Researchers at Stanford University have built a prototype of an all-carbon solar cell that includes carbon nanotubes in both the photoactive layer and the electrodes. (Source: Mark Shwartz / Stanford University)
Exactly: efficiency is king - especially now as the cost of photoabsorbers is becoming a fraction of the cost of a solar module. For an emerging technology, the first number to look at is the theoretical efficiency with the guesstimate that ultimately volume production product will achieve approximately 80% of that.
Don't rain on their parade! They acknowledge that efficiency is being worked on, and one would expect it to be low at this point. This is something others have been chasing for decades with other solar cell materials too, which had horrible efficiency at first. (Or still does.) But say this costs half as much, but has half the energy efficiency. A net zero, disregarding real estate required. And if you can put it on the glass of a office tower which is already a net waste of energy, awesome.
I get excited at every article like this, whether it's batteries, solar, wind, wave, etc. I'm hoping for those big breakthroughs, i.e. game-changing scientific and engineering accomplishments that will go a long way to eliminating fossil fuels. That carbon was sequestered for eons, and we are freeing it without much regard for future effects.
GeorgeG, 'photoabsorbers' is a new term for me, and I found nothing on a Google search page.
Full disclosure- I have a lovely FL home which at high tide, is just a few feet above sea level!
The photoabsorber is a diminishing part of the cost of a solar module and efficiency is it's salient attribute. As for abundance, silica is 60% of the continental crust - it's literally everywhere, even if you restrict yourself to clean beach sand. And, it's literally dirt cheap. The cost in a photoabsorber material is in the processing of it not the raw material.
The transparent conductor in most production thin film panels is tin oxide (not ITO) where tin oxide coated glass is a commodity in the glazing industry i.e. not specific to solar modules and therefore cost optimized. The next alternatives are various zinc oxide alloys.
The back contact/mirror in production modules is generally not silver although, even when it is, it is a very thin coat. More commonly it is a nickel or aluminum alloy.
Keep in mind that the primary value proposition of thin film is low cost offsetting low efficiency. The problem for thin film is that the cost of solar grade silicon has plumeted (~10X since I started with solar), the utilization of silicon (grams per Watt) has been reduced (~3X) and efficiency has increased (~50%). Over my brief history, the cost of silicon photoabsorer in $/W terms has gone down ~45X. Another advantage of silicon is that 25+ year operating lifetimes have been demonstrated.
It's easy to forget that any technology requires an entire ecosystem to support it - that's why it takes so long for it to emerge as a commercial product if ever. The first semiconductor solar cell was demonstrated in 1888, the first silicon cel in 1954 and yet silicon solar cells are still not a mature technology.
Silicon may be cheap as a raw material, but not so much when it's processed to make wafers, in this case, solar wafers and cells. On the one hand, the solar industry began by leveraging the huge existing infrastructure for manufacturing silicon wafers, assuming this would be the fastest way to getting costs down. That was a reasonable assumption at the time, but the reality has proven to be a bit more complex. As the article states, silicon processing steps can be many and they're not cheap. Thin-film is not a monolithic manufacturing method. The cost of thin-film to make solar cells is highly variable, and depends on many factors, including base materials, coating methods, and the coating itself. But this particular method does away with wafers altogether, which is a major potential of thin-film, and the material's potential means better conductivity and light absorption for low cost.
This is a perfect example of thinking out-of-the-box, which is necessary to make the advancements in solar photovoltaics. It won't take much to make solar photovoltaics mainstream and part of every home, everywhere. Sunlight is the largest and most under-utilized source of energy we have on the planet.
Thanks, Cadman-LT and akwaman. Thinking out of the box is something Stanford is known for, so I like to follow that university's research efforts (along with Harvard and MIT). But I'm still not convinced that any form of active solar--PV or otherwise--is the best way to do solar. Sunlight can be used for passive solar, which has a history of a few thousand years of human engineering. I've seen some amazing results of combining that old know-how with modern, precise engineering.
Hats off to those forward thinkers at Stanford! Ann, I know it is hard to believe, but the best passive use for solar is... tanning! LOL... just kidding. You are correct that passive use of solar it a good thing that is certainly not utilized enough. Light tubes and better house design should absolutely be integrated into all modern designs (but they are not). But seriously overlooked is solar hot water, which would save this country an enormous amount of power requirements (the avg is 30% of utility bill from hot water), and it is VERY cost effective, much more so than solar PV. There have been recent advancements in PV that I believe will provide 25% or bettter efficiency in the next 10 years commercially, using cheaper technology than available today. But it must be coupled with other forms of solar power generation, like the hot salt method, that retains heat and provides power through the night without batteries. The sun provides more power than we can even use, we just have to figure out how to harness it the best and most efficient way.
akwaman, I totally agree with you about solar. We've known for decades about how much energy there is free for our use and have done relatively little with that knowledge except invent an industry--PV solar--that makes all that sunlight a lot more difficult and expensive to use than it needs to be. I also agree about the hot water advantage: that's where I saw the heat storage potential of rocks and water used to best advantage--way back in the 70s.
