Friday, April 19, 2002
12:06 AM LINK
What the Heck is this Thing Called a Stirling Engine?
I'm embarassed to admit it, but I find myself scrambling to learn about the Stirling engine after the recent announcements regarding Dean Kamen's patent of an engine of this type.
Stirling engines are nothing new. Robert Stirling patented his original design in 1816. This site shows a simple Stirling engine that uses a coffee cup as its power source. Heck, there's a whole category on e-bay for them.
From a physics perspective, engines are defined by their basic design. I'm not talking about the V-8 or the Slant-6 or anything you'd find in a mass-produced automobile today. Those are all variations on one particular type of engine, namely the Otto engine, which is commonly called the internal combustion engine, and was one of the great inventions that defined the 20th Century.
In a physics sense, engines are defined by their thermodynamic cycles, specifically how the pressure, temperature, and volume vary throughout the cycle of the engine. When you study basic physics, you start off learning the Carnot cycle, which is the most zen-simple category of engine. The four-stroke Otto cycle is a little fancier. Another example is the Wankel engine, commonly called the rotary engine, which I wrote about a couple weeks ago.
So what exactly is Stirling engine, you ask? The bottom line is that unlike the internal combustion engine, which has intake and exhaust valves for the critical fuel-mix gasses, the Stirling engine gases remain forever inside the engine. There is no intake and no exhaust. Instead of being burned internally, the gases that drive the pistons are heated by an external source. This heat source be anything. Hence the Mr. Fusion appeal of the design. Anything that produces heat (including gasoline, hydrogen, biomass, plastic army men, the sun, etc.) can be used as the power source. With internal combustion, you have to use gasoline mixed in the right proportion with oxygen.
Thus the magic of the Stirling engine is that it can provide locomotion from an arbitrarily wide selection of possible fuels. Since the Stirling engine produces no inherent exhaust from its internal gasses, if this external fuel source is non-polluting, then voilà, you have a non-polluting way of providing useful work.
Another appeal of the Stirling engine is that with the proper design, it can run almost silently.
The Stirling engine is one of the those "curious phenomena" that every physics student is fascinated by. Many hobbyists love to build them from kits. The problem was that it was not considered practical to mass produce them for locomotion.
Furthermore, even if you did mass produce them, you still need to provide some source of heat. That is, something has to be burned. To run a heavy steel automobile off a Stirling engine, you might still need to burn a high-BTU fuel like gasoline, albeit not inside the pistons. In that case, you'd still get all the overhead that goes with our current energy economy. The real breakthrough would be a mass-produced Stirling engine that would provide enough horsepower for practical transportation without requiring the burning of a hydocarbon fuel.
Has Kamen done this? It's hard to tell right now. If the Ginger pattern is followed, we will get all the details in time, but first we will endure some requisite Kamenesque drumrolling. I personally am willing to cut the guy some slack. If I were to criticize him, it would only be out of pure jealously.
Thursday, April 18, 2002
11:58 PM LINK
Survivor
Well I survived my one day of fame as Fox News' "Blog of the Week" It was sure, well, yummy. The majority of the mostly-angry emails I received were responding to the headlines that Fox slapped over my paragraphs, rather than to the material I actually wrote. I'm beginning to see how this works. It was quite a lesson in how to generate lots of feedback.
Wednesday, April 17, 2002
4:18 PM LINK
Enron Wind Power?
Yes, Enron Wind. Sound strange, doesn't it? I stumbled into this site looking for more information about the power output of wind farms. One the things that disturbs me about wind-power articles in the press in how easily the authors throw around figures like "it will produce 420 MW" of electricity.
My immediate question is: what is the meaning of this figure? Is it the peak power output (when the wind is blowing so as to crank the turbine at its faster rate), or is it an expected average, based on how much the wind will actually blow. If it's the peak output, then really you are comparing apples to oranges, when you put the 400 MW from a wind farm next to 400 MW produced by, say, a nuclear power plant (unless you account for shutdowns in the plant, which do occur, even on a routine basis).
The peak number is pretty straightforward to calculate. The expected average is a lot more complicated. You have to know a lot of the how the winds blow in the exact spot where the wind farm is located. The only exception is if the wind blows all the time, at the same speed, which it doesn't, even at the South Pole.
The Enron Wind link above about a small wind farm in Wisconsin offers some clues. The 30 MW figure they quote is the "capacity." This is synonymous with "peak", so there is no mystery here. On the next line they offer how much energy they actually expect to harvest in a year. If the peak were the actual expected amount, you could obtain the energy in a year simply by multiplying the power by the number of hours in a year (giving you energy in megawatt-hours).
For example, under that scenario, 30 MW would translate to about 260 thousand kilowatt-hours. But Enron says they expect to harvest only about 52 thousand kilowatt-hours each each, which is almost exactly 1/5 of what the peak would bring. In other words, the real power output of the farm is about 6 MW, averaged over the year (The closeness to 20% makes me wonder if this is a standard rule-of-thumb).
On the other hand, a coal-fired plant with a capacity of 500 MW could, in theory, run at that level almost constantly, as if the "wind were always blowing."
From now on, I'm going to assume the numbers I see about wind farms are peak capacity numbers, unless I find out otherwise.
In that light, the advantages of running an offshore wind farm become much more obvious. If the wind blows at a fairly steady rate, as it does over the ocean, then you can come up with a much more reliable figure for the energy produced over time. This is an obvious advantage is raising the capital for such projects.
I don't mind if the articles in the press use peak power outputs to describe wind farms. But I just wish they would be more up front about this.
