New technique could lead to cheaper, more efficient solar power and LEDs

Researchers Valerio Adinolfi (left) and Riccardo Comin examine a perovskite crystal. Perovskites are attracting growing interest in the context of thin-film solar technologies, but had never been studied in their purest form: as perfect single crystals. Credit; Toronto

U of T experts are shining new light on an emerging family of solar-absorbing materials that could lead to cheaper and more efficient solar panels and LEDs.

The materials, called perovskites, are particularly good at absorbing visible light, but had never been studied in their purest form: as perfect single crystals.

Using a new technique, researchers grew large, pure perovskite crystals and studied how electrons move through the material as light is converted to electricity.

Led by Professor Ted Sargent of The Edward S. Rogers Sr. Department of Electrical & Computer Engineering at the University of Toronto in collaboration with Professor Osman Bakr of the King Abdullah University of Science and Technology (KAUST), the team used a combination of laser-based techniques to measure selected properties of the perovskite crystals.

By tracking down the ultrafast motion of electrons in the material, they have been able to measure the diffusion length – how far electrons can travel without getting trapped by imperfections in the material – as well as mobility – how fast the electrons can move through the material. Their work was published this week in the journal Science.

“Our work sets the bar for the ultimate solar energy-harvesting performance of perovskites,” says Riccardo Comin, a post-doctoral fellow with the Sargent Group. “With these materials it’s been a race to try to get record efficiencies, and there are no signs of stopping or slowing down.”

In recent years, perovskite efficiency has soared to over 20 per cent, very close to the current best performance of commercial-grade silicon-based solar panels you see mounted in Spanish deserts and on Californian roofs.

“In terms of efficiency, perovskites are perfectly comparable or better than materials that have already been commercialized,” says Valerio Adinolfi, a PhD candidate in the Sargent Group and co-first author on the paper. “The challenge is to make solar attractive from the business side. It’s not just matter of making it efficient – the point is to make it efficient and cheap.”

The study has obvious implications for green energy, but may also enable innovations in lighting.

Think of a solar panel made of perovskite crystals as a fancy slab of glass: light hits the crystal surface and gets absorbed, exciting electrons in the material. Those electrons travel easily through the crystal to electrical contacts on its underside, where they are collected in the form of electric current.

Now imagine the sequence in reverse – power the slab with electricity, inject electrons and release energy as light. A more efficient electricity-to-light conversion means perovskites could open new frontiers for energy-efficient LEDs.

Parallel work in the Sargent Group focuses on improving nano-engineered solar-absorbing particles called colloidal quantum dots. “Perovskites are great visible-light harvesters, and quantum dots are great for infrared,” said Sargent.

“In future, we will explore the opportunities for stacking together complementary absorbent materials,” says Dr. Comin. “There are very promising prospects for combining perovskite work and quantum dot work for further boosting the efficiency.”

Source: U of T

Ultrasounds dance the 'moonwalk' in new metamaterial

Silicone beads embedded in a water-based gel (photograph is ~2 cm across). Credit: © CRPP

Metamaterials have extraordinary properties when it comes to diverting and controlling waves, especially sound and light: for instance, they can make an object invisible, or increase the resolving power of a lens. Now, researchers at the Centre de Recherche Paul Pascal (CNRS) and the Institut de Mécanique et d'Ingénierie de Bordeaux (CNRS/Université de Bordeaux/Bordeaux INP/Arts et Métiers ParisTech) have developed the first three-dimensional metamaterials by combining physico-chemical formulation and microfluidics technology. This is a new generation of soft metamaterials that are easier to shape. In their experiment, the researchers got ultrasonic oscillations to move backwards while the energy carried by the wave moved forwards. Their work opens up new prospects, especially for high-resolution imaging (ultrasonography). It is published on 15 December 2014 in the journal Nature Materials.

Since the 2000s, the international scientific community has seen interest in metamaterials and their extraordinary properties grow exponentially. A metamaterial is a medium in which the phase velocity of light or sound waves can be negative (the material is said to have a negative refractive index).. In such a medium, the phase of the wave (the successive oscillations) and the energy carried by this same wave move in opposite directions. This property is not found in any natural homogeneous medium.

