Europe’s intense heat waves are drawing fresh attention to a longstanding problem: Abundant sunlight can also push PV modules beyond their most efficient operating temperatures. Crystalline-silicon modules typically lose around 0.4% to 0.65% of their performance for every 1 C increase in temperature above 25 C.

“Based on the operational data we reviewed from solar plants in several European countries, we saw lower generation during some periods of extreme heat,” said Šarūnas Stanaitis, CEO of energy technology company Inion Software. “For example, during the June 20-30 heatwave in Spain, one monitored plant generated 1.26 MWh on June 20, compared with around 1.4 MWh to 1.6 MWh on several days earlier.”

High temperature resilience is a concern, but actively keeping modules cool in the field remains a hard sell. “Customers are placing increasing importance on module thermal safety and quality following the rise in heatwaves,” said Spencer Kong from Chinese PV module maker Aiko. “Despite extensive research, the main obstacle for the adoption of thermal management in commercial PV power plants is cost.”

Cost of efficiency

PV module cooling technologies can be divided into two categories. Passive systems, such as fins, heat sinks, hydrogels, phase-change materials, and coatings, dissipate heat without energy input. Active systems use pumps, fans or other powered equipment to circulate air or liquid.

“Active and hybrid technologies can achieve greater temperature reductions and, under suitable conditions, higher electrical or combined electrical-thermal output. Intelligent control can further improve their performance by operating pumps or fans only when cooling provides a net benefit,” explained Sakhr Mohammed Sultan Al-Shaibani from the Solar Energy Research Institute of the National University of Malaysia. Al-Shaibani, who recently co-authored a scientific review of cooling technologies, added that “Passive and retrofit-compatible systems have an advantage because they require little or no auxiliary power and generally involve fewer components and lower maintenance requirements.”

A team led by scientists from Algeria’s Kasdi Merbah University developed a smart water-spray cooling system for PV panels that activates when module temperatures exceed a preset threshold. After a few days testing, the system improved the module’s efficiency by up to 28.8% (relative) while lowering its temperature by more than 20 C. “We still need to investigate the long-term effects of water quality on PV glass, including mineral scaling, soiling, and overall system performance, as well as the condition, durability, and maintenance requirements of the pumps and nozzles,” said co-author Mahmoud Bourouis.

Maintenance requirements, failure of moving parts, long-term durability and electricity demand from pumps seem to tilt the market’s potential toward passive cooling. “Demonstrating a reduction in module temperature is relatively easy, but demonstrating a sufficiently attractive lifetime economic benefit is much more difficult,” explained Al-Shaibani. “A few percentage points of additional output may not always compensate for these additional costs, particularly as the cost of PV modules has decreased considerably.”

One very low-cost option, developed by researchers at Australia’s University of New South Wales, reduced module temperatures by up to 2.5 C using arrays of small rectangular-wing vortex generators, made from either aluminum or a thermally conductive 3D-printable polymer, attached to the rear of the panel. However, even Zibo Zhou, one of the researchers behind its development, said the shift toward bifacial technology has made rear-mounted cooling solutions less relevant.

“A more practical approach, already being implemented by some module manufacturers, is to deposit a thin coating on the glass surface for improved radiation management,” he said.

Another passive approach uses hydrogels, which absorb water and release it through evaporation as the module heats up. In lab tests, a lightweight hydrogel developed at Thailand’s Vidyasirimedhi Institute of Science and Technology reduced solar-cell temperatures by 23 C and increased efficiency by 12.3%.

“To move toward practical applications, we are developing the hydrogels in two main aspects: size and mechanical integrity for panel application,” said Pichaya Pattanasattayavong, Daniel Crespy and Jutamas Sukaim, who developed the gel together. “We have adjusted the formula and employed a structural scaffold to improve mechanical properties; and fine-tuned the dynamic behavior of the hydrogel, extending water release time from 2.5 hours to four hours under constant 70 C. The hydrogel can sustain water for one full day and replenish itself with moisture from the atmosphere at night.”

Hybrid future

Jeff Newmiller, senior principal specialist at risk management firm DNV Group, said measures that increase irradiance generally add more power than the accompanying temperature rise takes away. “If the thermal control feature fails to present a convincing argument to designers and financiers and consultants in all respects, it generally ends up on the design-room floor,” he said.

The strongest business case may therefore lie in cooling systems that offer other benefits as well. German manufacturer Sunmaxx’s PVT modules, for example, remove heat from the panels and use it for heat-pump systems. Researchers at Germany’s FH Aachen University of Applied Sciences have also developed a temperature-triggered spray-cooling system for floating PV that could provide additional operational benefits.

“The real business case lies in the combined function,” said Nico Oellers, who developed this system together with Joachim Göttsche. “If one system also cleans the modules, prevents or clears light snow, and offers a fire-protection function, its value no longer depends on the cooling gain alone. First small-scale trials suggest that regular spraying discourages birds from settling and leaving droppings on the modules, which noticeably reduces soiling on floating PV.”

The post Module cooling: too hot to handle appeared first on pv magazine Global.