PPV Evolution Labs (PVEL) solar module scorecard: In a rush to innovate, some manufacturers ‘overlooked basic quality control’

PV Evolution Labs (PVEL), a test lab for the downstream solar market, just published its PV Module Reliability Scorecard. The lab notes the high level of innovation in the solar module industry and namechecks the market’s reliability leaders — but also observed a resurgence of known failure mechanisms — such as PID.

PV Evolution Labs (PVEL), a test lab for the downstream solar market, just published its PV Module Reliability Scorecard.

The reliability report report reveals some new “top performers” compared to last year — but, it also shows that some manufacturers “overlooked minimum safety and quality controls in the rush to bring innovative PV cell and module technologies to market.”

Here are the solar vendors that make it onto the test labs “top performer” list.

Flood of solar cell and module advancements

PVEL’s CEO Jenya Meydbray notes the crowd of solar module options and advancements:

• 8 different cell sizes: 125mm, 156mm, 156.75mm, 157.25mm, 158.75mm, 161.7mm, 162mm, 166mm
• 8 different cell technologies: p-type mono Al-BSF, p-type multi and mono PERC, n-type mono PERT, HJT n-type mono, p-type bifacial mono PERC, n-type bifacial mono PERT, CdTe
• Cells with 5 different counts of busbars 3, 5, 6, 9, 12
• Monofacial and bifacial glass-glass modules
• Monofacial and bifacial glass-backsheet modules
• 4 different cell interconnection types: Standard ribbons, ECA (shingled), interdigitated backcontact, metal wrap-through
• Half- cut and shingled cells, novel cell-to-cell interconnect methods.
• Thinner frames and glass, light-reflecting ribbon, novel encapsulants and backsheets.

Meydbray notes, “In this rush to innovate, some manufacturers have overlooked basic quality control.”

Three trends in PV module technology and their risks

PVEL has observed three important trends in PV module technology that are “particularly important for downstream stakeholders to consider from a risk-mitigation perspective.”

Large-scale adoption of PERC cell architectures: Passivated emitted rear contact (PERC) cells have quickly replaced the once-dominant aluminum back surface field cells. Although PERC cells are higher efficiency and can perform better in low-light and high-temperature conditions, some PERC cells are susceptible to light and elevated temperature induced degradation.

New cell designs: more busbars, new types of interconnect wires, various wafer sizes, as well as half-cut or smaller cells are driving higher efficiencies. “Some new cell designs are more susceptible to microcracks and may require process changes on manufacturing lines that can lead to increased defect rates,” according to PVEL.

New module designs: PV module manufacturers are introducing lighter weight modules, bifacial options, and physically larger modules. “Newer module form factors may be more susceptible to damage, and they may not be compatible with existing mounting systems,” claims the lab.

Resurgence of known failure mechanisms

As manufacturers rush to bring new technologies to market, PVEL is observing “a resurgence of known failure mechanisms,” along with new degradation modes.

This year, the median PID (potential induced degradation) in PVEL’s testing “was the highest it has ever been in the lab’s history. PID is a problem that many in our industry regarded as solved. Its resurgence is troubling, as are many of the other failures recorded in this report,” writes the CEO in the report.

Tara Doyle, chief commercial officer of PVEL notes that new bills of materials have “yielded surprising results for some vendors,” adding that some manufacturers thought that they had a “PID resistant bill of materials” but found out otherwise.

“A diverse array of PV technologies has upended conventional R&D timelines to achieve rapid commercialization, leading PVEL to test more cell and module combinations for our 2020 Scorecard than at any point in our ten-year history,” noted Doyle.

“Developers and investors need independent, reliable data to balance the reliability risks inherent to new products against the promise of higher-performing, more lucrative projects.

Source: PV magazine

Used EV batteries for large scale solar energy storage

MIT scientists have suggested used electric vehicle batteries could offer a more viable business case than purpose-built systems for the storage of grid scale solar power in California. Such ‘second life’ EV batteries, may cost only 60% of their original purchase price to deploy and can be effectively aggregated for industrial scale storage even if they have declined to 80% of their original capacity.

Used electric vehicle (EV) batteries can be repurposed to store electricity generated by large scale solar plants, according to an MIT study.

The U.S.-based researchers claimed even devices which have declined to 80% of their original capacity could offer a better investment prospect for solar-plus-storage projects in California than purpose-built, utility scale batteries, not least because such ‘second life’ EV batteries could cost as little as 60% of their purchase price.

MIT research co-author Ian Mathews conceded technical hurdles remained to the deployment of used EV batteries on a large scale, such as aggregating batteries from different manufacturers and screening which devices could be reused. However, Mathews insisted used EV batteries still offered a persuasive enough business case to justify the cost of recovering them, screening performance and redeploying them.