To obtain a metamaterial, it is necessary to make a heterogeneous medium that contains a large number of inclusions (known as microresonators). The usual way is to use micromechanical methods (etching, deposition, etc) to machine solid supports that will have the properties of metamaterials in one or two dimensions. However, this method cannot be used to work with soft matter at the micrometer scales required for ultrasounds, and the materials obtained remain limited to one or two dimensions.

In this study, the researchers developed a new type of metamaterial, in the fluid phase, formed of porous silicone microbeads embedded in a water-based gel. This metafluid is the first three-dimensional metamaterial to work at ultrasonic frequencies. In addition, due to its fluid nature, it can be made using physico-chemical processes and microfluidics technologies, which are much easier to implement than micromechanical methods.

One of the properties of porous media is that sound travels through them at very low speed (a few tens of meters per second) compared to water (1500 meters per second). Due to this sharp contrast, the whole suspension has the properties of a metamaterial provided the bead concentration is sufficient: when the researchers studied the propagation of ultrasonic waves through this medium, they directly measured a negative refractive index. Within such a metafluid, the energy carried by the wave travels from the emitter to the receiver, as expected, whereas the oscillations appear to move backwards in the opposite direction, rather like a dancer doing the 'moonwalk'.

These results open the way to numerous applications ranging from high-resolution ultrasound imaging to sound insulation and stealth in underwater acoustics. In addition, the soft-matter physico-chemical techniques used to make this metamaterial makes it possible to produce fluid or flexible materials with adaptable shapes, potentially at the industrial scale.

Source: CNRS (Délégation Paris Michel-Ange)

Sun's rotating 'magnet' pulls lightning towards UK

Big Ben and Houses of Parliament, London, UK. The Sun may be playing a part in the generation of lightning strikes on Earth by temporarily 'bending' the Earth's magnetic field and allowing a shower of energetic particles to enter the upper atmosphere. Credit: © TTstudio / Fotolia

The Sun may be playing a part in the generation of lightning strikes on Earth by temporarily 'bending' the Earth's magnetic field and allowing a shower of energetic particles to enter the upper atmosphere.

This is according to researchers at the University of Reading who have found that over a five year period the UK experienced around 50% more lightning strikes when the Earth's magnetic field was skewed by the Sun's own magnetic field.

The Earth's magnetic field usually functions as an in-built force-field to shield against a bombardment of particles from space, known as galactic cosmic rays, which have previously been found to prompt a chain-reaction of events in thunderclouds that trigger lightning bolts.

It is hoped these new insights, which have been published today, 19 November, in IOP Publishing's journal Environmental Research Letters, could lead to a reliable lightning forecast system that could provide warnings of hazardous events many weeks in advance.

To do so, weather forecasters would need to combine conventional forecasts with accurate predictions of the Sun's spiral-shaped magnetic field known as the heliospheric magnetic field (HMF), which is spewed out as the Sun rotates and is dragged through the solar system by the solar wind.

Lead author of the research Dr Matt Owens said: "We've discovered that the Sun's powerful magnetic field is having a big influence on UK lightning rates.

"The Sun's magnetic field is like a bar magnet, so as the Sun rotates its magnetic field alternately points toward and away from the Earth, pulling the Earth's own magnetic field one way and then another."

In their study, the researchers used satellite and Met Office data to show that between 2001 and 2006, the UK experienced a 50% increase in thunderstorms when the HMF pointed towards the Sun and away from Earth.

This change of direction can skew or 'bend' the Earth's own magnetic field and the researchers believe that this could expose some regions of the upper atmosphere to more galactic cosmic rays--tiny particles from across the Universe accelerated to close to the speed of light by exploding stars.

"From our results, we propose that galactic cosmic rays are channelled to different locations around the globe, which can trigger lightning in already charged-up thunderclouds. The changes to our magnetic field could also make thunderstorms more likely by acting like an extra battery in the atmospheric electric circuit, helping to further 'charge up' clouds," Dr Owens continued.

