Posts Tagged ‘Solar Junction’

26 April

Multijunction Solar Cells May Exceed 50% Efficiency In The Near Future

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Dear Friends, Visitors/Viewers/Readers,

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Just quickly sharing some of the things I’ve learned from a solar-cells course I’ve been taking recently at Stanford and from www.phys.org.

In the past decade, the best lab examples of traditional silicon solar cells have efficiencies around 25%, while current world record of multi-junction/3-junction solar cells is 43.5% (based on former Professor/Dr. Jim Harris & his group  at Stanford and then Solar Junction ) . Commercial examples of tandem cells are widely available at 30% under one-sun illumination, and improve to around 40% under concentrated sunlight. However, this efficiency is gained at the cost of increased complexity and manufacturing price. To date, their higher price and lower price-to-performance ratio have limited their use to special roles,   such as in aerospace (where their high power-to-weight ratio is desirable).

Sun Seen From Space Station (Credit:STS-129 crew, NASA), available @ Sun Is The Future of http://www.cafepress.com/sunisthefuture

In earthly applications, these multijunction (MJ)  solar cells are used in concentrated photovoltaics (CPV) with operating plants all over the world.

Tandem techniques can also be used to improve the performance of existing cell designs, although there are strict limits in the choice of materials. In particular, the technique can be applied to thin-film solar cells using amorphous silicon to produce a cell with about 10% efficiency that is lightweight and flexible.

At this point, please allow me to share a graph developed by NREL (now available at www.cafepress.com/sunisthefuture), the Best Research-Cell Efficiencies, summarizing the results of various solar cell efficiencies from 1975-2013, below:

Best Research-Cell Efficiencies (by NREL, available at www.cafepress.com/sunisthefuture)

Now, based on the collaboration of researchers from the California Institute of Technology in Pasadena; the National Institute of Standards and Technology in Gaithersburg, Maryland; the University of Maryland in College Park; and ,Boeing-Spectrolab Inc., in Sylmar, California. The team published a paper on their work in a recent issue of Applied Physics Letters.  These scientists have designed a new multijunction solar cell that can achieve an efficiency of 51.8%. This high performance exceeds the current goal of 50% efficiency in multijunction solar cell research as well as the current world record of 43.5% for a 3-junction solar cell. In multijunction solar cells each junction or subcell absorbs and converts sunlight from a specific region of the spectrum. The subcell can be stacked one on top of  another so that sunlight first strikes the highest bandgap subcell (tuned to light with shortest wavelengths or highest frequencies). The longer wavelengths pass through the first subcell and strike the lower band gap subcells. In order to approach its theoretical limit, multijunction solar cells not only need multiple subcells but also optimal semiconductor materials for the subcells to provide a combination of band gaps that cover as much of the solar spectrum as possible. To improve upon the current best 43.5% efficiency level of MJ solar cells, researchers focused on improving the current match between the different subcells, along with using a lattice-matched design. These two factors have previously limited MJ solar cell efficiency. Below is a video clip on new multijunction solar cell during a lecture given by Dr. Vijit Sabnis of Stanford University:

 

The lattice match corresponds to the matching between the crystal unit cells from the different subcells,” lead author Marina Leite, an energy researcher at the National Institute of Standards and Technology, told Phys.org. “By using subcells that are lattice-matched, we can minimize dislocations and other crystal defects that can significantly affect the performance of the device. A current match is required for two-terminal tandem configurations because in this case a single current passes through all the subcells and the voltages are added; therefore, if one subcell has less photocurrent it will limit the current generated by the entire device. The current match is desired so that each individual subcell works at its own maximum power point of operation.”

Solar energy world is definitely dynamic, with constant progress made beating the previous record ! We will look forward to the day when  a new Multijunction Solar Cell will be able to exceed 50% efficiency goal.

~have a bright and sunny day~

Gathered, written, and posted by sunisthefuture-Susan Sun Nunamaker

Any of your comments & suggestions are welcomed at sunisthefuture@gmail.com

Homepage: http://www.sunisthefuture.net

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22 February

We’re Going Further Than Reaching the Moon, We’re Reaching For The Sun

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Dear Friends, Visitors/Viewers/Readers,

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People! People! My belief/suspicion has been confirmed !  Solar Industry is going to be BIG! Huge! In time, solar energy will no longer represent less than one percent of our energy portfolio.  If I were to wager on the matter, I’d bet that  solar energy will  eventually take care of more than 50% of our energy needs…just wait…in 10-20 years….

