Researchers create tool to put the lid on solar power fluctuations

The finding comes at a time when the Obama administration is pushing for the creation of a smart power grid throughout the nation. The improved grid would allow for better use of renewable power sources, including wind and solar.
Also, more utilities have been increasing the amount of renewable energy sources they use to power homes and businesses. For example, Southern California Edison reported this month that it is adding more large-scale solar power plants to its grid and retooling its distribution system to accommodate the power fluctuations that will follow.
Kleissl and Lave’s finding could have a dramatic impact on the amount of solar power allowed to feed into the grid. Right now, because of concerns over variability in power output, the amount of solar power flowing in the grid at residential peak demand times — your typical sunny weekend afternoon in Southern California, say — is limited to 15 percent before utilities are required to perform additional studies. As operators are able to better predict a photovoltaic system’s variability, they will be able to increase this limit. In California, a law signed by Gov. Jerry Brown in April 2011 requires all electricity retailers in the state, including publicly owned utilities, to generate 33 percent of their power sales from renewable energy sources by 2020.
Incidentally, Kleissl and Lave’s research shows that the amount of solar variability can also be reduced by installing smaller solar panel arrays in multiple locations rather than building bigger arrays in just one spot, since a cloud covering one panel is less likely to cover the other panels, Lave said.
“The distance between arrays is key,” he said.
The variability in the output of photovoltaic power systems has long been a source of great concern for utility operators worldwide. But Kleissl and Lave found that variability for large photovoltaic systems is much smaller than previously thought. It also can be modeled accurately, and easily, based on measurements from just a single weather station. Kleissl presented the paper, titled ‘Modeling Solar Variability Effects on Power Plants,’ this week at the National Renewable Energy Laboratory in Golden, Colo.
His findings are based on analysis of one year’s worth of data from the UC San Diego solar grid — the most monitored grid in the nation, with 16 weather stations and 5,900 solar panels totaling 1.2 megawatts in output. Lave looked at variations in the amount of solar radiation the weather stations were receiving for intervals as short as a second. The amount of radiation correlates with the amount of power the panels produce.
Based on these observations, he found that when the distance between weather stations is divided by the time frame for the change in power output, a solar variability law ensues. This operation was inspired by a presentation by Clean Power Research, a Napa-based company, at the Department of Energy — California Public Utility Commission High Penetration Solar forum hosted by UC San Diego in March 2011. “For any pair of stations at any time horizon, this variability law is applicable” says Lave. In other words, the law can be applied to any configuration of photovoltaic systems on an electric grid to quantify the system’s variability for any given time frame.
But Lave didn’t stop there. He developed an easy-to-use interface in MATLAB that allows grid planners and operators to simulate the variability of photovoltaic systems. Data can be input as a text file, but the interface also allows users to simply draw a polygon around each system on a satellite Google Map. Based on solar radiation measurements at a single sensor on a given day, the model calculates the variability in total output across all systems.
“It is as easy as painting by numbers,” said Kleissl. “In Google Maps, photovoltaics show up as dark rectangles on rooftops. Draw some polygons around them, push the button, and out comes the total variability.”
Kleissl said he anticipates this tool will be useful to figure out whether problems in voltage fluctuation may occur in power feeder systems with a large amount of photovoltaic arrays. At this point, the solar installations on almost all feeders are still far below the capacity that would cause any major issues. But as the United States moves to affordable solar systems producing energy at lower costs through the Department of Energy’s SunShot initiative and continued robust growth in installations, this will change. That’s when the tool developed by Lave and Kleissl could become key.
The model development was sponsored by DOE’s High PV Penetration Program grant 10DE-EE002055. Further information is available at and
While the tool is being prepared for final public release, the authors would be happy to consider requests by third parties that can provide PV system location and size data to run the tool.

