Giant mirrors and solar panels in Northern Cape would reduce carbon emissions and generate one—tenth of the country's energy needs South Africa is to unveil plans this week for what it claims will be the world's biggest solar power plant — a radical step in a coal—dependent country where one in six people still lacks electricity.The project, expected to cost up to 200bn rand (GBP18.42bn), would aim by the end of its first decade to achieve an annual output of five gigawatts (GW) of electricity — currently one-tenth of South Africa's energy needs.Giant mirrors and solar panels would be spread across the Northern Cape province, which the government says is among the sunniest 3 per cent of regions in the world with minimal cloud or rain.

The government hopes the solar park will help reduce carbon emissions from Africa's biggest economy, which is still more than 90 per cent dependent on coal-fired power stations. Energy is already a high priority in South Africa where, at the end of racial apartheid, less than 40 per cent of households had electricity.

Over 16 years the governing African National Congress has undertaken a huge national expansion, with a recent survey showing that 83 per cent are now connected, but power outages are still not uncommon in both townships and middle-class suburbs.An estimated 200 foreign and domestic investors will meet this week in Upington, Northern Cape, with a view to funding the hugely ambitious solar project.

A master plan will be set out by the US engineering and construction group Fluor. This follows a viability study by the Clinton Climate Initiative, which described South Africa's “solar resource” as among the best in the world.De Vries, a special adviser to the energy minister, said the Northern Cape had been chosen for insolation readings (a measure of solar energy) that rank among the highest in the world. South Africa currently consumes 45-48GW of power per year. It is estimated this will double over the next 25 years.

“In South Africa over 90 per cent of our power comes from the burning of coal and we need to reduce this because of our international obligations on climate change,” de Vries said.

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ScienceDaily — Conventional solar cell efficiency could be increased from the current limit of 30 percent to more than 60 percent, suggests new research on semiconductor nanocrystals, or quantum dots, led by chemist Xiaoyang Zhu at The University of Texas at Austin.
Zhu and his colleagues report their results in this week's Science.

The scientists have discovered a method to capture the higher energy sunlight that is lost as heat in conventional solar cells.

The maximum efficiency of the silicon solar cell in use today is about 31 percent. That's because much of the energy from sunlight hitting a solar cell is too high to be turned into usable electricity. That energy, in the form of so-called "hot electrons," is lost as heat.

If the higher energy sunlight, or more specifically the hot electrons, could be captured, solar-to-electric power conversion efficiency could be increased theoretically to as high as 66 percent.

"There are a few steps needed to create what I call this 'ultimate solar cell,'" says Zhu, professor of chemistry and director of the Center for Materials Chemistry. "First, the cooling rate of hot electrons needs to be slowed down. Second, we need to be able to grab those hot electrons and use them quickly before they lose all of their energy."
Zhu says that semiconductor nanocrystals, or quantum dots, are promising for these purposes.

As for the first problem, a number of research groups have suggested that cooling of hot electrons can be slowed down in semiconductor nanocrystals. In a 2008 paper in Science, a research group from the University of Chicago showed this to be true unambiguously for colloidal semiconductor nanocrystals.

Zhu's team has now figured out the next critical step: how to take those electrons out.
They discovered that hot electrons can be transferred from photo-excited lead selenide nanocrystals to an electron conductor made of widely used titanium dioxide.

"If we take the hot electrons out, we can do work with them," says Zhu. "The demonstration of this hot electron transfer establishes that a highly efficient hot carrier solar cell is not just a theoretical concept, but an experimental possibility."
The researchers used quantum dots made of lead selenide, but Zhu says that their methods will work for quantum dots made of other materials, too.

He cautions that this is just one scientific step, and that more science and a lot of engineering need to be done before the world sees a 66 percent efficient solar cell.

In particular, there's a third piece of the science puzzle that Zhu is working on: connecting to an electrical conducting wire.

"If we take out electrons from the solar cell that are this fast, or hot, we also lose energy in the wire as heat," says Zhu. "Our next goal is to adjust the chemistry at the interface to the conducting wire so that we can minimize this additional energy loss. We want to capture most of the energy of sunlight. That's the ultimate solar cell.
"Fossil fuels come at a great environmental cost," says Zhu. "There is no reason that we cannot be using solar energy 100 percent within 50 years."

Funding for this research was provided by the U.S. Department of Energy. Coauthors include William Tisdale, Brooke Timp, David Norris and Eray Aydil from the University of Minnesota, and Kenrick Williams from The University of Texas at Austin.

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