Solar Energy  

The viability of solar energy is a big question for the near future.  With prices dropping, and the technology improving, how close are we to solar becoming competitive with fossil fuels?

The sun is a free, renewable energy source just waiting to be harvested. Many individuals have installed private solar power panels on their houses to supplement the power supply. The real question is whether solar power can be gathered and used commercially as a viable replacement for fossil fuel.

Availability

One problem with solar power is that it is not always available. It is not available at night, and clouds frequently block the sun during the day. The obvious solution is to try to store solar energy in some way for use when the sun isn't shining, but no one has come up with a truly economical way to store solar energy generated by photovoltaic panels.

According to an environmentalist who holds an online Electrical Engineering Master's degree, if a public utility decided to use solar power they would have to have a fossil fuel plant available as backup. They would have to switch back and forth between solar power and conventional power as the available sunlight shifted. This kind of switching is very inefficient. Starting and stopping a clean natural gas power plant uses up more energy than would be supplied by the solar panels, so a dirty coal power plant would have to be used instead.

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Due to its governmental policies, Germany is currently the top solar-energy producing nation the world. It also has extremely expensive energy, with the retail rate at 34 cents per kilowatt-hour; U.S. retail energy is 12 cents per kilowatt-hour. And Germany is producing large amounts of pollution because the areas served by solar energy during the day turn to coal-powered plants to provide energy the rest of the time.

Resource Issues

Unlike wind turbine power plants that can easily share space with agriculture, solar panelscannot share the land with any other user, including wildlife and plants. A concentrating thermal solar power plant needs 4 to 16 acres per megawatt generated. These plants also consume significant amounts of water, around 600 gallons per megawatt generated. The sunny deserts that are considered the best sites for large-scale solar plants have limited water supplies.

Image Source - U.S. Department of Energy

Prices Falling

On the other hand, the price of utility-scale solar energy had dropped to 11 cents per kilowatt-hour by 2013. Utility-scale energy is generated by small plants and sold to wholesale utility buyers, not directly to consumers. Utility-scale natural gas energy is being sold for around 6 cents per kilowatt-hour, so solar energy technology has to advance a bit further in efficiency before becoming a truly viable commercial energy source.

By Emma Sturgis

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 Solar Power  

Solar energy scientists have converted over 40 percent of the sunlight hitting a solar system into electricity, the highest efficiency ever reported.

Solar energy researchers have converted over 40% of the sunlight hitting a solar system into electricity, the highest efficiency ever reported.

"We used commercial solar cells, but in a new way, so these efficiency improvements are readily accessible to the solar industry."

The world-beating efficiency was achieved in outdoor tests in Sydney, before being independently confirmed by the National Renewable Energy Laboratory (NREL) at their outdoor test facility in the United States.

The work was funded by the Australian Renewable Energy Agency (ARENA) and supported by the Australia–US Institute for Advanced Photovoltaics (AUSIAPV)

“This is the highest efficiency ever reported for sunlight conversion into electricity,” University of New South Wales (UNSW) Scientia Professor and Director of the Australian Centre for Advanced Photovoltaics (ACAP) Professor Martin Green said.

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“We used commercial solar cells, but in a new way, so these efficiency improvements are readily accessible to the solar industry,” added Dr Mark Keevers, the UNSW solar scientist who managed the project.

The 40% efficiency milestone is the latest in a long line of achievements by UNSW solar researchers spanning four decades. These include the first photovoltaic system to convert sunlight to electricity with over 20% efficiency in 1989, with the new result doubling this performance.

“The new results are based on the use of focused sunlight, and are particularly relevant to photovoltaic power towers being developed in Australia,” Professor Green said.

Power towers are being developed by Australian company, RayGen Resources, which provided design and technical support for the high efficiency prototype. Another partner in the research was Spectrolab, a US–based company that provided some of the cells used in the project.

A key part of the prototype’s design is the use of a custom optical bandpass filter to capture sunlight that is normally wasted by commercial solar cells on towers and convert it to electricity at a higher efficiency than the solar cells themselves ever could.

