Nanowire Forests Use Sunlight To Split Water 56
An anonymous reader sends this excerpt from IEEE Spectrum's Nanoclast blog:
"One of the fundamental problems with fuel cells has been the cost of producing hydrogen. While hydrogen is, of course, the most abundant element, it attaches itself to other elements like nitrogen or fluorine, and perhaps most ubiquitously to oxygen to create the water molecule. ... Now researchers at University of California, San Diego have developed a quite different approach to mimicking photosynthesis for splitting water molecules by using a 3D branched nanowire array that looks like a forest of trees. ... The nanowire forest [uses] the process of photoelectrochemical water-splitting to produce hydrogen gas. The method used by the researchers, which was published in the journal Nanoscale (abstract), found that the forest structure of the nanowires, which has a massive amount of surface area, not only captured more light than flat planar designs, but also produced more hydrogen gas."
Hmmm... ZnO band gap is 3.37 eV (Score:5, Interesting)
The experiment is interesting as regards the benefits of the nanostructure of the materials, but the 3.37 eV band gap of ZnO must be kicked across by a photon of no less energy (no longer wavelength) than 367 nm: ultraviolet.
The good news is that you have plenty of energy relative to 1.25eV minimum needed to split water. The bad news is that you need high energy photons that are relatively scarce in sunlight by the time it reaches the earth's surface.
Re:Efficiency? (Score:2, Interesting)
At what point will the technology provide more useful energy output than is required to manufacture and maintain the system? Will it substantially reduce fossil fuel usage, or is it another ruse, like the wind farms?
Oh dear, a Slashdot poster has made what appears to be a false claim about the EROI of wind farms.
Time to google around a bit and see if there's anything to it [academia.edu]....
This analysis reviews and synthesizes the literature on net energy return for electric power generation by wind turbines. Energy return on investment (EROI) is the ratio of energy delivered to energy costs. [...] Our survey shows an average EROI for just the operational studies is 19.8 (n=60; std. dev=13.7) This places wind in a favorable position relative to fossil fuels, nuclear, and solar power generation technologies in terms of EROI."
So, to sum up the above summary -- parent poster is wrong. As a matter of historical record, the average wind farm produces about 20 times more much energy than it expends on construction and maintenance.
Oh dear, a Slashdot poster appears to share the same opinions as the Big Energy Companies. Please google a little further and take a look at http://www.wind-watch.org/ [wind-watch.org] for a different point of view. BTW - I live in West Texas - we're surrounded by these beasts. It's all a scam foisted on us by companies like (early adopter) Enron. The winners are the developers, the losers are the customers neighbors, and wildlife. Ask the folks in North Texas, who had to deal with a brownout a few years ago when the winds died. Ask Big Energy why they must build more conventional plants when they add wind to the grid, and why those conventional plants have to be running while the wind farms are generating. Ask the residents of Great Britain and Europe how wonderful wind is. Ask how much carbon does wind energy eliminate from overall emissions. (/soapbox)
Re:Solar cells? (Score:4, Interesting)
I've heard that concentrating light on a solar cell increases the efficiency. So if a concentrator captures 4x light from a 4x aperture onto the same size solar cell surface, you get more electrical energy than just 4 like surfaces. If that's true, the intensity is doing something to avoid the losses, which I assume are heat losses, which should normally be higher with a concentration due to the higher temperature. Any truth or applicability to that?
The Holy Grail of solar power is, of course, to turn 100% of sunlight energy (across a huge spectrum) into an energy form that can be directly used. So I'm looking for that (without all that science background to know the details about things that can really work. My last look into this was trying to find if anyone was building nano Sterling Engines.
Re:Efficiency? (Score:1, Interesting)
Ask Big Energy why they must build more conventional plants when they add wind to the grid, and why those conventional plants have to be running while the wind farms are generating.
Ok, the answers to that one are so blazingly obvious I wonder why you bothered to ask. The obvious answer is that demand is increasing all the time so they need to build more plants anyway. Also the wind doesn't blow all the time, so it needs to be supplemented. As for those plants running while the wind farms are generating... Hmm, maybe because they cost a lot to build, the companies that built them want to run them as much as they can and sell the power?
Seriously, the stuff you're saying comes off like a bit of a crazy rant. I certainly get that some people don't like these wind farms being built next to them. How that equates into the wind farms being some giant conspiracy to erect towers that don't really generate power (which seems to be what you're implying), I have no idea.
I apologize - perhaps this will explain my viewpoint.
The conventional plants aren't being built to meet new demand, but as a backup to the wind farms. When a large portion of power provided on the grid is from wind, there must be an almost equivalent capacity available as spinning reserve, because the grid is a demand driven system. In other words, the reserve must be up and running, and ready to be switched onto the grid at a moment's notice if the wind dies. In Texas, that usually equates to a gas or coal fired generator. So, how do wind farms remove any carbon dioxide from electric generation, when the conventional generators have to run, even when not supplying anything to the grid? Why not just build the conventional plants, and forget about the wind?
The reason the developers build wind farms is that the Gum'mit makes it highly profitable to do so. Besides the Feds supplying almost all of the funds, there's also accelerated depreciation, carbon credits, local goverment tax abatements, and so forth. One of the first guys to jump on the wind farm bandwagon was Ken Lay, of Enron infamy.
I advocated wind generation for nearly forty years. When I took a serious look at it, I found that it makes no sense in a grid system. The entire "wind" movement is a method of moving tax dollars into the pockets of companies who don't need them.
Here is one (of many) links which may help explain: http://www.wind-watch.org/news/2011/11/22/wind-energy-realities/ [wind-watch.org]