I especially like the part about the elimination of indium and silver in this process. As exotic and rare minerals become hard to procure (and with their unequal distribution for each country), this characteristic will make this option more and more attractive.
Akwaman--You are absolutely correct. Water heating is a significant factor in energy usage and solar water heating is definitely one viable solution to that problem--when possible. Years ago, I worked for a water heater manufacturer and one item in our product line was a water heater using solar roof-top panels to "collect" the sun's rays and provide for heating. We had auxilary heating elements when needed during inclement weather. The issue in the southeast was considerable cloud cover that negated available sunlight--and lengthened the ROI. Any advancement such as the one Ann is describing is definitely welcomed to that particular industry. As advancements in solar technology progress, we will see added sales and resurgence in usage even in the most difficult environmental situations.
It's also the case that storing heat for heating water--in large sealed water bottles, rocks and even earth walls--is a lot easier to do than storing "energy" in some other form. It's also been done already.
Earlier posts mentioned 'efficiency' being the #1 issue. While that may be true, it begs the question: How do you measure efficiency? In a spacecraft, it's watts per sq in & watts per pound. But for an individual user like me who wants to make electricity for my home & vehicles, that's meaningless. The only thing I care about is watts per dollar. If this tech can reduce environmental costs, materials costs, production costs, and installation costs (all 'per watt'), that's where I'll put my money.
Charlie, you took the words right out of my mouth. As a consumer, I am continually frustrated by the apparent inability of manufacturers to give performance specs about their products in terms that not only make sense to me, but that are actually usable in an on-the-ground kind of way, not abstract numbers. My anti-favorite one is "joule", used by home office UPS makers. I can never, ever remember what it means and when I look it up, it still means nothing in terms of my home office equipment. But the first thing UPS makers ask is "how many joules do you need?" Sure, I'm an electrician and I think in joules every day, uh-huh. No guys--you're supposed to tell me how many I need based on the info I can provide you.
Hi: Very nice summary, and, I am interested in the topic. What I would like to know however is what the efficency is of the device. I know it is extremely early in its' developement, but, I like to know such things. This is extremely early: I remember when a high efficency cell was a fantastic 5% because it was that new silicon stuff!
I rarely look at the mail but I find your lead-ins enticeing.Earl.
scifi tech guy, I like your handle :). Regarding efficiency, that's a good question: it can be measured in several different ways. Also, this is a prototype, not a working product, and definitely not a product that's been transferred to a volume manufacturing process. Check out the discussion below: many of the comments concern the subject of efficiency.
Hello again Amy and tech oriented correspondents: I did as Amy suggested and found more material on subjects I am interested in. Some background: I have been interested in "alternative energy" since the 1960s. This is in part due to my long term interest in space exploration. There was a very large amount of practical ( for powering space systems version of practical) and advanced research done on systems that could be used for space power plants that we thought we would need in the relatively near future. This included thermoelectric and thermo ionic sources ( for Venus and Mercury probes Molybdenum Silicide thermoelectric conversion elements as an example). I also read about the work on Earth based applications, such as water heating devices that was mentioned as a desirable, economic way of using the Sun, during the 1970s and onward. This is a significant source of water heating for homes in Japan. As for the carbon based cells versus the present units with rare elements: I have looked into the various material used in Silicon and other cells ( and L.C.Ds. as well) and found that Indium, courtesy of Indium Corporation of America, is somewhat pricy except in thin films: a retail price for a pound ( from a Mc Master Carr catalog) was ~$350/ pound. Sorry for the long message,but, I think these points might be of interest to your audience, and you, Amy.
Thank you, Earl.
P.S.: I am intersted in energy beamed from space and have been on panels, and attended talks, on this subject.
Earl, thanks for the comments on alternative energy and space exploration. I didn't realize that alt energy projects/technologies had been developed in that context, but it sure makes sense. The high and continually rising price of indium and its projected scarcity, as mentioned in the article, is a major reason the researchers were interested in developing a carbon alternative. No problem re length--we love long comments! (BTW, my name is Ann).
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