Making Jet Fuel From Seawater While at Sea • Hacker News Board

Re: Making Jet Fuel From Seawater While at Sea

#81

Post by stcredzero » Sun, Sep 30, 2012, 3:37 PM UTC

jrabone wrote: post #80

jnw2 wrote: post #74

Earlier quoted context omitted.

Several strings of solar panels + lithium ion batteries might very well be cheaper than paying your local electric monopoly for transmission line capacity in 20 years. And if the non-redundant parts (the inverter, perhaps) fail, it might not be all that different from your water heater failing today. (Although if we had that technology in cheap enough form, some of the major loads in your house may switch to DC to av…

I don't think you necessarily need Li-ion for that - in my experience lead acid works well enough in the domestic case, is a lot cheaper and probably safer (although hydrogen venting is perhaps an issue). I built a little mixed DC (lighting) + AC (1kW inverter) system out in the garden (far enough from the flat that running a cable would be a nightmare of planning permissions & digging trenches). Since it's for inter…

Nickel-Iron batteries have a life measured in decades and are very robust against deep discharge. They can also be refurbished. Their formulation has been around since Edison. In fact, I think he invented them. Their big disadvantage: they're heavy. Perfect for home use.

EDIT: Edison did not invent NiFe batteries, but he developed and championed them.

Re: Making Jet Fuel From Seawater While at Sea

#82

Post by ChuckMcM » Sun, Sep 30, 2012, 7:03 PM UTC

jnw2 wrote: post #72

jrabone wrote: post #43

Earlier quoted context omitted.

And in fact, here is another illustration of just how hard it is to replace conventional energy storage systems with electricity. High pressure steam stores an enormous amount of energy. EMALs effectively uses 4 flywheels as rotational energy stores, suggesting battery / supercap technology just isn't viable. It does have an efficiency advantage over steam though.

I bet batteries don't tend to like going from full to empty in the time it takes to launch a plane. I wouldn't be surprised if later in the Ford class's life, we do see supercapacitors taking over.

Batteries operate by the principle of ion formation. The chemical process is exothermic with respect to the transfer of electrons from the cathode to the anode. So the more charge that is moved the hotter the batteries get. This is often the limiting factor for charge conversion.

Capacitors on the other hand simply store charge using electrostatic field attraction, the only barrier to their current flow are the i2r heat generated in the conductive paths (a superconducting supercapacitor for example could dump all of its charge instantly without any problems, if such a thing existed, its manufacturer would be worth more than Apple :-)

Flywheels store energy mechanically as angular momentum, they have good energy density, and can return it quickly by being attached to a generator, but are generally hard to deal with in systems with an external acceleration because their tendency to precess if that acceleration results in a rotation that is perpendicular to the flywheel. The proposed carrier ones I've seen are shown as being on gimbals for that reason.

Re: Making Jet Fuel From Seawater While at Sea

#83

Post by dctoedt » Mon, Oct 01, 2012, 4:01 PM UTC

sophacles wrote: post #62

dctoedt wrote: post #40

Earlier quoted context omitted.

> when you're just sitting around in the ocean Watch any of the documentary series about life aboard an aircraft carrier [1] and you'll see that there's essentially no "just sitting around in the ocean." But your main point is still accurate: If there's power available, putting it to work making jet fuel might be a good trade-off for the additional drain on the nuclear fuel. [1] E.g., http://www.pbs.org/weta/carrier/

From friends and family in the navy: whenever you see a fleet or battle group "stationed" somewhere, it means they are basically doing right turns in the middle of the ocean (a joke being that someone has to balance the effect of all those left turning NASCAR races). While they are doing operations etc, a lot of this time is considered extremely boring, more so than even long voyages going somewhere. Further, they us…

Former Navy aircraft-carrier nuclear engineering officer here. The basic point --- that a carrier might be able to refine its own jet fuel --- is certainly valid. But so that future readers don't get the wrong idea: Any time a carrier is at sea, it does a lot of flight ops just about every day, whether for actual missions, for war games, or just refresher training. That in turn means most of the crew is hustling, usually 12 to 14 hours a day minimum, and sometimes 'round the clock. Maintenance has to be done in the gaps. When we were at sea, it was rare to get six hours of uninterrupted sleep in a night. Somehow I doubt that has changed.

Re: Making Jet Fuel From Seawater While at Sea

#84

Post by jnw2 » Tue, Oct 02, 2012, 4:54 AM UTC

dalke wrote: post #78

jnw2 wrote: post #74

Earlier quoted context omitted.

Several strings of solar panels + lithium ion batteries might very well be cheaper than paying your local electric monopoly for transmission line capacity in 20 years. And if the non-redundant parts (the inverter, perhaps) fail, it might not be all that different from your water heater failing today. (Although if we had that technology in cheap enough form, some of the major loads in your house may switch to DC to av…

There will still be a grid. The scenario you mention will be useful for some, but assuming $80/month for electricity over a paid-for grid vs. $10,000 for installation of cheap solar panels+batteries gives a pay-off time of about 10 years. (Currently solar water heaters cost about $5,000, so the best is 5 years.) I don't think most will be willing to take that capital investment. It would be interesting to see how dis…

IIRC, solar prices have been dropping at a rate of 7% per year. If that keeps up, and if the grid price remains constant, solar will eventually become cheaper than grid.

In 1992, would you have told me today's smartphones would be impossible?

If you only lose a few solar panels in a storm, and most of the panels on your roof survive, you may just use a bit less electricity for a while.

Re: Making Jet Fuel From Seawater While at Sea

#85

Post by jnw2 » Tue, Oct 02, 2012, 5:01 AM UTC

jrabone wrote: post #80

jnw2 wrote: post #74

Earlier quoted context omitted.

Several strings of solar panels + lithium ion batteries might very well be cheaper than paying your local electric monopoly for transmission line capacity in 20 years. And if the non-redundant parts (the inverter, perhaps) fail, it might not be all that different from your water heater failing today. (Although if we had that technology in cheap enough form, some of the major loads in your house may switch to DC to av…

I don't think you necessarily need Li-ion for that - in my experience lead acid works well enough in the domestic case, is a lot cheaper and probably safer (although hydrogen venting is perhaps an issue). I built a little mixed DC (lighting) + AC (1kW inverter) system out in the garden (far enough from the flat that running a cable would be a nightmare of planning permissions & digging trenches). Since it's for inter…

There are some interesting questions about economies of scale, etc, though.

If we figure an average American has a lead acid car battery and maybe a laptop battery pack, we currently have more lead acid batteries than lithium ion, certainly by weight, but probably also by total watt hours.

Tesla and Nissan might end up inverting that ratio in a market where they merely have to get the battery to beat the cost of gas; and if we get to the point where every American has an 85 kwH battery pack in their car, that's multiple days of average US electrical consumption (I believe average per capita electrical consumption is about 1.5 kw, and average per capita total energy consumption around 6 kw in the US).

Meanwhile, there's no path to pushing up volumes of lead acid battery production significantly. Maybe there will be a few old lead acid car batteries getting recycled after Tesla conquers the world, but if that's all we're relying on, those recycled batteries won't power very much in the grand scheme of things.