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View Diary: What Greens on Kos Need to Know about Energy (52 comments)

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  •  Okay... (1+ / 0-)
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    R rugosa alba

    We already beat plants by burning a whole lot of dead ones in the form of fossil fuels.  My question is can we beat plants without cheating.  I.e. without tapping geologic reserves of energy.

    By your own calculation the answer is probably no.  If our solar cells are only twice as efficient we'd need to cover more than half the country with solar cells.  This, needless to say, would be vastly costly and, yes, probably exhaust our Neodymium and Cadmium supplies (As Cadmium is only 1 part /10 million of the earth's crust).  Sure we might have wind and hydro, but I wouldn't hold my breath.

    I'm not trying to argue against renewables.  They are a sensible investment and are the only source of energy that will ultimately last.  But I am against the idea that investments in renewables alone will solve the ecological crisis.

    •  I don't know if investments in renewables (0+ / 0-)

      alone either will be sufficient or economically feasible to replace energy derived from greenhouse gas emitting sources. It's an engineering problem, the answer is quantitative (needs numbers), and it isn't a simple answer to arrive at in the real world.

      Cadmium is about 100 times more abundant than platinum and there is a small amount of platinum in every modern car - tens of millions of them - in the catalytic converter. Cadmium is used in low quality photocells (CdS) and the 'cad' in NiCad rechargeable batteries is cadmium. If you open up any cheap piece of electronics that's more than 10 years old, the steel mechanical parts (chassis, etc) will have an iridescent appearance - that's cadmium plating. It's a toxic heavy metal, so its use is being eliminated, but it's cheap and common. It's a waste product (or would be if not reclaimed) of several types of mining.

      As to a calculation for beating plants, it's not that hard to do. 100 Quads = 100 Exajoules more or less is the amount of energy you want (actually more than what we want, because we both want increased efficiency and conservation).

      100 Exajoules = 2.8 E15 watt-hours (E15 is 10 to the 15th power)

      Solar flux is around 1300 W/m^2, but let's use 1000W for simplicity and to be conservative. 2.8E15/1E3 = 2.8E12 m^2-hr. The units are odd, but it's an intermediate step - we have square meters-hours. We can get the area of the array we need by making an assumption about hours.

      Let's say we get 5 hours of sunlight every day (average - some days a lot more, some days a lot less, but even cloudy days provide some energy, and we've already discounted solar flux 30%).  That's more than 1800 hours, but rounding to 1800, we then  need about 1.5E9 square meters of solar arrays.

      My goodness, that's a big number! It's a square 38,729 meters on a side - about 120,000 feet. There are 5280 feet in a mile, so we need an array 23 miles on a side to capture all of the energy the US uses in a year.

      But we haven't looked at efficiency! 23 miles assumes 100% efficiency. At 20% efficiency (pretty much achievable with solar cells, esp in the sloppy context of this calculation) we'd need 5X the area, or a square a little over 51 miles on a side (2650 sq miles - about 1/4 the area of MA).

      One-quarter of MA for all of the US energy needs without resorting to fossil fuels or any non-renewable source.

      Whether or not it's practical is another question (there are all kinds of problems producing this many cells and distributing the energy, depending on how centralized the generation is, for example) .

      But compared to the scale of plants, extracting 100 quads of energy from sun, wind and water alone is not a daunting problem because of scale. In fact, ONLY in terms of scale, it's pretty trivial. Scale isn't the problem. No matter how much you want to change my assumptions, you'll have to be unrealistic to get to even a TX sized array - about 100X the calculated area - and TX is less than 7% of the area of the US, meaning the array is only .07% of the US area.

      Oh and --- an exajoule is about 5% bigger than a quad, so the calculation is extremely conservative - I've overestimated the area needed by at least 5%, and probably a lot more. And we passed 1 exajoule in wind generation (actual output, not nameplate) a few years ago. The solar energy falling on the entire US (incl AK and HI) is probably somewhat more than 10,000 exajoules annually.

      Modern revolutions have succeeded because of solidarity, not force.

      by badger on Thu Mar 07, 2013 at 09:06:32 PM PST

      [ Parent ]

    •  Burning those dead plants . . . (0+ / 0-)

      This is the key point. Oil and coal have been very effective  (and uncomplaining) substitutes for slavery and serfdom. They have enabled ordinarly people in the developed world to live much better than royalty did in past centuries.

      For many applications in industry and transportation there is no substitute for fossil fuels, and it's a serious problem that so many people think we'll just be able to substitute solar, biomass, or wind and continue business as usual indefinitely.

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