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Finnish scientists have developed a new method to evaluate the long-term performance of vertical bifacial photovoltaic systems in Nordic conditions. The experimental setup consisted of an east-west oriented vertical array equipped with power, temperature, and irradiance sensors in the array plane, wind speed and global horizontal irradiance sensors, and a weather station.
Scientists at the University of Turku (Finland) have created a new method to calculate the yield loss rate (PLR) in vertical bifacial photovoltaic systems. This metric is commonly used by project developers to evaluate the expected energy production of a PV system over its installed life.
The researchers state in a recently published academic paper that there is currently no standardized method for measuring PLR, and note that the different methods applied to date have resulted in highly variable PLRs. “In our study, several methods are carefully considered and analyzed for each step of the calculation, resulting in more than 1,600 filter-metric-aggregation-model combinations to calculate the PLR, thus contributing to global efforts to develop frameworks for standardized and reliable PLR ??calculation,” the article explains.
The group applied the proposed methodology to vertical bifacial photovoltaic systems operating in Nordic conditions. These systems are characterized by large seasonal variations in temperature, solar radiation and day length.
The experimental setup consisted of an east-west oriented vertical array equipped with power, temperature, and irradiance sensors in the plane of the array (POA), wind speed and global horizontal irradiance (GHI) sensors, and a weather station. The measurements performed resulted in a high-resolution, long-duration, up-to-the-minute data set.
“Each module has a DC-DC optimizer to keep the module at maximum power point (MPP), a DC energy meter (EM) to measure DC current and voltage, and a T-type thermocouple (TC) set to the front part to measure the surface temperature of the module,” the document says. “The irradiance of the POA is monitored by two reference cells (RC) on the top of the modules, one facing east and one facing west.”
The method excludes data not relevant to performance analysis, affected by system failures, or recorded under conditions that are difficult to model or not suitable for a given performance model. “This includes, for example, nighttime hours, sensor problems, shadows, and low irradiance conditions,” the document notes.
The new method allows obtaining a reference PLR ??of -1-46% per year. “The interannual method with a performance model corrected for daily/weekly aggregated temperature and irradiance was robust and reliable in the face of high Nordic seasonality,” the researchers state in the paper. “In contrast, several commonly used methods, such as the PVUSA model, yielded unrealistic results.”
They presented the novel approach in the article “ Comparing methods for the long-term performance assessment of bifacial photovoltaic modules in Nordic conditions, ” published in Renewable Energy . .
In July, the same research group unveiled a methodological workflow to increase the electrical performance of bifacial vertical photovoltaic systems connected to low voltage (LV) networks located at high latitudes and with different panel locations, orientations and technologies. . |
