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Comment by jbert | Hacker News Reader

What about micro-fuel cell + hydrocarbons?

The energy density of gas/petrol is fantastic. Recharge time is quick ("pour some in").

http://www.gizmodo.com.au/2011/12/a-gallon-of-petrol-can-pow...

http://www.mtimicrofuelcells.com/

Sure, we have limited supplies of hydrocarbons in the ground, but to me the key energy technology would be "synthesise hydrocarbons from water + CO2 + energy in". i.e. stop focusing on hydrocarbons as a source of energy and start thinking of them as a 'transport' of energy.

That would also mean we can move to clean, renewable power generation without retooling the globe's transport fleet.

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I had the chance to analyze a solid-state gas engine a few months ago, based on this technology:

http://web.mit.edu/newsoffice/2011/sun-free-photovoltaics-07...

The solid-state engine has much lower efficiency than a regular power engine would (a hypothetical 12%/realized 5% vs. a realized efficiency of about 30%), but it can be made much smaller - and even at a 5% conversion rate, the energy density just blows everything else out of the water. Aside from being energy dense, it's also much cheaper than high-end lithium-ion batteries; and unlike regular fuel-cells, the technology is just based on regular photovoltaics, and is relatively easy to manufacture.

Awesome, so we'll have the tech to consume the hydrocarbons, but where is the production side?

What do we need to be able to hook up a nuclear power plant, a supply of clean water and a big air pump and starting sucking in H2O+CO2 and piping out CnH(2n+2) and pumping out O2?

So at 5% efficiency, a solid state engine in a battery form factor in my cellphone is going to need to get rid of approx 20 times the Watts used...

Hot :-)

My understanding is that hydrocarbon using fuel cells run hot, really, really HOT. Which is why they are regularly used in race cars, but not in many other places.

They share names, but racing fuel cells are just small tanks.

Tough tanks, filled with foam so that leaks are slow.

The energy density of hydrocarbons may be high but the thermal efficiency in most applications is horrible. Gasoline automobile engines are only about %20 efficient for example.

>"synthesise hydrocarbons from water + CO2 + energy in"

I believe this is called photosynthesis.

Yes, but the process then becomes biofuel, which also soaks up land area and has other issues (warping world food prices).

It would also be nice to be able to capture the energy output of other energy sources, e.g. nuclear in a nice, energy-dense liquid form.

Using food for fuel is dumb, I concur. I'm a fan of algae.

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