First Solar’s Photovoltaic Expertise Completes 25 Years of Testing
Determining the service life of a solar module can take years. Solar panels that are designed to function for 25 years or more must withstand the elements. In some cases, panels continue to work beyond their planned operating time. Nowhere is this more evident than on the sunny hill in Golden, Colorado, where the National Renewable Energy Laboratory (NREL) operates the Outdoor Test Facility (OTF).
The OTF continues to run tests on photovoltaic modules made by companies that are still very interested in the result. The OTF is equipped for accelerated testing of PV modules that identify issues with the design or the materials used, said Dirk Jordan, a physicist who works as a senior engineer at NREL. However, it is difficult to make long-term performance and degradation predictions for different environments with just accelerated testing. Multi-year outdoor tests complement and validate accelerated testing. This is critical feedback to the manufacturer. Jordan studies the long-term performance of PV systems and analyzes the physics and chemistry of changes. For more information, see the IDTechEx report on Energy Harvesting Microwatt to Gigawatt: Opportunities 2020-2040.
The gallery contains a cadmium telluride (CdTe) panel, a competitive solar technology developed at NREL with First Solar Inc, a public PV manufacturer based in Arizona. In the early 1990s, the US Department of Energy, which oversees NREL, funded initial research into CdTe as a solar material and commissioned scientists in the laboratory with the project. Among the companies that were involved in researching the use of CdTe for solar panels included Solar Cells Inc, which later became First Solar. By using CdTe, First Solar can manufacture PV modules faster, more cost-effectively and with lower CO2 emissions than silicon. After silicon, CdTe solar modules are the second most popular solar technology in the world and are often used to generate electricity on a utility scale.
First Solar’s technology has reached a milestone at NREL this year after 25 years of continuously monitored performance testing. the longest running research project at the OTF.
“This technology developed by NREL led to a track record in manufacturing in-house,” said Stephen Gorin, director of strategic partnerships for materials, chemical and computer science at NREL. “Silicon manufacturing has all moved out of the US as First Solar has grown into a billion dollar company with annual sales.”
Ben Kroposki, an electrical engineer who has been with NREL for 27 years, installed the first PV modules for First Solar at OTF. “We wanted to keep the modules / arrays installed with the OTF at all times as long as the technologies are relevant to get very long-term reliability data,” he said. Kroposki, now director of the NREL Power Systems Engineering Center, performed some of the first analysis of the performance of the CdTe solar modules.
An important measure of the performance of a solar cell is the service life. Solar cells lose efficiency over time. By measuring this change, manufacturers can guarantee their panels. The initial studies on First Solar’s solar modules showed that the company’s power loss after five years was a relative 0.6% per year and their stability compared to silicon modules was cheap.
Now, a quarter of a century after installation, the long-term study found a rate of deterioration of 0.5% per year, which means that the energy conversion efficiency of the panels when first installed was about 88% of their performance.
The initial absolute efficiency of the PV system installed in 1995 was low by today’s standards. Since then, First Solar, headquartered in Arizona, has consistently set and broken world records for efficiency. First Solar set the record for a CdTe solar cell in 2016 with 22.1%. First Solar and NREL have continued to work together on the development of CdTe solar cells and most recently published a paper last year that unlocked a fundamental improvement by removing copper from the cells and unlocking further gains.
First Solar, which now operates the largest solar factory in the western hemisphere in Ohio, as well as factories in Malaysia and Vietnam, is not selling the model of PV modules that operate at OTF. Why is ongoing research important? Nick Strevel, vice president of product management for the company, said the information gained allowed First Solar to have more confidence in its product. The encapsulation layer, which shields the semiconductor, for example, is a 25-year-old technology that has been proven to prevent known thin-film defects such as corrosion.
“Our product encapsulation technology and materials are far superior today,” said Strevel. “This helps us understand an ancient performance foundation and provides further confidence in the superior long-term durability and long-term degradation performance of today’s product.”
Lou Trippel, director of product management at First Solar, said the lessons the company learned from the experience at NREL had “added confidence to a recently announced extension of our module performance guarantee” from 25 to 30 years to support.
Source and top image: NREL