The results build on a previous study by University of Reading researchers, also published in Environmental Research Letters, which found an unexpected link between energetic particles from the Sun and lightning rates on Earth.

Professor Giles Harrison, head of Reading's Department of Meteorology and co-author of both studies, said: "This latest finding is an important step forward in our knowledge of how the weather on Earth is influenced by what goes on in space. The University of Reading's continuing success in this area shows that new insights follow from atmospheric and space scientists working together."

Dr Owens continued: "Scientists have been reliably predicting the solar magnetic field polarity since the 1970s by watching the surface of the Sun. We just never knew it had any implications on the weather on Earth. We now plan to combine regular weather forecasts, which predict when and where thunderclouds will form, with solar magnetic field predictions. This means a reliable lightning forecast could now be a genuine possibility."

Source:  Institute of Physics

Glimpsing pathway of sunlight to electricity

Andrew H. Marcus and Mark C. Lonergan stand by UO spectroscopy equipment. Credit: Image courtesy of University of Oregon

Four pulses of laser light on nanoparticle photocells in a University of Oregon spectroscopy experiment has opened a window on how captured sunlight can be converted into electricity.

The work, which potentially could inspire devices with improved efficiency in solar energy conversion, was performed on photocells that used lead-sulfide quantum dots as photoactive semiconductor material. The research is detailed in a paper placed online by the journal Nature Communications.

In the process studied, each single photon, or particle of sunlight, that is absorbed potentially creates multiple packets of energy called excitons. These packets can subsequently generate multiple free electrons that generate electricity in a process known as multiple exciton generation (MEG). In most solar cells, each absorbed photon creates just one potential free electron.

Multiple exciton generation is of interests because it can lead to solar cells that generate more electrical current and make them more efficient. The UO work shines new light on the little understood process of MEG in nanomaterials.

While the potential importance of MEG in solar energy conversion is under debate by scientists, the UO spectroscopy experiment -- adapted in a collaboration with scientists at Sweden's Lund University -- should be useful for studying many other processes in photovoltaic nanomaterials, said Andrew H. Marcus, professor of physical chemistry and head of the UO Department of Chemistry and Biochemistry.

Spectroscopic experiments previously designed by Marcus to perform two-dimensional fluorescence spectroscopy of biological molecules were adapted to also measure photocurrent. "Spectroscopy is all about light and molecules and what they do together," Marcus said. "It is a really great probe that helps to tell us about the reaction pathway that connects the beginning of a chemical or physical process to its end.

"The approach is similar to looking at how molecules come together in DNA, but instead we looked at interactions within semiconductor materials," said Marcus, an affiliate in UO's Institute of Molecular Biology, Materials Science Institute and Oregon Center for Optics. "Our method made it possible to look at electronic pathways involved in creating multiple excitons. The existence of this phenomenon had only been inferred through indirect evidence. We believe we have seen the initial steps that lead to MEG-mediated photo conductivity."

The controlled sequencing of laser pulses allowed the seven-member research team to see -- in femtoseconds (a femtosecond is one millionth of one billionth of a second) -- the arrival of light, its interaction with resting electrons and the subsequent conversion into multiple excitons. The combined use of photocurrent and fluorescence two-dimensional spectroscopy, Marcus said, provided complementary information about the reaction pathway.

UO co-author Mark C. Lonergan, professor of physical and materials chemistry, who studies electrical and electrochemical phenomena in solid-state systems, likened the processes being observed to people moving through a corn maze that has one entrance and three exits.
People entering the maze are photons. Those who exit quickly represent absorbed photons that generate unusable heat. People leaving the second exit represent other absorbed photons that generate fluorescence but not usable free electrons. People leaving the final exit signify usable electrical current.

"The question we are interested in is exactly what does the maze look like," Lonergan said. "The problem is we don't have good techniques to look inside the maze to discover the possible pathways through it. The techniques that Andy has developed basically allow us to see into the maze by encoding what is coming out of the system in terms of exactly what is going in. We can visualize what is going on, whether two people coming into the maze shook hands at some point and details about the pathway that led them to come out the electricity exit."