I’d like to invite you to a live discussion with Secretary of Energy Steven Chu on Friday, Feb. 22, 2013, at 2:00 pm EST, that was later streamed on Google +, Youtube, and energy.gov/live on the progress of  SunShot Initiative and the role solar power is playing in our growing clean energy economy.  Questions were taken in advance and during the Hangout: via emailing newmedia@hq.doe.gov, posting comments on the Energy Department’s Facebook page,  Google+ event, or tweeting @ENERGY using #askEnergy. In addition to Secretary Chu, various representatives from across the U.S. solar energy industry were also on the panel of discussion: Jeffery Halsey from Broward County (Broward County of Florida’s Director of Pollution Prevention, Remediation, and Air Quality division), Jeff Allen of Solar Junction‘s Vice President of Business Development, and Joe Desmond, Senior Vice President at Bright Source Energy. Video below:

Jeffery Halsy shared that homeowners from his community, due to their participation in the SunShot Initiataive’s Rooftop Solar Challenge,  were able to save time and money on installations by addressing the soft costs (including permitting, interconnection, and inspection requirements accounting for as much as 40% of the total cost of a single solar installation).  With preapproved design plans,Broward County residents are now able to get a solar energy system permit online in just half an hour, saving both time and money. Jeff Allen shared insight on how Solar Junction shattered an existing technical barrier with its commericia-ready SJ3 multijunction solar cell this year. Below, on the left, a graph of Bandgap vs. Max. Efficiency shows the Shockley-Queisser limit for efficiency of a single junction solar cell. It is essentially impossible for single-junction solar cell, under unconcentrated sunlight, to have more than 34% efficiency. Multijunction cell, however, can exceed that limit. The chart on the right below indicates various solar cell efficiencies researched and presented by NREL (National Renewable Energy Laboratory). The SJ3 multijunction solar cell, with its concentrating PV cell, using a focused lens to magnify light to 418 times the intensity of the sun, was able to set a new world record of 43.5% for solar cell conversion efficiency.

NREL (National Renewable Energy Laboratory)’s Best Research-Cell Efficiencies

Shockley-Queisser limit for the efficiency of a single junction solar cell. It is essentially impossible for a single-junction solar cell, under unconcentrated sunlight, to have more than ~34% efficiency. A multijunction cell, however, can exceed that limit.

Joe Demond talked about Ivanpah Solar Generating  Complex in California’s Mojave Desert;this utility-scale solar installation is the world’s largest solar thermal power plant under construction. Supported by an Energy Department loan guarantee, this project using mirrors to focus the power of the sun on solar receivers (through high temperature high pressure steam to turn the turbines) and is expected to generate enough electricity to power about 140,000 homes annually.  Bright Source hired over 2,300 workers to complete this project’s construction and installation phase. Furthermore, majority of this project’s supply chain comes from more than 17 states (such as Michigan-based Guardian Industries that supplied 160,000 of its EcoGuard Solar Boost mirrors).

View of Ivanpah Solar Electric Generating System from Yates Well Road, The Clark Mountain Range can be seen in the distance.

Evidently, SunShot Initiative has already accomplished a great deal in reducing the soft costs, in developing new approach in technological advancement, and improvement of old way of doing things to utility-scale. It will continue its aim in reducing the cost of solar energy to be competitive with any other form of energy, without the need of subsidy. The future looks bright for solar industry. The potential of reaching below $1/watt is within reach;cost of solar will be comparable to the new cost estimate of energy from natural gas within 10 years, without any need of subsidy.  As Secretary Chu indicated, “Without any subsidy, solar energy will be able to hold its own with any other form of energy. This is our SunShot! We’re going further than reaching the moon. We’re reaching for the Sun!”This is very exciting! It is so palpable that all solar enthusiasts can feel the energy soaring…now we need to spread this good news so to speed up the process of reaching that clean, healthy and war-free Clean Energy World.  Earthlings, get ready to learn more about Solar Energy so we can all apply ourselves in this Solar Future! Thank you, Secretary Chu, for making SunShot Initiative a reality!

~have a bright and sunny day~

Gathered, written, and posted by sunisthefuture-Susan Sun Nunamaker

Any of your comments/suggestions/questions will be welcomed at sunisthefuture@gmail.com

Homepage:  http://www.sunisthefuture.net


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