Doubling energy - is it so easy?

Factual Questions
1

What do you need in order to save people from dying of thirst and hunger? The answer is fresh water - so here is my project:
Build wind or wave energy near the coasts of Morocco. Use electrolysis and get hydrogen. Build pipes from the Atlantic up to the Atlas Mountains. As the H2 goes up you get lifting energy. Burn the gas and get more electricity. The waste is water and through pipes it goes down to Western Sahara and you get even more energy.
I calculated that you need 200 wind mills to get a million litres of fresh water per day. A million litres isn’t that much, but in ten years it would turn into a great lake. By doing this you would get over three times the energy of the wind mills.

Can someone check my calculations?
http://turunen.hopto.org/sahara.jpg

2

if you got over 3 times the energy out that would be tripling the energy not doubling.

if you think that you could get three times the amount of energy that it took to generate the hydrogen by the lift of it, generating electricity at the mountain top and getting energy from the water running downhill then you should make a small scale backyard pilot project and see if it’s true.

also the costs of a project are not just operating costs but you need to include the construction costs of the system. how long before you generate enough power and water to pay for the wind/wave machines, generators and pipes?

3

Your daily fresh-water production target of 1,000,000 liters is off.

Your stated target (line 2) was 3650 cubic kilometers of water over the course of ten years.

3650 cubic kilometers is 3,650,000,000 cubic meters.

That’s 3,650,000,000,000 liters.

Over the course of ten years (3650 days), that’s 1,000,000,000 liters of water per day.

Assuming the rest of your energy math is correct, you will need to multiply the number of windmills by 1000. Yes, you will need at least two hundred thousand (200,000) windmills.

In your infrastructure, you will also need to add massive condensers to liquify all the steam you will generate by burning all that hydrogen. Whereas an ordinary steam-cycle power plant has a big cooling tower to dump waste heat from the steam used in power generation, your plan specifically requires cooling the flue gas. If you cool it enough to condense completely, then great, no excess hydrogen production required. But you probably won’t, which means you’ll need excess hydrogen production, and therefore more windmills than originally estimated.

[sub]Can someone check MY math?[/sub]

4

how do you get lifting energy out of hydrogen in pipes? Hydrogen rises in air because the air is heavier. In pipes there is no buoyancy effect. You have to compress and pump the gas through the pipes, which costs energy. You need to take that into account.

5

A pipe in the sea where you produce hydrogen and the other end on the top of a mountain plus you burn it. Underpressure it is - or is it not? Even though the scale is different, would it not work like
http://www.youtube.com/watch?v=Qg1KdcUwOTI

6

If the hydrogen is permitted to undergo a natural buoyant-convection process that transfers it from the ocean to the mountains, then yes, you have an opportunity to extract energy from that process.

But in this case, it’s not going to happen. The hydrogen will be contained in a pipe(s), and the lower end of the pipe won’t be exposed to atmosphere - a necessary condition for a natural convection process.

Furthermore, unless you want HUGE pipes, you will need to pressurize the H2 to deliver it. My math shows a hydrogen requirement of 111 million kilograms per day. At atmospheric pressure, the density of H2 is 0.0989 grams (not kilograms) per liter; that’s 1.235 trillion liters per day, 14.3 million liters per second, or 14,300 cubic meters per second. A massive, costly duct 14 meters in diameter would result in a flow velocity of 100 meters per second. Even if you could use buoyancy to somehow assist this process, it won’t be enough: you will need massive fans (and massive power) to make this happen.

Alternatively, you can pressurize the H2, allowing smaller pipes.

Either way, you will not be extracting energy from buoyant convection; it’s going to require a massive power input to move all of this hydrogen from the ocean to the mountains.

7

Yeah, but if the byouant force could lift the gas up, it doesn’t matter if I miscalcuated by 1000 times. You can always use the extra energy in electrolysis and get even more water without new turbines. If you can lift up rockets with hydrogen why not water.

