Fun with Energy NumbersAn (energetic) rebuttal to Robert Bryce's article at the WSJ |
2 Comments |
| By Steve Balogh in Energy, Peak Oil, Solar, Wind Power | April 14, 2009 | |
Since I can’t leave my comment at the WSJ forums on this article (I guess the discussion is closed), I’ll have to do it here.
from the article:
Let’s Get Real About Renewable Energy
We can double the output of solar and wind, and double it again. We’ll still depend on hydrocarbons.
[snip]
Mr. Bush’s record aside, the key problem facing Mr. Obama, and anyone else advocating a rapid transition away from the hydrocarbons that have dominated the world’s energy mix since the dawn of the Industrial Age, is the same issue that dogs every alternative energy idea: scale.
Let’s start by deciphering exactly what Mr. Obama includes in his definition of “renewable” energy. If he’s including hydropower, which now provides about 2.4% of America’s total primary energy needs, then the president clearly has no concept of what he is promising. Hydro now provides more than 16 times as much energy as wind and solar power combined. Yet more dams are being dismantled than built. Since 1999, more than 200 dams in the U.S. have been removed.
If Mr. Obama is only counting wind power and solar power as renewables, then his promise is clearly doable. But the unfortunate truth is that even if he matches Mr. Bush’s effort by doubling wind and solar output by 2012, the contribution of those two sources to America’s overall energy needs will still be almost inconsequential.
and so forth…
Here’s the issue that I have with this article – the math:
For the sake of convenience, let’s convert the energy produced by U.S. wind and solar installations into oil equivalents.
The conversion of electricity into oil terms is straightforward: one barrel of oil contains the energy equivalent of 1.64 megawatt-hours of electricity. Thus, 45,493,000 megawatt-hours divided by 1.64 megawatt-hours per barrel of oil equals 27.7 million barrels of oil equivalent from solar and wind for all of 2008.
Now divide that 27.7 million barrels by 365 days and you find that solar and wind sources are providing the equivalent of 76,000 barrels of oil per day. America’s total primary energy use is about 47.4 million barrels of oil equivalent per day.
My rebuttal:
Politics aside, I believe that the math in the article is a little misleading.
It’s true that 1 barrel of oil contains 6119 MJ of energy, or 1.64 MWh of energy. However, electricity is highly refined energy, i.e. one must burn 3 MJ worth of coal to create 1 MJ of electricity (roughly the same for oil). The author’s math assumes that there is a process for converting all of the 1.64 MWh in a barrel of oil into electricity. At best the conversion rate is 30-40%. Looking at a barrel of oil in that light, one would consider a barrel of oil to “equal” 0.55 MWh of electricity. Or, conversely, a barrel of oil would be displaced for every 0.55 MWh of renewable electricity production.
Redoing the math:
45,493,000 megawatt-hours divided by 0.55 megawatt-hours per barrel of oil equals 82.7 million barrels of oil equivalent from solar and wind for all of 2008.
Dividing by 365, the numbers remain grim – 227,000 barrels of oil equivalent per day. Still a drop in the bucket of the roughly 19 million barrels per day of crude oil consumption, but much rosier than the picture that Mr. Bryce paints.
This is one of the tricky issues of energy conversion, and using “energy equivalents” in arguing your point – especially when comparing electricity to raw fossil fuels. I would expect that the economists and energy analysts at the WSJ would understand this concept, especially someone who is the managing editor at the www.energytribune.com website.
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Kiashu said,
Both comparisons are dumb, it’s apples and oranges. The writer you’re quoting is a denier of the problems we’re facing, he wants us to do nothing, so he deliberately tries to confuse us by wrong comparisons – not mathematically wrong, but categorically wrong. Apples and oranges.
We’re talking about two different things here: transport, and electricity. One uses almost all the oil, the other uses almost none.
Electricity is quite funky in that we can get it from lots of different sources; change the power plant, and you don’t have to change anything else. My lightbulb works as well whether its electricity comes from coal, nuclear, wind, solar, someone pedalling, or whatever.
Transport’s a bit more difficult because we can’t just change a power plant (or refinery), we have to change the world’s billion or more cars and buses and trucks and so on. It’s as though to change my electricity I had to change all my light bulbs and appliances in the house.
The thing is that looking at oil, oil is not often used in electricity generation – just by a few oil-exporting countries. Most oil is burned in transport. So that trying to figure out how much electricity-equivalent energy there is in a barrel of oil is like trying to figure out how many bricks it’d take to build the Empire State building – it’s not built out of bricks! It’s a different kind of building.
So the US could stop all oil imports and production tomorrow, and electricity generation would not change very much at all; they could shut down every last electricity generator, and it wouldn’t stop everyone truckin’ around.
When talking about renewably-generated electricity, it’s much more useful to talk about how much COAL or NATURAL GAS renewables could replace.
Then in talking about transport, we can talk about how to reduce oil consumption.
Okay, let’s look at COAL. [http://www.eia.doe.gov/cneaf/electricity/epm/epm_sum.html] In the US, coal produces 48.5% of all electricity. This was 1,994,385,000 MWh in 2008.
A 1.5MW wind turbine [like these beasts: http://www.evolvegreen.ca/catalog/item/6320001/6373009.htm produces full power about 25% of the time (it begins at maybe 40% in the best spots, but after you’ve installed a lot and run into NIMBYism, you have to choose some bad spots and it drops down to 15% or so, it all averages out to about 25%). So it generates 1.5MW x 25% x 8,760h = 3,285 MWh.
Thus it would take 607,118 of those things to generate the same electricity as coal does today in the USA. They’re retailing at US$1,647,500 each. Of course if you ordered 607,138 of the things presumably you’d get a discount, but let’s be pessimistic. This would cost about a trillion dollars. That’s an enormous sum, but is less than the USA has already spent propping up dying banks, less than it’s costing them to lose two wars, and so on. It’s conceivable to spend and build that much in, say, a decade.
Of course you wouldn’t rely on wind for half your electricity, you’d want solar PV, solar thermal, hydro, geothermal, tidal and so on, too – just for resilience, since it’s NEVER happened that it was heavily overcast with still air across a whole continent at once, but still.
Replacing natural gas generation and sorting out wasteful transport and reducing overall consumption are other issues again, and as I said you wouldn’t choose any one generation method, but this gives you an idea of the scale of the problem, and a clearer idea of what the world is facing. The world does not have to replace oil with wind; it has to replace coal and natural gas with wind, solar PV/thermal, hydro, geothermal, and tidal.
Then it has to deal with oil and transport as a separate issue. For example, with the electricity conserved by reduced distribution losses (renewables are more distributed than central, so we have shorter distances between generation and consumption) we could have more electrified rail, so that people could get rid of their cars.
And so on. We have to be clear about the issues and their scale, and not fall into deniers’ traps of comparing apples to oranges.
Guenter Sperling said,
It seems that all three articles are not very helpful. In my opinion, the questions should be:
A) How many kW are required to convert a gallon of oil into gasoline?
B) How much gasoline can be produced from one gallon oil?
C) How much electricity can be produced with the resulting gasoline?
D) How many miles can a medium size electric car run on that electricity?
F) How much money can be saved by switching to electric cars running on wind power that has the smallest cabin footprint and has become the least expensive energy in the U.S. in 2008?