The project began when Tonu Pullerits, who studies ultrafast photochemistry in semiconductor molecular materials at Lund University, approached Marcus about adopting his spectroscopic system to look at solar materials. Khadga J. Karki, a postdoctoral researcher in Pullerits' lab, then visited the UO and teamed with the Marcus and Lonergan groups to reconfigure the equipment.

UO doctoral student Julia R. Widom was a co-leading author on the paper. Other co-authors with Pullerits, Marcus and Lonergan were Joachim Seibt of Lund University and UO graduate student Ian Moody.

Source:  University of Oregon

Scientists get to the heart of fool's gold as a solar material

This crystal of iron pyrite shows the characteristic cubic crystals of 'fool's gold.' A new study led by Song Jin at the University of Wisconsin-Madison identifies defects in pyrite's crystal structure as a critical obstacle to building commercial solar cells from the cheap and abundant iron pyrite material. Credit: University of Wisconsin-Madison Geology Museum

As the installation of photovoltaic solar cells continues to accelerate, scientists are looking for inexpensive materials beyond the traditional silicon that can efficiently convert sunlight into electricity.

Theoretically, iron pyrite -- a cheap compound that makes a common mineral known as fool's gold -- could do the job, but when it works at all, the conversion efficiency remains frustratingly low. Now, a University of Wisconsin-Madison research team explains why that is, in a discovery that suggests how improvements in this promising material could lead to inexpensive yet efficient solar cells.

"We think we now understand why pyrite hasn't worked," says chemistry Professor Song Jin, "and that provides the hope, based on our understanding, for figuring out how to make it work. This could be even more difficult, but exciting and rewarding."

Although most commercial photovoltaic cells nowadays are based on silicon, the light-collecting film must be relatively thick and pure, which makes the production process costly and energy-intensive, says Jin.

A film of iron pyrite -- a compound built of iron and sulfur atoms -- could be 1,000 times thinner than silicon and still efficiently absorb sunlight.

Like silicon, iron and sulfur are common elements in Earth's crust, so solar cells made of iron pyrite could have a significant material cost advantage in large scale deployment. In fact, previous research that balanced factors like theoretical efficiency, materials availability, and extraction cost put iron pyrite at the top of the list of candidates for low-cost and large-scale photovoltaic materials.

In the current online edition of the Journal of the American Chemical Society, Jin and first author Miguel Cabán-Acevedo, a chemistry Ph.D. student, together with other scientists at UW-Madison, explain how they identified defects in the body of the iron pyrite material as the source of inefficiency. The research was supported by the U.S. Department of Energy.
In a photovoltaic material, absorption of sunlight creates oppositely charged carriers, called electrons and holes, that must be separated in order for sunlight to be converted to electricity. The efficiency of a photovoltaic solar cell can be judged by three parameters, Jin says, and the solar cells made of pyrite were almost totally deficient in one: voltage. Without a voltage, a cell cannot produce any power, he points out. Yet based on its essential parameters, iron pyrite should be a reasonably good solar material. "We wanted to know, why is the photovoltage so low," Jin says.

"We did a lot of different measurements and studies to look comprehensively at the problem," says Cabán-Acevedo, "and we think we have fully and definitively shown why pyrite, as a solar material, has not been efficient."

In exploring why pyrite was practically unable to make photovoltaic electricity, many researchers have looked at the surface of the crystals, but Cabán-Acevedo and Jin also looked inside. "If you think of this as a body, many have focused on the skin, but we also looked at the heart," says Cabán-Acevedo, "and we think the major problems lie inside, although there are also problems on the skin."

The internal problems, called "bulk defects," occur when a sulfur atom is missing from its expected place in the crystal structure. These defects are intrinsic to the material properties of iron pyrite and are present even in ultra-pure crystals. Their presence in large numbers eventually leads to the lack of photovoltage for solar cells based on iron pyrite crystals.
Science advances by comprehending causes, Jin says. "Our message is that now we understand why pyrite does not work. If you don't understand something, you must try to solve it by trial and error. Once you understand it, you can use rational design to overcome the obstacle. You don't have to stumble around in the dark."

