HAMNET Report 7th November 2021


The Southern Africa Seasonal Update of the World Food Programme (WFP) has flagged western and southern provinces of Angola as area of high concern. Drought is affecting agricultural producing areas and below-average rainfall is again expected for October 2021 – February 2022.

A recent IPC report shows that 1.58 million people are likely to be food insecure through to the end of 2021 and on until March 2022. Malnutrition is sharply increased, affecting thousands of children. Deaths among children and the adult population are reported.

Angola is now entering the lean season, and emergency food assistance is urgently needed.  Angolan citizens (mainly women and children) presenting with high rates of severe malnutrition are crossing to seek for assistance in Namibia. In Omusati region, Etunda is hosting 2875 people and conditions are critical, with weekly influxes of 30 arrivals. Namibian local government has been providing food in some areas, but assistance is insufficient and conditions are difficult, with no basic services available. The regional government is calling for assistance and similar reports are coming from the Kunene region.

TechXplore reports that a research group at the Norwegian University of Science and Technology (NTNU) has developed a method for making an ultra-high material efficient solar cell using semiconductor nanowires. If this is placed on top of a traditional silicon-based solar cell, it could potentially double the efficiency of today’s Si solar cells at low cost.

“We have a new method of using gallium arsenide (GaAs) material in a very effective way through nanostructuring, so we can make solar cells much more efficient using only a tiny fraction of the material that is normally used,” says Anjan Mukherjee, a Ph.D. candidate at the Department of Electronic Systems. Mukherjee is the main developer of the technique.

Gallium arsenide (GaAs) is the best material for making high efficiency solar cells because of its extraordinary light absorption and electrical characteristics. It is commonly used to make solar panels mainly for use in space.

However, high-quality GaAs solar cell components are quite expensive to make, which has driven a demand for techniques that can cut the use of the material.

In recent years, it was realized that a nanowire structure can potentially enhance solar cell efficiency compared to standard planar solar cells, even as less material is used.

“Our research group has found a new way to make an ultrahigh power-per-weight ratio solar cell that is more than 10 times more efficient than any other solar cell, by using GaAs in a nanowire structure,” says Helge Weman, a professor at the Department of Electronic Systems at NTNU.

The group’s research has been published in ACS Photonics, a journal from the American Chemical Society.

GaAs solar cells are most often grown on a thick and expensive GaAs substrate, which leaves little room for reducing costs.

“Our method uses a vertically standing semiconductor nanowire array structure on a cheap and industry-favourable Si platform to grow the nanowires,” Weman said.

The development of this technology can be straightforward and cost-effective with appropriate investments and industrial-scale R&D projects.

“We grow the nanowires using a method called MBE (molecular beam epitaxy), which is not a tool that can produce materials at a high volume. However, it’s possible to produce these nanowire-based solar cells at a large scale by using an industrial-scale tool such as metal organic vapour deposition (MOCVD),” Mukherjee said.

Integrating this product on top of a Si cell can potentially improve solar cell efficiency to as much as 40 % – which would mean a doubling of efficiency when compared to today’s commercial Si solar cells.

The researchers say their approach could be adapted so that the nanowires are grown on different substrates, which could open the door to many other applications.

“We are exploring growing this type of light-weight nanowire structure on atomically thin two-dimensional substrates such as graphene. This could open up enormous opportunities to produce light-weight and flexible solar cells that can be used in self-powered drones, micro-satellites and other space applications,” Mukherjee said.

Thanks to Phys.org for drawing my attention to this technology.

TechXplore notes, in another article, that a combined team of researchers from the U.S. Advanced Battery Consortium (USABC) and battery maker A123 Systems has developed a new way to reclaim some of the materials from the cathodes that are used in lithium batteries, which can then be used to make new batteries. In their paper published in the journal Joule, the group claims the process can be used to make new batteries that are more efficient than batteries made with newly mined metals.

Currently, very few new batteries are made using materials recycled from old batteries—instead, old, dead batteries wind up in landfills and new batteries are made using fresh materials. In this new study, the researchers have found that it is possible to use at least some of the materials in old batteries to make new ones. They have developed a recycling system that can remove the metals used in the cathodes of lithium batteries, specifically the metals—nickel, manganese and cobalt.

The technique begins with discharging the batteries. Next, the batteries are shredded and sent through a sieve where materials from the case, wires, plastics and other parts of the battery are removed. The resulting mixture holds cathode materials, other metals and some graphite. These materials are separated using both filtering and leaching. The output is nickel, manganese and cobalt in powder form. The researchers note that the powders can be used to create new cathodes for new batteries. They also note that under a microscope, particles in the powder had larger pores than metals taken directly from a mine, and they were also less brittle. They note that more porous metals make better batteries because they enable better ion diffusion. They are also less likely to crack after repeated charging and discharging.

The researchers also made batteries using their recycled material and tested them using a protocol developed by USABC. They found they performed as well as or better than batteries made with virgin metals. Also, some of the members of the team have formed a start-up called Battery Resources and they have already started selling their recycled materials. They have plans to build a facility capable of processing 10,000 tons of batteries a year by the end of next year.

What to do with expired Lithium batteries has been a headache for all of us. Here’s a potential solution to the problem.

This is Dave Reece ZS1DFR reporting for HAMNET in South Africa.