Optimal operation

The researchers used a semi-empirical model – including some ‘pre-cooked’ calculations – to estimate battery degradation, and concluded operating such aggregated storage devices at 15-65% of full charge would extend their second life. “This finding challenges some earlier assumptions that running the batteries at maximum capacity initially would provide the most value,” the scientists stated.

Mathews said the feasibility of second-life EV battery storage would depend on the regulatory and rate-setting regimes under which they would operate. “For example, some local rules allow the cost of storage systems to be included in the overall cost of a new renewable energy supply, for rate-setting purposes, and others do not,” he said.

Algorithms

The academic added, longer-term pilot studies are needed to assess the potential of such systems.

The MIT researcher noted control algorithms may be adapted during projects to lengthen the feasible lifetime of such facilities. “We think this could be a great application for machine-learning methods,” said Mathews, “trying to figure out the kind of intelligent methods and predictive analytics that adjust those control policies over the life of the project.”

The successful reuse of electric vehicle batteries for grid scale storage would also require buy-in from EV manufacturers, energy storage businesses, solar project developers and power electronics specialists, added Mathews.

The MIT research project was backed by the European Union’s Horizon 2020 research program as well as the Quantum Sustainable Solar Technologies engineering research center funded by the U.S. Department of Energy and National Science Foundation, and the Singapore National Research Foundation, through the Singapore-MIT Alliance for Research and Technology.

Bern University of Applied Sciences, in Switzerland, is also investigating how used solar modules and EV batteries can be repurposed. That Horizon 2020 project runs until 2022.

Source: PV magazine

Sharp unveils black, half-cut-cell module

The solar panel will be part of the half-cut-cell series recently launched by the Japanese manufacturer and the company claims it is ideal for rooftop PV projects with aesthetic requirements. The 19.0%-efficient product has a power output of 320 W.

Japanese electronics brand Sharp has launched a black, half-cut-cell, PERC, monocrystalline solar panel with a power output of 320 W.

The manufacturer said the product was intended for residential and commercial projects with aesthetic requirements

The NU-JC320B module is made of 120 half-cells measuring each 1,684 by 1,002 by 40mm. The product has power tolerance of up to 5% according to its manufacturer, with Sharp claiming the panel has a yield up to 3% higher than similar standard panels featuring full-cell architecture.

A multiple junction box design means each half of the module can function independently and the three junction boxes are each equipped with a single bypass diode in a system which is said to transfer less heat to cells, improving durability and performance.

Coating

The IEC61215 and IEC61730-certified panel features MC4 connectors made by Swiss company Stäubli and an anti-reflective front-glass coating from Canadian firm DSM. The coating, according to Sharp, reflects 1.2% less light than rival solutions.

Sharp said its module for “style-conscious commercial customers and homeowners” offers 19.0% efficiency and comes with a 25-year, linear power output guarantee and a 15-year product guarantee.

The Japanese manufacturer in January launched a PERC, monocrystalline module series featuring half-cut cells. That range followed three PERC mono products with a claimed 19.1% efficiency in April 2018. Two years ago, Sharp achieved 25.09% conversion efficiency in a cell featuring heterojunction and back-contact technology, as certified by the Japan Electrical Safety and Environment Technology Laboratories.

Source: PV magazine

Colored PV module performance is underestimated

In a recent conversation with pv magazine Roland Valckenborg, business developer and project manager at the Netherlands Organisation for Applied Scientific Research (TNO), has described the results of a multi-year testing program for colored BIPV modules. Just a few years ago, it it was thought that power yield could be up to 50% lower than conventional panels, but tests have shown a difference of just 10%. Valckenborg says that losses can vary depending on the color of a panel.

Since 2014, the Netherlands Organisation for Applied Scientific Research (TNO) has been testing different kinds of innovative solar panels, including BIPV modules with different colors, at its SolarBEAT testing facility at Eindhoven University of Technology.

According to Roland Valckenborg, the manager of the project, colored modules are still more expensive than traditional PV modules, but consumer interest is increasing. “People want to have a choice between different models, just as with cars,” he told pv magazine.

Performance parameters

Valckenborg said the performance of colored BIPV modules has been underestimated. “It was such a pleasant surprise to find out in our research that the textured modules have no performance loss when compared to a normal reference module,” he claimed. “So the small losses due to the extra layer of textured glass are offset by the gain of capturing a bit more yield during low angles of incidence.”

When the first tests started in 2017, it was still believed that colored panels would reduce yield by 40% to 50%. “We demonstrated in 2018 that it is just 11% for grey modules,” Valckenborg stated.

The results have been confirmed by research institutes such as the University of Applied Sciences and Arts of Southern Switzerland (SUPSI).

Light reflection

When asked how much color affects light reflection, Valckenborg said a minimal reduction must be taken into account. “When we want a colored PV panel, we have to accept that not all the visible solar spectrum will be transmitted to the cell, but part of it will be reflected or absorbed,” he stated. In conventional, uncolored PV panels, all layers on top of the solar cells – the front glass and the encapsulant – must be optimized to be as transparent as possible, in order to allow light to be transmitted and reach the solar cells.

