The accelerating technological advancement of solar modules risks exacerbating the challenges of durability and cell degradation, according to a new review from the National Renewable Energy Laboratory (NREL), which examined the reliability implications of emerging trends in crystalline-silicon photovoltaic (PV) module design.

The trends, grouped into four categories, cover larger module sizes, new cell interconnection methods, the rise of bifacial modules, and a transition to next-generation high-efficiency solar cells.

The reliability challenges in ‘cell-cracking,’ or degradation, arise from their multistep nature: cracks develop, then propagate, and cell fragments from cracking move, wearing out the fragment-bridging metallization, potentially causing electrical contact loss.

Cell cracking is an umbrella term for a multistep degradation process that can lead to power loss.

Degradation rates also vary due to factors like module design and environmental conditions, complicating accurate reliability assessment. Consequently, technology changes can affect all or none of the degradation steps.

In one study, 84% of PV modules had at least one type of crack, but only 60% had cracks that caused significant power loss.

The research found maintaining module reliability is critical as solar deployments accelerate around the globe and new technologies are introduced before they have been thoroughly field-tested. Determining accurate degradation rates usually requires at least three years of testing in the field.

Increasing module sizes up to 3 square meters may increase the risk of cell cracking and failures from severe weather unless installation methods are improved. According to the research, moving to multi-wire interconnection methods and conductive adhesives instead of solder could introduce new degradation pathways if not adequately tested.

Bifacial modules

The growing adoption of bifacial modules is driving the use of thinner glass to reduce weight. However, researchers warn thinner glass may compromise mechanical integrity and require new hail testing protocols.

Bifacial solar modules capture sunlight from both sides, increasing efficiency. However, if the materials used to seal these modules trap acetic acid, corrosion can accelerate, potentially damaging the modules.

Acetic acid can originate from several sources within solar modules. One common source is the degradation of certain materials used in the encapsulation or backsheet of the modules. When these materials degrade due to exposure to heat and moisture, they can release acetic acid as a byproduct. Acetic acid is also produced if moisture enters the module and reacts with metal components.

Perhaps the biggest reliability unknowns surround the anticipated transition to next-generation solar cells made from n-type silicon, such as silicon heterojunction and tunnel oxide passivating contact architectures. Their ultra-thin surface layers and higher efficiencies create new reliability sensitivities that require updated accelerated testing procedures.

The researchers proposed a continuous “PV reliability learning cycle” to incorporate the latest scientific findings into standards and product improvements, ensuring quality control despite the industry’s relentless technological evolution. Multi-factor modeling, alongside improved field data collection, will be needed to validate models against real-world results.

Another recent study by NREL found that climate change-induced extreme weather events like hail, flooding, and high winds accelerate solar module damage above certain thresholds, causing greater long-term losses in system performance.

Recently, scientists from MIT said that perovskite solar panels could become more efficient and sturdier over longer periods by engineering the nanoscale structure of perovskite devices.