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  • richardmitnick 9:19 am on April 10, 2017 Permalink | Reply
    Tags: , , , Nanoporous materials, , Solar Energy, , Stanford scientist’s new approach may accelerate design of high-power batteries, Storing electricity, Supercapacitors   

    From Stanford: “Stanford scientist’s new approach may accelerate design of high-power batteries” 

    Stanford University Name
    Stanford University

    April 6, 2017
    Danielle Torrent Tucker

    1
    Electric vehicles plug in to charging stations. New research may accelerate discovery of materials used in electrical storage devices, such as car batteries. (Image credit: Shutterstock)

    In work published this week in Applied Physics Letters, the researchers describe a mathematical model for designing new materials for storing electricity. The model could be a huge benefit to chemists and materials scientists, who traditionally rely on trial and error to create new materials for batteries and capacitors. Advancing new materials for energy storage is an important step toward reducing carbon emissions in the transportation and electricity sectors.

    “The potential here is that you could build batteries that last much longer and make them much smaller,” said study co-author Daniel Tartakovsky, a professor in the School of Earth, Energy & Environmental Sciences. “If you could engineer a material with a far superior storage capacity than what we have today, then you could dramatically improve the performance of batteries.”

    Lowering a barrier

    One of the primary obstacles to transitioning from fossil fuels to renewables is the ability to store energy for later use, such as during hours when the sun is not shining in the case of solar power. Demand for cheap, efficient storage has increased as more companies turn to renewable energy sources, which offer significant public health benefits.

    Tartakovsky hopes the new materials developed through this model will improve supercapacitors, a type of next-generation energy storage that could replace rechargeable batteries in high-tech devices like cellphones and electric vehicles. Supercapacitors combine the best of what is currently available for energy storage – batteries, which hold a lot of energy but charge slowly, and capacitors, which charge quickly but hold little energy. The materials must be able to withstand both high power and high energy to avoid breaking, exploding or catching fire.

    “Current batteries and other storage devices are a major bottleneck for transition to clean energy,” Tartakovsky said. “There are many people working on this, but this is a new approach to looking at the problem.”

    The types of materials widely used to develop energy storage, known as nanoporous materials, look solid to the human eye but contain microscopic holes that give them unique properties. Developing new, possibly better nanoporous materials has, until now, been a matter of trial and error – arranging minuscule grains of silica of different sizes in a mold, filling the mold with a solid substance and then dissolving the grains to create a material containing many small holes. The method requires extensive planning, labor, experimentation and modifications, without guaranteeing the end result will be the best possible option.

    “We developed a model that would allow materials chemists to know what to expect in terms of performance if the grains are arranged in a certain way, without going through these experiments,” Tartakovsky said. “This framework also shows that if you arrange your grains like the model suggests, then you will get the maximum performance.”

    Beyond energy

    Energy is just one industry that makes use of nanoporous materials, and Tartakovsky said he hopes this model will be applicable in other areas, as well.

    “This particular application is for electrical storage, but you could also use it for desalination, or any membrane purification,” he said. “The framework allows you to handle different chemistry, so you could apply it to any porous materials that you design.”

    Tartakovsky’s mathematical modeling research spans neuroscience, urban development, medicine and more. As an Earth scientist and professor of energy resources engineering, he is an expert in the flow and transport of porous media, knowledge that is often underutilized across disciplines, he said. Tartakovsky’s interest in optimizing battery design stemmed from collaboration with a materials engineering team at the University of Nagasaki in Japan.

    “This Japanese collaborator of mine had never thought of talking to hydrologists,” Tartakovsky said. “It’s not obvious unless you do equations – if you do equations, then you understand that these are similar problems.”

    The lead author of the study, “Optimal design of nanoporous materials for electrochemical devices,” is Xuan Zhang, Tartakovsky’s former PhD student at the University of California, San Diego. The research was supported by the Defense Advanced Research Projects Agency and the National Science Foundation.

    See the full article here .

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    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

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  • richardmitnick 9:18 am on January 25, 2017 Permalink | Reply
    Tags: , , Electron holes, How solar cells turn sunlight into electricity, Negative and positive silicon or n- and p-type silicon, Solar Energy   

    From COSMOS: “How solar cells turn sunlight into electricity” 

    Cosmos Magazine bloc

    COSMOS

    25 January 2017
    Andrew Stapleton

    1
    Some solar power plants contain more than a million panels. But how do they convert the sun’s energy to electricity? Rolfo Brenner / EyeEm / Getty Images

    Renewables have overtaken coal as the world’s largest source of electricity generation capacity. And about 30% of that capacity is due to silicon solar cells. But how do silicon cells work?

    A silicon cell is like a four-part sandwich. The bread on either side consists of thin strips of metallic electrodes. They extract the power generated within the solar cell and conduct it to an external circuit.

    Just like a sandwich, it’s the filling which is the most interesting part – this is where photons from the sun are converted into usable electricity. The filling of a solar cell consists of two different layers of silicon: negative and positive silicon, or n- and p-type silicon.

    2
    Credit: COSMOS MAGAZINE

    Creating positive or negative types of silicon is relatively easy. The silicon is impregnated with elements known as dopants. Dopants replace some of the silicon atoms in the crystal structure, allowing the number of electrons present in each layer to be manipulated.

    For instance, phosphorus is used to create n-type silicon while boron is used to create p-type silicon. Phosphorus has one more electron than silicon. When substituted into the silicon structure, the electron is so weakly bound to the phosphorus that it can move freely within the crystal, creating a negative charge.

    On the other hand, boron has fewer electrons than silicon and sucks up silicon’s electrons. This creates “electron holes” – regions of mobile positive charge in the crystal structure.

