A group of experts from ACCIONA Energía and the Solar Energy Institute of the Universidad Politécnica de Madrid (IES-UPM) has obtained the world record for power measurement in the characterization of photovoltaic (PV) generators during a test campaign at the El Romero Solar photovoltaic plant, which is owned by the company and located in the Atacama Desert.
One of the key factors in the characterization tests for the PV installations is the measurement of I-V curves. These curves express the relationship between current and voltage in photovoltaic generators (a combination of modules connected in series or in parallel). This means that the key parameters of the generator can be measured (e.g. peak power point) and compared with the manufacturer's documentation, plus an analysis of their evolution over time.
In the test campaign carried out in El Romero last May and June, I-V curves in PV generators were measured, showing a total capacity of more than 1 MW corresponding to the input power to the inverters installed in the plant. The measurement of power of this magnitude is a world record for this kind of analysis, in which commercially-available devices to measure I-V curves are limited to 150 kilowatts (kW), i.e. seven times less. The study performed involved a high level of technical sophistication, and was possible thanks to the great experience and capacity of the team that carried it out.
Graph: I-V curve recorded in El Romero Solar on 25 May 2017 at 12:33 hours (local time).
The peak power curve was obtained with an irradiance of 853 W/m2 and a cell temperature of 40.1oC. The peak power point in the measured curve was 1001 kW (1535 A and 652 V, and that of the curve corrected to Standard Test Conditions (STC) was 1324 kW (1817 A and 729 V). The corresponding short-circuit currents were 1663 and 1947 A, and open-circuit voltages of 819 and 873 V.
Obtaining I-V curves for complete generators, as was done in El Romero Solar, is part of the advanced on-site characterization procedure for photovoltaic plants applied by ACCIONA to its plants. This includes the measurement of the efficiency curves of the inverters and the observation of different operating modes (with or without reactive power, shadows, etc.). The results achieved using this procedure have a very low level of uncertainty and provide a reference for (a) analyzing compliance with technical specifications for the design of each element of the plant, and (b) detailed monitoring of the operation of the facility (automatic fault detection and aging assessment, among others).
The study also confirmed the theoretical generation model forecast for El Romero, a 246 MWp (196 MW rated capacity) facility, highlighting the efficiency of the production forecasts made by the company's technical personnel.
The El Romero Solar PV plant is located in the municipality of Vallenar, in the Atacama region. It consists of 776,230 PV modules of 315/320 watts each, with a mirror surface area equivalent to 211 soccer pitches, and its production is equivalent to the average consumption of 240,000 Chilean homes.