An international research group has developed a novel solar module passive cooling system that integrates three-dimensional oscillating heat pipe (3D-OHP) with different combinations of nanofluids based on hybrid graphene oxide (GO) and a two-dimensional titanium carbide known as MXene (Ti3C2Tx).

MXene compounds take their name from their graphene-like morphology and are made via selective etching of certain atomic layers from a bulk crystal known as MAX. Recently, these materials have also shown promise for use in PV technology due to their unique optoelectronic properties, such as their large charge carrier mobility, excellent metallic conductivity, high optical transmittance, and tunable work function (WF).

“The main novelty lies in integrating a 3D-OHP with a surfactant-free hybrid GO–MXene nanofluid for urban PV cooling, and evaluating it comprehensively from thermal, electrical, exergy, and economic perspectives in real outdoor conditions,” corresponding author Mahyar Kargaran told pv magazine. “To our knowledge, this is the first experimental study to combine 3D-OHP + GO–MXene and evaluate it holistically for urban PV.”

Kargaran explained that the system is passive, stable, and surfactant-free. “We are currently exploring the simultaneous use of multiple 3D-OHP units, two or three operating together, to cool larger PV arrays and evaluate multi-unit thermal behavior,” he added. “Additional follow-up work includes optimization of geometry and concentration, integration with PV-battery systems, and comparisons with other advanced nanofluids and surface treatments.”

The OHP is a sealed tube in which liquid and vapor naturally move back and forth, carrying heat from a hot area to a cooler one without a pump. In this research, the 3D-OHP was attached to a 50 W PV module, with an efficiency of 13.82%. The cooling device was constructed from red copper tubing, with an internal diameter of 2 mm and an external diameter of 4 mm. It had a 7-turn configuration that comprised three distinct sections: a 200 mm evaporator, a 109 mm adiabatic zone, and a 200 mm condenser.

Half of the tubing volume was filled with nanofluids based on deionized water. GO, MXene, or a 1:1 hybrid of both was added at concentrations of 0.1 wt% and 0.2 wt%. The 3D-OHP system was therefore tested using GO, MXene, and the hybrid fluid at both concentrations, and compared to a reference PV panel without cooling. Experiments were conducted in August in Mashhad, northeastern Iran, under solar irradiance ranging from 660 to 1,090 W/m².

“Two findings were particularly notable,” said Kargaran. “First, the performance gains exceeded expectations, with temperature reductions of over 24 C, a 14.9% increase in power output (from 42.1 W to 48.3 W), and efficiency improving from 10.02% to 11.51%. Second, despite a 31% increase in viscosity, the hybrid nanofluid maintained excellent stability and delivered strong exergy performance of up to 30.9%, while remaining economically competitive, with a levelized cost of electricity (LCOE) of $0.083/kWh and a levelized cost of storage (LCOS) of $0.273/kWh.”

The system was presented in “Hybrid GO-MXene nanofluids in 3D oscillating heat pipes for efficient urban PV cooling: Improved energy, exergy, and economic performance,” published in Energy and Buildings. Researchers from China’s Xi’an University of Science and Technology, Iran’s Islamic Azad University, University of Tabriz, the United States’ Texas A&M University, and the United Kingdom’s London South Bank University have participated in the study.

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