8

For one thing, it’s already been shown that buoyancy can’t provide any meaningful assistance in transfering the gaseous hydrogen from the ocean to the Atlas mountains 200 miles away.

And your miscalculation does matter. Your OP was titled in part “is it so easy?” As the corrected numbers demonstrate, no, it’s not easy. 200,000 windmills is a LOT of windmills.

Big windmills have a rotor diameter of nearly 100 meters. If spaced a suitable distance apart (4 diameters cross-wind and 7 diameters up/downwind), 200,000 windmills would require 56,000 square kilometers of land/sea. That’s a square 237 kilometers on a side.

If a windmill costs US$2 million, then our vast array of windmills would cost US$400 billion. The cost is probably much higher if located off-shore.

Now consider the power plants up in the mountains, running on hydrogen delivered from the windmills. Assume a 300-MW plant costs $1B. For the hydrogen delivery rate calculated earlier (111M kg/day), assuming the power plants are 50% efficient, we’re talking about 91 GW of electrical generation. If you build 300 MW power plants, you’d need 300 of them, at a cost of US$1 billion each. Total, $300 billion.

Add in the cost of:

electrolysis hardware
hydrogen pumps
200-mile-long pressurized hydrogen transfer ducts (more, depending on how spread out the wind farm is, and on how spread out the power plants are in the rough terrain of the Atlas mountains)

massive condensers to condense the flue gas (pure steam) into liquid water for the lake
A North-African electrical grid to distribute all that electrical power ('cuz there’s no way Morocco can use it all)

and the entire project is likely to cost well over a trillion US dollars.

No, not easy.

9

For the sake of interest, what about a really big tower - water being electrolysed at the bottom, hydrogen captured into balloons attached to a chain that loops up to the top of the tower and back down again - balloons inflated with hydrogen lift one side of the chain - when they reach the top, the hydrogen is burned to produce heat to drive some kind of generator - the resulting water vapour is either condensed or vented. Deflated baloons exert a downward force on the other side of the chain - work is extracted from the rotation of the sprockets on which the chain is strung.

Apart from the practical mechanics of the thing, how much energy can we extract from it? I’m not sure it’s necessarily less than the amount required to split the water, because of the balloon cycle - the energy obtained from burning the hydrogen cannot exceed the energy expended splitting the water, but the buoyancy bit is not part of that transaction.

10

Remember the Three Laws: You can’t win, you can’t break even, and you can’t get out of the game. Even assuming 100% efficiency in all components (which is impossible, as per the second law), you still wouldn’t get any more energy out than you put in. The bit it’s easy to overlook is the thermal energy in the hydrogen gas: If you’re filling balloons with the hydrogen, you have to let the hydrogen expand, which will cause it to cool off. So the hydrogen that goes into your generator at the top of the tower will be colder than the hydrogen that came out of your electrolyzer at the bottom, which will cost you energy.

11

Perpetual motion does not work.

(Someone had to say it).

Besides which, you would also have to separate the hydrogen from the oxygen after the electrolysis (which takes energy).

12

Shouldn’t that be 3,650,000,000,000 cubic meters? So 3,650,000,000,000,000 liters and 200 million windmills?

13

Part of the electrical energy used in the electrolysis process will go toward pushing back the earth’s atmosphere to make room for your growing bubble of hydrogen. That’s not even accounting for any effects from tension in the balloon; assuming you just have an unstretched gas bag, it still takes work (at sea level, 101 kPa x the volume of the hydrogen in the gas bag) to push back the atmosphere.

Let’s assume a you produce, via electrolysis at sea level, a 1 cubic meter balloon of hydrogen. Youve done 101 kJ of work just to push back the atmosphere.

