Understanding 'Invisible' Losses: Beyond weather and degradation, what other factors affect my actual solar power generation, such as soiling, shading, or losses from cables and inverters?

Panorama of "Hidden Losses" in Photovoltaic Systems

Note: Percentages are empirical ranges. Site-specific calculations require climate, module brand, and system architecture data.

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Recommended Process for Revenue Forecasting Using "Loss Inventory"

1. Baseline Inputs
   • Ground or satellite irradiance data (≥10 years)
   • Module nominal power, temperature coefficient, degradation curve
   • Inverter efficiency curve, derating curve

2. Optical-Thermal Modeling
   Establish POA (Plane Of Array) model → Temperature model (NOCT or Sandia) → Derive ideal DC output.

3. Stepwise Deduction of Losses
   a. Fixed annual losses: Reflection 2%, inverter 2%, cables 1%...
   b. Variable losses: Temperature, shading, airborne dust; iterative calculation at monthly/hourly resolution.
   c. Annual incremental losses: Module degradation, PID, etc., modeled as functions.

4. Scenario Analysis
   • "Optimal maintenance" vs. "Standard maintenance"
   • "No grid curtailment" vs. "5% curtailment"
   Output IRR and LCOE via Monte Carlo or P90/P50 statistics.

5. Operational Closed Loop
   SCADA actual generation benchmarking → Rapid loss source identification → Iterative model and O&M strategy updates.

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Conclusion

Total annual losses in PV plants often reach 10%–20%, extending far beyond weather and natural module degradation. By systematically identifying "hidden losses" and implementing targeted measures, an additional 3%–8% energy yield can typically be achieved, significantly improving LCOE and IRR.

In addition to weather variations (such as solar irradiance intensity, duration, and cloud cover) and the inherent long-term degradation of the modules themselves (e.g., an annual power output decline of around 0.5%), the actual power generation of a photovoltaic (PV) system is also affected by various "invisible" factors. These factors are commonly referred to as system losses and primarily include the following categories:

1. Optical Losses

   • Soiling/Dust: Dust, sand, bird droppings, pollen, industrial pollutants, etc., accumulate on the surface of PV modules. This dirt blocks sunlight from reaching the solar cells, reducing the module's light transmittance and directly decreasing power generation. This loss is particularly significant in dry, dusty, or heavily polluted areas, potentially causing power losses of several percentage points or more.
   • Partial Shading: Buildings, trees, utility poles, chimneys, adjacent modules, or even the module frame itself or snow can cast shadows on modules during certain times of the day. Partial shading causes the shaded cells to heat up (hot spot effect) and activates bypass diodes, limiting the current of the entire series string and resulting in significant power loss.

2. Electrical Losses

   • Cabling/Line Loss: Both DC (Direct Current) and AC (Alternating Current) cables in a PV system have electrical resistance. Current flowing through the cables generates heat, leading to energy loss. Cable length, cross-sectional area (wire gauge), material quality, and the tightness of connections all affect the magnitude of loss. Undersized cables or excessive cable length increase losses.
   • Inverter Efficiency: The inverter converts the DC electricity generated by the PV modules into AC electricity usable by the grid or loads. This conversion process is not 100% efficient; some energy is always dissipated as heat. Efficiency varies between inverter models and brands, typically ranging from 95% to 99%. Furthermore, inverter efficiency varies with power output, usually being highest near the rated power.
   • Module Mismatch Loss: Even PV modules from the same production batch exhibit slight variations in electrical characteristics (such as maximum power point voltage and current). When these modules are connected in series or parallel to form an array, the performance of the weaker modules limits the output of the entire string or parallel branch, resulting in overall power generation being lower than the sum of the outputs of all individual modules.
   • MPPT Efficiency: The Maximum Power Point Tracking (MPPT) function built into the inverter aims to continuously track and maintain the PV array at its optimal operating point to extract maximum power. However, the accuracy and response speed of MPPT algorithms are not perfect. Especially under rapidly changing irradiance or partial shading conditions, the MPPT may not always precisely lock onto the optimal point, leading to minor efficiency losses.
   • Connector and Junction Box Losses: Various connectors (e.g., MC4 connectors) and components within the junction box on the back of modules (such as diodes and busbars) have contact resistance. Loose connections, oxidation, or poor quality can increase resistance, causing energy loss and localized heating.

3. Temperature-Related Losses

   • High Temperature Effect: The power generation efficiency of PV modules decreases as temperature rises. The module temperature under Standard Test Conditions (STC) is 25°C. However, during actual operation, module surface temperatures are often significantly higher than ambient temperature, especially during hot summers or in installations with poor ventilation. Typically, module efficiency decreases by 0.3% to 0.5% for every 1°C increase in temperature.

4. System Operation & Maintenance Losses

   • Grid Curtailment/Quality Issues: In some cases, if grid voltage is too high, frequency is unstable, or the grid lacks sufficient capacity to accept all generated PV power, the inverter may reduce output power or even shut down based on grid instructions to protect grid stability. This is known as curtailment.
   • System Faults & Insufficient Maintenance: Various faults can occur during PV system operation, such as module damage, loose connections, inverter failure, ground faults, etc. Without effective monitoring systems and regular maintenance checks, these faults may not be promptly detected and repaired, causing the system to operate sub-optimally for extended periods and resulting in sustained power losses. Examples of insufficient maintenance include untimely module cleaning and shading from weeds.
   • Initial Light-Induced Degradation (LID/LeTID): Certain types of PV modules (especially P-type crystalline silicon modules) experience a small, irreversible power drop during the first few days or weeks after initial exposure to sunlight, typically between 1% and 3%. This is distinct from the long-term, slow degradation and is determined by the material properties of the module.

In summary, these "invisible" loss factors significantly impact the actual power generation of PV systems during operation and are crucial aspects that must be considered when evaluating and optimizing system performance.