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A long awaited solar power milestone for unconcentrated silicon PV cells has been reached, thanks to steady improvement and research

While many traditional fossil fuel technologies show slow growth in efficiency and design, solar power has instead yielded steady and rapid advances.  While many question why a "killer app" solar product has not yet reached the market after years of hype, it is hard to deny the fact that solar costs both subsidized and unsubsidized have been dropping dramatically, being halved every 10 years. 

With current costs ranging from 15 to 20 cents per kWh, and wholesale coal power costs between 1.5 and 2.5 cents per kWh (and nuclear in a similar range -- 1.7 cents per kWh by estimates from the Nuclear Energy Institute), solar still has a ways to go and likely a few decades before being ready for full deployment.  Still, few technologies show the rapid growth in efficiency solar has and few utilize such a common resource as silicon, so the value of ongoing solar research is apparent.

UNSW's ARC Photovoltaic Centre of Excellence reported a significant milestone this week, with the announcement of the world's first 25 percent efficient unconcentrated solar silicon cells.  They had previously held the 24.7 percent efficient silicon cell record, but were denied the 25 percent milestone due to gaps in the understanding of sunlight and its effect on silicon.

New research has led to revisions in how incident light efficiency is calculated.  As a result, their record-holding design has reached the 25 percent mark, a "magic" number according to many industry experts.  The cell, designed by Professors Martin Green and Stuart Wenham has a wide lead over competitive offerings, according to the Centre.  UNSW holds six solar world records now.

Centre Executive Research Director, Scientia Professor Martin Green described how the new research improved the understanding of the efficiency.  He states, "Since the weights of the colours in sunlight change during the day, solar cells are measured under a standard colour spectrum defined under typical operational meteorological conditions.  Improvements in understanding atmospheric effects upon the colour content of sunlight led to a revision of the standard spectrum in April. The new spectrum has a higher energy content both down the blue end of the spectrum and at the opposite red end with, dare I say it, relatively less green."

While suggesting less green of anything may seem like heresy in the alternative energy industry, it’s good news for the Centre as it means their cells are operating more efficiently than expected.  The Centre's cell posted larger gains than its competitors following the revision.  It is now 6 percent more efficient than the next most efficient competitor, according to Professor Green.

The Centre's cell is approaching the important 29 percent efficiency threshold -- the maximum theoretical efficiency for a first generation silicon photovoltaic solar cell.  Dr Anita Ho-Baillie, who heads the Centre's high efficiency cell research effort, says the new research is a big boost "because our cells push the boundaries of response into the extremities of the spectrum."

She states, "Blue light is absorbed strongly, very close to the cell surface where we go to great pains to make sure it is not wasted. Just the opposite, the red light is only weakly absorbed and we have to use special design features to trap it into the cell."

Professor Green states, "These light-trapping features make our cells act as if they were much thicker than they are. This already has had an important spin-off in allowing us to work with CSG Solar to develop commercial 'thin-film' silicon-on-glass solar cells that are over 100 times thinner than conventional silicon cells."

The biggest goal of UNSW is now to adapt the ultra-high efficiency cells for mass production which should lead to more cost reductions.  ARC Centre Director, Professor Stuart Wenham, adds,"Our main efforts now are focused on getting these efficiency improvements into commercial production.  Production compatible versions of our high efficiency technology are being introduced into production as we speak."

The center has a close relationship with the world's biggest solar manufacturers, thanks in part to Dr Jianhua Zhao and Dr Aihua Wang, who fabricated the record-setting cell and have since left the Centre to establish China Sunergy, one of the world's largest photovoltaic manufacturers.  Professor Green describes, "China was the largest manufacturer of solar cells internationally in 2007 with 70 per cent of the output from companies with our former UNSW students either Chief Executive Officers or Chief Technical Officers."

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RE: 25% = 24.7%
By cblais19 on 10/24/2008 9:34:17 AM , Rating: 2
Amusingly enough, I just did a small paper advocating exactly that for one of my classes. One thing I did note that was news to me is that world production capability for the one-piece forged reactor shells is currently very low-which the top models like the Westinghouse AP1000 require. Various companies are looking into tooling up to increase production though, or countries can utilize a model like the CANDU reactors that do not require it.