Source: University of Wisconsin-Madison

A New technique could harvest more of the sun's energy

An ultra-sensitive needle measures the voltage that is generated while the nanospheres are illuminated.
Credit: AMOLF/Tremani - Figure: Artist impression of the plasmo-electric effect.

As solar panels become less expensive and capable of generating more power, solar energy is becoming a more commercially viable alternative source of electricity. However, the photovoltaic cells now used to turn sunlight into electricity can only absorb and use a small fraction of that light, and that means a significant amount of solar energy goes untapped.

A new technology created by researchers from Caltech, and described in a paper published online in the October 30 issue of Science Express, represents a first step toward harnessing that lost energy.

Sunlight is composed of many wavelengths of light. In a traditional solar panel, silicon atoms are struck by sunlight and the atoms' outermost electrons absorb energy from some of these wavelengths of sunlight, causing the electrons to get excited. Once the excited electrons absorb enough energy to jump free from the silicon atoms, they can flow independently through the material to produce electricity. This is called the photovoltaic effect -- a phenomenon that takes place in a solar panel's photovoltaic cells.

Although silicon-based photovoltaic cells can absorb light wavelengths that fall in the visible spectrum -- light that is visible to the human eye -- longer wavelengths such as infrared light pass through the silicon. These wavelengths of light pass right through the silicon and never get converted to electricity -- and in the case of infrared, they are normally lost as unwanted heat.

"The silicon absorbs only a certain fraction of the spectrum, and it's transparent to the rest. If I put a photovoltaic module on my roof, the silicon absorbs that portion of the spectrum, and some of that light gets converted into power. But the rest of it ends up just heating up my roof," says Harry A. Atwater, the Howard Hughes Professor of Applied Physics and Materials Science; director, Resnick Sustainability Institute, who led the study.
Now, Atwater and his colleagues have found a way to absorb and make use of these infrared waves with a structure composed not of silicon, but entirely of metal.

The new technique they've developed is based on a phenomenon observed in metallic structures known as plasmon resonance. Plasmons are coordinated waves, or ripples, of electrons that exist on the surfaces of metals at the point where the metal meets the air.
While the plasmon resonances of metals are predetermined in nature, Atwater and his colleagues found that those resonances are capable of being tuned to other wavelengths when the metals are made into tiny nanostructures in the lab.

"Normally in a metal like silver or copper or gold, the density of electrons in that metal is fixed; it's just a property of the material," Atwater says. "But in the lab, I can add electrons to the atoms of metal nanostructures and charge them up. And when I do that, the resonance frequency will change."

"We've demonstrated that these resonantly excited metal surfaces can produce a potential" -- an effect very similar to rubbing a glass rod with a piece of fur: you deposit electrons on the glass rod. "You charge it up, or build up an electrostatic charge that can be discharged as a mild shock," he says. "So similarly, exciting these metal nanostructures near their resonance charges up those metal structures, producing an electrostatic potential that you can measure."

This electrostatic potential is a first step in the creation of electricity, Atwater says. "If we can develop a way to produce a steady-state current, this could potentially be a power source. He envisions a solar cell using the plasmoelectric effect someday being used in tandem with photovoltaic cells to harness both visible and infrared light for the creation of electricity.

Although such solar cells are still on the horizon, the new technique could even now be incorporated into new types of sensors that detect light based on the electrostatic potential.
"Like all such inventions or discoveries, the path of this technology is unpredictable," Atwater says. "But any time you can demonstrate a new effect to create a sensor for light, that finding has almost always yielded some kind of new product."


This work was published in a paper titled, "Plasmoelectric Potentials in Metal Nanostructures." Other coauthors include first author Matthew T. Sheldon, a former postdoctoral scholar at Caltech; Ana M. Brown, an applied physics graduate student at Caltech; and Jorik van de Groep and Albert Polman from the FOM Institute AMOLF in Amsterdam. The study was funded by the Department of Energy, the Netherlands Organization for Scientific Research, and an NSF Graduate Research Fellowship.

Source: California Institute of Technology

In world first, researchers convert sunlight to electricity with over 40 percent efficiency

Solar panels

UNSW Australia's solar researchers have converted over 40% of the sunlight hitting a solar system into electricity, the highest efficiency ever reported.

