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New Solar Cell Harvests Hydrogen From Water
Engadgets is reporting that researchers at Penn State have built a new kind of solar cell that can harvest hydrogen directly from water. "The folks at Penn State have now developed a process that more closely mimics the photosynthesis process in plants, and while we won't pretend to understand all the nitty gritty of dye usage and other such nonsense, we do know that such a system could eventually attain 15% or so efficiency, providing a nice and clean way to gather power for that fuel cell car of the future."
The summary = the article.
The original article was on Science Daily a few days back.
ad logicam Claiming a proposition is false because it was presented as the conclusion of a fallacious argument.
Step 4 is "put it outside in sunlight" I think the point is that they have bypassed using electrolysis, instead using the sunlight to stimlate a dye and catylist that splits the water directly. If so, it would be much more efficient than using a solar cell and electrolysis.
GE/CS/IT d- s: a- C++++$ UL+++ P-- L++++ E W+++$ N+ o? K- w---() !O M- V- PS+ PE(++) Y+ PGP+++(+) t+++ !5 X++> R- t
Yep. And 40% is a bad number; the cells that have that efficiency rating are a long way from production. 15% is pretty similar to what most solar cells on the market get today.
ad logicam Claiming a proposition is false because it was presented as the conclusion of a fallacious argument.
15% efficiency would actually be pretty good considering by some calculations photosynthesis efficiency is around 5 to 20%.
:( )
Here is one calculation showing ~6.6% photosynthesis efficiency
It takes into account things like canopy shading, which wouldn't necessarily apply to this, but here's the link:
http://www.upei.ca/~physics/p261/Content/Sources_Conversion/Photo-_synthesis/photo-_synthesis.htm
I tried to find a peer reviewed one, but can't find one right now(I'm at work, break almost over...
Accentuate the positive, don't waste your mod points on the negative.
Not necessarily. If this new technology could eventually reach 15% efficiency, then it's still nothing particularly wonderful when you take into account the fact that some firms like Boeing Spectrolabs boast solar cells with efficiencies as high as 40% (they do use "solar concentrators", so it's possible that their panels may take up several square meters of surface area for every square meter of panel surface. Not having seen their designs, I wouldn't know).
Take a 40%-efficient solar cell and use it to feed power to a 50%-efficient electrolyzer, and you get a net total efficiency of 20%, which is better than the maximum estimated efficiency of this dye-based approach.
If they dye approach proves to be cheaper or can also be enhanced by solar concentrators or what have you, then it may have some value from an economic perspective, but I don't see anything 15% efficient providing dense solar power solutions compared to other technologies already available.
The other thing to keep in mind is that the output from this dye is hydrogen, not electricity. If you need electricity from one of these dye-based hydrogen generators, you'll need to marry it with a fuel cell or something long those lines which will further degrade efficiency. In terms of raw electrical output-per-square meter of deployed solar collectors, you'd be better off with conventional solar cells in the 15-20% efficiency range.
Of course we also need to get engines that run on hydrogen that are also safe and efficient, but this is a step at any rate.
If you own a four stroke, spark ignited, internal combustion engine, you have one now. The conversion to run on hydrogen gas instead of liquid gasoline is quite trivial.
Let's take your average car. Not being picky, I'll surf over to Carmax and choose whatever pops-up first
- Engine: 2.4L 166-hp (~575kW) inline-4
- Outside dimensions: 172" x 72" (4.4m x 1.8m)
So you've got 7.92 sq.m. of available roof area. I'll assume you can cover that 100% with your solar converter, and I'll further assume you can keep it pointed normal to the incident light. Typical insolation is 1000W/m^2, so your roof-mounted collector can harvest 7.92kW. Period (i.e. you don't get more energy than what is incident on the vehicle's cross-section.) You're collecting solar energy, and storing it in the potential reactive energy between hydrogen and oxygen. With a 15% efficiency, your converter stores 1.188kW while it's illuminated.
Getting back to our example Honda Element - 575kW engine
And therein lies the fundamental limitation. There isn't enough energy intercepted in a vehicle's cross section to make this structure viable. At 100% conversion efficiency, you just start to be able to power the econobox-class vehicles for around-town drives. Anything with distance or power requirements will need to be fueled by something much larger than the vehicle itself.