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Researchers create tool to put the lid on solar power fluctuations

New solar cell: Engineers crack full-spectrum solar challenge

The U of T researchers, led by Professor Ted Sargent, report the first efficient tandem solar cell based on colloidal quantum dots (CQD). “The U of T device is a stack of two light-absorbing layers — one tuned to capture the sun’s visible rays, the other engineered to harvest the half of the sun’s power that lies in the infrared,” said lead author Dr. Xihua Wang.
“We needed a breakthrough in architecting the interface between the visible and infrared junction,” said Sargent, a Professor of Electrical and Computer Engineering at the University of Toronto, who is also the Canada Research Chair in Nanotechnology. “The team engineered a cascade — really a waterfall — of nanometers-thick materials to shuttle electrons between the visible and infrared layers.”
According to doctoral student Ghada Koleilat, “We needed a new strategy — which we call the Graded Recombination Layer — so that our visible and infrared light-harvesters could be linked together efficiently, without any compromise to either layer.”
The team pioneered solar cells made using CQD, nanoscale materials that can readily be tuned to respond to specific wavelengths of the visible and invisible spectrum. By capturing such a broad range of light waves — wider than normal solar cells — tandem CQD solar cells can in principle reach up to 42 per cent efficiencies. The best single-junction solar cells are constrained to a maximum of 31 per cent efficiency. In reality, solar cells that are on the roofs of houses and in consumer products have 14 to 18 per cent efficiency. The work expands the Toronto team’s world-leading 5.6 per cent efficient colloidal quantum dot solar cells.
“Building efficient, cost-effective solar cells is a grand global challenge. The University of Toronto is extremely proud of its world-class leadership in the field,” said Professor Farid Najm, Chair of The Edward S. Rogers Sr. Department of Electrical & Computer Engineering.
Sargent is hopeful that in five years solar cells using the graded recombination layer published in the Nature Photonics paper will be integrated into building materials, mobile devices, and automobile parts.
“The solar community — and the world — needs a solar cell that is over 10% efficient, and that dramatically improves on today’s photovoltaic module price points,” said Sargent. “This advance lights up a practical path to engineering high-efficiency solar cells that make the best use of the diverse photons making up the sun’s broad palette.”
The publication was based in part on work supported by an award made by the King Abdullah University of Science and Technology (KAUST), by the Ontario Research Fund Research Excellence Program, and by the Natural Sciences and Engineering Research Council (NSERC) of Canada. Equipment from Angstrom Engineering and Innovative Technology enabled the research.

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New solar cell: Engineers crack full-spectrum solar challenge

Metal particle generates new hope for hydrogen energy

Led by Associate Professor Greg Metha, Head of Chemistry, the researchers are exploring how the metal nanoparticles act as highly efficient catalysts in using solar radiation to split water into hydrogen and oxygen. “Efficient and direct production of hydrogen from solar radiation provides a renewable energy source that is the pinnacle of clean energy,” said Associate Professor Greg Metha. “We believe this work will contribute significantly to the global effort to convert solar energy into portable chemical energy.”

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Inkjet printing could change the face of solar energy industry

Inkjet printers, a low-cost technology that in recent decades has revolutionized home and small office printing, may soon offer similar benefits for the future of solar energy. Engineers at Oregon State University have discovered a way for the first time to create successful “CIGS” solar devices with inkjet printing, in work that reduces raw material waste by 90 percent and will significantly lower the cost of producing solar energy cells with some very promising compounds.

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Putting sunshine in the tank

The researchers are working on harnessing the vast energy of the Sun to produce clean fuel. The scientists are presenting their research at the Royal Society’s annual Summer Science Exhibition . There aim is to use the same technology to create alternatives for other fuels and feedstock chemicals, including turning methane into liquid methanol and carbon dioxide into carbon monoxide.

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Putting sunshine in the tank