    At the interface of the p- and n- type silicon, the positive electron holes and the electrons combine. It’s not a simple electrostatic interaction, but the upshot is that you get a slightly positive charge in the n-type silicon and a slightly negative charge in the p-type silicon at the interface of the n- and p- type silicon – the opposite of what you might expect.

    Photons from the sun pass between the strips of the top electrode and strike silicon atoms in the crystal structure. Like the strike of a cue ball, the colliding photon gives some of the silicon electrons enough energy to escape from their parent silicon atom.

    The “free” electrons move to and accumulate within the n-type silicon.

    Once free electrons have accumulated in the n-type silicon, it’s time to put all the free electrons to work. In order to use their energy, the electrodes must be connected via an external circuit. Electrons flow through the electrodes and the external electric circuit from the n-type to the p-type. The p-type silicon acts as an electron sink. Without it, the electron flow would clog up.

    It is this flow of electrons that creates the electrical current we can use to power appliances or charge batteries for when the sun isn’t shining.

    See the full article here .

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  • richardmitnick 3:08 pm on August 25, 2016 Permalink | Reply
    Tags: , , Solar Energy   

    From EPFL: “An effective and low-cost solution for storing solar energy” 

    EPFL bloc

    École Polytechnique Fédérale de Lausanne EPFL

    25.08.16
    Laure-Anne Pessina

    1
    An effective and low-cost solution for storing solar energy © Infini Lab / 2016 EPFL

    Solar energy can be stored by converting it into hydrogen. But current methods are too expensive and don’t last long. Using commercially available solar cells and none of the usual rare metals, researchers at EPFL and CSEM have now designed a device that outperforms in stability, efficiency and cost.

    How can we store solar energy for period when the sun doesn’t shine? One solution is to convert it into hydrogen through water electrolysis. The idea is to use the electrical current produced by a solar panel to ‘split’ water molecules into hydrogen and oxygen. Clean hydrogen can then be stored away for future use to produce electricity on demand, or even as a fuel.

    But this is where things get complicated. Even though different hydrogen-production technologies have given us promising results in the lab, they are still too unstable or expensive and need to be further developed to use on a commercial and large scale.

    The approach taken by EPFL and CSEM researchers is to combine components that have already proven effective in industry in order to develop a robust and effective system. Their prototype is made up of three interconnected, new-generation, crystalline silicon solar cells attached to an electrolysis system that does not rely on rare metals. The device is able to convert solar energy into hydrogen at a rate of 14.2%, and has already been run for more than 100 hours straight under test conditions. The method, which surpasses previous efforts in terms of stability, performance, lifespan and cost efficiency, is published in the Journal of The Electrochemical Society.

    Enough to power a fuel cell car over 10,000km every year

    “A 12-14 m2 system installed in Switzerland would allow the generation and storage of enough hydrogen to power a fuel cell car over 10,000 km every year”, says Christophe Ballif, who co-authored the paper. In terms of performance, this is a world record for silicon solar cells and for hydrogen production without using rare metals. It also offers a high level of stability.

    High voltage cells have an edge

    The key here is making the most of existing components, and using a ‘hybrid’ type of crystalline-silicon solar cell based on heterojunction technology. The researchers’ sandwich structure – using layers of crystalline silicon and amorphous silicon – allows for higher voltages. And this means that just three of these cells, interconnected, can already generate an almost ideal voltage for electrolysis to occur. The electrochemical part of the process requires a catalyst made from nickel, which is widely available.

    “With conventional crystalline silicon cells, we would have to link up four cells to get the same voltage,” says co-author Miguel Modestino at EPFL.“So that’s the strength of this method.”

    A stable and economically viable method

    The new system is unique when it comes to cost, performance and lifespan. “We wanted to develop a high performance system that can work under current conditions,” says Jan-Willem Schüttauf, a researcher at CSEM and co-author of the paper. “The heterojunction cells that we use belong to the family of crystalline silicon cells, which alone account for about 90% of the solar panel market. It is a well-known and robust technology whose lifespan exceeds 25 years. And it also happens to cover the south side of the CSEM building in Neuchâtel.”

    The researchers used standard heterojunction cells to prove the concept; by using the best cells of that type, they would expect to achieve a performance above 16%.

    The research is part of the nano-tera SHINE project.

    See the full article here .

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    EPFL is Europe’s most cosmopolitan technical university with students, professors and staff from over 120 nations. A dynamic environment, open to Switzerland and the world, EPFL is centered on its three missions: teaching, research and technology transfer. EPFL works together with an extensive network of partners including other universities and institutes of technology, developing and emerging countries, secondary schools and colleges, industry and economy, political circles and the general public, to bring about real impact for society.

     
  • richardmitnick 10:09 am on June 30, 2016 Permalink | Reply
    Tags: , , Financial Review, Solar Energy   

    From CSIRO via Financial Review: “CSIRO shows how 150-year-old turbine technology will power a sustainable future” 

    CSIRO bloc

    Commonwealth Scientific and Industrial Research Organisation

    1

    Financial Review

    Jun 28 2016
    Mark Abernethy

    2
    Concentrated solar power uses the sun’s heat, rather than its light, from a field of heliostat mirrors in Newcastle. James Brickwood

    At the CSIRO’s Energy Centre campus on the northern outskirts of Newcastle are two 40-metre “power towers”: one is curved and elegant, the other a mess of girders and gantries, ducts and pipes.

    “This is the tower designed by the architects,” says the CSIRO’s Robbie McNaughton, pointing to the elegant solar receiver. “And this is the new one, designed by engineers. One looks better, one works better.”

    In a world where many propose overturning industrial infrastructure to save the planet from carbon emissions, McNaughton and his team of visionaries are retaining technology used since the 1860s.

    “Generating power by driving a turbine with steam has been perfected for 150 years,” McNaughton says. “We’re keeping the turbine – we’re just changing the front end.”

