–15% value instead of running detailed PV system modeling tools (e.g., PVsyst, SAM).
• This avoids spending excessive time on minor refinements for early-stage feasibility studies or sales quotes.
• In preliminary designs, it’s considered “close enough” unless specific site conditions suggest otherwise.
4. Variability in Site Conditions
• Losses vary by location, climate, and installation quality. A system in Arizona with little cloud cover and frequent cleaning may have lower losses (~10%), while one in a humid, polluted area with frequent overcast conditions could be higher (~15–20%).
• Some designers use 12% as a middle-ground default if no site-specific data is available.
5. Software and Default Assumptions
• Some solar design tools (e.g., Aurora Solar, Helioscope, PVsyst) use default loss factors in this range unless a user customizes them.
• Many companies standardize a single derate value (e.g., 13%) across all projects to maintain consistency in estimations.
Hope this helps!