Science questions not worth a thread I: I'm a moron!

I almost feel bad asking this one. My biology textbook describes light reactions as light and H2O being used to provide electrons for NADP+. The oxygen is released, so the hydrogen can then be split to yield two electrons and two protons. One of the electrons is used to oxidize NADP+ into NADPH. Then another electron is carried by the carrier molecule, and is neutralized by a proton. My question is, where does the extra proton go?

HardRocker said:

Is it a reliable replacement for fossil fuels? I mean, it sounds like you could just run it on water if you had the capability to split it into it's perspective components then run it through a PEM or whatever you have to do, right?

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You've figured out the crux of the issue.

As of now, fuel cells remain a promising replacement for liquid transportation fuels... Exactly the same as they were 20 years ago.

The membrane technology has improved somewhat, but there is no infrastructure in place for supplying hydrogen hydrogenated drogen fuel. Plus, until hydrogen is being produced by a solar process, there is still likely a carbon footprint associated with it.

Ballard Power Systems in B.C. Used to have a pretty good presentation on their website. But it's been years since I looked at them.

HardRocker said:

Is it a reliable replacement for fossil fuels? I mean, it sounds like you could just run it on water if you had the capability to split it into it's perspective components then run it through a PEM or whatever you have to do, right?

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Asking whether it is a replacement for fossil fuels is the wrong question to ask. It cannot replace fossil fuels, because it needs fuel. In fact you can operate a fuel cell with fossil fuels if you want to. Whatever goes into the fuel cell has to be the replacement for fossil fuel, not the cell itself.

The question you want to ask, is whether hydrogen can be a replacement for fossil fuels. This is somewhat independent from the fuel cell, as there is in principle nothing preventing an internal combustion engine running on hydrogen. So you could try to replace fossil fuels with hydrogen without fuel cells.

If we had an infinite power source, we could indeed just split up water and use that as fuel. As we don't we have to consider efficiencies. And there is the problem: Although the conversion inside the fuel cell is quite efficient, you also have to consider the conversion efficiency when you produce the hydrogen and the losses you have while transporting and distributing the hydrogen. Because the atoms are so small, hydrogen is a very trick gas to store and while the energy content per mass is quite high, it is difficult to get a high energy content per volume while minimizing losses.

As it is, it seems more economical to store the electricity in batteries instead of using hydrogen as an intermediate energy carrier. I think its more likely we're going to see most cars powered by batteries instead of hydrogen.

There are some other uses for fuel cells, though. It can be uses to produce electricity from methane. So if you are having a biological process generating methane (maybe as a waste product) you can use a fuel cell to efficiently convert that into electricity.

The hydrogen fuel cell is just a battery, not a fuel or a power source. It produces no energy, only moves it around by storing energy produced in another fashion, and releasing it when it is required. It's good if the energy comes from solar power or some other renewables, but not if it comes from fossil fuels.

Unless if we mine something in a higher energy state than its final state, that is all it can ever be used for; a battery. We mine coal and oil because we can use it as energy directly. We refine oil to remove the not as energy efficient parts of it so it can be used in our machines which require more consistency when burning fuels.

Since hydrogen has to come from either water or methane, you have to input energy to turn it into hydrogen, and you can get no more than that energy back when you react it with oxygen to turn it back into water. (while you can get energy out of methane - hydrogen - water, you might as well be burning the methane directly, because it is more efficient that way with less steps for energy loss.) In reality less because of thermodynamic inefficiencies.

A pretty glaring problem with hydrogen fuel cells is that water is a really happy molecule. It costs a lot of energy decomposing water and recombining it. Almost of a two steps forward two steps backward sort of deal. But like Bluemofia said, if you had a solar cell on top of a HFC you could get some decent energy conversion outta it.

Yeah it is always going to cost more energy to split water into hydrogen and oxygen (and then compress and store/transport the hydrogen) than you will get out of it. This is not the case with oil at this point, which gives out more energy than it takes to extract IIRC. So unless you have a *free* energy source like really cheap solar panels, reliable and cheap wind power or access to awesome geothermal power like Iceland, then there is no really viable way to make hydrogen for fuel cells economically.

Which is exactly what everyone else already said. :facepalm:

Also Hydrogen has a very low energy density in terms of volume. It's very hard to carry enough to power a car for long unless it's in liquid form, but that requires refrigeration etc. and is dangerous and impractical.

iirc Lithium Ion batteries actually have better energy density than hydrogen at this point, and the old hydrogen economy dream is basically dead.

We get fooled by cognitive tricks on this topic. Yes, hydrogen costs more energy to produce that it delivers. So does everything else.

