Hybrid PV Leaf Design Beats the Efficiency of Conventional Solar Panels

Researchers from Imperial College London have developed a solar photovoltaic (PV) leaf design that generates around 10% more electricity than conventional solar panels. 

 

A conceptual rendering of the solar PV leaf’s structure. Image used courtesy of Imperial College London/by Gan Huang

 

The concept has other benefits beyond increased efficiency: Using heat recovered from the solar cell, it can simultaneously co-generate thermal energy and fresh water. This boosts its overall solar utilization efficiency – electrical + thermal, as the study specifies – from around 13% to more than 74.5%. (Commercial solar panels typically have a solar utilization efficiency of under 25%.)

As another advantage, the PV leaf uses cheap materials and minimizes the need for control units, pumps, fans, and porous materials. It can also cool the target surface to a significantly lower temperature, serving multi-generation applications. 

Through indoor and outdoor testing, the researchers demonstrated the PV leaf’s ability to adjust its transpiration rate to ambient temperatures and varying solar irradiance conditions. 

 

Image a) shows the internal structure of a typical leaf; b) shows the engineered PV leaf’s internal structure; c) is an expanded view of the PV leaf’s transpiration structure; d) depicts the working principle of the structure; e) is a photograph of the single-leaf prototype. Image used courtesy of the authors - Figure 1 (Creative Commons Attribution license)

 

Here’s How the PV Leaf Works

In a typical biological plant, the internal structure moves water from its roots to its leaves through transpiration. The Imperial College London researchers designed the PV leaf around the same process, enabling water movement, distribution, and evaporation. As in tree transpiration, the PV leaf can passively control its transpiration rate according to ambient temperatures and internal conditions. 

Experiments saw the design produce around 10% more electricity than conventional solar PV panels, which typically lose up to 70% of incoming solar energy to the environment, with energy dissipated as heat. This raises a given PV system’s operating temperature and degrades its electrical performance. However, the researchers’ transpiration concept could remove 590 watts per square meter (W/m2) of heat from a PV cell, reducing its temperature by around 26 degrees Celsius (78.8 degrees Fahrenheit) under a solar irradiance of 1,000 W/m2. The result is a 13.6% increase in electrical efficiency. 

At the same time, it produces water amounting to 1.1 liters per square meter (L/m2) every hour. At scale, assuming a 20% electrical efficiency and 100 sunny days in a year, the PV leaf structure could produce 40 billion cubic meters of freshwater annually in 2050 if it’s used in the 8.5 terawatts of PV installations projected by 2050 (referencing International Renewable Energy Agency estimates).

 

A conceptual rendering of the PV leaves on a branch. Image used courtesy of Imperial College London/by Gan Huang

 

The leaf’s parts can be fabricated using widely available materials and components. The capital cost of the transpiration components, including hydrogel, fiber bundle, supporting mesh, and piping, is around 2% of the price of commercial PV panels. 

Also, testing found that the design is compatible with seawater as its working fluid, which is more abundant than freshwater, without sacrificing its thermal management performance. Simulation tests indicated it has higher transpiration performance in dry and hot climates. 

Ultimately, the concept could be up-scaled to large collectors or divided into small areas of interconnected PV leaves. The researchers mentioned that global PV capacity is expected to surpass 22 terawatts by 2050, per Rethink Research estimates. Assuming nearly one-third of PV panels have access to water resources as a coolant, the PV leaf design could generate an additional 650 gigawatts of power worldwide.