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Outdoor Test Facility

Aerial photo of the Outdoor Test Facility.

The Outdoor Test Facility at NREL is used to evaluate prototype, precommercial, and commercial modules.

Outdoor Test Facility (OTF) researchers study and evaluate advanced or emerging PV technologies under simulated, accelerated indoor and outdoor, and prevailing outdoor conditions. One of the major roles of researchers at the OTF is to work with industry to develop uniform and consensus standards and codes for testing PV devices. Researchers also calibrate primary reference cells for in-house use and for use by other national laboratories, calibration and testing labs, and PV manufacturers.

Indoor Testing at the OTF

Integral to indoor testing at the OTF is a wide variety of equipment, tools, and techniques to test and analyze modules and systems under standard simulated conditions, as well as diverse environmental and stress conditions. Tests include environmental testing, indoor accelerated testing, failure analysis, and cell and module characterization.

Environmental Testing

Specialized chambers in the highbay area test the performance of modules when exposed to varying weather conditions such as heat, cold, humidity, moisture, and ultraviolet light. Modules are tested in high-voltage and wet conditions to evaluate electrical insulation and moisture intrusion that can cause corrosion, ground faults, or pose an electrical safety hazard.

Indoor Accelerated Testing

In accelerated testing, relative and absolute performance of PV modules is determined for samples exposed to continuous light; to intense simulated lighting conditions; to elevated levels of temperature and humidity; and to accelerated cycles of temperature and humidity.

Failure Analysis

Researchers in the laboratory perform destructive and non-destructive analysis to determine failure mechanisms in cells and modules. New measurement techniques and tests are developed to help identify future problems.

Module Characterization

The electrical output performance of modules is determined under simulated conditions using three different current versus voltage (I-V) measurements systems. The performance characteristics measured by these systems includes the open-circuit voltage of the module; short-circuit current; fill factor; maximum power output of the module; voltage at maximum power; current at maximum power; and the module's conversion efficiency. To perform these measurements, researchers use two systems that use pulsed light and one system that uses continuous light to simulate the solar spectrum. The systems can test modules as large as 200 cm x 200 cm.

Photo of a large area continuous solar simulator.

The large-area continuous solar simulator (LACSS) is a custom-designed system that is used for measuring current versus voltage performance of larger modules.

Outdoor Testing at the OTF

Nearly 40 test beds surround the OTF laboratory building. These test beds allow researchers to characterize the electrical output performance of modules under outdoor conditions, test the long term performance and stability of PV modules and systems under standard and accelerated outdoor conditions, and measure the performance of hybrid systems. Systems used for PV measurement include the Standard Outdoor Module Characterization, Long Term Module Outdoor Performance and Stability, Grid-Tied PV Systems Testing, Stand-alone PV Systems Testing, Outdoor Accelerated Testing, Flexible Test Bed, and Qualification Testing.

Standard Outdoor Module Characterization

Researchers use two I-V measurement systems to measure the electrical output performance of PV modules under outdoor conditions that are as close to possible to Standard Test Conditions. One system is the Standard Outdoor Measurement System (SOMS), a fixed system upon which modules are place for testing and can track the sun. The other is a portable system used in the field to measure output characteristics of modules.

Long-Term Module Outdoor Performance and Stability

Long-term module performance testing is conducted on the Performance and Energy Rating Testbed (PERT), located on the roof of the OTF, and in the array field. The PERT is used to continuously monitor more than 30 modules of various technologies for performance under various weather conditions. And in the adjacent array field, nine test beds are used to conduct outdoor exposure and stability tests on more than 50 PV modules.

Grid-Tied PV Systems Testing

Seven grid-tied, 1- to 2-kW PV systems are installed at the OTF. These systems employ various photovoltaic module technologies, including copper indium diselenide, cadmium telluride, amorphous silicon and crystalline silicon. These systems are monitored for long-term performance and reliability.

Outdoor Accelerated Testing

Two test beds are dedicated to stressing photovoltaic modules under accelerated conditions outdoors. The high-voltage stress testbed (HVST) places 600-2000 volts across the module leads and frame and then measures leakage currents.

Qualification Testing

On this test bed, in accordance with recommended procedures, manufacturer's modules are short-circuited and subjected to specified exposures to solar radiation and to defined amounts of electrical, mechanical, and thermal stress in order to qualify that modules meet or exceed standard performance criteria.