‘Cling-film’ solar cells could lead to advance in renewable energy

A scientific advance in renewable energy which promises a revolution in the ease and cost of using solar cells, has been announced. A new study shows that even when using very simple and inexpensive manufacturing methods — where flexible layers of material are deposited over large areas like cling-film — efficient solar cell structures can be made.
The study, published in the journal Advanced Energy Materials, paves the way for new solar cell manufacturing techniques and the promise of developments in renewable solar energy. Scientists from the Universities of Sheffield and Cambridge used the ISIS Neutron Source and Diamond Light Source at STFC Rutherford Appleton Laboratory in Oxfordshire to carry out the research.
Plastic (polymer) solar cells are much cheaper to produce than conventional silicon solar cells and have the potential to be produced in large quantities. The study showed that when complex mixtures of molecules in solution are spread onto a surface, like varnishing a table-top, the different molecules separate to the top and bottom of the layer in a way that maximises the efficiency of the resulting solar cell.
Dr Andrew Parnell of the University of Sheffield said, “Our results give important insights into how ultra-cheap solar energy panels for domestic and industrial use can be manufactured on a large scale. Rather than using complex and expensive fabrication methods to create a specific semiconductor nanostructure, high volume printing could be used to produce nano-scale (60 nano-meters) films of solar cells that are over a thousand times thinner than the width of a human hair. These films could then be used to make cost-effective, light and easily transportable plastic solar cell devices such as solar panels.”
Dr. Robert Dalgliesh, one of the ISIS scientists involved in the work, said, “This work clearly illustrates the importance of the combined use of neutron and X-ray scattering sources such as ISIS and Diamond in solving modern challenges for society. Using neutron beams at ISIS and Diamond’s bright X-rays, we were able to probe the internal structure and properties of the solar cell materials non-destructively. By studying the layers in the materials which convert sunlight into electricity, we are learning how different processing steps change the overall efficiency and affect the overall polymer solar cell performance. ”
“Over the next fifty years society is going to need to supply the growing energy demands of the world’s population without using fossil fuels, and the only renewable energy source that can do this is the Sun,” said Professor Richard Jones of the University of Sheffield. ” In a couple of hours enough energy from sunlight falls on the Earth to satisfy the energy needs of the Earth for a whole year, but we need to be able to harness this on a much bigger scale than we can do now. Cheap and efficient polymer solar cells that can cover huge areas could help move us into a new age of renewable energy.”

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‘Cling-film’ solar cells could lead to advance in renewable energy

New way to store sun’s heat: Modified carbon nanotubes can store solar energy indefinitely, then be recharged by exposure to the sun

A novel application of carbon nanotubes, developed by MIT researchers, shows promise as an innovative approach to storing solar energy for use whenever it’s needed.
Storing the sun’s heat in chemical form — rather than converting it to electricity or storing the heat itself in a heavily insulated container — has significant advantages, since in principle the chemical material can be stored for long periods of time without losing any of its stored energy. The problem with that approach has been that until now the chemicals needed to perform this conversion and storage either degraded within a few cycles, or included the element ruthenium, which is rare and expensive.
