Artificial leaf cooling boost lifetime, efficiency of PV panels ...

The PV-leaf carries water to cool photovoltaic panels without the need for pumps to boost efficiency and lifetime and can also be used to produce fresh water.

Heat is the enemy of PV panels. More sunlight and warmer temperatures mean more of the panel heats up, so the efficiency of most common Si-based PV panels typically decreases by 4.0 to 6.5% and their ageing rate doubles for every 10 °C increase in operating temperature.

The system developed at Imperial uses a combination of bamboo fibres and hydrogel to transport water along the back of a PV panel without having to be pumped. The hotter the cell, the more liquid is pulled through the cooling system in the same way that trees cool themselves.

The transpiration performance of the PV-leaf is demonstrated experimentally as being capable of removing 590 W/m2, 75% of the heat in the PV cell, significantly decreasing the PV cell’s operating temperature by ~26 °C relative to a standalone PV cell.

The PV-leaf is shown to have a capability of passive control, adapting to different ambient temperatures and can also use different working fluids such as seawater. Experimental results showed the cooling boosts the open-circuit voltage from 0.58 V to 0.63 V and the electrical efficiency increases 13.6% rom 13.2% to 15.0%.

The 1mm thick biomimetic transpiration (BT) layer is attached to the back of a solar PV cell in order to remove the heat generated in the cell. Around 30 branches of bamboo fibre bundles are homogeneously embedded into the potassium polyacrylate (PAAK) superabsorbent polymer (SAP) hydrogel cells, distributing water over the entire area covered by the BT layer.

The fibre bundles mimic the vascular bundles in transporting and distributing liquid water over the cell’s surface, while hydrogel cells with large specific surface area and excellent water absorption performance are used to mimic the sponge cells in providing effective evaporation.

The transpiration performance of the PV-leaf was tested under a solar simulator with an irradiance 1000 W/m2 with no wind and then compared to that of a standalone PV cell of the same material. The standalone PV cell was also covered and protected by a 0.7-mm-thick high-transmittance glass layer but without any insulation or back sheet on the back of the cell and was cooled by natural air convection. The ambient temperature and relative humidity in the laboratory were 33.5 °C and 10%, respectively.

During the tests the standalone PV cell reached a temperature of 68.8 °C whereas the PV-leaf with biomimetic transpiration cooling reached a temperature of only 43.2 °C.

To examine the effect of wind, a 3D model was developed and validated against the experimental results. This shows the PV-leaf temperature can be lower than the ambient temperature when the wind speed is higher than 1.5 m/s. and the temperature reduction is almost linear from ~26 °C to 0 °C as the relative humidity increases from 10% to 100%.

“This innovative design holds tremendous potential for significantly enhancing the performance of solar panels, while also ensuring cost-effectiveness and practicality,” said Dr Gan Huang, Honorary Research Fellow in the Department of Chemical Engineering, and co-author of the study.

Professor Christos Markides, Head of Clean Energy Processes Laboratory, and author of the study, said: “Implementing this innovative leaf-like design could help expedite the global energy transition, while addressing two pressing global challenges: the need for increased energy and freshwater.”