There are currently two main approaches to coloring PV panels: a technique consisting of pigment-based coloration, and a structural coloration method. The first technique refers to the application of dyes and pigments that mainly absorb and partially reflect specific parts of the spectrum. This is the case, for instance, with colored dots printed on the front PV glass or on colored encapsulant.

Structural coloration is obtained through the interaction of the light itself with nano-structured surfaces or multi-layer thin-film coatings. Interference filters deposited on glass exploit the interference effect to selectively reflect only a narrow portion of the visible spectrum.

The way a color is obtained, and how it affects the performance of a PV panel, therefore strongly depends on the specific technology used and the optical phenomena taking place.

“Ideally, a colored PV panel should be able to reflect only a narrow band of the visible spectrum and transmit all the rest,” Valckenborg explained. “In this way we will perceive the module with the color corresponding to that specific reflected wavelength, while the rest of the sunlight spectrum can be effectively used for power generation”

In order to avoid additional losses, the colored layer (glass or encapsulant or extra layer) should be non-absorptive, he noted.

Performance losses

The performance losses of colored PV are mainly due to the lower amount of photons that are transmitted to the solar cells, which in turn leads to lower current and reduced power production. Power losses for colored PV products now available on the market range from approximately 10% to 40%. Losses also strongly depend on the specific color, because each color is characterized by a specific reflection spectrum, according to Valckenborg.

“Pigment-based colors always absorb part of the spectrum. In this respect, paintings which can be considered better than others are those characterized by low absorption,” he claimed.

In terms of higher performance, interference coating is currently the best option. Filters can be made with completely non-absorptive materials, and their reflection peak can be tuned to be as narrow as possible.

“Drawbacks of this technology are more related to price and other aspects, such as the angular dependency of the color,” Valckenborg explained. “In general, a compromise must always be found between electrical performance, cost and aesthetic quality.”

Vertical PV

One reason colored modules are still significantly more expensive than conventional panels is because the building industry is actually quite conservative, and for good reason, according to Valckenborg. As a facade element, BIPV colored modules must comply with strict safety requirements and be strong enough to avoid failures of any kind. “Because if something fails then the costs of repair can be huge,” he explained.

Colored modules are considered ideal for facade applications. “First, because facades  are much more visible than roofs,” Valckenborg said. “Secondly, because the euro/m2 for a facade is already significantly higher than for a pitched roof. So the relative added cost of color is much lower for the facade application.”

Valckenborg noted that BIPV panels on pitched roofs are still a niche market.

“In the Netherlands we start to see more infrastructure integrated PV (IIPV), which includes all applications into noise barriers, dikes, and roads. Because these applications are visible, they might become colored one day,” he concluded.

Source: PV magazine

Harvesting atmospheric water to cool down PV panels

Scientists from Saudi Arabia’s King Abdullah University of Science and Technology have developed a cooling solution for photovoltaic panels that uses a sorption-based atmospheric water harvester (AWH).

The device, which can be placed on the back of commercials PV panels, collects atmospheric water during the evening and at night. The collected water is then vaporized and released during the day using waste heat from the PV panel as energy source. The evaporation of the water in turn takes away a significant portion of heat from the panel itself and lower its temperature.

Cooling power

This new solution, according to the researchers, can be applied to both small-scale PV installations and big solar parks.

“Our results show that the AWH can provide an average cooling power of 295 W m–2 when the solar cell is exposed to 1-Sun illumination, leading to a decrease in temperature of >10 °C and an increase in electricity generation of the solar cell of up to 15% relative to the solar cell without the AWH in laboratory conditions,” the research group stated. Outdoor field tests were conducted in the summer and winter in Saudi Arabia and showed that the power yield of the modules was increased by between 19% and 13%. The harvester consists of a substrate made of carbon nanotube (CNT)-embedded cross-linked polyacrylamide (PAM) and a water vapor sorbent made of calcium chloride.

Cleaning

The group explained that the AWH system can also be modified to produce clean water by integrating the hydrogel cooling layer within a water condensation chamber with an enlarged heat dissipation surface area. “In one experiment, an aluminum condensation chamber was attached right beneath the AWH cooling layer (dimensions 5 × 5 × 0.5 cm3), which led to a stable surface temperature of the panel of ~50 °C during the test,” it stated. Through this condensation chamber, the device may also be extended to produce liquid water, which may be used for the cleaning of the modules or simply as potable water.

The scientists added the device may be further improved by enhancing water vapour sorption–desorption kinetics, which would in turn increase its harvesting capacity and reduce material corrosion.

The system is described in the study Photovoltaic panel cooling by atmospheric water sorption–evaporation cycle, published in nature sustainability.

Source: PV magazine