Last year, MIT associate professor Jeffrey Grossman and four co-authors figured out exactly how fulvalene diruthenium — known to scientists as the best chemical for reversibly storing solar energy, since it did not degrade — was able to accomplish this feat. Grossman said at the time that better understanding this process could make it easier to search for other compounds, made of abundant and inexpensive materials, which could be used in the same way.
Now, he and postdoc Alexie Kolpak have succeeded in doing just that. A paper describing their new findings has just been published online in the journal Nano Letters, and will appear in print in a forthcoming issue.
The new material found by Grossman and Kolpak is made using carbon nanotubes, tiny tubular structures of pure carbon, in combination with a compound called azobenzene. The resulting molecules, produced using nanoscale templates to shape and constrain their physical structure, gain “new properties that aren’t available” in the separate materials, says Grossman, the Carl Richard Soderberg Associate Professor of Power Engineering.
Not only is this new chemical system less expensive than the earlier ruthenium-containing compound, but it also is vastly more efficient at storing energy in a given amount of space — about 10,000 times higher in volumetric energy density, Kolpak says — making its energy density comparable to lithium-ion batteries. By using nanofabrication methods, “you can control [the molecules’] interactions, increasing the amount of energy they can store and the length of time for which they can store it — and most importantly, you can control both independently,” she says.
Thermo-chemical storage of solar energy uses a molecule whose structure changes when exposed to sunlight, and can remain stable in that form indefinitely. Then, when nudged by a stimulus — a catalyst, a small temperature change, a flash of light — it can quickly snap back to its other form, releasing its stored energy in a burst of heat. Grossman describes it as creating a rechargeable heat battery with a long shelf life, like a conventional battery.
One of the great advantages of the new approach to harnessing solar energy, Grossman says, is that it simplifies the process by combining energy harvesting and storage into a single step. “You’ve got a material that both converts and stores energy,” he says. “It’s robust, it doesn’t degrade, and it’s cheap.” One limitation, however, is that while this process is useful for heating applications, to produce electricity would require another conversion step, using thermoelectric devices or producing steam to run a generator.
While the new work shows the energy-storage capability of a specific type of molecule — azobenzene-functionalized carbon nanotubes — Grossman says the way the material was designed involves “a general concept that can be applied to many new materials.” Many of these have already been synthesized by other researchers for different applications, and would simply need to have their properties fine-tuned for solar thermal storage.
The key to controlling solar thermal storage is an energy barrier separating the two stable states the molecule can adopt; the detailed understanding of that barrier was central to Grossman’s earlier research on fulvalene dirunthenium, accounting for its long-term stability. Too low a barrier, and the molecule would return too easily to its “uncharged” state, failing to store energy for long periods; if the barrier were too high, it would not be able to easily release its energy when needed. “The barrier has to be optimized,” Grossman says.
Already, the team is “very actively looking at a range of new materials,” he says. While they have already identified the one very promising material described in this paper, he says, “I see this as the tip of the iceberg. We’re pretty jazzed up about it.”
Yosuke Kanai, assistant professor of chemistry at the University of North Carolina at Chapel Hill, says “the idea of reversibly storing solar energy in chemical bonds is gaining a lot of attention these days. The novelty of this work is how these authors have shown that the energy density can be significantly increased by using carbon nanotubes as nanoscale templates. This innovative idea also opens up an interesting avenue for tailoring already-known photoactive molecules for solar thermal fuels and storage in general.”