    3
    “When you have 170 heliostats pointing at one 4.5‑metre hole, the problem isn’t generating the heat,” Robbie McNaughton says. “The challenge is not melting everything.” James Brickwood

    McNaughton’s team sought to replace the coal that generates steam with solar energy; and now they’ve replaced the water itself with carbon dioxide. The seven-year-old project retains the turbine at the centre of large-scale power generation because this solar power project is not about photovoltaic panels on roofs.

    There are about 1.5 million Australian households and businesses with PV panels on their roofs and most feed into the power grid. But the National Energy Market (NEM) is 6000 kilometres long, and small-scale PV power lacks the frequency and inertia to be efficiently pushed hundreds of kilometres down the line, McNaughton says.

    Enter utility solar, also known as concentrated solar power (CSP), which uses the sun’s heat, rather than its light. CSP concentrates the heat from a field of heliostat mirrors. The heliostats at Newcastle are slightly curved to create a first‑stage concentration and they’re controlled by actuators that track the sun.

    The sun’s heat is reflected upwards at a receiver, a 4.5-metre square hole at the top of the tower containing a coil of pipes. When water runs through the very hot pipes it turns to steam, which drives a turbine. “When you have 170 heliostats pointing at one 4.5‑metre hole, the problem isn’t generating the heat,” McNaughton says. “The challenge is not melting everything.”

    ‘Supercritical’ steam

    Typical coal-powered boilers run at about 540 degrees and pressure of 17 megapascals. In June 2014, McNaughton’s team created supercritical steam at 570 degrees and 23.5 megapascals – a world record for solar.

    McNaughton isn’t, however, too concerned about the temperatures from well-engineered power towers: there are already CSP operations in Australian power stations, two of which augment fossil fuels and one at Jemalong, NSW, a small pilot CSP plant. “We’ve run it at 1500 degrees,” he says of the receiver at the CSIRO facility. “Heat isn’t the issue – storage and efficiency are the issues.”

    Just as home owners can buy batteries to store rooftop power for later use, if utility solar is going to simulate the baseload capacity of fossil fuel power generation, it has to store its thermal energy so the turbines can be turned at any time. “To be utility-grade it has to produce power when the sun isn’t shining, and it has to be dispatchable between 6pm and 7pm,” says McNaughton, referring to the peak load window of the national grid, when demand is greatest and power at its most expensive.

    In Spain’s Gemasolar power plant and the United States’ Crescent Dunes, where utility solar is being used commercially, the heat is stored in molten salt (Jemalong also uses salt). It is heated by the solar receiver and when the sun goes down, heat from the stored salt is used to drive the turbine.

    4
    Spain’s Gemasolar power plant

    5
    Crescent Dunes

    McNaughton’s team has used salt. But Australia has the world’s highest rate of insolation – the solar radiation that reaches the Earth’s surface – in populated areas (similar insolation levels in Africa and the Americas occur in desert zones) and the CSIRO team plans to use it to achieve higher thermal efficiency rates.

    The problem, says McNaughton, is that while salt is an excellent medium for running a turbine and storing heat, it has a natural limit of 590 degrees – well short of the temperatures that create optimum thermal efficiency. So his team has moved on from water and salt and are using carbon dioxide instead. The CSIRO project heats the CO2 to 720 degrees, at which point they run a CO2 turbine at greater than 50 per cent thermal efficiency (water and salt run at just over 40 per cent).

    In the ugly-but-effective power tower at Newcastle, McNaughton’s team reticulate 100 kilograms of CO2 through the receiver. It is heated to 720 degrees and runs a fridge‑sized turbine which has produced enough power to run a small town.
    Technology partnerships

    Storing the heat is done through a steel tank at the base of the tower in which special ceramic balls are heated by the initial solar process; a secret heat-transfer liquid is run down the tank and into a heat-exchanger, from which a turbine can be driven when there’s no sun. “No other publicly acknowledged project in the world is doing this with CO2,” McNaughton says.

    McNaughton’s team set itself benchmarks well beyond simple proof of concept. This project delivers a technology that a power company will actually build and rely on, and just to emphasise its acceptance by the engineering world, the solar-CO2 project is in technology partnerships with power giants GE and Mitsubishi.

    “We don’t see the value in a technology that isn’t producing at least 50 megawatts,” says McNaughton, referring to a minimum size at which a CSP plant would be viable.

    “You could build a small plant to power a remote community, but realistically it would be a larger investment and it would provide power to the east coast grid.”

    He says the bold new vision of solar power is slightly more expensive than PV but the costs of building it reduce with every project. He points to the 300MW Ivanpah solar power station south of Las Vegas. “They have three power towers in that project – the cost of the heliostats fell by 50 per cent between building the first tower and the third.”

    McNaughton’s team will have a prototype plant operating by the end of 2016, and he expects it to run for at least two years before the big banks and super funds consider it to be sufficiently low risk to be worth investing in. One risk they don’t have to worry about is fossil fuel price volatility, a fact McNaughton says will see financiers backing the technology.

    “Once you’ve built a solar power plant, the sun doesn’t charge you any more for its energy.”

    See the full article here .

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    CSIRO, the Commonwealth Scientific and Industrial Research Organisation, is Australia’s national science agency and one of the largest and most diverse research agencies in the world.

     
  • richardmitnick 7:34 am on June 22, 2016 Permalink | Reply
    Tags: , , , Solar Energy   

    From CSIRO: “Watt-ever floats your boat: solar on water” 

    CSIRO bloc

    Commonwealth Scientific and Industrial Research Organisation

    22nd June 2016
    Natalie Kikken

    1
    Is it a pool? Is it a raft? No, it’s float-ovoltaics! Credit: Photo courtesy of Lightsource

    Close your eyes and ponder what a commercial solar photovoltaic (PV) farm looks like. Do you envisage arid desert plains glistening with thousands of solar PV panels under abundant sunshine?

