Researchers at SUPSI found that six Swiss PV systems installed in the late 1980s and early 1990s show exceptionally low degradation rates of just 0.16% to 0.24% per year after more than 30 years of operation. The study shows that thermal stress, ventilation, and material design play a greater role in long-term module reliability than altitude or irradiance alone.

A research group led by Switzerland's University of Applied Sciences (SUPSI) has carried out a long-term analysis of six south-facing, grid-connected PV systems installed in Switzerland in the late 1980s and early 1990s. The researchers found that the systems’ annual power loss rates averaged 0.16% to 0.24%, significantly lower than the 0.75% to 1% per year commonly reported in the literature.

The study examined four low-altitude rooftop systems located in Möhlin (310m-VR-AM55), Tiergarten East and West in Burgdorf (533m-VR-SM55(HO)), and Burgdorf Fink (552m-BA-SM55). These installations use ventilated or building-applied rooftop configurations. The analysis also included a mid-altitude utility-scale plant in Mont-Soleil (1270m-OR-SM55) and two high-altitude, facade-mounted systems in Birg (2677m-VF-AM55) and Jungfraujoch (3462m-VF-SM75).

All systems are equipped with either ARCO AM55 modules manufactured by US-based Arco Solar, which was the world’s largest PV manufacturer with just 1 MW capacity at the time, or Siemens SM55, SM55-HO, and SM75 modules. Siemens became Arco Solar’s largest shareholder in 1990. The modules have rated power outputs between 48 W and 55 W and consist of a glass front sheet, ethylene-vinyl acetate (EVA) encapsulant layers, monocrystalline silicon cells, and a polymer backsheet laminate.

The test setup included on-site monitoring of AC and DC power output, ambient and module temperatures, and plane-of-array irradiance measured using pyranometers. Based on site conditions, the researchers classified the installations into low-, mid-, and high-altitude climate zones.

“For benchmarking purposes, two Siemens SM55 modules have been stored in a controlled indoor environment at the Photovoltaic Laboratory of the Bern University of Applied Sciences since the start of the monitoring campaign,” the researchers said. They also applied the multi-annual year-on-year (multi-YoY) method to determine system-level performance loss rates (PLR).

The results show that PLRs across all systems range from -0.12% to -0.55% per year, with an average of -0.24% to -0.16% per year, well below typical degradation rates reported for both older and modern PV systems. The researchers also found that higher-altitude systems generally exhibit higher average performance ratios and lower degradation rates than comparable low-altitude installations, despite exposure to higher irradiance and ultraviolet radiation.

The study further revealed that modules of the same nominal type but with different internal designs show markedly different degradation behaviour. Standard SM55 modules exhibited recurring solder bond failures, leading to increased series resistance and reduced fill factor. By contrast, SM55-HO modules benefited from a modified backsheet design that provides higher internal reflectance and improved long-term stability.

Overall, the findings indicate that long-term degradation in early-generation PV modules is driven primarily by thermal stress, ventilation conditions, and material design, rather than altitude or irradiance alone. Modules installed in cooler, better-ventilated environments demonstrated particularly stable performance over multiple decades.

The test results were presented in the paper “Three decades, three climates: environmental and material impacts on the long-term reliability of photovoltaic modules,” published in EES Solar.

“The study identified the bill-of-material (BOM) as the most critical factor influencing PV module longevity,” they concluded. “Despite all modules belonging to the same product family, variations in encapsulant quality, filler materials, and manufacturing processes resulted in significant differences in degradation rates. Early-generation encapsulants without UV stabilisation showed accelerated ageing, while later module designs with optimised backsheets and improved production quality demonstrated outstanding long-term stability.”

Dutch utility Eneco is testing low-noise air-to-water heat pumps from startup Whspr in around 20 homes, aiming to ease installation constraints near property boundaries. The systems reportedly achieve coefficients of performance of up to 5 and show up to 80% noise reduction in laboratory testing.

Dutch utility Eneco has begun testing an”innovative” type of air-to-water heat pump with low sound levels in residential buildings.

The company said conventional heat pumps rely on outdoor units that emit a constant hum, requiring installations several metres from property boundaries under Dutch building regulations and often forcing placement in prominent locations on terraced houses. By contrast, the “silent” heat pumps under test can be installed just 30 cm from the boundary.