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New way to store sun’s heat: Modified carbon nanotubes can store solar energy indefinitely, then be recharged by exposure to the sun

Power from the air: Device captures ambient electromagnetic energy to drive small electronic devices

Researchers have discovered a way to capture and harness energy transmitted by such sources as radio and television transmitters, cell phone networks and satellite communications systems. By scavenging this ambient energy from the air around us, the technique could provide a new way to power networks of wireless sensors, microprocessors and communications chips.
“There is a large amount of electromagnetic energy all around us, but nobody has been able to tap into it,” said Manos Tentzeris, a professor in the Georgia Tech School of Electrical and Computer Engineering who is leading the research. “We are using an ultra-wideband antenna that lets us exploit a variety of signals in different frequency ranges, giving us greatly increased power-gathering capability.”
Tentzeris and his team are using inkjet printers to combine sensors, antennas and energy scavenging capabilities on paper or flexible polymers. The resulting self powered wireless sensors could be used for chemical, biological, heat and stress sensing for defense and industry; radio frequency identification (RFID) tagging for manufacturing and shipping, and monitoring tasks in many fields including communications and power usage.
A presentation on this energy scavenging technology was given July 6 at the IEEE Antennas and Propagation Symposium in Spokane, Wash. The discovery is based on research supported by multiple sponsors, including the National Science Foundation, the Federal Highway Administration and Japan’s New Energy and Industrial Technology Development Organization (NEDO).
Communications devices transmit energy in many different frequency ranges, or bands. The team’s scavenging devices can capture this energy, convert it from AC to DC, and then store it in capacitors and batteries. The scavenging technology can take advantage presently of frequencies from FM radio to radar, a range spanning 100 megahertz (MHz) to 15 gigahertz (GHz) or higher.
Scavenging experiments utilizing TV bands have already yielded power amounting to hundreds of microwatts, and multi-band systems are expected to generate one milliwatt or more. That amount of power is enough to operate many small electronic devices, including a variety of sensors and microprocessors.
And by combining energy scavenging technology with supercapacitors and cycled operation, the Georgia Tech team expects to power devices requiring above 50 milliwatts. In this approach, energy builds up in a battery-like supercapacitor and is utilized when the required power level is reached.
The researchers have already successfully operated a temperature sensor using electromagnetic energy captured from a television station that was half a kilometer distant. They are preparing another demonstration in which a microprocessor-based microcontroller would be activated simply by holding it in the air.
Exploiting a range of electromagnetic bands increases the dependability of energy scavenging devices, explained Tentzeris, who is also a faculty researcher in the Georgia Electronic Design Center at Georgia Tech. If one frequency range fades temporarily due to usage variations, the system can still exploit other frequencies.
The scavenging device could be used by itself or in tandem with other generating technologies. For example, scavenged energy could assist a solar element to charge a battery during the day. At night, when solar cells don’t provide power, scavenged energy would continue to increase the battery charge or would prevent discharging.
Utilizing ambient electromagnetic energy could also provide a form of system backup. If a battery or a solar-collector/battery package failed completely, scavenged energy could allow the system to transmit a wireless distress signal while also potentially maintaining critical functionalities.
The researchers are utilizing inkjet technology to print these energy scavenging devices on paper or flexible paper-like polymers — a technique they already using to produce sensors and antennas. The result would be paper-based wireless sensors that are self powered, low cost and able to function independently almost anywhere.
To print electrical components and circuits, the Georgia Tech researchers use a standard materials inkjet printer. However, they add what Tentzeris calls “a unique in house recipe” containing silver nanoparticles and/or other nanoparticles in an emulsion. This approach enables the team to print not only RF components and circuits, but also novel sensing devices based on such nanomaterials as carbon nanotubes.
When Tentzeris and his research group began inkjet printing of antennas in 2006, the paper-based circuits only functioned at frequencies of 100 or 200 MHz, recalled Rushi Vyas, a graduate student who is working with Tentzeris and graduate student Vasileios Lakafosis on several projects.
“We can now print circuits that are capable of functioning at up to 15 GHz — 60 GHz if we print on a polymer,” Vyas said. “So we have seen a frequency operation improvement of two orders of magnitude.”
The researchers believe that self-powered, wireless paper-based sensors will soon be widely available at very low cost. The resulting proliferation of autonomous, inexpensive sensors could be used for applications that include:
Airport security: Airports have both multiple security concerns and vast amounts of available ambient energy from radar and communications sources. These dual factors make them a natural environment for large numbers of wireless sensors capable of detecting potential threats such as explosives or smuggled nuclear material.
Energy savings: Self-powered wireless sensing devices placed throughout a home could provide continuous monitoring of temperature and humidity conditions, leading to highly significant savings on heating and air conditioning costs. And unlike many of today’s sensing devices, environmentally friendly paper-based sensors would degrade quickly in landfills.
Structural integrity: Paper or polymer-based sensors could be placed throughout various types of structures to monitor stress. Self powered sensors on buildings, bridges or aircraft could quietly watch for problems, perhaps for many years, and then transmit a signal when they detected an unusual condition.
Food and perishable material storage and quality monitoring: Inexpensive sensors on foods could scan for chemicals that indicate spoilage and send out an early warning if they encountered problems.
Wearable bio-monitoring devices: This emerging wireless technology could become widely used for autonomous observation of patient medical issues.

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Power from the air: Device captures ambient electromagnetic energy to drive small electronic devices