    You’re probably not alone thinking such sunny thoughts. But believe it or not, the ideal temperature conditions and landscape for solar PV panels to work most efficiently doesn’t always have to be hot and sunny weather. The amount of energy produced is often influenced by the material of the panels themselves, and recent research has unveiled that sometimes thousands of solar panels floating on water is the best way to increase energy output.

    Floating a bright idea

    We all know PV panels look great on rooftops, but where else can they be installed to maximise the amount of energy being produced and to utilise space? All PV panels become slightly less efficient as their temperature rises, so cooling them can lead to better energy production, especially in warm climates. This is where the idea of building solar PV farms on or near water starts to look more attractive.

    Solar ideas coming up from Down Under

    As is often the case, an Australian company led the way, with one of our former scientists, Phil Connor, designing the first ever floating solar PV system around a decade ago for the Australian company Sunengy Pty Ltd. We tested the first prototype of that system, which is now on the way to becoming commercialised in India.

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    Australian company Sunengy’s world-first large floating solar photovoltaic array, and the first installed on a hydro-electric dam. No image credit.

    Thinking outside the solar box

    Scientists across the globe are investigating how to most efficiently build solar PV systems on water to ensure you can power-up using the sun, and enable some industries to generate enough power for their operational requirements. These floating solar farms utilise space that would otherwise go wasted and can also help reduce evaporation. Placing the collectors in a hydro dam, as Sunengy has done, gives free access to the large transmission line, allowing considerably better economy from the PV installation.

    Australia first large floating solar plant was built in Jamestown, South Australia in April 2015, generating up to 45 percent more energy per panel than a rooftop solar system. The city of Lismore announced a call for tenders this year to build the first ever community funded floating solar farm.

    Europe’s largest floating solar power farm was unveiled in London, UK. Built by Thames Water, the farm consists of 23,000 solar panels and will produce enough power to operate the utility’s local water treatment plants including enough clean drinking water for nearly 10,000 people. More construction for bigger and better floating solar farms are already underway.

    Catching the solar floating wave

    So what does this mean for Australia’s energy future, and our landscape? Will we be seeing a sea of solar farms pop up along our Aussie waterways, dams and coastlines?

    One of our solar research gurus, Dr Greg Wilson, thinks floating solar farms could be the way of the future for semi-arid regions of Australia, in particular farmland and waterways for irrigation.

    “Floating solar PV panels reduce evaporation so there is significant potential to create better and more efficient energy systems when used near open irrigation systems or for water treatment plants or large drinking water catchment areas,” said Dr Wilson.

    “Water quality is maintained by circulation of the main body of water so the energy required for this can be offset by the energy produced by the solar panels. It can be far more energy efficient and cost effective to have reduced evaporation than purely generating electrical energy,” he adds.

    Sunengy’s vision is to incorporate hundreds of megawatts of floating solar on the surface of each of our hydroelectric dams to create the lowest cost addition to our renewable energy supplies.

    Looking at the Australian and international examples of floating solar farms that have emerged over the last 12 months, it’s certainly an area for growth.

    We aren’t walking on water just yet but we are leaders in the solar energy space with two active solar research fields including photovoltaic and concentrating solar thermal power. We also recently challenged the status quo for energy innovation by holding our first ever Solar Hackathon.

    3
    These heliostats might not be floating on water, but they can spell our name!

    See the full article here .

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  • richardmitnick 9:29 am on June 6, 2016 Permalink | Reply
    Tags: , Chile is producing so much solar power it's giving it away for free, , Solar Energy   

    From Science Alert: “Chile is producing so much solar power, it’s giving it away for free” 

    ScienceAlert

    Science Alert

    3 JUN 2016
    DAVID NIELD

    1
    Anyaivanova/Shutterstock.com

    Market forces often produce strange quirks in the economic system, like the one we’re seeing in Chile this year: the country is producing so much solar power that it’s being sold for… nothing at all.

    While it’s incredibly encouraging to see so much expansion in the country’s renewable energy output, this huge amount of supply does actually cause problems for the companies looking to invest in solar energy.

    Solar capacity on Chile’s central power grid (called SIC or Sistema Interconectado Central) has more than quadrupled over the past three years to 770 megawatts – good news for the environment and customers paying their electricity bills.

    Now the challenge is to upgrade the infrastructure to cope with the influx of solar energy.

    As Vanessa Dezem and Javiera Quiroga report at Bloomberg, spot prices (set by supply and demand) for electricity have hit zero for 113 days this year up to the end of April. That compares with 192 days in total in 2015.

    Increasing energy demands and investment followed by a slowing of economic growth means that regions are being oversupplied with power – 29 solar farms are now online in the country with a further 15 in the pipeline.

    It’s fantastic to see so much solar energy being produced, but next-to-nothing prices will discourage future investment and mean power plants just aren’t profitable, warn experts.

    The solution lies in increasing the country’s ability to take on extra capacity, and there are plans to build a 3,000-kilometre (1,854-mile) transmission line to link the SIC with Chile’s northern power network for the first time.

    Once this is built, it’ll mean that, when there is a surplus, it can be re-routed to areas that need it. Basically it’s just increasing the demand on the sustainable product by giving more people access to it.

    There are also transmission lines within the two grids that need to be upgraded to allow electricity to be more evenly distributed.

    Chile is way ahead of other countries in Latin America when it comes to renewable energy capacity – producing more than the rest of the continent combined, according to Bloomberg’s figures – which is partly helped by the abundance of sunshine, wind, and water in the country.

    But they’ve also invested in some awesome technology that are helping them maximise these natural resources. One of the biggest renewable energy sources in the country is the Atacama-1 solar tower, in the middle of the Atacama desert.