“The pilot will provide insight into both ease of installation and real-world performance,” Eneco said in a statement. “The results will be used to further optimize the system, with the aim of making it widely available by the end of the summer.” The company added that around 20 homes are currently equipped with the systems to assess noise levels without “compromising residents’ everyday heating comfort.”

The heat pumps are supplied by Dutch startup Whspr. “Our 4 kW freestanding hybrid monoblock systems are designed for domestic space heating,” founder Hugo Huis in ’t Veld told pv magazine.

The unit measures 60 cm × 60 cm × 90 cm and weighs around 70 kg. “It is compact yet robust,” Huis in ’t Veld said, adding that initial measurements show efficiencies in line with the market, with coefficients of performance (COP) of between 4.5 and 5.0.

According to the manufacturer, the heat pump uses propane (R290) as its refrigerant and shows up to 80% noise reduction in laboratory testing.

Whspr also highlights ease of installation, stating that a single installer can fit and connect the unit, including the water side, in one day. A dedicated control and thermostat system has also been developed to reduce compatibility issues and simplify commissioning.

Further technical details have not yet been disclosed. “We are not at liberty to share designs at this stage, as patents are still pending,” Huis in ’t Veld said.

Eneco noted that pilot installations include both standard locations and more complex sites, such as rooftops and sheds at the end of gardens. The systems have also been installed in several rental homes owned by housing association Wooncompagnie. “Testing will continue until the end of April, after which the heat pumps will be further optimized,” the company said.

Conceived for stationary energy storage, the proposed sodium-ion battery configuration relies on an P2-type cathode material and an hard carbon anode material that reportedly ensure full-cell performance. Electrochemical testing revealed initial capacities of 200 mAh/g for the cathode and 360 mAh/g for the anode with capacity retentions of 42% and 67.4% after 100 cycles.

An international research team has designed a sodium-ion battery (SIB) storage system based on a P2-type cathode material known as Na0.67Mn0.33Ni0.33Fe0.33O2 and an anode relying on a hard carbon material fabricated from lavender flowers.

The proposed system configuration is intended for low-cost fabrication while ensuring scalability and environmental sustainability, as the two electrode materials are described as “widely accessible” precursors.

“Plant diversity and production capacity are important factors affecting the commercialization of SIBs, as plant-derived hard carbons s are both sustainable and economical,” the researchers explained. “Hard carbon derived from plants preserves the microstructures of the plant tissues, thereby enhancing the penetration of the electrolyte and sodium diffusivity.

The scientists estimated global lavender production at approximately 1,000–1,500 tons annually. However, only a small fraction of this production can be used for electrode materials, as only the flower residue is suitable for conversion into hard carbon.

They also noted that the hard carbon anode and P2-type cathode in the full cell have insufficient sodium reservoirs, leading to poor electrochemical performance. “The present work addresses this gap by evaluating the full-cell performance of P2-Na_0.67Mn_0.9Ni_0.1O₂ coupled with lavender flower waste-derived hard carbon under different presodiation approaches,” they further explained.

The scientists used X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy to characterized the SIB system's cathode and anode and found the cathode has an hexagonal P63/mmc structure, while the anode showed characteristic broad peaks of amorphous carbon.

SEM and TEM revealed, in particular, micrometer-sized cathode grains and a porous hard carbon surface, with EDS and XPS indicated the material has good structural stability. Further analysis also demonstrated that nickel (Ni) incorporation improved the cathode’s structural, electronic, and electrochemical performance.

Moreover, electrochemical testing revealed initial capacities of 200 mAh/g for the cathode and 360 mAh/g for the anode with capacity retentions of 42% and 67.4% after 100 cycles. Overall, Ni doping was found to improve the cathode’s conductivity and stability, and the anode demonstrated good sodium storage performance, supporting strong half-cell and potential full-cell performance, according to the researchers.

“This comprehensive study highlights the potential for developing SIBs with low-cost and sustainable electrode materials,” they concluded. “The optimization of presodiation strategies offers an opportunity for advanced commercial and scalable SIB technologies.”

The system was described in the study “Cost-effective sodium-ion batteries using a Na_0.67Mn_0.9Ni_0.1O₂ cathode and lavender-flower-waste-derived hard carbon with a comparative presodiation approach,” published in the Journal of Power Sources. The research team comprised scientists from Turkey's Inonu University, Istanbul Technical University, Malatya Turgut Ozal University and Aksaray University, as well as from Korea Institute of Science and Technology and Pakistan's Quaid-i-Azam University, among others.