Improved hybrid solar collector has higher efficiency, longer lifespan

For his graduation project, TU Delft student of Sustainable Energy Technology Stefan Roest developed a new type of hybrid solar collector with a higher efficiency and a longer lifespan than the current hybrid systems. Hybrid solar collectors combine photovoltaic solar cells that convert sunlight into electricity with a solar heater that provides warm water.
Roest built a prototype and also built an actual solar simulator that he used to test the efficiency of his prototype. There turned out to be considerable commercial interest in this solar simulator. This motivated Roest and a partner to start the TU Delft spin-off company Eternal Sun, so they could put the solar simulator on the market. Eternal Sun recently came out on top at the European finals of the BE.Project, a competition for student-entrepreneurs.
Solar collector
A hybrid solar collector is a combination of a photovoltaic solar panel and a thermal solar collector. The residual heat from the PV solar panel is used to heat water. The water flows through a system of pipes on a copper sheet. A great deal of heat is needed to heat the water in the pipes. That is why the solar collector has been fitted with a transparent cover that helps to retain the heat. Unfortunately, the material used in the PV solar cell degrades quickly under temperatures of around 120 degrees. As a result, its efficiency is reduced by around 20 per cent and it has a lifespan of between five and ten years.
For his graduation research as part of a Master’s degree in Sustainable Energy Technology, Stefan Roest developed a new type of hybrid solar collector with increased electrical efficiency and a longer lifespan. For a start, Roest’s solar collector does not require a transparent cover. The water flows through a large number of small aluminium channels directly under the solar panel instead of through copper tubing and a copper sheet. Consequently, less heat is required to heat the water sufficiently for household use. Roest also chose not to use a crystalline silicon PV solar panel, opting for a thin film solar panel instead. It is easier to draw heat from this type of solar cell. Getting rid of the cover meant that the heat of the solar panel could be limited to around 80 degrees.
An additional benefit of thin film solar panels is that these perform relatively well at high temperatures. At a temperature of 80 degrees, an efficiency loss of around 10 per cent occurs, instead of the 20 per cent in the case of crystalline silicon solar panels. Roest’s hybrid solar collector has an estimated lifespan of 15 to 20 years.
Roest developed the new solar collector under the supervision of the professor of Photovoltaic Materials and Devices, Miro Zeman, who comments: “This innovative design could play an important role in the development of affordable and efficient hybrid systems for household use.”
Solar simulator
Roest developed a special solar simulator to measure the efficiency of his prototype. Almost immediately, there was commercial interest in this simulator and the relevant technology was quickly patented by TU Delft. Roest and his partner Chokri Mousaoui have since introduced the simulator onto the market via their TU Delft spin-off company Eternal Sun. Eternal Sun recently came out on top in the European finals of the BE.Project competition for students from top universities with an innovative business case, which was organised by the technology consulting company BearingPoint. The Eternal Sun team has now grown to include six students and recent graduates, and five solar simulators have already been sold since January.
Roest’s affinity with solar energy goes back quite a while. In 2007, he was the team leader of the Nuon Solar Team that won the World Solar Challenge in Australia with the solar car Nuna4.

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Improved hybrid solar collector has higher efficiency, longer lifespan