Such filters reflect particular wavelengths of light while transmitting others.

ARENA CEO Ivor Frischknecht said the achievement is another world first for Australian research and development and further demonstrates the value of investing in Australia’s renewable energy ingenuity.

“We hope to see this home grown innovation take the next steps from prototyping to pilot scale demonstrations. Ultimately, more efficient commercial solar plants will make renewable energy cheaper, increasing its competitiveness.”


SOURCE  University of New South Wales

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 Solar Cells  

Researchers have discovered that the controlled placement of carbon nanotubes in nanostructures could result in a huge boost in electronic performance in photovoltaic solar cells.

Carbon nanotubes are becoming increasingly attractive for photovoltaic solar cells as a replacement to silicon. Researchers at Umeå University in Sweden have discovered that controlled placement of the carbon nanotubes into nano-structures produces a huge boost in electronic performance. Their groundbreaking results are published in the journal Advanced Materials.

"We have found that the resulting nano networks possess exceptional ability to transport charges, up to 100 million times higher than previously measured carbon nanotube random networks produced by conventional methods."

Carbon nanotubes, or CNTs, are one dimensional nanoscale cylinders made of carbon atoms that possess very unique properties.  For example, they have very high tensile strength and exceptional electron mobility, which make them very attractive for the next generation of organic and carbon-based electronic devices.

There is an increasing trend of using carbon based nanostructured materials as components in solar cells. Due to their exceptional properties, carbon nanotubes are expected to enhance the performance of current photovoltaic solar cells through efficient charge transport inside the device.

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In order to obtain the highest performance for electronic applications, the carbon nanotubes must be assembled into a well-ordered network of interconnecting nanotubes. Unfortunately, conventional methods used today are far from optimal which results in low device performance.

In a new study, a team of physicists and chemists at Umeå University have joined forces to produce nano-engineered carbon nanotubes networks with novel properties.

For the first time, the researchers show that carbon nanotubes can be engineered into complex network architectures, and with controlled nano-scale dimensions inside a polymer matrix.
 “We have found that the resulting nano networks possess exceptional ability to transport charges, up to 100 million times higher than previously measured carbon nanotube random networks produced by conventional methods,” says Dr David Barbero, leader of the project and assistant professor at the Department of Physics at Umeå University.

“This new architecture enables a higher degree of interconnection between nanotubes and more robust charge transport pathways in the device,” Barbero told KurzweilAI. “This is expected to increase device efficiency, but also to reduce materials costs because at least 100 times less nanotubes are necessary to form efficient charge transport networks.”

Barbero could not predict when this new technology might go into production, but hinted that “this field is moving fast and things can happen quickly, so stay tuned.”


SOURCE  Umeå University

By 33rd Square

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 Solar Energy  

Scientists from Stanford and Illinois have created a heat-resistant thermal emitter that could significantly improve solar cell efficiency. The novel component is designed to convert heat from the sun into infrared light that can be absorbed by solar cells to make electricity -- a technology known as thermophotovoltaics.

Scientists have created a heat-resistant thermal emitter that could significantly improve the efficiency of solar cells. The novel component is designed to convert heat from the sun into infrared light, which can than be absorbed by solar cells to make electricity – a technology known as thermophotovoltaics. Unlike earlier prototypes that fell apart at temperatures below 2200 degrees Fahrenheit (1200 degrees Celsius), the new thermal emitter remains stable at temperatures as high as 2500 F (1400 C).

"This is a record performance in terms of thermal stability and a major advance for the field of thermophotovoltaics," said Shanhui Fan, a professor of electrical engineering at Stanford University. Fan and his colleagues at the University of Illinois-Urbana Champaign (Illinois) and North Carolina State University collaborated on the project.

The researchers' results are published in the journal Nature Communications.

A typical solar cell has a silicon semiconductor that absorbs sunlight directly and converts it into electrical energy. But silicon semiconductors only respond to infrared light. Higher-energy light waves, including most of the visible light spectrum, are wasted as heat, while lower-energy waves simply pass through the solar panel.

