Mitigation of Clipping Variability on Bifacial Performance Ratio of Photovoltaic Systems

该项目是国家物理实验室（NPL）和Statkraft之间的合作项目，旨在建立一种新的性能指标，用于准确评估超大和双面光伏（PV）系统。这将增加未来太阳能项目的价值，降低金融风险，改进故障识别，从而提高可再生能源发电的能源生产、收入和二氧化碳抵消。在太阳能产业中，性能比（PR）是评估太阳能光伏（PV）系统性能的最成熟的指标。它是基于系统额定功率的实际发电量与预期发电量之间的比率。它被广泛地用作电厂性能的合同保证，因此可以决定一个项目在其预计生命周期内的价值。根据光伏系统的软件模拟和初步评估，各方之间达成保证的PR值。然而，在测量期间（通常为1年）的实际天气条件与模拟中使用的“典型气象年”数据之间的差异可能会对PR测量产生强烈影响。最严重的由天气引起的错误发生在“超大”光伏系统上。当光伏阵列的额定直流功率大于逆变器的额定交流输出功率时，就会发生超大尺寸；这是光伏行业的常见做法，导致逆变器“削波”，在高日照期输出平坦的发电曲线。实际天气条件可能会夸大剪影，影响PR，特别是在高日照年份。这种效果在双面光伏系统中得到进一步增强，双面光伏系统从光伏模块的背面获得额外的电力。这有效地使系统变得更加庞大，现有的性能指标不再可靠。尽管提出了对温度变化的修正，但目前的IEC性能指标标准未能评估超大光伏电站的性能。在这个项目中，我们的目标是确定一个改进的度量并评估其优点，以便准确地评估我们开发的光伏系统。NPL和Statkraft将为单面和双面系统定义这一指标，并将根据当前标准指标，针对不同的光伏系统配置和故障，针对季节性和年度天气变化进行基准测试。该指标将根据真实数据、多个位置和系统配置进行验证。建议的量度将：*对评估期间的实际天气情况不敏感。*在实际天气情况下，对系统表现较差及预期表现较敏感。*在合同中使用简单明了。

This project is a collaboration between the National Physical Laboratory (NPL) and Statkraft and aims to establish a novel performance metric for the accurate evaluation of oversized and bifacial photovoltaic (PV) systems. This will lead to increasing the value of future solar projects, reducing financial risks and improving fault identification, thus energy production, revenue and CO2 offsets from renewable generation.The performance ratio (PR) is the most established metric for assessing solar photovoltaic (PV) system performance in the Solar Industry. It is the ratio between the actual to the expected generation based on a system's rated power. It is widely applied as a contractual guarantee for a power plant's performance and therefore may determine the value of a project over its projected lifetime.A guaranteed PR value is agreed between parties based on software simulation of the PV system and an initial evaluation. Nevertheless, PR measurements can be strongly affected by differences between actual weather conditions during the measurement period (typically 1 year) and "typical meteorological year" data used in modelling. The most serious weather-induced errors occur on "oversized" PV systems.Oversizing occurs when a PV array has a rated DC power larger than its inverter's rated AC output power; a common practice in PV industry, which leads to inverter "clipping", outputting a flat generation curve during high insolation periods. Clipping can be exaggerated by actual weather conditions, impacting PR, especially in high insolation years. This effect is further enhanced for bifacial PV systems, which harvest additional power from the rear side of PV modules. This effectively makes the systems even more oversized and the existing performance metrics no longer reliable.Despite the proposed corrections for temperature variations, current IEC standards for performance metrics fail to assess the performance of oversized PV plants. In this project, we aim to identify an improved metric and assess its merit, in order to accurately assess the PV systems that we develop.NPL and Statkraft will define this metric for monofacial and bifacial systems and will benchmark with current standard metrics against seasonal and annual weather variability, for different PV system configurations and faults. The metric will be validated against real data, multiple locations and systems' configurations.The proposed metric will be:* Insensitive to the actual weather conditions during the evaluation period.* Sensitive to underperformance of systems compared to their expected performance given the actual weather conditions.* Simple and unambiguous to use in contracts.