    Standing more than 200 metres (656 feet) tall, the US$1.1 billion project uses mirrors to concentrate sunlight onto a steel solar receiver that weighs 2,000 tonnes, as Jonathan Watts reports for The Guardian. Thanks to 10,600 heliostatic mirrors and 50,000 tonnes of molten salt, the tower will eventually be able to supply electricity around the clock.

    As well as upgrading its infrastructure to support projects like Atacama-1, Chile has plans to export its solar power energy too: “We are in a region of the world that has huge opportunities for integration and interconnection,” Chile’s Energy Minister Maximo Pacheco told Bloomberg.

    This is something that countries like Denmark, which has a lot of wind energy production, does in order to maintain the price of wind power even when there’s a surplus.

    “There are huge opportunities for Chile… [to] export some of this renewable energy to other countries in the region,” added Pacheco.

    What’s exciting is that we’re halfway there – we’re getting so much better at harnessing renewable energy, now we just need to find out a way to make it a good idea economically.

    See the full article here .

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  • richardmitnick 1:39 pm on May 30, 2016 Permalink | Reply
    Tags: , , CST presents a salty solution to solar after dark, Solar Energy   

    From CSIRO: “CST presents a salty solution to solar after dark” 

    CSIRO bloc

    Commonwealth Scientific and Industrial Research Organisation

    30th May 2016
    Claire Ginn

    1
    The rotation of the Earth really makes our day.

    It’s hard to be upset about planetary rotation, but it does present a challenge for generating consistent solar energy.

    When looking to store and use solar energy when it’s dark or cloudy, most people think of battery devices, but when it comes to powering cities we need to think much bigger – and saltier.

    As you may expect, solar energy is most effectively generated when it’s … sunny. Sunlight can be converted into electricity via solar photovoltaic panels (like your rooftop PV) or into heat via large solar thermal heliostat fields focusing on a collection tower. This is called ‘concentrating solar thermal’ (CST), and it’s a pretty exciting large-scale renewable technology.

    Instead of using the collected heat straight away to power a turbine for energy production, molten salt is used to retain the thermal energy collected, to then be used as demand dictates. The ‘dispatchable’ nature of CST with thermal storage means that the stored energy can be used to fill gaps in energy supply, overcoming intermittency issues usually associated with renewables.

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    SolarReserve’s whopping Crescent Dunes Solar Energy Project in Nevada, US uses over 10,000 heliostats (mirrors) to concentrate sunlight, then collected in a central tower. The heat is then stored in molten salt. Image credit – Solar Reserve

    Recently, representatives from international research, industry and government bodies convened in Melbourne to discuss concentrating solar thermal, including ways to best store solar energy for when the sun isn’t shining.

    The event was hosted by the Australian Solar Thermal Research Initiative (ASTRI) – an international collaboration seeking accelerate the commercial deployment of CST technologies. ASTRI Director Dr Manuel Blanco said CST with thermal storage has the potential to provide many services to the electricity grid.

    “CST plants can be designed to function as a ‘baseload’, ‘mid-load’, and ‘peaking’ power plants, without the associated emissions or fuel costs. They also provide inertia, and other ancillary services to the grid,” Dr Blanco said.

    CST has been in commercial operational around the world for more than twenty years, and molten salt for commercial storage is also several years old. We operate Australia’s largest CST research hub at our Energy Centre in Newcastle, and are looking at ways to make this technology more effective as a large-scale renewable energy solution.

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    Our concentrating solar thermal research facility in Newcastle. Image credit – CSIRO

    According to our Chief Solar Research Scientist Wes Stein, the advent of other new storage technologies such as batteries means the CST industry needs to keep on its toes to remain ahead, and that research and industry must work together to provide even lower-cost options for the energy market.

    “CST with thermal energy storage is right now one of the lowest cost forms of dispatchable renewable energy. Indeed if renewables are to continue to grow, the storage that CSP can provide through a spinning turbine could underpin further PVs and wind. The business case for CST technology comes from this ability to store the heat at very low cost,” Stein said.

    “Australia has for a long time been producing world-class solar thermal R&D, and the time is now right for industry to come on board to deploy it in Australia, just as it is overseas.”

    International Energy Agency (IEA) Renewables Analyst Cedric Philibert highlighted Australia’s R&D track record and the need for continued collaboration, saying “Australia needs CST, the world needs CST, CST needs Australia, and the world needs Australia’s CST”.

    According to the IEA’s modelling, CST will play a major role in the world’s decarbonised energy future, with energy storage also playing a critical role in response to the penetration of renewable energies.

    Under the ASTRI research program, we and a number of Australia’s leading universities are focused on CST R&D, collaboration and knowledge sharing in order to further develop CST and increase its cost-competitiveness.

    Check out our solar research program and our expertise in energy storage. We’re also a keen collaborator to the Australian Solar Thermal Research Initiative.

    See the full article here .

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  • richardmitnick 1:27 pm on May 28, 2016 Permalink | Reply
    Tags: , Hot new solar cell, , Solar Energy,   

    From MIT: “Hot new solar cell” 

    MIT News
    MIT News
    MIT Widget

    May 23, 2016
    David L. Chandler

    1
    While all research in traditional photovoltaics faces the same underlying theoretical limitations, MIT PhD student David Bierman says, “with solar thermal photovoltaics you have the possibility to exceed that.” In fact, theory predicts that in principle this method could more than double the theoretical limit of efficiency, potentially making it possible to deliver twice as much power from a given area of panels. Photo courtesy of the researchers.

    System converts solar heat into usable light, increasing device’s overall efficiency.

    A team of MIT researchers has for the first time demonstrated a device based on a method that enables solar cells to break through a theoretically predicted ceiling on how much sunlight they can convert into electricity.

