186 comments on Energy Transitions Past and Future
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I think that this
should be "...commonly extracted with power densities of 102 or 103 W/m2 of coal or hydrocarbon fields...."
Is that correct?
Chris
Yes, thanks.
I didn't know the html tag for that when this was first posted.
It is worth noting that you get that power density for a one time use of say 20 years but then you have to move on and tear up some other portion of the Earth. With solar power operatiing at say 90 W/m^2 average power density, you get continual use and one only need wait 25 to 250 years before you've our performed fossil fuels by this measure.
Another place where one might make a comparison is in fig. 4 where the energy produced per kg of silicon used in solar power is about 200 times greater than for coal if we stop to refurbish the silicon after 25 years or so. In fact, owing to the smaller distances traveled for silicon compared to uranium, silicon beats uranium in terms of ton miles of transportation for a given amount of energy delivered. One would need to expand the plot boundries to include this though.
Chris
Not sure I agree on the solar numbers. but I agree that the area of land needed to provide a watt of power is a meaningless measure when that power comes from depletion of a nonrenewable fossil fuel. If you were to compute the area of, say, shallow tropical seas needed to create the fossil fuels, and the time that takes, you'll end up with far lower areal power densities than the 1W/m^2 of current photosynthesis.
The calculation is pretty easy. A 200 Watt panel weighs about 42 pounds. With 5 hours a day peak equivilent illumination you get about 9 MWh over 25 years, or about 200 kWh per pound. Coal gives about 1 kwh per pound. So, silicon requires much less hauling than coal for the same amount of energy.
If you want to compare to uranium, just figure the distance between you and a panel factory. For me it is about 70 miles. Then consider uranium mined in Australia, enriched in France and used in Maryland together with the shielding needed to transport it and you'll see that silicon also gives more energy than uranium in terms of how much lugging is involved.
I see that the anonymous cowards who have been rating my comment down don't like physics much, but that is really all that is going on here.
CHris
In 2007, the 439 operating nuclear reactors produced 2608 billion kWh requiring 76,200 tonnes of U3O8.
76,200 tonnes = 167,640,000 lbs
Therefore Energy/mass = 2608e9/1.68e8 = 15,557 kWh/lb
What shielding would that be, Chris? Uranium is a low activity alpha emitter. A sheet of paper would suffice. As for the distances you mention, it is worth again considering how small 76,200 tonnes is. You could easily transport it all with a small fleet of clipper ships!
So, if you carry out the math, you'll see that silicon wins. It is not all that important. It just puts the geewizz aspects of fission power into perspective. It ain't that cool. Fusion from a safe distance is much better.
A container for shipping 45 kg plutonium in a MOX assembly weighs 3.9 tonne. http://www.ccnr.org/lyman_casks.html#typ
So, you can call it packaging or shielding but it is a little more extra mass than solar panels ship with.
Chris
Could you be any more dishonest? Really, think about your argument here.
1. MOX isn't used for a majority of power plants.
2. Plutonium in mox is about 1% of the fuel load.
Worse and worse. I thought the plan was to put reactors down all over the world and reprocess the fuel in nuclear weapons states. You're just walking right into it.
Look, this really isn't important. Getting coal from the mine to the power plant probably reduces its EROEI by a good bit (in fig. 6 the value for coal is mouth-of-the-mine while that for oil is likely delivered), but that is not the case for moving solar panels around or nuclear fuel unless there is an accident. Silicon is superior to uranium by a bit but neither have the problems carbon for combustion has. I have heard of plans to ship uranium ore. That could be stupid I guess.
Chris
I know thats what a lot of people want to do, but I think its just a good way to waste money. Spent fuel doesn't hurt anyone while sitting in dry storage casks in a cordoned off parking lot of the power plant, and should stay there for the next several hundred years. You don't save money by reprocessing and you complicate the fuel cycle. As far as I can tell it has some potential for being a money saver in some fluid fuel reactor regimes, but with operating reactors today theres just no reason to do it except politics.
Not anymore stupid than shipping coal. All uranium mines today have ores that have higher energy density than coal when burned in LWRs.
It is worth noting that we've been over some other ground in response to this same article about a year ago: http://www.theoildrum.com/node/2856#comment-224123
The reason for controling spent fuel in non-nuclear weapons states is to avoid proliferation problems. So, on-site storage is not what people have in mind.
Chris
Right. Unenriched uranium yields 54 electrical MWh per kilogram in the plant near me, 24.5 electrical MWh per pound, more than 100 times the supposed 25-year yield of a solar panel, and requires no shielding.
--- G.R.L. Cowan, H2 energy fan 'til ~1996
http://www.eagle.ca/~gcowan/Paper_for_11th_CHC.html
I presume you are using a CANDU reactor, and very likely your uranium came from Canada. So, the transportation involved is likely less than typical. What I'm using now was likely mined in the Soviet Union, enriched and down blened there and then transported to the East Coast of the US. That would make lbs miles per kwh about the same as solar not counting packaging. I was thinking more of what to expect in 2013 or so.
