A reader writes:
I've just read an article in Popular Science about Sun Catalytix' "artificial photosynthesis" being used to power houses.
Which got me questioning, is it even viable? Using water as an energy source, as you've said previously, involves electrolysis, and the power it can generate won't exceed what was used in the electrolysis process.
He is using sunlight as the energy source, so I guess it's not one of those water-powered-car scams. But wouldn't it be easier if we use batteries to store the electricity from the solar panel?
And where does the photosynthesis comes in?
Please enlighten me here.
Andhika
The photosynthesis is supposed to replace the electrolysis. See, electrolysis is really inefficient, and batteries aren't awesomely efficient either, and you need a pretty darn big battery bank, which wears out, to run a whole house. But photosynthesis can manage efficiency as high as 8%, so... uh...
Look, buddy - "photoelectrochemical cell" is 24 letters - 25, including the space. We're already really pushing the brainpower of the voting public with the word "photosynthesis", all right?
I started doing a series of actual calculations about this, then stopped, because there's not enough information in the article, the marginally-more-informative Scientific American article, or...
...the less-than-entirely-satisfying accompanying video, for any really solid numbers to be made.
(You can't say that that video doesn't alert the viewer to the fact that it's not aimed at people who know a single damn thing about anything. "In the next forty years, you're going to need more energy than is available from every source you can imagine", says actual MIT professor Dan Nocera. Never mind that decreasing human energy consumption, while continuing to improve quality of life, is a real and serious goal; I can also "imagine" fusion power, dude. So clearly I'm not part of this clip's intended audience. Paging Mr Bush; Mr Bush to the coal-fired courtesy phone, please...)
In neither the Popular Science nor the Scientific American piece does the writer seem to have paid any attention to that core "30 square metres of solar cells in Boston making 30 kilowatt-hours in four hours" claim. It seems fishy to me. As does the idea that this magical catalyst is actually a useful breakthrough.
I'd be willing to believe that this was a real, if slightly oversold, option, if it weren't explicitly about a system that you're supposed to install on your roof to run your house. This didn't, early in the Scientific American article, seem to be the case - "We emulated photosynthesis for large-scale storage of solar energy", says Dan Nocera.
And yeah, you might perhaps actually be able to get the stated output from the stated area of cutting-edge panels at Boston's latitude if they're all on expensive sun trackers and/or overpumped by extra reflectors and water-cooled. Which they can be, relatively economically, if they're part of a municipal solar farm and not stuck on someone's roof.
No matter how good the magic catalyst is, though, nothing's going to give you all of those 30 kW/h back again, and Mr Nocera goes on to say "...We need to do it the old American way of making one small one and then manufacturing that system to give it to the masses."
Which brings us back to the cheerful notion of an easy $35,000 worth of cutting-edge solar panels and sun-tracking hardware on everybody's roof, much of which will need repairs after every storm. Unless you ditch the trackers, reflectors, cooling system, et cetera, in which case the stated energy output becomes impossible with even maximum-efficiency commercial solar cells of the stated area. You're likely to need something like twice that area for well-aimed never-shaded cutting-edge commercial cells, an easy three or four times the area for cheaper panels installed on a real-world roof...
A couple of commenters on the articles, and on this Engadget writeup, managed to briefly poke their heads above the SOCIALIST TEA PARTY MASONIC JOHN BIRCH GRR comments to point out some of these issues.
Fortunately, even if Mister Nocera is being outrageously misquoted (occasionally by himself!), his company is only about the hundred-thousandth-worst outfit to have had US taxpayers' money sprinkled upon it lately. And who knows, maybe there's something to this, even if it depends upon solar panels that haven't yet been invented, or something.
I wouldn't rush out to place a deposit, though.
7 March 2010 at 9:03 pm
I'm not actually expecting any answer before tomorrow, yet you made a blog post. You just never fail, Dan. Thanks for the answer. :D
I'm not exactly sure what to say, the notion of "brand new totally efficient energy for everyone" always makes the alarm goes off, but this one seems somewhat promising. And while it seems rather off, not much can be said since we just don't know much about what it is they are making.
I guess I should just wait and see. If they really do manage to bring it up and running, then it'll be good for everyone.
7 March 2010 at 9:13 pm
A system that uses photosynthesis to store energy until you need it? Brilliant!
Can it release that energy as light & heat?
Can you put it in your backyard?
It only requires water?
And sunlight?
And, er, maybe a bit of nitrogen?
That would be a tree, right?
8 March 2010 at 3:25 am
I always liked photosynthesis as a way to dodge the high manufacturing cost of solar cells. Particularly for developing nations, instead of sending all kinds of money away to get sheets of highly-pure silicon, why not plant some weeds, and throw the lot into a big digester every few months?
Unfortunately, land where you can grow and harvest lots of biomass tends to be used to grow and harvest food, or other crops that are of direct economic benefit. And farming doesn't generally produce a lot of biomass that's genuinely waste; lots needs to get plowed back into the soil to keep it healthy. The one example I can think of easily is something that would grow on seawater in a desert; but seawater has so much sulfur in it, whatever fuel your digester spits out is going to be full of sulfur, like the foulest coal.