Transition to renewable energy stimulates the economy, German researchers say

The transition to renewable energy is set to deliver an economic pay off as well in the years to come. Various studies show that a shift to alternative energy sources will raise the GNP in the coming decade and create new jobs, as Prof. Eicke Weber, spokesperson for the Fraunhofer Energy Alliance, points out. Fraunhofer scientists are developing concepts and solutions for the transition as it takes shape.
The disaster at Fukushima has raised public awareness and made the shift to renewable sources of energy more desirable than ever. It is accompanied, too, by a political willingness to rethink and correct the policies followed until now. The question is often posed in public debate as to whether the shift to renewable energies will be too expensive, or whether it indeed poses a threat to Germany’s competitiveness as an industrial location.
Over the last two years, however, studies have suggested that fears of this sort are unfounded. On the contrary, according to an EU study performed by the Fraunhofer Institute for Systems and Innovation Research ISI in Karlsruhe, a shift towards renewable energies will stimulate growth in the job market in the coming decade. By 2020 scientists predict that some 2.8 million people will be employed in Europe’s renewable energy sector, once implementation of EU objectives in this area has taken hold. The negative impact of a shift to alternative energy is far outweighed by the remaining positive net effect of some 400,000 additional jobs in the EU as a whole. What is more, Europe’s GDP is expected to grow by 0.24 % (some 35 billion Euro).
Similar results were reported in a study of Germany contracted by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety BMU, in which ISI scientists participated. One of the study’s findings showed that “the short and long-term effects on the German labor market derived from expansion of renewable energy use, indicate a positive trend. When all negative effects and influences on the economic cycle are taken into account, the number still falls in the range of 120.000 — 140,000 new jobs (2020, optimistic scenario, price path A).”
Presenting the study’s finding at a press conference, Fraunhofer President Prof. Hans-Jörg Bullinger emphasized the Fraunhofer-Gesellschaft’s committed efforts in this field of research: “We are perfectly positioned to develop concepts and solutions for a transition to renewable energy. Within the Fraunhofer Energy Alliance alone there are some 2000 scientists from 16 organizations whose work is focused in this sector. They develop system technologies such as power grids and energy storage systems and research new ways to increase energy efficiency. There are also additional teams of scientists from the Building Innovation and Traffic and Transport Alliances, who also devote a significant part of their work to the question of energy.”
Renewable energy is affordable
“The transition to sustainable energy supplies is one of the greatest challenges of the 21st century,” asserts Prof. Eicke Weber, spokesperson for the Fraunhofer Energy Alliance and Director of the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg. “To keep electricity, heat and transportation prices affordable in the future, we have to use energy more efficiently and devote more research to the development of renewable sources.” Dr. Mario Ragwitz of the ISI, who coordinated the EU study, further emphasizes, “We must sustain investment in renewable energy. And we must be patient.” But it is worth the effort, not only to secure the supply of raw materials and to protect the environment, but also economically from a mid- to long-term perspective, a conclusion also reached in a study by the Renewable Energy Research Association FVEE.
Another study entitled “Vision for a 100 percent renewable energy system,” illustrates how a reliable, affordable and robust energy supply based on renewable sources can be achieved in Germany by the year 2050. “The expansion of renewable energy creates additional costs initially; however, costs should peak in 2015 at a total of about 17 billion Euro. That is only about eight percent of total costs for energy in Germany, and costs will sink again after that. Between 2010 and 2050, overall savings of some 730 billion Euro can be achieved in the electricity and heating sectors alone,” reports Prof. Jürgen Schmid, Director of the Fraunhofer Institute for Wind Energy and Energy System Technology IWES in Kassel, summarizing the results of the study.
Solar energy will become increasingly more competitive
It is also clear that the costs of renewable energy will fall. “We predict, for example, that the price trend for photovoltaic modules (PV) will continue to follow a price-learning curve in the years ahead,” says Eicke Weber. This trend assumes that the price of PV modules, currently between € 1.50 und € 2.00/Wp (net), could fall below € 1.00/Wp as early as 2016, which would put electricity generation costs in Germany in a range between 11 and 14 cents per kilowatt hour. The prerequisites for this reduction in costs are the further development of production, effective utilization of production capacities through corresponding growth in the global PV market, the continual implementation of technological innovations in production, and minimization of production processes and costs.
“These goals present a significant challenge to the PV industry, but they are attainable with advances in technology.” Optimizing the costs of supplying power will necessarily lead to a greater percentage of PV in the power mix, according the ISE. “Photovoltaic energy will not only lower electricity production costs in Germany in the future, while offering the benefits of being both free of emissions and noise pollution, it also makes it possible to decentralize the generation of electricity and decrease grid load. Capacities can also be built up rapidly with minimal impact on nature,” says Weber. The minimum percentage for a sensible PV share in the power mix is 14 percent, but in principle researchers at the ISE find a PV ratio of over 30 percent feasible in the medium term.
High standards for wind power stations
With a share of 6.4 percent, wind power in Germany holds first place in power production from renewable sources. “Wind power is already relatively inexpensive. Depending on the location, generating electricity with wind costs between 3 and 6 cents per kilowatt hour,” says Jürgen Schmid. In a new study by the German Wind Energy Association (BWE), experts from the IWES have shown that, according to geo-data, about 8 percent of the land area in Germany outside of forests and protected areas is available for use in wind energy generation. Using just 2 percent of the area per state would yield 198 gigawatts of installable output. In purely mathematical terms, then, onshore wind power could contribute about 390 terawatt hours to Germany’s annual energy consumption, which currently lies at about 600 terawatt hours.
