I am unfortunate enough to live in southern California. As most of the world knows, some idiots thought that deregulation of everything else had been going so well (hence the Valujet crash) that they should radically change things with the electrical utilities. The net effect seems to be continuous news coverage of the likelihood of “rolling blackouts” not to mention skyrocketing bills. So now, the question…
Back when I was in high school, I remember taking two small electrical motors, connecting the driveshafts with a rubber band, hooking one to a power source and the other to a light bulb and getting light. It seemed to me that with a good transmission (possibly distributing the motor’s power to several generators), and actual generators instead of motors, couldn’t you viably generate (more) electricity this way? I was told that it would be impossible to get net+ electricity out of such a thing, but the reasoning why wasn’t clear to me. Yes, efficiency would be critically important, but when you consider the Rube Goldberg-ian method we use to get electricity from nuclear reactors, couldn’t this be a possible renewable energy source? Even with advances in superconductors and such?
Or was there a reason I did so badly in said electronics class?
The input power to the motor will always be greater than the total output power of the generators hooked to it, unless you succeed in breaking a few fundamental laws of physics …
Each generator presents a load on the motor, which forces it to draw more power from whatever is power the motor. If everything were ideal, you’d break even, which means you might as well have hooked the motor’s power source directly to whatever the generators are powering.
I am curious why you propose a sort of perpetual motion machine that seems to violate both the First and Second laws of Thermodynamics, yet refer to nuclear power generation as “Rube Goldberg-ian”?
Would you really like to hear a more detailed explanation of exactly why your system will not work, and why in fact it will produce less energy than other systems we all currently use?
What’s nuclear power got to do with this? Are you saying, because nuclear power is really complex, I can get more power out of a system than I put in? Think conservation of energy.
Nuclear power just involves heating water to generate steam, and expanding said steam in a turbine to generate electricity. Not so complex.
[hand goes up in air]
Well, hey, I would! Seriously. Now that you mention it, it does seem like an interesting idea. He’s talking about using an electric motor to run a whole bunch of generators, right? So, okay, why wouldn’t it work? Speak slowly and use little words, please. Pretend you’re Bill Nye the Science Guy.
Or is it just a conspiracy by the power companies?
Well, I don’t know who Bill Nye the Science Guy is, and I don’t know exactly what kind of explanation Anthracite had in mind, but I’ll give it a try.
There’s a rule called the 1st law of thermodynamics that has never been known to be broken. It’s commonly known as the law of conservation of energy (to be exact, it’s mass-energy that’s conserved, but let’s not go there).
Basically, it says that energy can’t be created or destroyed. If you carefully track all the energy (heat, electricity, chemical energy, whatever) flowing into a system, and all the energy flows out of a system, and the amount of energy stored in the system, it will all be correctly accounted for. Like a bank account (starting balance + money lodged = closing balance + money withdrawn).
If you found a machine that broke this rule, it would be a perpetual motion machine of the first kind. We would say its efficiency was greater than 100%, meaning that you got more energy out than you put in.
It would mean you could have as much energy as you wanted, just by building some of these machines and having them feed one into another. We would have no more need for nuclear or coal power stations.
Efficiency is a figure that you get when you divide the useful energy you get out by the energy that you put in. For example, in a coal power station, that means (electricity generated)/(coal burned). At a certain coal power station I know, the efficiency is 40%. The very best power stations have an efficiency of around 55%.
But hang on, if energy can’t be destroyed, how come the power stations don’t have an efficiency of 100% (energy out = energy in)?
Well, the key phrase here is “useful energy”. This is where the second law of thermodynamics comes in, which says that energy will always be degraded by any physical process. What that means is that in the real world, efficiency will always be less than 100%. You put in a hundred (energy units) of coal, you get out forty (energy units) of electricity, and the remaining sixty energy units comes out in the form of heat, which you dump into the nearest river or into the air.
So the first law says “you can’t win”. The second law says “not only can you not win, you can’t even break even”.