Buoyant lifting capacity of a cubic meter of H[sub]2[/sub] at STP is 10.8 N. If that buoyancy remained constant at all altitudes, you’d only have to ascend that gas bag up to 9300 meters to recover that energy. But buoyancy decreases with altitude, which means you have to float your gas bag up even higher. How high? As it turns out, you’d have to float that gas bag all the way up to the absolute top of the atmosphere (letting the entire atmosphere come back down to where it was before you filled the gas bag) to recover all 101 kJ of energy (I ran my spreadsheet up to 100,000 meters and got 99% energy recovery). And the buoyancy would be steadily decreasing toward zero when you got all the way to the top. IOW, it would be virtually impossible to recover all of that buoyancy energy.

More to the point of the OP, that buoyancy energy wasn’t free; you used windmills to create electricity to push the atmosphere back to make room for the H[sub]2[/sub] you were producing.

Note too that the electrolysis process will waste significant energy by also pushing back the atmosphere to make room for all of the waste oxygen you are producing. O[sub]2[/sub] is near neutral buoyancy, so you wouldn’t expect to extract energy from an O[sub]2[/sub]-driven version of your balloon conveyor.

14

The title was doubling the energy - if you can have a system over 100% efficiency, you can use the spare energy to create even more with only one wind turbine. So balloon, pipe or rocket, can we get hydrogen to 3000 meters with less energy than created?

15

3650 km[sup]3[/sup] * (1000 m/km)[sup]3[/sup]

= 3650 km[sup]3[/sup] * 1,000,000 m[sup]3[/sup]/km[sup]3[/sup]

= 3,650,000,000 cubic meters.

Nope, just a mere 200,000 windmills. :smiley:

16

Actually, you don’t need more than a trivial fraction to physically separate the oxygen, and hydrogen from each other in electrolysis. You just place the anode and cathode in separate collecting regions, connected with only water. Just like you did in high school, if your high school actually let you do experiments.

Tris

17

Maybe not.

For Lake Mead in the southwestern United States (climate similar to northern Africa), evaporation rates have been estimated to be about 7.5 vertical feet per year.

If your artifical lake were filled to a depth of 75 feet at the beginning of the project, it would be completely gone by the end of the tenth year simply due to evaporation. That doesn’t even account for water that soaks into the soil, or water that gets used for drinking/irrigation.

18

Nothing is over 100% efficiency. In this case you’re trying to extract all the energy you can from the wind turbine. The highest efficiency is directly driving a generator.

19

Somehow I missed this extremely significant sentence. Let’s go through the energy sources and sinks.

So far the only source of energy is the windmills, extracting kinetic energy from the wind and generating electrical power.

OK, so all of our windmill-produced electrical power is going into electrolysis. Some of this energy goes into breaking the H[sub]2[/sub]O bonds, some of it goes into pushing back the atmosphere to make room for those gases, and some of it is wasted as heat.

Even if you could somehow recover the buoyancy energy, that’s just energy your windmills put into the system to start with. The highest point in the Atlas mountains is about 4100 meters, which would permit us to recover only about 40% of the available buoyant work.

As described earlier, enclosing the H[sub]2[/sub] in a closed piping system will not permit recovery of buoyancy energy. You will have to compress and/or pump the H[sub]2[/sub] to get it up to the mountains, and that will take energy.

When you bond a kilogram of hydrogen with oxygen, you only get as much energy out as you put into breaking those hydrogen-oxygen bonds during the electrolysis process. This ignores the inefficiency of the electrolysis process. You do not get out more energy than you put in.

As noted upthread, 50% is a reasonable efficiency figure for modern large-scale steam-cycle power plants. So if your windmill puts 1 watt into an inefficient electrolysis process, your Atlas Mountain power plant will produce much less than half a watt of electrical power.

Odd, I’m struggling with this one. Folks, we’ve got a bunch of liquid water 4100 meters up in the Atlas Mountains. As this stuff flows down to our basin in the Sahara, we definitely can generate some hydroelectric power with it along the way.

So where did the energy in this 4000-meter-high water come from? :confused:

20

I considered mentioning evaporation, but did not want to make the first message too long. Clouds are good against global warming. Also thought that chemical reaction in brine could work against CO2 - pretty much the same as in submarines.