Oh, and from what I've seen, solar has an average of 12-15% operating efficiency vrs an industry average of 86% for nuclear. Honestly, the next best energy source is by far wind, with 40-60%, depending on locale and generator used.

RE: 25% = 24.7%
By randomly on 10/24/2008 10:36:02 AM , Rating: 2
Japan Steel works is currently the only company capable of producing a one piece forged reactor pressure vessel for the large 1000-1650 MW reactors. They can only produce 4 per year. They plan to double that capacity in 2 years time.

There are 8 more companies adding large forging capability. Four in China, one each in Japan, France, Russia, and India.

China plans to deploy 100 Westinghouse AP1000 reactors by 2020. Cost of a single AP1000 (1100MW) reactor is $6-7 Billion USD with a planned construction time of 5 years. A rather big nut to swallow in the current credit crunch.

The first built units will undoubtedly take 6-10 years as much of the knowledgeable trained workforce in the US was lost during the 30 year hiatus in new nuclear plant construction. Most of the workforce on the new nuclear plant constructions have no previous experience in the field.

The average capacity factor for US wind power is around 35%. The average capacity factor for US nuclear plants is slightly over 90%.

RE: 25% = 24.7%
By Chernobyl68 on 10/24/2008 11:39:16 AM , Rating: 2
if you're talking about energy efficiency, any nuclear reactor that uses steam to drive turbines will at most run about 25% efficiency.

RE: 25% = 24.7%
By randomly on 10/24/2008 5:01:23 PM , Rating: 2
I believe he is talking about capacity factor, the actual average amount of energy produced over time vs the name plate rating of the equipment.

Most modern nuclear reactors have a thermal efficiency in the low 30% range. This is mostly a factor of how hot you run the coolant temperature.

RE: 25% = 24.7%
By Chernobyl68 on 10/24/2008 6:51:30 PM , Rating: 2
ah, ok. Not familiar with that term - the reactors I worked on weren't commercial! they are "corvettes" compared to the "trucks" of commercial power generation.

I was just pointing out the inefficiencies of the Carnot cycle. Any mainline plant is going to be operating at or near capacity while online. This would include most plants opearting on a steam system (nuclear, oil, coal), as it takes a very long time to bring the steam system up to operating temperature and pressure. Smaller plants with adjustable capacity like hydro, wind, or solar are mostly used as peak plants - because their generators can be brought online in a matter of minutes.
Solar requires daylight obviously and so that's 50% right there, and only certain hours of the day are ideal for power generation due to the angle of the sun and atmosphere. Not to mention clouds. So taking that in mind, yes, the 86 and 12 % sound good.

RE: 25% = 24.7%
By Clauzii on 10/24/2008 5:07:48 PM , Rating: 2
I don't get why You got rated down. Your 25% is definitely more correct than 85%.

RE: 25% = 24.7%
By Spuke on 10/24/2008 5:34:59 PM , Rating: 4
I don't get why You got rated down. Your 25% is definitely more correct than 85%.
I guess you can't read very well. Try it again but this time with less influence from your biases.

RE: 25% = 24.7%
By Clauzii on 10/24/2008 7:24:04 PM , Rating: 2
I was thinking about lightwater reactors, but Yes, it's me not being enough up to date though, since I found this and learned some new stuff:

and this:


So the thermal efficiency is a total expected vs. actually power output - including building and running the plant?

RE: 25% = 24.7%
By randomly on 10/24/2008 9:27:09 PM , Rating: 2
Efficiency is Power out to the grid vs Thermal energy input.
Most nuclear reactors are either Boiling Water reactors or Pressurized Water Reactors. Their output temperatures are usually less than 320 Centigrade so their thermal efficiency is much less than a modern coal or gas powered generator.

There are some high temperature reactor designs (Gen IV) that would have much higher thermal efficiency but none of these are currently developed to a state where they can be commercially deployed.

Some developmental reactors have operated at very high temperatures such as the Tory IIc reactor that was used in a nuclear powered ram jet engine. It ran at 513 Megawatts at 1600 C (2500F), just 150 degrees below the auto-ignition temperature of the reactor base plate. The design was largely ceramic and since it was intended for an unmanned cruise missile it was also completely unshielded. The design called for an extremely low flight level at Mach 3+ speeds. The intense radiation and shock wave would have killed anything it flew over making it problematic if you had to overfly friendly territory. However the reactor/engine was run at those temperatures.

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