    Ever since 1961 it has been known that there is an absolute theoretical limit, called the Shockley-Queisser Limit, to how efficient traditional solar cells can be in their energy conversion. For a single-layer cell made of silicon — the type used for the vast majority of today’s solar panels — that upper limit is about 32 percent. But it has also been known that there are some possible avenues to increase that overall efficiency, such as by using multiple layers of cells, a method that is being widely studied, or by converting the sunlight first to heat before generating electrical power. It is the latter method, using devices known as solar thermophotovoltaics, or STPVs, that the team has now demonstrated.

    The findings are reported this week in the journal Nature Energy, in a paper* by MIT doctoral student David Bierman, professors Evelyn Wang and Marin Soljačić, and four others.

    While all research in traditional photovoltaics faces the same underlying theoretical limitations, Bierman says, “with solar thermophotovoltaics you have the possibility to exceed that.” In fact, theory predicts that in principle this method, which involves pairing conventional solar cells with added layers of high-tech materials, could more than double the theoretical limit of efficiency, potentially making it possible to deliver twice as much power from a given area of panels.

    “We believe that this new work is an exciting advancement in the field,” Wang says, “as we have demonstrated, for the first time, an STPV device that has a higher solar-to-electrical conversion efficiency compared to that of the underlying PV cell.” In the demonstration, the team used a relatively low-efficiency PV cell, so the overall efficiency of the system was only 6.8 percent, but it clearly showed, in direct comparisons, the improvement enabled by the STPV system.

    The basic principle is simple: Instead of dissipating unusable solar energy as heat in the solar cell, all of the energy and heat is first absorbed by an intermediate component, to temperatures that would allow that component to emit thermal radiation. By tuning the materials and configuration of these added layers, it’s possible to emit that radiation in the form of just the right wavelengths of light for the solar cell to capture. This improves the efficiency and reduces the heat generated in the solar cell.

    The key is using high-tech materials called nanophotonic crystals, which can be made to emit precisely determined wavelengths of light when heated. In this test, the nanophotonic crystals are integrated into a system with vertically aligned carbon nanotubes, and operate at a high temperature of 1,000 degrees Celsius. Once heated, the nanophotonic crystals continue to emit a narrow band of wavelengths of light that precisely matches the band that an adjacent photovoltaic cell can capture and convert to an electric current. “The carbon nanotubes are virtually a perfect absorber over the entire color spectrum,” Bierman says, allowing it to capture the full solar spectrum. “All of the energy of the photons gets converted to heat.” Then, that heat gets re-emitted as light but, thanks to the nanophotonic structure, is converted to just the colors that match the PV cell’s peak efficiency.

    In operation, this approach would use a conventional solar-concentrating system, with lenses or mirrors that focus the sunlight, to maintain the high temperature. An additional component, an advanced optical filter, lets through all the desired wavelengths of light to the PV cell, while reflecting back any unwanted wavelengths, since even this advanced material is not perfect in limiting its emissions. The reflected wavelengths then get re-absorbed, helping to maintain the heat of the photonic crystal.

    Bierman says that such a system could offer a number of advantages over conventional photovoltaics, whether based on silicon or other materials. For one thing, the fact that the photonic device is producing emissions based on heat rather than light means it would be unaffected by brief changes in the environment, such as clouds passing in front of the sun. In fact, if coupled with a thermal storage system, it could in principle provide a way to make use of solar power on an around-the-clock basis. “For me, the biggest advantage is the promise of continuous on-demand power,” he says.

    In addition, because of the way the system harnesses energy that would otherwise be wasted as heat, it can reduce excessive heat generation that can damage some solar-concentrating systems.

    To prove the method worked, the team ran tests using a photovoltaic cell with the STPV components, first under direct sunlight and then with the sun completely blocked so that only the secondary light emissions from the photonic crystal were illuminating the cell. The results showed that the actual performance matched the predicted improvements.

    “A lot of the work thus far in this field has been proof-of-concept demonstrations,” Bierman says. “This is the first time we’ve actually put something between the sun and the PV cell to prove the efficiency” of the thermal system. Even with this relatively simple early-stage demonstration, Bierman says, “we showed that just with our own unoptimized geometry, we in fact could break the Shockley-Queisser limit.” In principle, such a system could reach efficiencies greater than that of an ideal solar cell.

    The next steps include finding ways to make larger versions of the small, laboratory-scale experimental unit, and developing ways of manufacturing such systems economically.

    This represents a “significant experimental advance,” says Peter Bermel, an assistant professor of electrical and computer engineering at Purdue University, who was not associated with this work. “To the best of my knowledge, this is a new record for solar TPV, using a solar simulator, selective absorber, selective filter, and photovoltaic receiver, that reasonably represents actual performance that might be achievable outdoors.” He adds, “It also shows that solar TPV can exceed PV output with a direct comparison of the same cells, for a sufficiently high input power density, lending this approach to applications using concentrated sunlight.”

    The research team also included MIT alumnus Andrej Lenert PhD ’14, now a research fellow at the University of Michigan, MIT postdocs Walker Chan and Bikram Bhatia, and research scientist Ivan Celanovic. The work was supported by the Solid-State Solar Thermal Energy Conversion (S3TEC) Center, funded by the U.S. Department of Energy.

    *Science paper:
    Enhanced photovoltaic energy conversion using thermally based spectral shaping

    See the full article here .

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  • richardmitnick 11:16 am on May 21, 2016 Permalink | Reply
    Tags: , , Solar Energy, Storing Heat to Make Solar Electricity All the Time   

    From SA: “Storing Heat to Make Solar Electricity All the Time” 

    Scientific American

    Scientific American

    May 19, 2016
    Umair Irfan

    1
    The PS10 and PS20 solar power plant near Seville, in Andalusia, Spain. Credit: Koza1983/Wikimedia Commons, CC BY 3.0

    COLOGNE, Germany—At Germany’s aerospace agency, the next frontier is capturing the sun here on Earth and keeping it on tap.