"In theory, conventional single-junction solar cells can only achieve an efficiency level of about 34 percent, but in practice they don't achieve that," said study co-author Paul Braun, a professor of materials science at Illinois. "That's because they throw away the majority of the sun's energy."

Thermophotovoltaic devices are designed to overcome that limitation. Instead of sending sunlight directly to the solar cell, thermophotovoltaic systems have an intermediate component that consists of two parts: an absorber that heats up when exposed to sunlight, and an emitter that converts the heat to infrared light, which is then beamed to the solar cell.

"Essentially, we tailor the light to shorter wavelengths that are ideal for driving a solar cell," Fan said. "That raises the theoretical efficiency of the cell to 80 percent, which is quite remarkable."

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So far, thermophotovoltaic systems have only achieved an efficiency level of about 8 percent, Braun noted. The poor performance is largely due to problems with the intermediate component, which is typically made of tungsten – an abundant material also used in conventional light bulbs.

"Our thermal emitters have a complex, three-dimensional nanostructure that has to withstand temperatures above 1800 F (1000 C) to be practical," Braun explained. "In fact, the hotter the better."

In previous experiments, however, the 3D structure of the emitter was destroyed at temperatures of around 1800 F (1000 C). To address the problem, Braun and his Illinois colleagues coated tungsten emitters in a nanolayer of a ceramic material called hafnium dioxide.

The results were dramatic. When subjected to temperatures of 1800 F (1000 C), the ceramic-coated emitters retained their structural integrity for more than 12 hours. When heated to 2500 F (1400 C), the samples remained thermally stable for at least an hour.

The ceramic-coated emitters were sent to Fan and his colleagues at Stanford, who confirmed that devices were still capable of producing infrared light waves that are ideal for running solar cells.

"These results are unprecedented," said former Illinois graduate student Kevin Arpin, lead author of the study. "We demonstrated for the first time that ceramics could help advance thermophotovoltaics as well other areas of research, including energy harvesting from waste heat, high-temperature catalysis and electrochemical energy storage."

Braun and Fan plan to test other ceramic-type materials and determine if the experimental thermal emitters can deliver infrared light to a working solar cell.

"We've demonstrated that the tailoring of optical properties at high temperatures is possible," Braun said. "Hafnium and tungsten are abundant, low-cost materials, and the process used to make these heat-resistant emitters is well established. Hopefully these results will motivate the thermophotovoltaics community to take another look at ceramics and other classes of materials that haven't been considered."



SOURCE  Stanford University

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 Graphene  

Researchers have found that graphene retains its properties even when coated with silicon. These findings pave the way for entirely new possibilities to use in thin-film photovoltaics.

Graphene has extreme conductivity and is completely transparent while being inexpensive and nontoxic. This makes it a perfect candidate material for transparent contact layers for use in solar cells to conduct electricity without reducing the amount of incoming light - at least in theory. Whether or not this holds true in a real world setting is questionable as there is no such thing as "ideal" graphene - a free floating, flat honeycomb structure consisting of a single layer of carbon atoms: interactions with adjacent layers can change graphene's properties dramatically.

The research recently appeared in the journal Applied Physics Letters.

"We examined how graphene's conductive properties change if it is incorporated into a stack of layers similar to a silicon based thin film solar cell and were surprised to find that these properties actually change very little," Marc Gluba explains.

To this end, they grew graphene on a thin copper sheet, next transferred it to a glass substrate, and finally coated it with a thin film of silicon. They examined two different versions that are commonly used in conventional silicon thin-film technologies: one sample contained an amorphous silicon layer, in which the silicon atoms are in a disordered state similar to a hardened molten glass; the other sample contained poly-crystalline silicon to help them observe the effects of a standard crystallization process on graphene's properties.

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Even though the morphology of the top layer changed completely as a result of being heated to a temperature of several hundred degrees Celcius, the graphene is still detectable. "That's something we didn't expect to find, but our results demonstrate that graphene remains graphene even if it is coated with silicon," says Norbert Nickel.

Their measurements of carrier mobility using the Hall-effect showed that the mobility of charge carriers within the embedded graphene layer is roughly 30 times greater than that of conventional zinc oxide based contact layers.