The study makes clear that the potential of onshore wind power is by far not yet exhausted. “Currently, there are just 28 gigawatts of installed wind power,” confirms Dr. Kurt Rohrig, who led the study and summarized the results. In addition, massive wind farms are to be built offshore, which will generate some 20 to 25 gigawatts, or about 15 percent of Germany’s energy needs by the year 2030, according to targets set by BMU. The first German offshore wind farm, alpha ventus, was completed in 2010 and serves as both a demonstration and research platform. The related BMU research initiative is coordinated by the IWES.
Offshore wind farms present a particularly urgent need for innovation. They have to be designed and constructed to withstand wind, water, salt, UV radiation and waves over their entire life-span of some 20 years. A special offshore test chamber has been developed at the IWES in Bremerhaven that makes it possible for the first time to simultaneously simulate the changing mechanical and climatic stress factors to which the systems are exposed. Components are exposed to salt spray mist, waves, UV light and moisture, while at the same time being bent and stretched. The simulation allows researchers to draw conclusions about the reliability and durability of the systems being tested. In other test facilities for mechanical stress on large-scale rotor blades, static and dynamic tests are performed with millions of load alternations at various amplitudes. The facilities accommodate rotor blades up to 70 meters long. A new facility for blade lengths of up to 90 meters will go into operation on 9 June 2011. “The new site will give us the largest test facilities in Europe for rotor blades used in systems working at outputs of up to around 10 megawatts,” says Prof. Andreas Reuter, Director of the IWES in Bremerhaven.
New, intelligent networks and storage devices
A decentralized energy supply derived from renewable sources requires a different grid structure than those currently available, which are designed for a few central large-scale power plants. In the future, a large number of solar, wind, and biomass power plants will have to be coordinated so that predictions on their yield and load can be reasonably balanced. Gaps in supply arising from irregularities in the availability of sun and wind must be compensated for with quick intermediate energy supplies and control plants.
“We do not need nuclear power as a transitional technology,” agree Institute Directors Eicke Weber und Jürgen Schmid. They believe the rapid build-up of renewable sources witnessed in the last years will more likely be impeded by the lack of flexibility of nuclear power plants. Gas-fired combined heat and power systems in combination with storage units and network expansion are more suitable transitional technologies.
Ultimately, it is about making networks more intelligent with a good deal of technical finesse. Experts refer to a smart grid through which the many power generating systems and consumers communicate and match their requirements between themselves in accordance with the availability of wind or sun power. A good deal of research still needs to be done here. Fraunhofer is working intensively on the development and implementation of new concepts.
Scientists at the IWES, for example, are participating in the new research project “Kombikraftwerk 2” together with nine other partners in industry and science. The project employs models and field tests to network wind, biogas and solar power systems using modern data and communications technologies, bringing them together to create a virtual unit which functions like a power plant. Researchers hope to demonstrate in detail that complete coverage of our energy needs with renewable energy sources is realistic and that the lights won’t go out even if the wind lies down and sunlight is scarce.
Redox flow batteries, for example, may be well-suited to providing the necessary temporary energy storage. These are large, robust, long-life vanadium flow batteries in which chemical vanadium compounds alternately absorb and discharge electrons across a membrane. Several Fraunhofer institutes are cooperating in the development of these flow batteries. The researchers’ long-term goal is to construct a battery facility with the size of a handball field. It would have a capacity of 20 megawatt hours, sufficient to meet the energy needs of about 2000 homes during a long winter night or a cloudy day. But, they are not quite that far yet. The largest laboratory facilities at the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT in Oberhausen currently produce several kilowatts of power. Researchers hope to reach megawatt levels in about five years.
Unconventional thinking for a new energy supply
There is a call, too, for innovative ideas that draw on as yet untapped potential. One possibility would be to use the heat storage capacity of buildings in an intelligent network as passive energy storage via electric heat pumps and intelligent energy meters. Researchers at the ISE are currently investigating the potential for remote storage employing tariff-controlled heat pumps. Yet another possibility involves using the batteries of tomorrow’s electric cars as energy storage devices when they are connected to the power grid.
A further unconventional idea is to use any surplus electricity for the electrolysis of water. The hydrogen derived would be used together with carbon dioxide to produce methane in massive volume that can be put to use to store energy in chemical form or be fed into existing natural gas grids. This would make use of today’s existing natural gas infrastructure and its immense capacity to store energy, while significantly reducing our dependence on imported gas.
All efforts towards sustainable energy must naturally be accompanied by reductions in consumption and improved efficiency. How this might look in practice has been demonstrated by the ISE through its participation in the refurbishment of energy systems in a 16-storey apartment building in Weingarten, a district of Freiburg. Primary energy needs for heating, warm water, ventilation, lighting and household electricity were reduced by 40 percent. In the next two years, ISE scientists will record and analyze the building’s energy consumption under real operating conditions. Results of the study, as with the project as a whole, will serve as a model and be taken into account in similar energy system renovation plans.

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