    In a 4-year-old glass and steel building near the Cologne-Bonn Airport, researchers at the German Aerospace Center (DLR), Germany’s equivalent of NASA, are working on new ways to produce more heat than light in order to smooth over intermittency, one of the biggest drawbacks of solar power on the grid.

    DLR Bloc
    German Aerospace Center (DLR)

    “The focus of this organization is to test ideas as close to production as possible,” said Christos Agrafiotis, a researcher in solar chemical engineering at DLR.

    With global solar capacity surging over 200 gigawatts, solar energy is maturing into its technological adolescence. However, it has to start pulling its own weight on the grid instead of relying on elder power sources to bail it out on cloudy days and to step in once the sun sets.

    Storing solar energy is one way to make power from the sun a productive member of the grid, especially as utilities work to accommodate photovoltaic panels distributed across rooftops (ClimateWire, Jan. 20).

    But battery technology isn’t up to the job just yet in terms of cost and performance to shift solar power across all hours. To keep the electrons flowing even when the sun isn’t shining, many researchers are increasingly looking for better ways to capture and store thermal energy, in concentrating solar plants as well as independent storage systems on the grid.

    Concentrating solar plants do have a higher levelized cost of energy compared with photovoltaics, said Thomas Bauer, team leader for thermal process technology at DLR, over the din of compressors in a fabrication shop.

    “This is not the full story, because we have a dispatchable system,” he said. “The message is politically not addressed.”

    A thermal storage system coupled to a solar plant would make it easier to compete head to head with coal- and natural-gas-fired generators. It would also relieve intermittency anxiety for utilities who have to ramp up generation on cloudy days and sometimes sell electricity at negative prices on especially sunny and windy days.

    Bauer noted that in some power markets, the value of having power on tap is underrated next to overall power capacity, a problem that requires a policy fix.

    DLR developed some of the technology behind the world’s first commercial concentrating solar thermal tower plant, the 11-megawatt PS10 plant near sunny Seville, Spain, which went online in 2007.

    Plants like PS10 use mirrors to concentrate sunlight on a central tower to generate intense heat. Those high temperatures can produce steam to spin a turbine or warm up a material that can hang on to the heat until it’s needed.

    Such materials include molten salt. Solar thermal plants like the 110-MW Crescent Dunes facility in Nevada hold the molten salt in giant insulated tanks to dispatch power as needed (Greenwire, March 29).

    “Half of the cost of the [typical solar thermal] system is in the molten salt itself,” said Bauer. “If we save half of the molten salt, it means we can reduce dramatically the capex [capital expenditure]. This is usually our aim.”

    Excess energy from photovoltaics and wind turbines could also be converted to and stored as heat, offering a lower-cost alternative to batteries on the grid. “Battery prices are more than an order of magnitude, more than a factor of 10, higher than heat storage,” Bauer said.

    Experimenting with salt, ceramics

    To this end, researchers are experimenting with new thermal storage materials that can get hotter, more than 1,000 degrees Celsius, and hold on to the heat for longer.

    Researchers at DLR are experimenting with new salt mixtures and have constructed a test facility to observe their performance along with also validating associated components like valves, sensors and storage tanks. The laboratory work would help reduce the sticker price of solar thermal power plants, Bauer said.

    Another approach is to use ceramic materials, which can handle higher temperatures than metals and have been used for more than 100 years in the steel and glass manufacturing sector to store heat for 15- to 30-minute intervals. Researchers at DLR are working to make ceramics more durable and store heat for longer.

    In some functional ceramics, the material undergoes a chemical change when heated and releases the heat when the reverse reaction is triggered, explained Stefan Reh, associate head of the Institute of Materials Research at DLR. “You use the oxide as a thermochemical storage mechanism,” he said.

    “The other one is where you use hydrogen as the storage mechanism,” he added. “At high temperatures, [the ceramic materials] have a higher affinity to oxygen than to water, which means when you expose it to steam, it steals the oxygen from water, leaving the hydrogen behind.”

    To make ordinarily brittle ceramics durable enough to withstand the rigors of a power plant, scientists are reinforcing them with fibers to make them damage tolerant. The aluminum oxide fibers are drawn off a spool through a slurry of water and alumina powder. After weaving the fibers into the desired shape, researchers dry the product and heat it in a kiln.

    ‘Economies of scale’ have not yet kicked in

    The result is a light, tough, heat-tolerant material. With a sharp, loud hammer strike, Reh demonstrated that a white coaster-sized sheet of fiber-reinforced ceramic would deform, but not break.

    “It is not immune to damage,” he said. “But it does not shatter and break into a thousand pieces.”

    Once the heat is saved up, engineers can use it for many purposes, not just boiling water. Agrafiotis noted that high-grade heat is an important resource in many industries as it is used to treat materials and trigger chemical reactions that couldn’t occur at lower temperatures.

    “Essentially what we’re going to do is to use high-temperature heat from the sun to perform endothermic chemical reactions that are difficult to be performed under normal conditions,” he said, standing next to a laminar flow hood where a white, tubular infrared heater exuded an orange glow as it warmed up to 1,300 C.

    These reactions include splitting water into hydrogen and oxygen, and breaking carbon dioxide into carbon monoxide and oxygen.

    “If you can achieve this, you can then combine CO [carbon monoxide] and hydrogen to produce syngas,” Agrafiotis said. Syngas, or synthesis gas, is a starting material to make synthetic fuels like methane and gasoline.

    Solar thermal power plants still have to grow up a bit further to drop in price and increase in competitiveness, but they have immense potential. “This technology is better suited for large-scale applications,” Agrafiotis said.

    “Big power, big plants that sell their energy to the grid. … The economies of scale become significant.”

    See the full article here .