Tuesday, April 16, 2002
2:48 PM LINK
Off-Shore Windfarming in the Kennedys' Backyard
This article in today's NYTimes by Karen Lee Ziner is about a controversial proposal by Cape Wind Associates of Boston to spend 600,000 dollars (financed through conventional loans) to build a 170-unit windfarm on 28 square miles of Horseshoe Shoals in the waters off Hyannis, Massachussetts.
It seems off-shore windfarming is not a new idea. Although there are existing fields in Europe, this one would be unprecedented in the U.S. because of its scale. The towers themselves would be enormous compared to the ones typically seen in California. The carbon-steel turbine columns would tower 270 feet high, over 40 stories high at the tallest blade tip. They would be spaced one-third to one-half mile apart and would deliver up to 420 MW of electricity to the New England regional grid (equivalent to a small nuclear reactor; up to one-half million homes, using the "1 MW = 1000 residences" rule of thumb). The farm would supposedly be operational by 2005.
Local residents are less than enthusiatic. Greenpeace is in favor of it.
Here's a U.S. Army Corps of Engineers article about the project. Evidently such a project requires a "Section 10/404 Individual Permit."
This article from the National Geograhpic a couple month's ago is about a proposal by the same company to build a 200-turbine offshore windfarm off the coast of Ireland that would produce up to 520 MW.
"Currently Europe leads the world in its use of wind power. Denmark generates 15 percent of its energy needs using wind power with Germany and Sweden close behind. By 2020 Denmark expects to generate 50 percent of it power demands using wind."
The article gives some interesting figures about the difference in subsidies for wind power between Europe and the U.S.:
"Brian Parsons of the National Renewable Energy Laboratory in Golden, Colorado, believes that 5 percent of the country's energy demands could be met with wind power by 2020. "But it would be a big challenge," he said.
According to
this article in Scientific American, one of the principal advantages of offshore farms is that ocean winds are steadier than those on land. The article also mentions that the Massachussets farm would be visible from the
Kennedy compound.
1:44 PM LINK
Real Lifespans of Nuclear Power Plants
Some informed comments from Eric Epstein, the Chairman of TMI-Alert in a letter to the edtior of the Pennsylvania DEP newsletter, regarding the "premature" shutdowns of nuclear generation stations. He provides numerous examples of plants that did not fulfill their projected lifespans, and cites data to show that performance declines with age.
One example he provides is the Fort Saint Vrain Nuclear Generating Station in Plattesburg, Colorado. During the ten years it was in operation, it was the only helium-cooled commercial reactor in the U.S. It produced a mere 330 MW of electrcity (on the low side, definitely). It was operational for only 27.5% of its projected lifespan, from 1979-1989.
Fort St. Vrain is near to my heart. In 1986, while I was a sophomore in college, I held a summer job in Colorado at the Radiation Biology Dept. at Colorado State, as a part of the official monitoring of the plant for leakage of radioactive waste materials into the environment. We had to go to all the nearby dairy farms to collect milk samples once a week, and on two occassions I had to grind up carp that were caught with stun guns from a nearby pond. I had a date that night and had to wash the smell off in the shower with salt.
We would run the samples through a Silicon-Germanium crystal looking for signature peaks in the gamma spectrum. One thing you learn is that for a reactor, "there is no such thing as perfect containment." But if all goes well, the radioactivity of the waste products is barely noticeable above the natural radioactivity present in all living tissues.
It was right after Chernobyl. My boss would have his friends who had returned from Europe get measured in our lab's whole-body detector, which was surrounded by a big lead tank remanufactured from the doors of a nuclear submarine (my boss liked to take naps on the cot in there). There were always traces of radioiodine in our visitors' bodies, but by that time, several half lives had passed, so the gamma peaks weren't very big. "No cause for alarm!"
Monday, April 15, 2002
9:40 PM LINK
Nuclear Tourist
I had fun all morning with this site by Joseph Gonyeau. You can find out loads of information on the nuclear generating stations around the U.S., although the links to pages on the Nuclear Regular Commission site no longer work, because of Sept. 11.
What I did find out that interested me were some "typical numbers" about nuclear plants. A typical load of uranium oxide fuel for a plant is between 100-150 tons, of which 3% or less is fissionable U-235.
A typical power output from a reactor is between 2000 and 3000 MW, although only one-third of this gets translated into electrical energy. Thus your typical nuclear power plant unit generates somewhere around 600-1000 MWe (MWe="megawatts of electricity").
Often, a single "plant" has several reactor units. It is not untypical for these units to be owned by different private utility entities. An example is the split ownership of the two reactors at the Indian Point facility up the Hudson from New York, which is currently the subject of a lot of controversy from nearby citizens, mainly because of a breach in the reactor circulation system of Unit 2, which leaked radioactive water from the reactor into the turbines.
"...in NY state, nuclear power represents only 16.1% of the capacity, it provides 33.8% of the generated energy. Thus Indian Point 2, in actuality, provides about 5 % of total electrical energy generated in the state."
It must drive the citizens near the plant into a frenzy that the NRC also removed its own
page detailing this incident.
12:12 AM LINK
FossilFuels.org
Perhaps a Christian-based site, based on this lead in:
"Fossil fuels are one of the Creator's greatest gifts to humamankind..."
O.K. Let's run with that idea. God apparently gave the U.S. enough oil to get us all hooked on the stuff, but he gave the Moslems a lot more, so that they'll have plently of it to sell us when we run out of our stocks. Nice little power play. Who's side is God on?
They published this article on how the Internet is essentially a coal-powered phenomenon. This is true. Quite Dickensian, when you think about it, but 51% of U.S. electricity comes from burning the shiny black rock, all of which is mined right here within our borders.
But the article contains some rather interesting claims about how much of U.S. electrical demand increase is actually due to the growth of the Internet. I don't even bother reading these numbers. They might as well be made up out of thin air, coming from a site like that one, without a detailed explanation of how they were obtained.