The record 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," UNSW Scientia Professor and Director of the Advanced Centre for Advanced Photovoltaics (ACAP) Professor Martin Green said.

"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."

The 40% efficiency achievement is outlined in a paper expected to be published soon by the Progress in Photovoltaics journal. It will also be presented at the Australian PV Institute's Asia-Pacific Solar Research Conference, which begins at UNSW Monday, December 8.

Source: University of New South Wales.

The Matched 'hybrid' systems may hold key to wider use of renewable energy

Wind farms such as this one in Idaho might be combined with other forms of alternative energy to better balance the output of sustainable energy. Credit: Nordex USA/US Department of Energy

The use of renewable energy in the United States could take a significant leap forward with improved storage technologies or more efforts to "match" different forms of alternative energy systems that provide an overall more steady flow of electricity, researchers say in a new report.

Historically, a major drawback to the use and cost-effectiveness of alternative energy systems has been that they are too variable -- if the wind doesn't blow or the sun doesn't shine, a completely different energy system has to be available to pick up the slack. This lack of dependability is costly and inefficient.

But in an analysis just published in The Electricity Journal, scientists say that much of this problem could be addressed with enhanced energy storage technology or by developing "hybrid" systems in which, on a broader geographic scale, one form of renewable energy is ramping up even while the other is declining.

"Wind energy is already pretty cost-competitive and solar energy is quickly getting there," said Anna Kelly, a graduate student in the School of Public Policy at Oregon State University, and an energy policy analyst. "The key to greater use of these and other technologies is to match them in smart-grid, connected systems.

"This is already being done successfully in a number of countries and the approach could be expanded."

For instance, the wind often blows more strongly at night in some regions, Kelly said, and solar technology can only produce energy during the day. By making more sophisticated use of that basic concept in a connected grid, and pairing it with more advanced forms of energy storage, the door could be opened for a much wider use of renewable energy systems, scientists say.

"This is more than just an idea, it's a working reality in energy facilities around the world, in places like Spain, Morocco and China, as well as the U.S.," Kelly said. "Geothermal is being paired with solar; wind and solar with lithium-ion batteries; and wind and biodiesel with batteries. By helping to address the price issue, renewable energy is being produced in hybrid systems by real, private companies that are making real money."

Advanced energy storage could be another huge key to making renewable energy more functional, and one example is just being developed in several cooperating states in the West. Electricity is being produced by efficient wind farms in Wyoming; transmitted to Utah where it's being stored via compressed air in certain rock formations; and ultimately used to help power Los Angeles.

This $8 billion system could be an indicator of things to come, since compressed air can rapidly respond to energy needs and be readily scaled up to be cost-competitive at a significant commercial level.

"There are still a number of obstacles to overcome," said Joshua Merritt, a co-author on the report and also a graduate student in mechanical engineering and public policy at OSU. "Our transmission grids need major improvements so we can more easily produce energy and then send it to where it's needed. There are some regulatory hurdles to overcome. And the public has to more readily accept energy systems like wind, wave or solar in practice, not just in theory."

The "not in my back yard" opposition to renewable energy systems is still a reality, the researchers said, and there are still some environmental concerns about virtually any form of energy, whether it's birds killed by wind turbine rotors, fish losses in hydroelectric dams or chemical contaminants from use of solar energy.

The near future may offer more options, the researchers said. Advanced battery storage technologies are becoming more feasible. Wave or tidal energy may become a real contributor, and some of those forces are more predictable and stable by definition. And the birth of small, modular nuclear reactors -- which can be built at lower cost and produce no greenhouse gas emissions -- could play a significant role in helping to balance energy outflows from renewable sources.

The long-term goal, the report concluded, is to identify technologies that can work in a hybrid system that offers consistency, dependability and doesn't rely on fossil fuels. With careful matching of systems, improved transmission abilities and some new technological advances, that goal may be closer than realized, they said.

"With development, the cost of these hybrid systems will decrease and become increasingly competitive, hopefully playing a larger role in power generation in the future," the researchers wrote in their conclusion.

Source: Oregon State University