The example of the motor being used to drive the generator would be a perpetual motion machine if you got more energy out than you put in. What will actually happen is:
The motor uses 10 watts of electricity, which it gets from the wall outlet. If the motor is 90% efficient, it will produce 9 watts of mechanical power at its output. The remaining watt is used to make whirring noises and warm up the room a little bit. Let’s say the generator is also 90% efficient. It then produces 8.1 watts of electricity, which is used to light a bulb.
If we had just used electricity from the mains to light the bulb in the first place, we would have saved 1.9 watts.
So, overall, we’ve lost useful energy, rather than gaining anything.
That’s as clearly as I can explain it. I’m sure Bill Nye’s job is safe!
(looks around, sees that she is not needed yet, and ducks back out…)
(ducks back in to ask hibernicus which coal plant has an efficiency of 40%, and how is that being measured? That’s a NPHR of 8532 Btu/kWhr after all - pretty darn low. You’re not talking about Moneypoint Station for ESB, are you? Because I thought their best was about 9300 Btu/kWhr?
And surely your 55% efficient plant is a combined cycle GT, right?)
what was de-regulated was the price the utilities bought power for (input fuels). Consumer prices were still regulated. Polution standards were still regulated.
So lets say you are a power producer and the gov’t says that the price you can charge for power is $10/unit and can never change. At the time you pay $5/unit to produce it and pay $2/unit to clean it up.
…time goes by…prices increase to $6/unit and $3/unit cleanup…
Now some you would like to build a plant to expand capacity but you will have to pay the equlivant of $4/unit over the life of the plant to pay it off (to cover construction cost and newer, stricter enviormental standards). your existing plants are costing you $9 (the $6 for fuel and $3 for cleanup) the new plant will cost and additional $4 - meaning you will be loosing money. So you being a smart business man request a rate hike for the consumers but are denied - so you don’t build the plant.
…time goes by… prices for fuel double to $12/unit and $4/unit cleanup (so you are paying $16/unit of power produced and selling it at the regulated rate of $10/unit)
How long can you stay in business, you are loosing $6/unit you produce, if you proiduce more then you loose more - why produce any (if you can get away w/ that), better to have rolling blackouts, at least you don’t loose money there.
Now I know this is a very oversimplified example that doesn’t take into account all aspects… but it does hit on the main point. By freezing consumer prices but ‘freeing’ fuel prices you create a shortage when fuel price goes up. this is the law of supply and demand, and how it is effected when good ol’ Unc. Sam gets his hands on it.
Now you’re scaring me, Anthracite. I am left with no option but to defer to you as the undisputed queen of energy-related threads.
Yes, I was talking about Moneypoint. Yes, the heat rate (based on power exported) is not as high as 9000kJ/kWh. But how the heck do you know what it is? Surely this is commercially sensitive information. I’ve no idea what the efficiency is at Drax, for example (Here I’m trying to beat you at your own game by guessing where you work), except that it’s presumably “around” 40%.
Anyway, I’ve been trying to avoid any further public humiliation by only posting when I’m damn certain I can stand over it, and in this case I feel an approximate figure was quite appropriate to the context, so I can skip the retraction this time.
Oh and yes, of course the 55% refers to a new CCGT.
How about just “coal”. There are others here that know as much as I do about energy in general.
Oh, I know a lot about coal plants. I have a very large database of info, and can tell you exact details, like what the forced draft fan motor power is at Moneypoint, or the boiler efficiency of Drax, or the Superheater tube bank configuration of King’s North. In fact, I know a lot about UK plants. Since I saw you lived in Dublin, I didn’t even need to look for info - I know Moneypoint.
Besides - heat rate changes so often, esp. depending on which coal(s) Moneypoint is importing - my numbers are just general figures anyhow.
Be gentle with me–all I know about science I learned from reading Popular Science in the bathroom.