8 March 2010 at 9:44 am
I'm familiar with quite a bit of Dan Nocera's prior research. He's not just an obscure MIT professor, he's one of the world's leading authorities on proton-coupled electron transfer reactions, and has been presenting the research towards this particular catalyst (with a particular eye to the biomimetic aspect) at universities for a couple of years now. I'm not intimately familiar with the workings of this particular compound, but the buzz from the people best placed to call him on any bullshit is that it's up to scratch.
8 March 2010 at 10:11 am
"30 square metres of solar cells in Boston making 30 kilowatt-hours in four hours"
Assuming my arithmetic is right (which isn't a 100%-reliable assumption), that translates to a quarter-kW per square metre. Modern silicon solar cells in sunlight with half-decent Maximum Power-Point Trackers (not sun-trackers) can manage about 1kW/m^2, or four times that, at Sydney's latitude (which from memory is fairly close to Boston's) so it's not an entirely unbelievable statistic.
8 March 2010 at 2:29 pm
1kW/m^2 is your standard back-of-the-envelope solar irradiance, so a solar cell would have to be 100% efficient to harness that much energy.
The given figures work out to 25% efficiency, which is quite optimistic.
8 March 2010 at 9:29 pm
@Anne - weeds of the sea you say?
http://planetearth.nerc.ac.uk/news/story.aspx?id=226
I like the idea of putting it in the desert - although evaporation would be a problem.
8 March 2010 at 9:54 pm
The way the article confused energy and power was not reassuring, but the research still seems exciting.
If hydrogen is to become a viable means of storing energy, it needs research just like this to improve the efficiency and cost of generating it.
9 March 2010 at 11:04 am
@kamikrae-z: That article is interesting, though they don't address the sulfur issue. I'm also leery of farming vast swatches of the shallows, since it's an ecosystem, and one we don't understand very well at that. But if you pick a hunk of desert not too far from the sea, it shouldn't be too hard to build an artificial pond to grow seaweed, or algae, or whatever. Evaporation isn't a problem, since you're running it on salt water: just pump more in to replace the evaporation (and in fact even more in, to flush the brine back to the sea). Of course some deserts are ecosystems too, but much of the Sahara (for example) is almost totally devoid of life. (And since the Sahara is expanding, I wouldn't worry too much about threatening the habitats of any Sahara-dwelling life.)
9 March 2010 at 5:53 pm
I like the trees idea. A couple acres of trees is more than enough for a continuous supply of wood for heating a house. Will take about 5 years before you can start harvesting...But then you have a supply of carbon neutral biofuel.:) Not exactly low on the labor requirements for harvesting though. But anything that requires you to use chainsaws I approve of.
11 March 2010 at 8:33 pm
When Richard Branson announced a prize for an invention to remove CO2 from the atmosphere, I had a good mind to send him my 3yo's drawing of a tree!
I did a back-of-the-envelope calculation aways back and figured the 'Typical Aussie Family' would need to plant about 3,000 trees to be carbon neutral, only accounting for direct energy use of household & 2 cars. There's a whole lot more when you start to include cradle-to-grave energy accounting...
To those that have mentioned algae, I reckon you're on the right track. I sincerely believe algal biofuel is the way of the future - for our transport fuel woes, anyhow. At least, until we have fusion online... Then we'll just pump electrons straight into our cars instead of wasting them on this "Hydrogen Economy" nonsense.
There's a guy* in Western Australia that's done a lot of research into it. He reckons marine algae can produce upto 10x as much biodiesel than agricultural crops per unit of surface area. He figures - on an industrial scale - it would become viable at about $80 per barrel. Hello?
It doesn't need to take up precious arable land. It can be done anywhere there is lots of sunshine (desert), saline water (sea, or bore-water), and a ready supply of CO2 (coal-plant, or geological). It's done in 'bioreactors' (tanks with kms of transparent piping), not ponds.
The beauty is, biodiesel isn't the only thing you can produce with algae! With genetic engineering, you can produce all manner of pharmaceuticals, and other high-value molecules. Once those are extracted, you can pass the remainder through a fermentation process to produce alcohol fuels, then feed the remainder of that into a composting process to produce methane gas for cooking, heating, etc! With the remainder of that, you can produce fertiliser, animal feed, compressed carbon brickettes for burning, pure carbon for industrial / scientific / medical use...
One waste stream feeds another process. That's how Nature works. That's how we should do things. Currently, we only extract one energy phase from a resource, and then throw it away!
Carbon is the most precious resource we have, being abundant and most useful! Oh, and diamonds.
Moving away from the whole Gaianistic "Great Carbon Cycle" thing... The other great thing about biofuels is that it's backyard technology... Low-tech. Barely removed from pressing olives, grapes and breweries. You can use the very same infrastructure we have in place to fill up the car you drive NOW, without modification (if it's a diesel...)! None of this high-pressure liquid hydrogen gas operator licensing... Just drive up, fill it with algae juice, and drive away!
I've heard that it would take an area the size of Australia to produce enough biofuel to supply global demand. With algae, it might take a tenth. With true hybrids that mostly run off batteries, and have a small diesel generator in the boot to recharge while you're parked... Maybe halve that again...
Apologies for the essay. And to be clear, below is reference to research guy, not me!
* Michael Borowitzka, Murdoch University, WA.