[numbers are made up]
I require 120 l of 'hydrogen equivalents' to give you 100 liters hydrogen. 100 l of that is what you'll get. 20 l is the inefficiency of generating the power. Those 120 l of hydrogen equivalents can be from burning oil or methane or harnessing a renewable.

It's the same with oil. I need 120 liters of oil in order to give you 100 liters. I use 20 liters to pull the 100 liters out of the ground. I had 120 (in total). Now you have 100.

I see what you're saying. That makes sense, thanks.

El_Machinae said:

We get fooled by cognitive tricks on this topic. Yes, hydrogen costs more energy to produce that it delivers. So does everything else.

[numbers are made up]
I require 120 l of 'hydrogen equivalents' to give you 100 liters hydrogen. 100 l of that is what you'll get. 20 l is the inefficiency of generating the power. Those 120 l of hydrogen equivalents can be from burning oil or methane or harnessing a renewable.

It's the same with oil. I need 120 liters of oil in order to give you 100 liters. I use 20 liters to pull the 100 liters out of the ground. I had 120 (in total). Now you have 100.

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Well, instead of "oil" in your second example, I would use crude oil and gasoline to be more clear. And probably use units of energy. 120 Joules of crude oil, spend 20 Joules to make 100 Joules of gasoline.

So, let's say you start with Water. You use 120J of energy to turn that water into Oxygen and Hydrogen, separately. Then, at the other end, you put them back together and it releases 100J. So you need 120J at one end to release 100J at the other end.

With oil, you use 20J of energy to get the oil out of the ground. Then you burn it and it releases 100J of energy. So you need 20J at one end and 100J at the other end. The difference is that there is 100J of energy stored in the oil -- but you don't need to provide this, because the dinosaurs and plate tectonics provided this for us already. You only need to provide the extra 20J of energy to get it out of the ground.

Is this simply EROEI in a different guise?

Hydrogen is an energy storage method, not an energy source. It's more comparable to a lithium ion battery than it is to oil, solar, or wind energy. Though, if you want to be picky about it, oil is also an energy storage method -- but the energy it stores ultimately comes from solar energy a long time ago.

Just wanted to mention that there are a few different kind of fuel cells with different operating temperatures (PEMS, MCFC,SOFCs and so on).
The big advantage of fuel cells is the direct conversion of chemical bound energy to electrical energy. As this is not a Carnot type process like a power generation via heat there are different limitations.
Some types of fuel cells can use alternate fuels like methanol or CO.

It should also be mentioned that fuel cells can also be used in the reverse process to generate hydrogen an oxygen from water.

One big disadvantage for most types of fuel cells are the expensive resources. Often platinum or rare earth elements are required for the electrochemical properties. E.G. the cathode of SOFCs is often made of a lanthanum strontium cobalt ferrite compound.

Say I want to find the turning radius of my automobile on a given surface. I'm sure that the arc of the wheel and the velocity of the car are the two variable factors here. Is there a closed-form two-variable equation that I can use to find this turning radius? Hell, I'll even accept a differential equation if that's all you have.

Distance between front and rear wheels, and left and right wheels too I guess.

You can probably just look it up online.

http://db.theautochannel.com/db/newcarbuyersguide/rank_car_criteria.php?stylename=Sedan&titleid=184

IdiotsOpposite said:

Say I want to find the turning radius of my automobile on a given surface. I'm sure that the arc of the wheel and the velocity of the car are the two variable factors here. Is there a closed-form two-variable equation that I can use to find this turning radius? Hell, I'll even accept a differential equation if that's all you have.

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Mise said:

Distance between front and rear wheels, and left and right wheels too I guess.

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What Mise said... plus the weight of the car would definitely be necessary. Also how much are we simplifying?

i.e. is it ok if the wheels skid? Are we going to allow a 'power slide' sort of deal where the car travels laterally while applying power to push the front end towards the center of the circle? etc.

In those cases the math will get WAY harder.

IdiotsOpposite said:

Say I want to find the turning radius of my automobile on a given surface. I'm sure that the arc of the wheel and the velocity of the car are the two variable factors here. Is there a closed-form two-variable equation that I can use to find this turning radius? Hell, I'll even accept a differential equation if that's all you have.

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There are two parts to this: One is the geometric limit, which is determined by the arc of the wheel and the placement of the wheels. This limit applies at low velocities. At higher velocities the limit is the amount of friction force between the car and the surface. The force needs to be high enough to force your car into the desired curve, overcoming your forward momentum. To calculate that you would need the friction coefficient between your tires and the surface, the total downward force generated by the car, the mass and the velocity of the car.

Why is it that the vast majority of species, not to mention a significant portion of humanity, are homogenous in appearance? On top of that, what made humans, and cats and dogs, develop a wider variety of physical appearances, in terms of shades and colors at least?