Okay. I understand the part about the generator not being 100% efficient. But they’ve got something called “superconductors”, right? Where you super-cool it and then it becomes a perfect conductor? In theory, would that help, if you dunked the generators in super-coolant? Has anybody ever tried this, I mean at a commercial level, not just in the lab?
P.S. Bill Nye is TV’s Mr. Wizard for the 90s–glossier graphics, more editing jump cuts.
All a superconductor is is a material that can conduct electricity with no losses due to resistance. This does not mean that it can create energy, simply that it does not lose energy while conducting it. Superconductors are limited by the amount of energy they can carry, or current density, but in small applications work well, provided you keep the temperature really loooooooow.
A motor would benefit some from use of superconducting materials, true. But overall, there are other factors to consider. The bearings of the motor create a drag on the shaft, and this drag requires energy to overcome (and shows up as heat). Even the resistance of air on the rotor is an energy loss. The magnetic field has energy losses. Yes, you could make a motor that is 99% efficient perhaps, with magnetic bearings and operating in a vacuum.
Yes, it would help. But overall, let’s assume that we have a perfect, 100% efficient motor, with superconducting wires, and a perfect, 100% efficient generator.
What does this device do? It uses a motor to turn a generator. No useful work is done whatsoever. Due to conservation of energy. The generator will not produce more power than goes into it. And 100% of it’s power is needed to drive the motor. If you try to tap off power to light a light, or do anything else, the system now has an imbalance. And thus runs out of energy.
I think part of the reason that this motor-generator hookup seems like it would be able to generate more power than it draws is that people are mostly familiar with generators when they aren’t hooked up. The rotor seems to spin freely, so it seems like one motor could spin a lot of them. That would be true, but only when the generators are not connected to any load. In other words, as long as you didn’t try to actually get electricity from them.
When you draw from a generator, it no longer spins as freely. There is a counter-force created by the electromagnetic forces that create the power. If you tried to draw more and more power, the mechanical resistance would build up until the system stops turning.
If you have a windmill hooked to a generator, you can see the mill turn slower when you flip the switch on whatever load you have hooked up. In many electric car designs, the motors that drive the wheels are used as brakes by simply letting them generate power to charge the batteries. It causes the car to slow and stop.
It’s sort of (though not exactly) like the way that your engine has to rev higher when you load it by turning on the air conditioning.
Simply speaking is’t bcasuse we are converting the energy stored in fuel to heat first then power. Whenever you convert energy to heat - you have a heck of a time getting it to another form of energy.
Energy in = Energy out Always
but some of that energy out is heat that goes up the stack and lost.
Energy in (fuel) = Energy out (electric) + Energy out (heat)
efficiency = energy out (electric) / Energy in (fuel)=40% (in this case)
Now if you can use a fuel cell instead of burning it, you will directly convert the stored chem. energy to electrical energy and have much higher efficencies
Even at my youth challenged age, pure unadulterated competency still excites me, even more so than the exciter on an 1100 MW unit does it’s generator. And by a woman in a traditionally male dominated field. There is hope for the world! Electro-mechanical erotica abounds!*
I knew that what I was asking was impossible due to Newtonian laws (that I never fully understood–avoided physics like the plague). But I wanted a better understanding of why, and I’ve certainly gotten that. Particularly from this reply, which is something I hadn’t considered:
When you draw from a generator, it no longer spins as freely. There is a counter-force created by the electromagnetic forces that create the power. If you tried to draw more and more power, the mechanical resistance would build up until the system stops turning.
It also makes sense that the drive motor draws more power as you hook up a transmission and multiple generators, I was just hoping that somehow you could come out ahead. But as I wrote the question it did occur to me that it would be a perpetual motion machine, and I almost didn’t post it.
BTW, I had referred to Nuclear as “Goldberg-ian” because the water-steam-turbine phase (which I know other systems use as well) as opposed to my (impossible) direct system.
Ok, so anybody have any other ideas for a direct system? For example, could you make a solar panel that was sensitive to radioactivity, and store waste from reactors in containers made of the panels?
