Science

Cost-effective solar power module could also serve as an eco-friendly furnace

Cost-effective solar power mod...
A dish-shaped mirror focuses sunlight onto a glass ball, which distributes it evenly onto an array of photovoltaic cells (Photo: Blake Coughenour/UA)
A dish-shaped mirror focuses sunlight onto a glass ball, which distributes it evenly onto an array of photovoltaic cells (Photo: Blake Coughenour/UA)
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A dish-shaped mirror focuses sunlight onto a glass ball, which distributes it evenly onto an array of photovoltaic cells (Photo: Blake Coughenour/UA)
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A dish-shaped mirror focuses sunlight onto a glass ball, which distributes it evenly onto an array of photovoltaic cells (Photo: Blake Coughenour/UA)
The "tracker" consists of a steel frame that ultimately will support eight mirrors, together generating enough electricity to power about four to five homes (Photo: Blake Coughenour/UA)
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The "tracker" consists of a steel frame that ultimately will support eight mirrors, together generating enough electricity to power about four to five homes (Photo: Blake Coughenour/UA)
Regents' Professor Roger Angel has pioneered a new way to make glass mirrors to concentrate sunlight to make electricity (Photo: Patrick McArdle/UAnews)
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Regents' Professor Roger Angel has pioneered a new way to make glass mirrors to concentrate sunlight to make electricity (Photo: Patrick McArdle/UAnews)
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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 (Photo: Patrick McArdle/UAnews)
Regents' Professor Roger Angel has pioneered a new way to make glass mirrors to concentrate sunlight to make electricity (Photo: Patrick McArdle/UAnews)

"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.

The "tracker" consists of a steel frame that ultimately will support eight mirrors, together generating enough electricity to power about four to five homes (Photo: Blake Coughenour/UA)
The "tracker" consists of a steel frame that ultimately will support eight mirrors, together generating enough electricity to power about four to five homes (Photo: Blake Coughenour/UA)

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

Photo Slideshow: Building the Next Phase in Energy Technology

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32 comments
Gordon Buchan
Looks a lot like the stuff developed at Solar Systems in Australia nearly 20 years ago ... been installed for 15 years in the outback .. www.solarsystems.com.au
Ross Nicholson
This is nothing new. Indeed, this concept has been around for fifty years at least.
Bill Moore
This is an interesting technology and may have some place in providing our energy. Still, does requiring 49 square miles (7X7) to replace a single power plant sound like a good idea? How many like that do we want built? A lot of people don't like nuclear, but it sure looks like the best option when you look at all the costs (economic, social, and environmental).
L1ma
Concept was around since 1939, using solar mirrors to generate steam driven power in the deserts of Egypt. Using salt based heat stores electricity can be generated over 24 hours with a solar concentrator using mirrors rather than just during daylight hours with the system mentioned. It is energy storage which is the biggest problem not the photovoltaic cells. Also read Desertec - Energy for Everybody by Margaret Heckel. One of the best kept secrets of the energy industry is that it is actually far far cheaper to generate solar electricity in the desert and supply it to the north than by gas/coal/nuclear or photovoltaic panels. True also especially for the US which does not have security issues having plenty of its own desert areas ideal for generating electricity withing its borders. see: http://www.desertec.org/
JBar
Even the high efficiency solar cells are cost prohibitive. Run the light through a cube of fresnel lenses (external mirrors redirect the light at 90 degree angles) Use Freon misters within the cube to abosrb the amibient heat. Use the concentrated light to power a stirling engine. 40% yield at a fraction of the current cost. barbour@aai.textron.com
jerryd
2.5kw from 20sq yards at 1kw/yard solar input is only 12.5% eff. Not much here worth much as better systems are already in place. Why would one waste the heat. Gathering and using the waste heat would increase eff several more x's. Making a steam/Rankine engine with a small heat storage plus using waste heat could make 25% eff electric and 75% eff overall, soundly beating this.
zevulon
1) solar thermal needs water and operates far more efficiently at scale than any other method. 2) concentrated pv is good ONLY because pv cells are too expensive and this is a method to make pv cheaper 3) pv can be distributed right near you house as opposed to solar thermal---electric-- which operates mostly at scales requiring large turbines to create the electricity 4) if this system is creating a lot of waste heat, they can power a small waste heat turbine to capture it , and use the runoff for heating homes. perhaps the mirrors can be foccussed to temporarily heat small amount of aluminum side panels of a house to capture and store the heat for home heating prior to focussing on the solar cells for generating electricity. extra heat could very well be used to process sewage and garbage on site by pyrolysing it. biomass could also use this heat for pyrolisis thus creating a source of biochar/fuel for other purposes/rainy days. ----it is a fact that the majority of energy we utilize winds up as waste heat rather than work. 5)----the idea of using pv cells for large central 'farms' in the dessert is decades away because it will not be economical anytime soon. SPENDING money on this , rather than on funding new designs and basic research---is a waste. thus, only private investors should risk these ventures, as opposed to government, that socializes the cost of wasteful investment. 6) technology in the are of pv's and mirrors and heat management are progressing rapidly . people are impatient but within a few decades or a hundred more years there will truly be a revolution in the economics of solar power, namely because once installed, these systems require far less labor to maintain--particularly as both inflation, and the increasing cost of maintaining the aging electricity grid starts leaking into the price of consumer electricity.
VoiceofReason
If they could make the plant small enough, it could placed as helping cell plants and also use the waste heat to run a solar water heater for buildings and nearby homes. Plenty of roof space on many of these mega box stores.
jerryd
zevulon, CSP can be done eff in home sizes and where it is most eff, near where it is needed. PV panels are only $1/wt-$1k/kw retail so hardly expensive anymore if well shopped.
LBC
Another challenge with concentrating photovoltaic systems is the need for minimal cloud cover to operate at peak efficiency. The sun no longer acts as a point source to focus onto the cells when there is cloud cover that is diffusing. Not as much an issue in southwest climates but in many areas this has to be considered in the average power the system can generate over time. I think that the process of exploring this design space with rigor is important so it's great to see universities working to refine these products withteh full life cycle in mind.