Says Gluba: "Admittedly, it's been a real challenge connecting this thin contact layer, which is but one atomic layer thick, to external contacts. We're still having to work on that." Adds Nickel: "Our thin film technology colleagues are already pricking up their ears and wanting to incorporate it." The researchers obtained their measurements on one square centimeter samples, although in practice it is feasible to coat much larger areas than that with graphene.


SOURCE  Helmholtz Zentrum Berlin

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 Solar Power  

A discovery by researchers at the University of Alberta could make solar power cheaper, more accessible by using nanoparticle-based 'ink' to make printable or spray-on solar cells.

University of Alberta researchers have found that abundant materials in the Earth’s crust can be used to make inexpensive and easily manufactured nanoparticle-based solar cells.

The research, which was supported by the Natural Sciences and Engineering Research Council of Canada, is published in the latest issue of ACS Nano.

The discovery, several years in the making, is an important step forward in making solar power more accessible to parts of the world that are off the traditional electricity grid or face high power costs, such as the Canadian North, said researcher Jillian Buriak, a chemistry professor and senior research officer of the National Institute for Nanotechnology based on the U of A campus.

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Buriak and her team have designed nanoparticles that absorb light and conduct electricity from two very common elements: phosphorus and zinc. Both materials are more plentiful than scarce materials such as cadmium and are free from manufacturing restrictions imposed on lead-based nanoparticles.

“Half the world already lives off the grid, and with demand for electrical power expected to double by the year 2050, it is important that renewable energy sources like solar power are made more affordable by lowering the costs of manufacturing,” Buriak said.

“My goal is that a store like Ikea could sell rolls of these things with simple instructions and baggies of screws and do-dads and you could install them yourself,” said Buriak
Her team’s research supports a promising approach of making solar cells cheaply using mass manufacturing methods like roll-to-roll printing (as with newspaper presses) or spray-coating (similar to automotive painting). “Nanoparticle-based ‘inks’ could be used to literally paint or print solar cells or precise compositions,” Buriak said.

Buriak collaborated with U of A post-doctoral fellows Erik Luber of the U of A Faculty of Engineering and Hosnay Mobarok of the Faculty of Science to create the nanoparticles. The team was able to develop a synthetic method to make zinc phosphide nanoparticles, and demonstrated that the particles can be dissolved to form an ink and processed to make thin films that are responsive to light.

Buriak and her team are now experimenting with the nanoparticles, spray-coating them onto large solar cells to test their efficiency. The team has applied for a provisional patent and has secured funding to enable the next step to scale up for manufacturing.



SOURCE  University of Alberta, Top Image: Ed Kaiser, Edmonton Journal

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 Solar Panels  

Researchers at Australia's CSIRO institution have developed a new method for printing solar panels. devices could soon be coated onto buildings, into windows and on roofs to provide power in a range of different locations and circumstances.

Australian scientists have found a way to print large but extremely lightweight and flexible solar panels. The ability to print solar panels is not new in itself - but what is new is the ability to make them as large and powerful as the Australian version.

Researchers at the Commonwealth Scientific and Industrial Research Organisation(CSIRO) said the A3-sized panels, which are created by laying a liquid photovoltaic ink onto thin, flexible plastic could soon mean everyone has the ability to print their own solar panels at home.

"It would definitely be feasible to do that," said CSIRO materials scientist Dr Scott Watkins.  "The general concept of being able to manufacture on demand, in a house or in a workplace, is really a key feature of what we're doing."

Near-term uses include putting the panels, similar in feel to a glossy magazine page, onto laptops or mobile phones - offering an extra hour of power once the inbuilt battery dies.  They could also be printed onto windows or roof structures.

"We're actively talking to a Victorian company at the moment about incorporating them into windows," Dr Watkins added.

At the moment, the 30 centimetre-wide panels generate between 10 to 50 watts of power per square metre and have been proven to last at least six months.

But that lifetime and wattage will be boosted in the future and the printers needed to make the panels far smaller, Dr Watkins said.

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SOURCE  Sydney Morning Herald

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