Image source: Nazek El-Atab/KAUST
When it comes to making full use of the sunlight available every day, flat solar panels still face great limitations. A new spherical solar cell design aims to increase the solar energy harvesting potential from almost every angle without requiring expensive moving parts to track the apparent movement of the sun in the sky.
It is reported that the prototype of the spherical solar cell designed by Saudi researchers is a tiny blue sphere. One person can hold it with one hand as easily as a table tennis ball. Indoor experiments using solar simulator lights have shown that it can achieve 15% to 100% power output compared to flat solar cells with the same ground area, depending on how the background material reflects sunlight into spherical solar cells. The research team hopes that its nature-inspired design will be equally successful in future field tests at many different locations around the world.
Nazek El-Atab, a postdoctoral researcher in microsystems engineering at King Abdullah University of Science and Technology (KAUST), said: "The position and shape of the housefly eyes increase their angular field of view, so they can be viewed horizontally You can see an angle of about 270 degrees around it. Similarly, the spherical structure increases the'angular field of view' of the solar cell, which means it can collect sunlight from more directions."
To create a spherical solar cell design, El Atab and her colleagues demonstrated how to create a thinner and more flexible solar cell design based on the corrugated groove technology based on previous work. This new work is detailed in a paper submitted to MRS Communications for review.
Tests conducted using solar simulator lights have shown that spherical solar cells provide 24% more power output than traditional flat solar cells when directly exposed to sunlight. After these two types of solar cells began to heat up and suffered some loss in energy efficiency, this power advantage jumped to 39%, indicating that the spherical shape may have some advantages in heat dissipation.
When the spherical solar cell can only collect scattered sunlight under the simulated roof and cannot directly receive the sunlight, the output power of the spherical solar cell is also about 60% higher than that of the flat solar cell. Additional experiments on different reflective backgrounds such as aluminum cups, aluminum paper, white paper, and sand show that the hexagonal aluminum cup background helps spherical solar cells to outperform flat solar cells by 100% in power output.
The Saudi team made spherical solar cells using monocrystalline silicon solar cells, which currently account for nearly 90% of the world's solar power generation. This choice stems from the goal of helping to maximize the solar cell’s light collection potential, and if the design proves to be cost-effective, it may be easier to scale up production.
Zhe Liu, a postdoctoral researcher in solar engineering at the Massachusetts Institute of Technology, said: "What surprised me is that the author has demonstrated in a series of articles that the use of corrugated technology can achieve the ultra-flexibility of rigid silicon solar cells. I am more capable of manufacturing spherical cells Excited, this means you can make industrial IBC type (interdigitated back contact) silicon solar cells cover any shape and'daylight' anywhere."
Rabab Bahabry, an assistant professor of physics at the University of Jeddah in Saudi Arabia, said that previous solar cell designs have produced tiny, microscopic spherical batteries, sometimes made with nanowires or quantum dot batteries on a plane, to help better Collect direct and scattered sunlight. But in terms of collecting sunlight reflected from the background surface, larger spherical solar cells can provide higher efficiency and coverage than microsphere arrays.
To make large spherical solar cells, the researchers needed to etch alternate grooves on 15% of the flat solar cells to form an elliptical band pattern connected in the middle. The CO2 laser creates a suitable pattern in the polymer hard mask covering the solar cell and allows a deep reactive ion etching tool to create grooves in the exposed area of ​​the silicon solar cell. The bending of these recessed areas helped the researchers later fold the solar cell into a spherical shape.
In the etched area, the loss of solar cell material reduces the overall potential solar output. But the researchers believe that, over time, in certain regions of the world, spherical solar cells cost more than flat-panel solar cells because the spherical design is less prone to dust accumulation and may help to dissipate heat, otherwise it may reduce solar cells. s efficiency. In addition, spherical solar cells do not require additional expensive moving parts to continuously track the sun.
However, Professor Liu of the Massachusetts Institute of Technology said that in utility-scale solar power plants, spherical solar cells may not be able to replace traditional solar cell technology. In his view, this special spherical solar cell design can be used in more other market applications.
"Spherical design applications seem to be very limited, but the ability to make commercial silicon solar cells into any shape will make photovoltaics widely used in autonomous devices, such as Internet of Things (IoT) sensors and autonomous vehicles," Liu said. "If we can fully power these autonomous devices with formed photovoltaic panels, this may change the rules of the game."
In future tests, Liu said he wanted to see how spherical solar cells work in outdoor and indoor lighting environments at different times of the day. He also wanted to see to what extent spherical solar cells could be integrated into certain applications where they might provide energy. He would love to see a "quantified cost" summary, summarizing all the processing steps required to manufacture this spherical solar cell, in order to better understand the commercial potential of the technology.
Muhammad Mustafa Hussain, a professor of electrical and computer engineering at KAUST University and one of the co-authors of the study, said that Saudi researchers had to manually fold and form spherical solar cells in the latest demonstration, but they have already begun to design and develop and use them. "Robot hand" simulates an automated method of manual folding.
Eventually, Hussain and his colleagues envisioned the construction and testing of large spherical solar cell arrays. They are already studying new shapes like tents or umbrellas to see if they are of any benefit. They also integrated solar cells with unusually shaped UAV surfaces.
The COVID-19 pandemic that forced the closure of research laboratories delayed the initial outdoor testing plan of the Saudi research team. But Hussain said the organization still plans to advance field trials by the end of 2020. He hopes that the KAUST alumni network can help California and Bangladesh, China, India, South Korea, Germany, Spain, Brazil, Colombia, Mexico, South Africa, Australia and New Zealand to finally test spherical solar cells.
Hussain said: "We will create an array of spherical cells for areas from 100 square feet to 1,000 square feet and compare the functionality over cost-effectiveness with traditional cells. In the next step, we will deploy it in different geographic locations throughout the year, To understand its performance and reliability."
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