Nukulur kooks tend to get all excited about E=mc2 and drool all over fission. This just points out that silicon does E=mc2 with much greater elegance than uranium.
Chris
Chris, I know you derive particular enjoyment from these mathematical drivebys you like to do against nuclear power, but can't we agree - for the sake of truth and fluffy bunny rabbits - that lbs miles per kWh is a piss poor metric to judge either nuclear or solar. Transport costs are a minor fraction of the EI in their EROEIs. Essentially the whole argument in this thread is a proxy for EROEI and not a very good one at that. Kinda like two men arguing over which is tallest based on who's wearing the thickest socks.
I think I've said as much in the thread. It is just fun really. For coal, it does make a difference. Gas also loses something in translation. Oil begins to see some important cost over long distances too.
Chris
...Only photovoltaic generation, a technique not yet ready for mass utilization, can deliver more than 20 W/m2 of peak power...
assuming a peak insolation of 1kW/m2 the indicated photovoltaic peak power of 20W/m2 would need a meager 2% conversion efficiency. Currently even low cost PV modules (CdTe) reach 10% at a cost of less than 2$/Wp.
In less insolated places on earth such as Switzerland the average annual production of 1Wp installed capacity is 1kWh. Thus the annual average power is around 10W/m2 - in the Sahara 20W/m2 are reached.
Currently the best PV cells are 4 times better, which rises the power flux to 80W/m2 well within reach of the 100W/m2 indicated for an oilfield. rw
Solar thermal systems, specificly dish stirling can reach 312 W/m^2
85.7 m^2 intercept area
26.75 kW net output
31.25% conversion effeciency
Yes!
(poly)crystalline silicon PV cells are, uh, sub-optimal technology. If you insist on something that produces electricity in one step, the new thin-film techniques are much better.
But PV's problem has always been storage. Solar thermal systems (driving good old steam turbines) beat any PV-and-battery system hands down.
Solar thermal is much quicker to deploy and much more (down-)scalable than nuclear, too. This is important in small and less-developed countries.
Said by Cutler Cleveland:
Said by rolf_w:
I think Mr. Cleveland's figure of 20 W/m2 is the daily average. For example:
efficiency of monocrystalline PV: 15%
efficiency of thin film PV: 5%
average efficency: 10%
percentage of clear days (assume no power output on cloudy days): 75%
integration factor for PV pointing in fixed direction: 6 hours
insolation: 1000 W/m2
power produced during one day: 10% * 1000 W/m2 * .75 * 6 hr/day = 450 (W/m2)*hr/day
Convert the units by dividing by 24 hours / day to get: 18.75 W/m2
which is close to his 20 W/m2.
I swear, people keep comparing apples to oranges. Solar power is ten times as valuable as nuclear power on a KWHr basis. Noon power is far more valuable than midnight power.
Midnight power in the winter in the north is substitutable by insulation. Try doing that with noon air conditioning power sometime.
Though technically you could use a zeolite air conditioner working off a thermal mass from night time electric power.
Item: The only reason current nuclear power generation is not a peaking resource today is because no-one asked it to be. The engineering is quite straight-forward, witness many aircraft carriers and submarines commonly operating at less than full power reliably, safely and often in the harbours in front of you.
If you think insulation can substitute for fuel in heavy heating zones, then you've clearly never lived through a winter in Canada. Stupidity. Lack of power/ fuel / energy in a subtropical zone makes you uncomfortable. Lack of same in Edmonton in winter WILL kill you.
Well, I like fission, but no one should expect fission to be a peaking power supply unless somehow it becomes cheaper than every competitor. I suppose it allready is for solar, but...
The real problem with using fission as a peaking power supply is it makes no sense. Nuclear fuel is so cheap and the risk of playing around with the reactor power based on demand is nonzero. Its far better to just run them at full power the entire time and dump the excess into resistors.
I know some reactors do play with load following, but its an awful big waste of time.
These two statements are somewhat contradictory, since nuclear gives both noon and midnight power.
Now if the capital cost of solar was 1/10th that of nuclear they would be complimentary. Perhaps it will be someday.
If I had to guess, I'd say you are right about this. Fig. 5 certainly looks like average power density and it neglects better solar thermal efficiencies. In the end, the measure is not all that important. Wind does not interfere much with farming on the same land while strip mining does. You can get all the energy you need putting solar panels on your roof without interfering with any other land use but you can't usually drill for oil in your basement with success.
The nuclear power industry likes this measure because they can bad mouth hydro which is cheaper and produces less carbon emissions. But uranium mines leave toxic tailings while reseviors have other uses than just generating electricity.
Once we realize the basic conceptual error that depletable resources don't have a high average power density measured on renewble energy timescales, then the usefulness of the measure pretty much evaporates.
Chris
You can refer to the Web Design Group page for a handy list of these little gems, where you'll find shortcuts like °, ±, ² or µ — or you can just enclose the superscript in <sup> tags.