The solar panel degradation is being addressed by an international team of researchers, led by the Unviersity of Manchester. This Light Induced Degradation (LID) .has been known about and studied for over 40 years, with over 270 research papers attributed to the issue with no solution.
Combining a specialised electrical and optical technique called deep-level transient spectroscopy (DLTS), the team uncovered a material defect which initially lies dormant within the silicon use to manufacture the cells, but can be solved by heating the panels at night. Understanding the process of degradation could signficantly change change the way panels are designed an operated.
“Because of the environmental and financial impact solar panel ‘efficiency degradation’ has been the topic of much scientific and engineering interest in the last four decades. However, despite some of the best minds in the business working on it, the problem has steadfastly resisted resolution until now,” said Prof Tony Peaker, who co-ordinated the research.
“During the first hours of operation, after installation, a solar panel’s efficiency drops from 20% to about 18%. An absolute drop of 2% in efficiency may not seem like a big deal, but when you consider that these solar panels are now responsible for delivering a large and exponentially growing fraction of the world’s total energy needs, it’s a significant loss of electricity generating capacity.”
The energy cost of solar panel degradation across the world is tens of gigawatts, more energy than is produced by 15 nuclear power plants.
The electronic charge within the bulk of the silicon solar cell is transformed under sunlight, part of its energy generating process. The team found that this transformation involves a highly effective ‘trap’ that prevents the flow of photo-generated electrons. “This flow of electrons is what determines the size of the electrical current that a solar cell can deliver to a circuit, anything that impedes it effectively reduces the solar cell efficiency and amount of electrical power that can be generated for a given level of sunlight. We’ve proved the defect exists, it’s now an engineering fix that is needed,” said Dr Iain Crowe.
The effect was reversible, the lifetime increased again when the material was heated in the dark, a process commonly used to remove the charge traps.