A dish-shaped mirror focuses sunlight onto a glass ball, which distributes it evenly onto an array of photovoltaic cells
Borrowing technology from sophisticated telescope mirrors as well as high-efficiency solar cells used for space exploration, a group of students and researchers at the University of Arizona is putting the final touches on a novel power plant that promises to generate renewable energy twice as efficiently as standard solar panel technology with highly competitive costs and a very small environmental impact.
Curved mirrors in solar power plants usually concentrate the sun's rays along a water pipe, heating the water into steam that is then fed to power-generating turbines. But rather than distributing the power over the area of a water pipe, researchers at the University of Arizona are working on focusing as much as possible of the sun's captured energy onto a precise point in space.
The target is a small glass ball that is only five inches in diameter. The ball contains a specially coated lens that redirects the light to an array of 36 small, high-efficiency solar cells, which were originally developed for space applications, that can absorb light over a broader spectrum than standard cells. And instead of mirrors shaped like a cylinder, the team had to develop dish-shaped mirrors that focus light onto a point.
Regents' Professor Roger Angel has pioneered a new way to make glass mirrors to concentrate sunlight to make electricity
"By using mirrors to focus on small but super-efficient photovoltaic cells, we have the potential to make twice as much electricity as even the best photovoltaic panels," Prof. Roger Angel, who is coordinating the research efforts, commented.
Because the rays concentrate on a small area, the process generates very high temperatures – so high, in fact, that they could melt the solar cells in seconds. To prevent this, the team designed an effective cooling system, a simple combination of fans and radiators that keeps the solar cells within 36° F (20° C) of the ambient air temperature.
Each module features two highly reflective, curved, 10 by 10 feet (3 x 3 m) glass mirrors mounted on a steel structure. The module automatically orients itself toward the sun for maximum performance: in the morning it turns to the east, tracks the sun's path for the entire day and, after sunset, predicts where the sun will be rising and preps itself for the next day of clean, efficient power generation.
A prototype with only two mirrors was shown to generate 2.5 kilowatts of electricity – enough to meet the demand of two average U.S. households – but the team plans to place eight mirrors on each module.
The manufacturing process for the dish-shaped mirrors is going to be optimized for mass production to reduce costs. The materials used are relatively cheap and, because no water is required to generate power, the plant's environmental footprint would be smaller than that of a conventional solar panel-based plant.
"Our technology holds the promise of getting the price of solar energy down to where it can be used on a large scale without depending on subsidies and be competitive in the electricity market," Angel commented. He says that an array of sun trackers on an area measuring about seven by seven miles (11 x 11 km) would generate 10 GW of power during sunshine hours – as much as a big nuclear power plant – and suggests that the system could be deployed in deserts for maximum effect.
The researchers have already patented their process for manufacturing their curved, highly reflective glass mirrors, and the team is now looking to find new applications for this technology.
One promising prospect, which would require little adaptation, would be to explore the thermal properties of the modules. Because the temperatures achieved are so high, Angel's team plans to adapt their system into a novel, eco-friendly furnace that can melt glass within seconds. The researchers were recently awarded a US$1.5 million grant by the Department of Energy to investigate just such a possibility.
The video below illustrates some of the challenges the team faced in developing their system.
Source: University of Arizona
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