Climate-Driven Performance Assessment and Loss Mechanisms of Utility- Scale Photovoltaic Systems

Technical Summary: Climate-Driven Performance Assessment and Loss Mechanisms of Utility-Scale Photovoltaic Systems

Problem Statement
Saudi Arabia possesses exceptional solar resources, characterized by high Global Horizontal Irradiance (GHI), making it a prime candidate for utility-scale photovoltaic (PV) deployment. However, the conversion of this resource into electricity is not linear; it is heavily influenced by site-specific climatic and environmental conditions. While high irradiance suggests high energy potential, elevated ambient temperatures, airborne dust (soiling), and coastal humidity can significantly degrade module efficiency and inverter performance. Existing literature often focuses on single-site analyses or small-scale systems, leaving a gap in understanding how utility-scale PV systems perform across the diverse climatic zones of Saudi Arabia—specifically the contrast between inland deserts, hot arid regions, and humid coastal areas. This study addresses the need for a systematic, multi-site assessment to quantify how variations in irradiance, temperature, and environmental factors translate into differences in key performance indicators like Performance Ratio (PR) and specific yield.

Methodology
The study employs a hybrid assessment framework to evaluate utility-scale PV systems across three representative climatic regions in Saudi Arabia:

1. Qassim: Representing an inland desert climate.
2. Makkah: Representing a hot-arid climate.
3. Jazan: Representing a hot and humid coastal climate.

The methodology integrates long-term satellite- and meteorological-data-derived climatic inputs from NASA POWER, Solargis, and Meteonorm with detailed simulations using PVsyst software. A reference utility-scale PV plant configuration was modeled for each site using realistic Bill of Materials (BOM) and inverter specifications typical of large-scale projects in the region. To ensure a fair comparison, the nominal DC capacity and system layout were kept constant across all sites, while climatic inputs varied according to local conditions.

Key performance metrics included:

• Specific Yield: Annual AC energy output normalized by installed DC capacity (kWh/kWp).
• Performance Ratio (PR): The ratio of actual energy output to theoretical output under standard conditions.
• Loss Analysis: A breakdown of system losses including thermal losses, soiling, inverter inefficiencies, and electrical losses.

Sensitivity analyses were conducted to quantify the impact of ambient temperature on PR, the non-linear relationship between GHI and energy yield, and the influence of the DC/AC ratio on system performance under different climatic conditions.

Key Results
The study reveals that high solar irradiance alone is not a sufficient predictor of PV energy generation in desert environments due to the counteracting effects of environmental losses and high module operating temperatures.

• Specific Yield: Annual specific yields varied significantly across locations, ranging from approximately 1,650 to 2,050 kWh/kWp. The inland desert site (Qassim) achieved the highest yield due to consistent high irradiance, yet it did not always achieve the highest monthly yields during peak summer due to thermal losses.
• Performance Ratio (PR): Annual PR values ranged from 0.76 to 0.84. The inland and hot arid sites (Qassim and Makkah) exhibited lower PR values (0.76–0.81) compared to the coastal site (Jazan, 0.78–0.84). This indicates that the thermal stress in desert regions significantly reduces system efficiency despite higher resource availability.
• Loss Mechanisms:
  • Thermal Losses: Dominant in inland and hot arid regions, accounting for 7–13% of annual energy yield. These losses are driven by elevated ambient temperatures and high plane-of-array irradiance.
  • Soiling Losses: More pronounced in the coastal humid environment (Jazan), ranging from 3–8%, due to the combined effects of dust deposition and humidity-enhanced particle adhesion. Inland sites experienced lower soiling losses (2–6%).
• Sensitivity Findings:
  • A clear negative correlation exists between ambient temperature and PR. The analysis indicates that PR decreases by approximately 0.35–0.45% for every 1°C increase in ambient temperature.
  • The relationship between GHI and energy yield is non-linear in high-GHI environments; incremental increases in irradiance during peak summer months contribute less to net yield due to concurrent temperature-induced efficiency degradation and inverter clipping.

Significance and Contributions
The paper claims that its primary contribution is providing a comparative, climate-driven performance assessment of utility-scale PV systems across distinct Saudi Arabian climatic zones using a consistent modeling framework. The study demonstrates that:

1. High Irradiance is Not Sufficient: Relying solely on solar resource intensity for yield prediction in desert climates leads to overestimation. Temperature-dependent module performance and environmental loss processes must be integrated into evaluations.
2. Site-Specific Optimization is Critical: The dominant loss mechanisms differ by location. Inland regions require strategies focused on thermal management (e.g., optimized DC/AC ratios, inverter selection), while coastal regions require enhanced soiling mitigation and cleaning strategies.
3. Improved Investment Reliability: By quantifying the specific impacts of temperature and soiling, the study offers climate-specific insights that can reduce uncertainty in techno-economic assessments and improve the accuracy of yield predictions for utility-scale PV projects in high-GHI desert climates.

The author notes that while the study relies on simulation and satellite data, it establishes a robust comparative framework. They acknowledge limitations regarding the lack of long-term operational SCADA data for direct validation and the exclusion of long-term degradation mechanisms like Potential Induced Degradation (PID), suggesting these as areas for future research.