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  • richardmitnick 9:48 pm on January 11, 2016 Permalink | Reply
    Tags: , , Solar Energy   

    From MIT: “Concentrating dawn-to-dusk solar energy” 


    MIT News

    January 11, 2016
    Denis Paiste

    1
    Solar panels at Sanctuary Dairy Farm Ice Cream in Sunapee, New Hampshire Photo: Denis Paiste/Materials Processing Center

    MOSAIC award spurs MIT research into concentrator solar cells that can run in shade and full sun with power control and wavelength separation.

    Lighter, more efficient flat-plate solar cells are the goal of MIT researchers who kicked off a collaborative research effort Dec. 15 with a three-year, $3.5 million award under the Department of Energy’s ARPA-E program. Their aim is to bring the technology to the marketplace.

    “We are early on looking for companies to collaborate with us who are interested in finding a way to bring that technology into the marketplace after the three-year project funding,” says principal investigator Jurgen Michel, senior research scientist at the MIT Microphotonics Center and senior lecturer in the Department of Materials Science and Engineering. “The best outcome is a solar cell and companies that will actually make those or take that into further development to make a product.”

    ARPA-E’s Micro-Scale Optimized Solar-Cell Arrays with Integrated Concentration (MOSAIC) program has challenging specifications, Michel says. The goal is to reach overall efficiency of greater than 30 percent, which is about 5 percentage points higher than the best efficiency achieved with crystalline silicon solar cells.

    Technical challenges

    The MIT-led project, “Integrated Micro-Optical Concentrator Photovoltaics with Lateral Multijunction Cells,” aims to develop a three-junction concentrator cell in a flat-plate system just under 1 inch thick. It includes a partnership with Arizona State University. Besides Michel, collaborators include:

    Juejun (JJ) Hu, the Merton C. Flemings Assistant Professor in Materials Science and Engineering, who will design and prototype a special microlens to split sunlight into wavelengths from visible to near infrared and concentrate sunlight up to 300 times;

    Eugene A. Fitzgerald, the Merton C. Flemings-SMA Professor of Materials Science and Engineering, who will work on solar cells made from indium gallium arsenide;

    David J. Perreault, professor of electrical engineering and associate department head, who will work on power management of the solar cells; and

    Cun-Zheng Ning, professor of electrical engineering at Arizona State University, who will work on nanopillar semiconductor material with a bandgap gradient that is grown in a single step.

    Ning developed a single-growth process for varying the bandgap in nanopillars by varying the temperature in the reactor. “That would be very low cost, but the challenge there is efficiency. For our approach, we have to get our substrate to low enough threading dislocation densities in order to get low-cost, high-efficiency solar cells,” Michel says.

    Multiple benefits

    The proposed solar system with a mix of cells to maximize collection of light a varying times of day addresses one of the key issues with solar energy, which is its intermittent nature. As more solar systems are deployed, they will have to be integrated with energy storage systems to achieve maximum benefit, according to The MIT Energy Initiative report, The Future of Solar Energy, released in May 2015. Without storage, solar systems can provide power only during the day.

    Solar has enormous potential over the long-term. According the MITEI report, installing solar on less than one-half of 1 percent of the continental United States could produce all the electricity the country needs today. Solar also can reduce the nation’s carbon dioxide emissions, the report noted.

    FOCUS results

    Michel previously received a one-year ARPA-E FOCUS grant for research on Spectrum Splitting for High-Efficiency Photovoltaic and Solar Thermal Energy Generation. Two papers are pending publication on that work, including significant reductions in threading dislocations in solar cells and enhanced performance of indium gallium phosphide (InGaP) solar cells. These indium gallium phosphide materials are called III-V materials because their elements come from columns III and V of the periodic table.

    “One of our main goals was to lower the cost of III-V semiconductor solar cells, so we’ve been using a silicon wafer with a germanium-on-silicon virtual substrate to grow our III-V cells on top of that,” Michel explains. “We’ve reduced the threading dislocation density to below mid-106 per square centimeter. Once you get down to about 106 per cm2 in threading dislocation density, you get actually high quality III-V semiconductor materials for high performance solar cells on a silicon substrate and that reduces the cost dramatically.” This technology is available for licensing through the MIT Technology Licensing Office.

    In the new MOSAIC work, researchers will include the indium gallium phosphide (InGaP) solar cells based on the germanium-on-silicon approach in the FOCUS program and add solar cells made from gallium arsenide (GaAs) and indium gallium arsenide (InGaAs) to cover the whole spectrum of sunlight. These cells will be connected to each other in a parallel layout. The lens will direct specific wavelengths of light to matching solar cells.

    The work builds on an earlier theoretical paper that showed that under realistic operating conditions over the course of a year, parallel cells coupled with wavelength separation, or spectrum splitting, outperformed a stacked array, or tandem, solar cell. “We found that if you split your spectrum in the way you spread it out onto separate solar cells, you have an overall gain in power output compared to the other solar cell,” Michel explains.

    In the new project design, Michel says, “We can optimize the power point for each of the cells individually, because we have now CMOS control. That means we can respond very quickly to shading, for instance, [as] a cloud moves across a panel.” Under cloudy skies, light absorbed by silicon cells in the structure will maintain power output at about 20 percent power efficiency.

    Despite the three-year prototype goal, it probably will take three to five years beyond that to bring to market a solar cell system that will last for 30 years. “If that can be done, then you’d actually have solar cells that would have a much higher output than current solar cells for thin plates, which makes it much easier to handle,” Michel explains. “Also if you have to, for instance, track your cells with the sun, weight is much lower, efficiency is high, and so that could be the next step in solar cell efficiency. We are not the only ones that are working on that. There are quite a few competitors. We just hope that one will be successful at least,” he says. “The best outcome is a solar cell and companies that will actually make those or take that into further development to make a product.”

    See the full article here .

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